Introduction and a question about Two class T-Fuse requirement.

[Egbert Jager]

Good evening,

My name is Egbert and I am barely able to keep my head above water some days...

Background story: I am planning the rebuild of the electrical system onboard our 40' sailboat. The previous owners had lived aboard for a decade plus and (professionally?) refitted some electrical about a year before we bought it. Within six months, all three of the Victron 175 Ah batteries were showing signs of bloating and two had fused together and would not come apart -  possibly some sort of a charging issue... or maybe a faulty battery led to cascading failure.... Not entirely sure of the reasons, but we uncovered a few interesting wiring configuration choices, a few gremlins, too many loose connections, some interesting equipment location choices, some equipment beyond the end of its expected life and a couple too many shortcuts...and then....  Soggy Paws came along and told us we could do our own lithium. I'm reasonably handy with tools, have re-wired my own home and think I'm smart.... til I met you all... OK enough self deprecating humour....

Working from the basic information in the soggy paws presentation " Are Lithium Batteries for You? "  (can be found at sv soggy paws . com) - I have been drawing out my own plans. In this diagram, and many others, there is a 400A T-class fuse between the batteries and load - no other device is going to be able to protect against a dead short. No doubt from me that it needs to be there. It would protect both loads and power sources (and related controllers).

My question is: since there can be nothing between the shunts and the batteries, and since there is no single location where a single fuse can protect both "upstream and downstream", does it make sense to install Class T fuses between the load bus and the shunt as well as between the charge buss and the shunt.

The pic was cropped from part of Soggy Paws presentation and edited to help explain my question.

[Dacian Todea (electrodacus)]

Egbert,

Not quite sure I understand your question.  In that diagram there are fuses both for Loads and for charge sources. I see a 400A T-class fuse for Loads and there is a 250A ANL fuse for charge sources.

If there is a short circuit on the Load side then it will only affect the load side as the 400A fuse will open and isolate the short while the charge sources being separated are not affected.

The two shunts will be very close to positive terminal of the battery no further than about 30 to 40cm and they can be inside an insulated box so that nothing can touch the current shunts and if you have a large enough box you can even include the two fuses.

You need to have two separate paths for Loads and charging and so each needs his own fuse for protection to overload or short circuit.

The SBMS0 needs to be able to control ON/OFF all Load's and separately all charge sources.

The diagram seems a bit complex as there is a lot of equipment that is not compatible with Lithium batteries so it has no remote ON/OFF control to be able to control with a BMS.

For example there is a Tristar MPPT and that will not be needed if the PV panels matched the battery then only the DSSR20's shown in that photo will be required.

Same with the sterling shore charger that seems to be using a FOTEK SSR to allow SBMS0 to disconnect the grid from the charger.

The alternators are a bad idea from multiple reasons but they should be connected trough a battery to battery charger assuming there is a Lead Acid starter battery there.

I do not find a 175Ah Victron battery on google. Can you provide a link and maybe what other equipment you already have ?

There is absolutely no reason for a LiFePO4 battery to fail if it was protected by a BMS. Batteries where either overcharged or over discharged meaning they did not had protection for at least one of this cases and so they got damaged.

[Chris R8]

Darcian is partly wrong here as the class T fuses have 2 functions in your diagram and system.

You need a class T or NH fuse in the 250A PV string, also by ISO (valid for european vessels) and ABYC standards (valid for US vessels) on a vessel which you don't have in off-grid installation like dacian has.

Function 1: cable fuse for what comes after the fuse, on load side the loads and on charge the charge side and ANL fuse for both would be sufficient BUT

Function 2: the fuse also works as main lithium bank fuse to a) protect it from overload/overcurrent and b) disconnect the bank in a failure which in most case is a internal cell short of minimum one cell in the bank due to eg system overload or by an external event eg a metal pole porking into 1 or more cells. This happen very very seldom but if it is catatrophic. A lithium bank of 400AH in 12V can create more then 15000A current floating and the fuse must be able to disconnect the bank from the rest of the system and only class

T OR NH fuses have the short circuit rating needed here, all other fuse types will be arched and useless in this case.

The current spec rating of the pv fuse need to be the cable rating but the possible 15000A short circuit current of a shortend bank require a 250A class T or NH 2 or 3 fuse type. On a vessel or RV that's mandatory but in an offgrid station not but I highly advise to use  this also in offgrid.

[Dacian Todea (electrodacus)]

Fuses are to protect cables not battery or equipment.

Any fault with the battery like internal cell short due to dendrite growth will have nothing to do with any of those two fuses.

Yes the battery will need to be large enough so it can handle the Load or charge current allowed by the fusses.

Maybe that ANL 250A fuse is rated for max 6kA of fault current (did not checked) and maybe depending on battery and the way the wiring is done that is not sufficient.

That is not my diagram but it looks like 2P EVE type cells 270Ah each so 540Ah and those cells have about 0.5mOhm internal DC resistance so two in parallel will be 0.25mOhm then 4 in series 1mOhm excluding connection resistance and any other cable  14V / 1mOhm = 14kA But this is some metal object with zero resistance shorted the terminals of a fully charged battery.

Also notice that charge current is rated only 150A meaning that continues current will be just 100A max for charging so it went overboard with cables and fuses.

The shunt itself adds 0.33mOhm so already down to 10kA

Then there are at least about 1m of wire from battery+ terminal multiple connections until after the shunt. Cable to be protected by this fuse will be fairly extreme so maybe the 1m of cable another 0.15mOhms plus the fuse resistance maybe similar 0.15mOhm

The there will be the negative path and whatever got in between to create the short circuit but is fairly safe to say is unlikely for the fault current to exceed 6kA in any realistic scenario.

That said overbuilding things come at a cost. Using a 250A fuse instead of  150A when you expect max continues charge current of 100A will result in cable that is about 2x the section and weight and maybe 3x the cost.

Then short circuit current will be much lower and easier to handle with lower cost fusses.

In any case I'm not a fan of fuses :) I have no fuse anywhere in my installation as I used circuit breakers with both thermal and electromagnetic protection.

A double pole 200A breaker could replace here both fuses and it can add extra protection by having trip coil that will be controlled by EXT IO set as type 5

Both the breaker and shunts can be in a box mounted on the battery box.

[Egbert Jager]

Thanks for the replies. Lots to digest in there.

Fuses protect wires. They can also protect equipment which are filled with wires and connections. I assume that is why we install 1Amp fuses on manufacturer-supplied 16ga wire ahead of such things as propane sensors (with solenoid control) and such.

Good catch on the battery size Damian - The Victron AGM's were  170aH (https://www.victronenergy.com/upload/documents/Datasheet-AGM-Super-Cycle-battery-EN.pdf). THe existing sytem probably isn't at all relevant but since someone asked...
There is (was) a Solar Boost 3024iL Solar Charge Controller, with add-on for a Duo-gen wind/water generator. Going to change it to Victron MMPT's. There is a Magnum Energy 2000 Watt 12V Pure Sine Inverter Charger (MS2012) that has spent 12+years in the fairly warm engine compartment. The battery disconnect switch in the 12 volt supply cable melted due to heat, the interior fans are defunct. Its so far outside its warranty period Magnum doesn't even want to look at it. It will be replaced with a shore-power battery charger and separate 2000W inverter.

Let me along and and talk about the system. The full diagram can be found in a PDF from SVSoggyPaws.com. It is not mine to share so I only used the small portion highlighting the shunts and OC protection.

BATTERY  ==  My system will be (as his is) 8 EVE cells for a 540Ah 12-volt system. I've got room enough in the existing battery compartment to contain the batteries and the shunts and the fuses, the SBMS will be outside the box but within the

CHARGING ==  Charging will occur via an engine-driven alternator, shore powered battery charger and solar panels.

ALTERNATOR == There is, as you can noted Damian, an SSR 10DD for an external alternator controller -I have Balmar’s MC-614 external controller and a 100A alternator. For those interested, I've bought into the magic and will add an AMP-12 Alternator Protection Module.
I've been reluctant to add a Dc to Dc charger. Not sure why anymore. Open to input on this too.

BATTERY CHARGER == I will be installing a MEAN WELL NPB-750-12 battery charger. Its a 750w charger, and utilizes the Canbus protocol for customization. Right now it will have a 40A DA SSR like the Fotek pictured

SOLAR == Presently there are 4x100W (ten year old 36 cell panels**) plus a 50W of unknown origin). I will probably upgrade the 10-year-old panels in the coming year depending on availability so I'm building it for two MPPT's  I had originally planned to have DSSR20's ahead of the MPPTs, but I have found that Victron controllers are a good deal right now and think the SBMS0 can control them directly.

CHARGING & LOAD CONTROL ==  There are ALSO two remotely-operated disconnect switches for both the charging cable and the load cable.  (in the picture its a 7700, I will use  Blue Sea 7713 battery disconnect switches as it is normally open -see manual here).   I understand these to work with the SBMS0 -not sure yet if that is directly controlled or through a relay. However, I'm still figuring out through my third reading of the beginner's guide, if I have too many shut-off options to be controlled. :-)

How many different load control circuits are there again? I will be installing a Mean Well

WHY ==

Mission-critical components and systems on a cruiser's sailboats are often quite over-engineered with double or triple safety margins. Everyone has their own level of risk tolerance, but when you regularly make long passages -  refrigeration, navigation, radar etc are factors that things people with land-based ( stationary ) systems rarely have to worry about. Solar's easier when you live in something that doesn't have to float and isn't exposed to salt air 24/7. Am I aware of the  ̶s̶t̶u̶p̶i̶d̶i̶t̶y̶  risks of dropping a wrench on the batteries or shunts?...of course. Do I do what I can to mitigate it? ...of course. Am I human, Yes (most days). Am I likely to make mistakes when I'm tired, the boat is rolling, and I am a long ways away from a destination that has never seen a torx screw and where Amazon guarantees three months delivery... of course that is when it would happen. ( "... this is some metal object with zero resistance shorted the terminals of a fully charged battery" ),

I like the idea of breakers instead of fuses - except where salt-related corrosion is a factor. 200A Marine grade breakers were the largest I could find except for the 300A triple pole parallel breakers.

Hope this sparks thought and discussion!

[Dacian Todea (electrodacus)]

I had the impression that was a Victron Lithium type battery. It sounds very strange for a AGM battery to get bloated and or melted.

BATTERY  ==  My system will be (as his is) 8 EVE cells for a 540Ah 12-volt system. I've got room enough in the existing battery compartment to contain the batteries and the shunts and the fuses, the SBMS will be outside the box but within the

Sounds like a good choice.

CHARGING ==  Charging will occur via an engine-driven alternator, shore powered battery charger and solar panels.

Quite a number of sources. In therms of cost if that is important for you solar PV will be the least expensive at $0.02/kWh then grid probably around $0.2 to $0.4/kWh depending on location and most expensive alternator at $1 to $2/kWh

So unless it is an emergency I will avoid the alternator charging.

ALTERNATOR == There is, as you can noted Damian, an SSR 10DD for an external alternator controller -I have Balmar’s MC-614 external controller and a 100A alternator. For those interested, I've bought into the magic and will add an AMP-12 Alternator Protection Module.
I've been reluctant to add a Dc to Dc charger. Not sure why anymore. Open to input on this too.

I'm going to asumme that alternators are connected to a small starter battery (Lead Acid) so you will need a battery to battery charger. Else how will the engine be started ?

BATTERY CHARGER == I will be installing a MEAN WELL NPB-750-12 battery charger. Its a 750w charger, and utilizes the Canbus protocol for customization. Right now it will have a 40A DA SSR like the Fotek pictured

Looks like a good choice.

SOLAR == Presently there are 4x100W (ten year old 36 cell panels**) plus a 50W of unknown origin). I will probably upgrade the 10-year-old panels in the coming year depending on availability so I'm building it for two MPPT's  I had originally planned to have DSSR20's ahead of the MPPTs, but I have found that Victron controllers are a good deal right now and think the SBMS0 can control them directly.

The newer panels will not offer any significant benefit. 400W is not that much for a 6.5kWh battery. Ideal amount of PV solar if you have the space will be around 1200 to 1600W

400W of solar can allow you about 2kWh per day not sure if that is sufficient or not for your use case.

CHARGING & LOAD CONTROL ==  There are ALSO two remotely-operated disconnect switches for both the charging cable and the load cable.  (in the picture its a 7700, I will use  battery disconnect switches as it is normally open -see manual here).   I understand these to work with the SBMS0 -not sure yet if that is directly controlled or through a relay. However, I'm still figuring out through my third reading of the beginner's guide, if I have too many shut-off options to be controlled. :-)

How many different load control circuits are there again? I will be installing a Mean Well

Not sure what the role of the role of the Blue Sea 7713 is ? I don't see why that will be needed.

WHY ==

Mission-critical components and systems on a cruiser's sailboats are often quite over-engineered with double or triple safety margins. Everyone has their own level of risk tolerance, but when you regularly make long passages -  refrigeration, navigation, radar etc are factors that things people with land-based ( stationary ) systems rarely have to worry about. Solar's easier when you live in something that doesn't have to float and isn't exposed to salt air 24/7. Am I aware of the  ̶s̶t̶u̶p̶i̶d̶i̶t̶y̶  risks of dropping a wrench on the batteries or shunts?...of course. Do I do what I can to mitigate it? ...of course. Am I human, Yes (most days). Am I likely to make mistakes when I'm tired, the boat is rolling, and I am a long ways away from a destination that has never seen a torx screw and where Amazon guarantees three months delivery... of course that is when it would happen. ( "... this is some metal object with zero resistance shorted the terminals of a fully charged battery" ),

I like the idea of breakers instead of fuses - except where salt-related corrosion is a factor. 200A Marine grade breakers were the largest I could find except for the 300A triple pole parallel breakers.

Best thing you can do is to have two separate systems. The safety margins like oversized wires are of no help. There is no situation where an oversized wire will help with anything.

Using an alternator to charge the battery unless it is an emergency is also a bad idea as each kWh will cost you at least 1 liter of fuel so you will need to bring a lot of extra fuel just to charge the battery.

I do agree that navigation and radar are not relevant for stationary systems. Refrigeration may be of similar importance.  I'm offgrid and it is possible to be stuck (unable to leave the house) for even a month if there is a very significant snow storm and roads are not cleaned but of course I do not need navigation or radar.

Yes salt is a problem for electrical circuits. A wrench dropped on the battery terminals will not be saved by a fuse installed after the battery terminals. So best to physically protect the battery terminals to exclude that possibility.

I have nothing against fuses is just not my preference for my own applications.

So I suggest a dual battery setup even if one is Lead Acid and the other LiFePO4. and a battery to battery charger that can be used in the other direction if one of the batteries need to be charged from the other.

Having a single battery seems like a bad idea for "mission-critical" applications.

[sailingharry]

Dacian lives in a stationary world where solar is relatively easy to install.  Us boaters have a slightly different view!  LOL.  In Dacian's world, engine driven charging sources are expensive in many ways.  They are expensive to build, expensive to run, and when the wear out, expensive to replace.  Solar is vastly better!

In our world, solar is a huge challenge.  It takes up a lot of space.  It gets a lot of random shade (making us look for higher voltage panels with MPPT controllers, rather than matching them like Dacian does).  The cost factor is much less of a driver for us -- we are much more focused on the challenges of "just make it work" with much less about money.  Over on a sailing forum, a member has spent many hours and thousands of dollars to make a system on his boat to have sliding panel storage -- increasing his solar by maybe 1kW for that cost!  I'm upgrading my panels, and the ones I bought were probably double the cost of others -- but these fit in the space, and others didn't.

Also in our world, we motor a lot.  Even if it's only 4 or 5 hours a week, as we move, it's a lot of potential power.  Missing out on that is a huge loss.  And limiting extra hours (when our limited solar doesn't keep up) makes it worth putting in the biggest alternator you can fit.  This also makes DC-DC a bad idea -- your 100A alternator may only make 100A for 15 minutes before the regulator backs off for heat, but to get that 100A means you need 100A of DC-DC.  Your Balmar regulator deals with heat protection, so you can feed it direct to the LFP bank and use the control output from Electrodacus to turn off the regulator -- no need for any protection from disconnects.

Dacian isn't wrong.  But his use case is different, and it's hard to see our use case.

Breakers -- I keep hearing Dacian on this, and it has my attention -- but I can't find good choices to actually buy.  Would love a link to a nice 400A breaker with a 12V shunt trip (without shunt trip, to make it a control as well as protection, a fuse is a much smaller and cheaper solution).

[Dacian Todea (electrodacus)]

sailingharry,

I'm not familiar with that world. And also when cost is not a factor then any system that will be convenient will win.

Many people seems to think that energy from alternator is free as long as you need to run the engine for propulsion but that is not the case.

Say you have a modest 2kWh / day of electrical energy requirement.

Assuming is mostly sunny a 400 or 500W PV array can cover that and a 4 to 6kWh battery can be used in combination for one or two days backup in case of clouds.

Now if you say do not want the hassle of those solar panels you can use the alternator so if engine is run about 5 hours a week and you need 14kWh per week you will need 2.8kW alternators so about 240A alternator or multiple alternators adding up to this.  In total it will require 14 liters of extra fuel (the engine will use 14 liter more fuel if you extract 14kWh of energy from them vs if you do not use the alternator and engine is just used for propulsion).

So when you go for say a 2 week sailing trip you need to bring up 28 liter of fuel (about as heavy as the solar panels thus no saving on weight) and it will cost you at least $28 depending on the price of fuel.

If this is full time it will cost you $750/year so if cost is not an issue then that is irrelevant but what are you saving as in therms of weight is about the same as the extra fuel needed to charge the battery is about the same as 400W panel.

Long therm panels are good for even 30 years and in just 10 year's it saves about $7500 in fuel.  If engine for any reason fails your electrical energy source is also gone and you have whatever is left in the battery.

Personally if sailing was my hobby there will not even be an engine and the entire boat will be solar powered including propulsion. Probably use 3 batteries two larger for propulsion and larger loads and one smaller dedicated for critical loads.

Maybe a very small water turbine (wind power is also a form of solar power).

With such a large solar setup I could do electric cooking and water distillation.  But I do like being on the ground :)

[Egbert Jager]

Thanks for the affirmative feedback SailingHarry,

Yeah, the 100A alternator can't put out full power for very long, but it can produce a lot of power for a long time. I can better appreciate now why the DCtoDC  isn't an option for "us". Those that live in "a dwelling so poorly built it will not float" also have another benefit...space. Our boat is what we once though was a large sailboat, 40'. There's no room for a lot of extra panels that can be pulled out on sunny days. The idea of slide away panels holds great appeal. And then we realize that all that stuff on deck has to capable of weathering storms..... 

Dacian:  I am starting with this plan and assumption:

• EXTIO 3 Default - Charge disconnect - This would be a circuit utilizing the DEXT16 for the

1.  DSSR20's -or possibly the MPPT controllers directly
2. Alternator controller - I think this is a 10DD SSR
3. Shore Power Battery Charger - this is a 40DA SSR

• EXTIO 4 Default - Load disconnect -This would be set at a higher cell voltage and would trigger a 7713 switch on the load side ahead of the non-critical distribution bus bar (but after the critical components like bilge pumps, nav lights, navigation & and radio) 

• EXTIO 5 Fault condition - Alarm triggers (Required by ABYC-13)

• EXTIO 6 Fault condition - Fail safe shut downs the 7713 in the charging side and a second 7713 on the the load side ahead of ALL loads (will eventually change this to a switch that will switch the critical loads to the charging battery)
  

I understand that the SBMS0 was intended for a home solar battery system with diversion. Its great. I know that the sailing community has appropriated it for our purposes presumably because it has the most options, and provides the best information on charging and battery.

I'd love to see more EXTIO circuits so we could have staggered shut-offs of different components. , I'd love to see Alarms circuits - even just one alarm for everything and its up to the user to seek out the why- 

[Dacian Todea (electrodacus)]

By default EXT IO3 is used for load control and EXT IO4 for charge sources.

See my comments with black

• EXTIO 4 Default - Charge disconnect - This would be a circuit utilizing the DEXT16 for the (DEXT16 is not needed unless you want to divert excess solar to something like heating)
  

1.  DSSR20's -or possibly the MPPT controllers directly  (DSSR20,DSSR50 or a Victron MPPT can be controlled by the SBMS0)
   
2. Alternator controller - I think this is a 10DD SSR   (If the alternator is already connected to a Lead acid you can not just parallel the Lead Acid to Lithium battery)
   
3. Shore Power Battery Charger - this is a 40DA SSR  (Yes you can use a AC SSR to disconnect the grid if the charger has no dedicated remote ON/OFF)
   

• EXTIO 3 Default - Load disconnect -This would be set at a higher cell voltage and would trigger a 7713 switch on the load side ahead of the non-critical distribution bus bar (but after the critical components like bilge pumps, nav lights, navigation & and radio)  (You mean low cell voltage ? The loads are disconnected if battery is empty so one of the cells is below say 2.8V (default value) Normally people use something like the Victron BP65 or for higher current BP220. Not sure if the 7713 works correctly meaning when EXT IOx is disconnected to turn OFF )  The critical loads should also be disconnected if you do not want to damage the battery. Maybe use an alarm to say at 30% SOC or whatever low limit you want so that you can disconnect non critical loads if necessary.
  

• EXTIO 5 Fault condition - Alarm triggers (Required by ABYC-13) Alarm yes can be set as type 4 with some limit maybe 30 or 40% SOC
  

• EXTIO 6 Fault condition - Fail safe shut downs the 7713 in the charging side and a second 7713 on the the load side ahead of ALL loads (will eventually change this to a switch that will switch the critical loads to the charging battery)
  

I understand that the SBMS0 was intended for a home solar battery system with diversion. Its great. I know that the sailing community has appropriated it for our purposes presumably because it has the most options, and provides the best information on charging and battery.

I'd love to see more EXTIO circuits so we could have staggered shut-offs of different components. , I'd love to see Alarms circuits - even just one alarm for everything and its up to the user to seek out the why- 

You mean type 5 but this should never happen in normal conditions so could be never and when it happens there may be no prior warning as this is to protect battery in case some equipment fails. You can add a delay circuit to this but it can not be more than a few seconds so you have say a 10 or 20 second alarm before everything is disconnected.

So for example if a charger fails to turn OFF the SBMS will not know the charger has failed until one of the cells is above 3.7V and getting from normal 3.55 to 3.7V may take just very few seconds depending on charge rate and once there the type 5 is already activated so if you add an alarm and delay the disconnection of the battery for say 10 seconds the cell may get to 3.8 or 3.9V in those seconds and maybe is still fine but you can not delay by say 1 minute as that will be to much the battery could get way over 4 or 5V doing permanent damage to battery and possible risk of fire.

In those 10 to 20 seconds of alarm you may be able to take the decision to manually override the decision and just manually disconnect the defective device.

That is why I recommend a separate battery for critical devices and that can even be a Lead Acid battery as it can be maintained at full charge at all time so it will not degrade. You will be using a small battery to battery charger to keep that battery in float and so in case of a fault on main battery you have plenty of time to react as critical loads are supplied by the separate battery (similar to an UPS).

[Egbert Jager]

I'm grateful for all the attention to this Dacien.
For confusion I'll add more comments in Green

1.  DSSR20's -or possibly the MPPT controllers directly  (DSSR20,DSSR50 or a Victron MPPT can be controlled by the SBMS0)
   

1. Alternator controller - I think this is a 10DD SSR   (If the alternator is already connected to a Lead acid you can not just parallel the Lead Acid to Lithium battery)  The alternator IS NOT CONNECTED to the Lead Acid. It outputs 100A (not for very long)at max and 50-75A typically so DC-DC charging from LA to Lithium is no realistic.
   

1. Shore Power Battery Charger - this is a 40DA SSR  (Yes you can use a AC SSR to disconnect the grid if the charger has no dedicated remote ON/OFF)
   

• EXTIO 3 Default - Load disconnect -This would be set at a higher cell voltage and would trigger a 7713 switch on the load side ahead of the non-critical distribution bus bar (but after the critical components like bilge pumps, nav lights, navigation & and radio)  (You mean low cell voltage ? The loads are disconnected if battery is empty so one of the cells is below say 2.8V (default value) Normally people use something like the Victron BP65 or for higher current BP220. Not sure if the 7713 works correctly meaning when EXT IOx is disconnected to turn OFF )  The critical loads should also be disconnected if you do not want to damage the battery. Maybe use an alarm to say at 30% SOC or whatever low limit you want so that you can disconnect non critical loads if necessary. Good catch, yes low cell voltage, triggering load disconnect. The 7713 is, I believe, a default to open circuit switch, requiring an OK-to-discharge signal from the BMS to close the circuit. If the cell voltage drops too low or the BMS fails, the circuit opens. The 7713 manual is here. It is capable of switching under load up to 500A - and has a manual disconnect for servicing the Victron BP220 look good too.

• EXTIO 5 Type 5 Fault condition - Alarm triggers (Required by ABYC-13) Alarm yes can be set as type 4 with some limit maybe 30 or 40% SOC. I chose Type 5 as I would like alarms for either high cell voltage or low cell voltage, as the ABYC-13 standards require - trying to maximize the time for human intervention, your suggestion of 40% is appropriate so that we could do manual load shedding at the breaker panel. Also an alarm at 85% (95%)? to ensure that the alternator is no longer charging.
  

• EXTIO 6 Type 5 Fault condition - Fail safe shut downs the 7713 on the charging side and a second 7713 on the load side ahead of ALL loads (will eventually change this to a switch that will switch the critical loads to the charging battery)
  

I understand that the SBMS0 was intended for a home solar battery system with diversion. Its great. I know that the sailing community has appropriated it for our purposes presumably because it has the most options, and provides the best information on charging and battery.

I'd love to see more EXTIO circuits so we could have staggered shut-offs of different components. , I'd love to see Alarms circuits - even just one alarm for everything and its up to the user to seek out the why- 

You mean type 5 (YES) but this should never happen in normal conditions so could be never and when it happens there may be no prior warning as this is to protect battery in case some equipment fails. You can add a delay circuit to this but it can not be more than a few seconds so you have say a 10 or 20 second alarm before everything is disconnected.

So for example if a charger fails to turn OFF the SBMS will not know the charger has failed until one of the cells is above 3.7V and getting from normal 3.55 to 3.7V may take just very few seconds depending on charge rate and once there the type 5 is already activated so if you add an alarm and delay the disconnection of the battery for say 10 seconds the cell may get to 3.8 or 3.9V in those seconds and maybe is still fine but you can not delay by say 1 minute as that will be to much the battery could get way over 4 or 5V doing permanent damage to battery and possible risk of fire. I agree, adding delay to the

In those 10 to 20 seconds of alarm you may be able to take the decision to manually override the decision and just manually disconnect the defective device. Yes, an alarm with 10-20 second delay could be enough time to shut off the engine, thus safely stopping the alternator, ahead of the SBMS tripping the 7713 charge disconnect switch. I was hoping that having the FIRST TYPE 5 Fault be an alarm - maybe 15-20 minutes ahead and the SECOND TYPE 5 Fault /disconnect- again...

I've just realized that the NODE RED software used by Soggy Paws might be a better way to get additional alarms and notifications......

That is why I recommend a separate battery for critical devices and that can even be a Lead Acid battery as it can be maintained at full charge at all time so it will not degrade. You will be using a small battery to battery charger to keep that battery in float and so in case of a fault on main battery you have plenty of time to react as critical loads are supplied by the separate battery (similar to an UPS). The second battery for critical loads is a good idea, not something I have seen anyone do on their boat yet. I'll give it more thought and see how it might work.....

More questions: Does the DSSR50 have load shedding or will it in the near future? How does the SBMSO "see" the alternator...just as an extremely large solar array? Any plans to make the SBMS more complicated with additional EXTIO Ports? maybe a third shunt for the alternators?

[Dacian Todea (electrodacus)]

If alternators are dedicated to Lithium battery and controller can protect the alternator then it should be fine.

The 7713 seems to require 7A or so for 20ms when changing state. Not sure if that is trough the remote ON/OFF connection or not as the EXT IOx can handle the 13mA constant but not the 7A peak.

Type 5 is not something that will be active in any normal conditions as it reacts to under voltage lock or over voltage lock thresholds 2.5V or 3.7V thus likely it will never be activated.

Also it makes no sense to have two EXT IOx set as type 5 the default one is EXT IO6 that is by factory already set as type 5

The Type 5 is designed to isolate the battery from both loads and charge sources in case of some equipment fault so it will not happen maybe ever in 10 or 20 years of operation.

Cells will only get to the 2.5V or 3.7V extremes if some equipment fails or settings are made incorrectly.

There is nothing that can predict equipment failure so no way to provide minutes of warning.

All loads will be turned OFF by EXT IO3 set as type 2 (2.8V) or by type 4 (40% SOC) so your choice. You can use say EXT IO3 set as type 2 to disconnect all loads and EXT IO5 set as type 4 to disconnect some non critical loads when battery SOC is at 40%.

All charge sources will be turned off by EXT IO4 set as type 1 when any cell voltage gets above 3.55V

So if all equipment works correctly with no faults all loads and charge sources will be turned off thus no cell can ever get to 2.5V or 3.7V and so type 5 will never need to isolate the battery but if an equipment fails then it takes only a few seconds before voltage gets to 3.7V or 2.5V and maybe you can delay isolating the battery for maybe 10 or 20 seconds but any more than that the battery will be damaged.

So not quite sure you understand what I'm saying about alarms.

You can get plenty of warning for normal operation before battery is empty as you can set an alarm at 40% and disconnect non critical loads.

But in case of hardware fault there is just no time no more than a few seconds before battery needs to be disconnected else battery gets damaged permanently.

If critical equipment needs to be ON you just need an UPS so a secondary battery that is always fully charged and takes over in case of fault on primary battery.

There is no way to know in advance that an equipment has fails like say a charger fails to turn OFF when asked by SBMS0. Since SBMS0 will ask the charger to turn OFF when battery is full so one cell got to 3.55V and if the charger fails to turn OFF because of fault then it takes maybe 10 seconds for the cell to get to 3.7V and type 5 to become open circuit and then maybe you can allow for another 10 seconds of alarm before cell is already at 4V and battery needs to be isolated else permanent battery damage will occur.

So everything looks normal and by the time it is no longer normal reaction time to isolate the battery is just seconds and not minutes.

A secondary battery with independent charge sources is the best way to have many minutes or hours to solve a problem on main battery.

I worked as hardware project manager in safety electronics designing airbag control modules for vehicles.  There we had large electrolytic capacitors inside the airbag control module so that if battery wires supplying the airbag electronics or even the battery itself was damaged in the impact there was enough energy in the electrolytic capacitors to still be able to activate the airbags.

So I highly recommend a separate battery for critical equipment even if that battery is a Lead Acid battery as the battery will spend most of the life fully charged and can easy last 10 years.

That way if the Lithium battery needs to be isolated due to some sort of faulty equipment the Lead Acid can take over ans supply even for a few hours the critical equipment thus you can have an alarm with plenty of time for you to react and solve the problem with main battery.

Does the DSSR50 have load shedding or will it in the near future? How does the SBMSO "see" the alternator...just as an extremely large solar array? Any plans to make the SBMS more complicated with additional EXTIO Ports? maybe a third shunt for the alternators?

Not quite sure what you mean by load shedding. If you mean diversion to water heating when battery is full that can be done with a second DSSR50.  I have no plans to add multiple EXT IO ports but there will be a DEXT see details here  https://groups.google.com/g/electrodacus/c/ANFzCOiT6Rw/m/1A3g0igSAAAJ  hope to have that available in a few months. It will multiply the existing EXT IOx but you still can have max of 4 types.

There is also no plan for a third shunt as it will just add complexity and cost and I try to keep this affordable.

[Egbert Jager]

Does the DSSR50 have load shedding or will it in the near future? How does the SBMSO "see" the alternator...just as an extremely large solar array? Any plans to make the SBMS more complicated with additional EXTIO Ports? maybe a third shunt for the alternators?

Not quite sure what you mean by load shedding. If you mean diversion to water heating when battery is full that can be done with a second DSSR50.  

Yes, I meant diversion.  Thanks. I have to start leaving the message up on my computer screen overnight and hit send AFTER a good nights sleep and a second edit!!

I have no plans to add multiple EXT IO ports but there will be a DEXT see details here  https://groups.google.com/g/electrodacus/c/ANFzCOiT6Rw/m/1A3g0igSAAAJ  hope to have that available in a few months. It will multiply the existing EXT IOx but you still can have max of 4 types.

That will certainly provide plenty more options for me! Great idea!

There is also no plan for a third shunt as it will just add complexity and cost and I try to keep this affordable.

It looks like this will offer a lot of opportunity to add the confusion and complexity I am looking for.... 😃

[Flint Smith]

I'm sorry to ask about what seems to have been explained, but I have a similar question regarding the lack of a second NH or T fuse on (in my case,) the PV.

In my mind, if I ground the PV+ wire, it looks to me like it's a direct battery short with nothing but 2 shunts and some 2 or 4-gauge wire to add to the miniscule internal resistance of my 2p4s.  I have EVE LF280Ks with the double-lug terminals so I should have good connections.  My dad has dropped hints about funding another 4 cells so would 4p4s change the math?  Halving the internal resistance for the battery bank makes it worse. (I followed your math above).

For the main power distribution bus I have some Socomec 250 A NH-1 fuses.  (Thanks Kampfsc and Captain for leading me. Industrial salvage FTW.)

Rated as 250A, the datasheet says they'll tolerate 1000A for 15 seconds, or 3000A for 0.1 seconds and work up to 80kA.  I had planned to put one directly attached to the main shunt with a second (faster) ANL fuse at the distribution bus. The ANL fuse would do the day-to-day wire protection while the NH stands by to protect the battery in case the ANL vaporizes. I thought I'd use 250A for both NH and ANL, designing for 200A.  

Having a stack of spare $6.50 250A NH-1 and room to put one on the PV+, what are the arguments for and against putting one in?  

NH-1 near the battery and a circuit breaker at the far end. Would I also want an ANL near the battery? I think so.

I see that most people get their T or NH fuse at 400A, higher than their ANL fuse.  My understanding is that they don't want their big expensive fuses to burn out for mundane reasons.  Is there more to it? Lower resistive losses? Lax tolerance on inexpensive ANL fuses?

Do I sound confused?  I feel confused.

Thanks

[Dacian Todea (electrodacus)]

Flint,

It makes no sense to have two fuses and especially it makes no sense to have a fuse at the load end of the wire.

Both fuses after the shunts both on battery shunt and on PV shunt are there to protect the wires in case they are shorted to negative or in case of overload.

You can not use a fuse that is not capable of handling the short circuit current as that will start a fire and the other fuse will not be able to help with anything as arc due to damaged fuse will add extra resistance so current may not be sufficient for the main fuse to melt and disconnect the current.

You can have smaller fuses for each individual load but those fuses need to handle whatever the max short circuit current can be in that part of the circuit.

If none of your sources can generate over 250A there is no use to have a 250A fuse on the other end of the PV wire before the buss bar. But after buss bar you need fuses to protect the thinner wires going to individual charge sources.

No properly spec fuse should ever burn unless there is an accident.

400A at 12V are for 5kW inverters and since a 5kW inverter can not normally exceed that limit for more than a few seconds there is no chance for the 400A fuse to get damaged.

But if you need a 5kW inverter it may be a good idea to move to 24V where current will be half that saves on wires and results in a bit less heat.

You only need another fuse on that line if you change the wire dimensions but you most likely can still not use an ANL fuse with 4 of those batteries in parallel (it depends on how long the cables are but inverters do not like very long cables as to not increase cable impedance).

[Dave McCampbell]

All,

 

My thoughts, comments and a few questions below on this interesting discussion.  Thanks for starting it Egbert.  There is a lot here for those of us SBMS0 users to digest.

 

As Kampfsc said regarding marine/boat LFP systems, the relatively new ABYC T13/ISO standards include using Class T fuses as main battery fuses not CBs or any other type of fuses.  I don’t think it will be long before most marine insurance companies, since they are not smart enough to figure it out for themselves, will require compliance with those standards for coverage.  So for those of us with boats, who want to maintain insurance coverage in the future, we don’t have a choice.  This does not apply to EV, RV or off grid systems.

 

In my system an MPPT is required as PVs are 24v nominal and the electrical system is 12v.  So the MPPT is required to make the voltage conversion.  It also adds convenience and does a good job at managing the charging voltages.  However, quality MPPTs are not cheap. 

 

As Dacian suggested to me early on MPPT, shore charger and alts can be controlled with proper placement of an appropriate relay controlled by the BMS.  This may mitigate the need to purchase all new equipment, although some new equipment may be required if their charge parameters are not suitable/adjustable or for age considerations. 

 

Dacian, agree alts may not be as efficient as solar for charging, but are always available on any marine LFP system with an engine and are a good idea for backup and in case of a failure emergency with the solar.  Best to use a quality external regulator, Wakespeed, Balmar or new Zeus, with the alt that can be turned off either by relay controlled by BMS or simple ignition wire switch.  None of this is cheap but worth every penny if the solar dies in the boonies overseas.  Ours are normally off and seldom needed because of adequate solar, but always available.  Adequate solar is the key to sufficient daily charging to keep up with daily loads. 

 

No need for a battery to battery charger if using simple trickle charge system with TCB and diode as indicated from house bank for the start battery.  All charge sources can then be run to the charge buss servicing the house battery, which is by far the most efficient use of big marine chargers.

 

Great idea, Dacian, to use a separate LA battery in an emergency to run the critical loads while the emergency is dealt with.  Would you think a separate fully charged starter battery would be suitable for this purpose?  I would not want to jeopardize engine starting capability, so care is needed in how long the critical loads could be used on this battery.  

 

I sized my 250a ANL fuse in my charge circuit for max charge possible which is:  about 55a from 800 watts of PVs plus 2x60a alternators so about 175 a.  Also, we will probably add another 400 watts solar in the near future.  But it seems my thinking may be flawed and it may be in the wrong place.  So in addition to the smaller CBs/fuses in the charge source wiring where is it best to place the larger fuse ANL/Class T to protect the charge wiring off the battery?

 

My 3+ year old grade A 271ahr RJ cells are similar to EVE and several others.  Current industry standard are EVE classic 280 or newer 304 ahr at very attractive pricing.  Grade A cells are the only ones to order.  Welded stud posts are preferred over the older bolt on posts.  According to EVE compression is required in order to get full service life.  Tops and posts of cells should always be covered unless being serviced.

 

For a marine system, best to keep all electronics out of hot and possibly moist engine rooms.  This includes batteries, BMS, regulators, inverters, shore chargers, MPPTs, etc.  If not they may suffer an early demise.  Cool and dry environment is best for all electronics.

 

In over 15 years of cruising in the tropics we have found that multiplying by 5 the daily load in ahrs gives the minimum wattage for solar to keep up with charging to 100% SOC by mid-day.  So if daily load is 100 ahrs, then install minimum of 500 watts unshaded quality solar. This applies to tropics only not mid Canada or similar location.  

 

As Dacian mentioned, if your panels and electrical system are same voltage a controller may not be necessary which could be useful if your controller dies.  Now that we have changed boats from a monohull to catamaran, and don’t need an inefficient wind generator, it is much easier to find room for adequate unshaded solar.

 

We prefer the more expensive but more useful Blue Seas relays with manual on-off switch and remote lighted control over the Victron BP for use in our system for buss control.  If necessary the BMS can shut down the entire load or charge buss separately at HVD lock, should the smaller individual relays, but not the BMS fail.

 

I too have wondered if that 7 amp peak load with the BS 7713 would be a problem for the SBMS0.  Hope someone can determine that as it is a wonderful CB.  

 

I think most serious cruisers agree that separate starter and house batteries are a good idea.  And for a 12v system I think 8 cells are better than 4, as it keeps the cell capacities reasonable while still allowing balancing.  That number also allows reducing the battery to 4 cells in the very rare case of a failed cell.  Even rarer for a cell to fail suddenly.  We also carry a spare cell, BMS and other system components because we are often in remote places overseas.  For a serious cruiser you can never have too many spares.

 

Dacian, the new expanded DXT will be a big help to those of us that have multiple charging sources and loads to connect to the SBMS0.  Thanks for taking that on.  I will be ordering one when they are available.

 

Dave and Sherry McCampbell

SV Soggy Paws in Malaysia

[Dacian Todea (electrodacus)]

Thanks Dave and Sherry for the comments. Your comments in blue:

Great idea, Dacian, to use a separate LA battery in an emergency to run the critical loads while the emergency is dealt with.  Would you think a separate fully charged starter battery would be suitable for this purpose?  I would not want to jeopardize engine starting capability, so care is needed in how long the critical loads could be used on this battery. 

Yes I was referring to a dedicated LA battery for emergency/UPS not the starter battery.

I sized my 250a ANL fuse in my charge circuit for max charge possible which is:  about 55a from 800 watts of PVs plus 2x60a alternators so about 175 a.  Also, we will probably add another 400 watts solar in the near future.  But it seems my thinking may be flawed and it may be in the wrong place.  So in addition to the smaller CBs/fuses in the charge source wiring where is it best to place the larger fuse ANL/Class T to protect the charge wiring off the battery?

You just do not need two fuses on same cable. A single Class T fuse on the charging path right after PV shunt is sufficient to protect the wire.  After buss bar if you use different size wires then you can add fusses to protect those wires from short circuit to GND.

So say you have two wires going to alternators and one going to PV and all of them need to handle about 60A continues then you can use 80 or 100A fuses assuming those wires can handle 100A

[sailingharry]

Dave,

E-13 does not add any specific additional requirements for over current protection.  The sum total of the language on this (in E-13) is:

13.6.6  Overcurrent Protection

13.6.6.1  Conductors shall be provided with overcurrent protection device(s) as per ABYC E-11, AC & DC Electrical Systems on Boats.

13.6.6.2  If necessary, a battery bank shall be subdivided into units such that ampere interrupting capacity (AIC) of the overcurrent protection device is not exceeded.

E-11 is unchanged, and allows main overcurrent protection devices to be either fuses or breakers, of any class/configuration, as long as they meet the required AIC (which of course rules out large numbers of devices!). 

While Class-T fuses may be the easiest and most common way to meet the requirement, other fuses, and breakers, can meet the requirement.

With regard to the Blue Seas 7713, I swear I've seen it written in an official place that the control switch is only a control, and the current to operate is drawn directly from the battery power leads.

[Dacian Todea (electrodacus)]

With regard to the Blue Seas 7713, I swear I've seen it written in an official place that the control switch is only a control, and the current to operate is drawn directly from the battery power leads.

That is also what I remember but is not clear from the spec so I can not be sure.

[sailingharry]

I meant to add in my earlier post that, while I've seen it officially written, I can't find it.  And "my memory" is a poor place to start a design project!  A note to Blue Seas might be worth while -- and a note from Dacian would be best, so you can then put it down as an officially supported switch.

[Chris Sailor]

sorry darcian

but that statement is simply completly wrong and dangerous plus it puts the user that follow your advise here in the situation that they are not covered by insurance in any battery related damage claim.

"Fuses are to protect cables not battery or equipment=> this is completely wrong and dangerous

Any fault with the battery like internal cell short due to dendrite growth will have nothing to do with any of those two fuses=> oh yes it will, if the cell shorts the bank sends 20-30kA current and that cable fuse if its any other fuse type then class T or NH will be arced and damage the installation and most likely cause a fire => boats and RV have lot 12V equipment while your offgrid house installation just have the inverters which are protected by their own internal fuse, mostly a class T as they are very fast type, so nothing happens here while you eg fry the watermaker with a huge amout of current or your the whole navigation electronics that cost 5x the cells...

Yes the battery will need to be large enough so it can handle the Load or charge current allowed by the fusses=> yes thats the overload function of the fuse but you have to pay attention that a 200A cable fuse type (means standard reacting times normally slow or fast) will let 400A or even 800A pass for couple of minutes but only blow with 1500A instanly. thats another reason you use class T as they are only avaliable in super fast means they will instantly blow if you put 600A at them or 400A for 1 minute.

requirements given by certifiying bodies that must be followed when installing in a RV or car or boat:

=> in mobile world RV and Boats the battery bank (doesn't matter which chemistry) must have a bank fuse reqiured by the installation requirements of ISO (Europe) or ABYC (US/Canada) or Loyds(UK). This is needed so the bank is isolated in case an internal short happens by the main battery fuse.

=> you also need a fuse to protect a cable if its longer then 50cm by the installation requirements of ISO or ABYC or Loyds.

=> LFP banks needs a current limiting device so you cannot overload the bank, this is provided by MosFet BMS or contactor BMS when they simply shut off when too high current for BMS (which is normally lower then what the cells can handle). But electrodacuse  BMS has nothing that limits the current, so the main battery fuse have to have the 3rd overload protection function too.

SO you need to spec it according to cable rating eg 200A, then check if the fuse blows when peak current of cells is reached (eg 560AH bank with eve so peak is 3C= 1620A (fits too) and it can withstand 30kA in short curcuit=> only class T and NH fuses fullfill this requirement.

in the diagram provided the fuse connected to main shunt is both, it protects the cable and on the other side protects the installation as main battery fuse and limits the current. thats why its correctly chosen to be a class T and not an ANL fuse. Reason is that a LFP with internal resistance close to short delivers a huge anount of current and only class T and NH fuses have enough short curcuit rating of above 30kA that needed.

so if that main cable and battery fuse blows you still have the full battery current flowing via the PV curcuit into your installation. An because this will also see the full battery current in an internal short it must be a class T and not an ANL which would be arced if that happens.

Normally you need 1 main battery fuse but because of the electrodacus having main and PV shunt first and then both fuses are cable, overload protection and main battery fuse all at once.

If you have an aluminium boat you a required to put even a 3rd main battery fuse directly on the negative terminal on the battery bank and this must be also a class T or NH fuse as you need to fuse negative and positive side of your battery bank..

you can find a test with a 50A winston cell that was shorted on purpose to show what happened and 4000A where floating around, so 100C...so imagine what a 8S 280AH bank will produce in short curcuit current. i burned one car down when a 400AH bank got internally shortend because we overloaded the cells and a 500A class T main battery fuse got arced, it had "only" 15kA spec....learned my 14000Euro lesson here...car insurance refused coverage but luckly that happened during a car stereo competition event and the event insurance paid 10k, so my damage was "only" 4k.

[Chris Sailor]

Alternator engine is basically free for us boaters:

on a boat you run the engine anyhow from propulsion and just harvest what the alternator delivers. I eg are massivly overpowered so motorsailing on 1300RPM on 0.7l Diesel per hour gives me 1.5-2kn faster speed and better velocity made good (means i keep better course so distance is shorter) when sailing close haul and the engine runs in that situation 2-3days straight through. an absolute nobrainer to do and well i have 80A straight for 2-3days for free from the alternator (ok cost 100ml additional diesel per hour, rest would have been wasted on heat otherwise) and the diesel like to have some load so its a good thing the alternator takes 3-4hp from the engine. plus the engine gives me hot water too.

i cut the alternator at 93% SOC, so it will never be cutoff by the BMS unless there is a desaster event.

my plan is now to add LTO battery (2p6S) with 20AH Toshiba SCIB LTO cells (acting as starter battery for the engine) and an electrodacus BMS with a victron argofe that connects to the alternator and output 1 of argofet goes to 4P4S 1088AH house with electrodaacus BMS and 2nd output to LTO. so in case the electrodacus cuts the LFP due to any reason the LTO will still be there as its chargig higher to 15V. so i can never get a surge load.

[Chris Sailor]

read my post. you must put an NH after PV shunt as well because in an internal battery short when the NH for the main shunt blows the PV still gets the full short curcuit current and the ANL will be arced.

I have a 500A NH3 as Main shunt battery fuse (also main load bus) and a NH2 250A fuse after PV shunt, which is my main charge bus as all charge sources are connected to it means alternator, MPPT/Solar, DC2DC charger, shore charger. The NH fuses also work well as disconnect switch, just pull the fuse.

[Dacian Todea (electrodacus)]

"Fuses are to protect cables not battery or equipment=> this is completely wrong and dangerous

How will the Load or charge fuse protect against a cell internal short due to dendrite growth ?

If a dendrite shorts the cell all that current flows trough dendrite the cell will overheat if that current is very high and cell get damaged or if current is smaller you will notice cell self discharge is significantly increased. None of the dendrite current flows trough any of those two main fuses.

You can imagine in extreme case you shorting one of the cells. All that fault current will flow trough whatever you use to short that cell and will not affect the current trough the Load or charge fuse.

=> oh yes it will, if the cell shorts the bank sends 20-30kA current

 

A shorted cell due to internal dendrite growth will not send any current outside the cell (a cell can not do that in any conditions). The amount of current "send" by the cell depends on the load and has nothing to do with the cell no matter what happens inside the cell.

Typical dendrites are fairly thin high resistance conductive crystals that grow inside the cell. They will usually result in fairly small currents and be seen from outside as cell self discharge and cell self heating.

 

Alternator engine is basically free for us boaters:

The cost will be 1 liter of extra fuel per kWh. If you only take 100W from alternator then yes it will be just 100ml per hour but after 1h you get just 0.1kWh

my plan is now to add LTO battery

What will the benefit of LTO be in comparison to Lead Acid ? for engine start applications.

read my post. you must put an NH after PV shunt as well because in an internal battery short when the NH for the main shunt blows the PV still gets the full short curcuit current and the ANL will be arced.

I already mentioned that you need a fuse that can handle fault current large enough to match the worst case scenario that will be battery voltage divided by the total circuit resistance.

As mentioned above an internal short in the battery will not flow trough that PV fuse thus that fuse will not offer any protection for that case.

I have a 500A NH3 as Main shunt battery fuse (also main load bus) and a NH2 250A fuse after PV shunt, which is my main charge bus as all charge sources are connected to it means alternator, MPPT/Solar, DC2DC charger, shore charger. The NH fuses also work well as disconnect switch, just pull the fuse.

That is probably OK choice for your application if your load can get close to 400A continues. Maybe you have a 5kW inverter or some large DC loads that require that 500A fuse.

[Chris Sailor]

"Fuses are to protect cables not battery or equipment=> this is completely wrong and dangerous

How will the Load or charge fuse protect against a cell internal short due to dendrite growth ?

If a dendrite shorts the cell all that current flows trough dendrite the cell will overheat if that current is very high and cell get damaged or if current is smaller you will notice cell self discharge is significantly increased. None of the dendrite current flows trough any of those two main fuses.

You can imagine in extreme case you shorting one of the cells. All that fault current will flow trough whatever you use to short that cell and will not affect the current trough the Load or charge fuse.

1) i don't have to discuss that, there are valid installation requirement by professional bodies like ISO, ABYC and Loyds, thats what they require and insurance of a RV, boat and car will take as base if installation was done correctly or not and if not bail out quickly. and what I described are the reasons why they request that. And eg at ABYC a large number of proffesional installers were creating these installation requirements based on huge experience and system failures happened togther with ABYC and the coastguard.

=> the fuse cannot protect the cells in an internal short but can and must isloate the rest of installation. an internal cell short can happen to various reasons, on a boat also due to groundiing or an object perferating hull and battery case.

=> oh yes it will, if the cell shorts the bank sends 20-30kA current

 

A shorted cell due to internal dendrite growth will not send any current outside the cell (a cell can not do that in any conditions). The amount of current "send" by the cell depends on the load and has nothing to do with the cell no matter what happens inside the cell.

Typical dendrites are fairly thin high resistance conductive crystals that grow inside the cell. They will usually result in fairly small currents and be seen from outside as cell self discharge and cell self heating

=> well i burned a car down due to an internal cell shortage and a class T with 15kA was acred, i don't need more proof plus again ISO, ABYC and Loyds requesting that. NH fuse are cheap and also works as disconnect switch, cheap peace of mind. tick insuance boxes too. my install is certified by a surveyor to insurance for coverage in the contract.

Alternator engine is basically free for us boaters:

The cost will be 1 liter of extra fuel per kWh. If you only take 100W from alternator then yes it will be just 100ml per hour but after 1h you get just 0.1kWh

=> well its an engine for propulsion and not a generator!! my flow meter in the diesel line doesn't lie, if i switch the alternator off or have it running with 40A i get no additional consuption of diesel, that is unused excess energy of the engine for the propulsion. running the alternator at around 80A (fluctuating between 70 and 85A due to internal temp regulation, in average 80A) i get 100ml at 1300RPM motorsailing an hour. ran the tank empty and total of flow meter and amount of diesel refueled matched to 1l with a 280l tank, so its accurate. again theory and real life doesn't always add up as a lot of additional factors are involved....yes a generator that will look different. And its also different in diesel consumption with an alternator running on full load on a vessel where the engine is undersized and already has troubles pushing the vessel compared to one thats oversized and pushing it with ease. unless alternator is not too big for engine running it while propulsion costs only the additional diesel and is actually in favour of the diesel as they don't like to run without or on small loads. thats why the growing trend to put heavy duty alternators on engine with big LFP banks and harvest when you use them for propulsion and throw out the gen.

my plan is now to add LTO battery

What will the benefit of LTO be in comparison to Lead Acid ? for engine start applications.

TOns of advantage.

No self discharge, no floating needs, much safer chemistry, 30years lifespan=do it once right and forget about starter. the charge curve allows to balance battery/cells at any state of charge. in 4S you only need a balancer, no BMS required. Toshiba SCIB LTO can do 25C peak so a 20AH cell will easly handle a 3kw starter from -30 till +80 degrees. They can be kept at any soc for as long as you want to. self-discharge not measurable. can be paralleled to LFP and charged with LFP settings so no different chemistry. LTO are far more robust that any lead, even any LFP. overvoltage you need to run >20V over longer time, even a faulty 12V regulator puts out max 18V...yes they are occasion where its more but they are rare.

They can be discharged to 0 and charged up again, yes they loose 300 of their 30000 cycles doing that but they work, no other chemistry would.

plus you get the Toshiba SCIB 20AH for 18$ the cell at batteryhookup.com, cheaper then a FLA when buying, absolute nobrainer.

read my post. you must put an NH after PV shunt as well because in an internal battery short when the NH for the main shunt blows the PV still gets the full short curcuit current and the ANL will be arced.

I already mentioned that you need a fuse that can handle fault current large enough to match the worst case scenario that will be battery voltage divided by the total circuit resistance.

As mentioned above an internal short in the battery will not flow trough that PV fuse thus that fuse will not offer any protection for that case.

=> my cells have printed on 14mohm resistance with 4 in parallel makes 3.25mOhm...i calculated it already somewhere, missing the correct formulas right now but i came to 28000A in worst case wil float to the connected 12V installation. Again i don't need to discuss as this is the clear requirement by certifing bodiies ISO, ABYC and Loyds that the main battery bank fuse must have a higher short curcuit rating then the bank can produce when at 100%SOC.

[Dacian Todea (electrodacus)]

captainrivet666,

I think I made my points and it will not make sense to answer again. You provided mostly anecdotal evidence.

A short circuit means just that current flows trough a shorter circuit. If you short circuit one cell in a battery made out of say 4 cells in series the fault current will only flow trough that shorted cell not trough the other 3 cells in series or trough the load or charge fuse.

40A * 12V = 480W going in to battery so about 0.5kWh  With a 50% efficient alternator that means 1000W extra load on the engine and with 20% efficient engine and about 10kW/liter of energy in fuel that means half a liter of fuel for half a kWh of energy

100ml of fuel contains 1kWh of thermal energy that will convert in to 200Wh of mechanical energy with a 20% efficient engine and that will convert in to 100Wh of electrical energy with a 50% efficient alternator (typical alternator efficiency).

LTO vs Lead acid

Pros LTO vs Lead Acid:

- Lower self discharge,

- Floating not required as there is no need to have it fully charged for long life

- slightly better low temperature discharge.

Pros Lead Acid:

- inexpensive  (not talking about deals on recycled LTO's)

- designed for engine start applications

- no monitoring or balancing (self balancing)

My old vehicle had the same battery for a bit over 10 years and it was inexpensive and simple to replace.

Yes I already mentioned that fuse needs to be selected based on multiple criteria including max short circuit current and fuse needs to be able to handle that.

The printed 0.14mOhm is great if true but that is the impedance at 1kHz not DC resistance witch is normally double that value 0.28mOhm. My cells where worse at around 0.25mOhm internal impedance and about double that 0.50mOhm DC resistance.

The fuse also have a resistance and so are the shunts that are in series with the fuse.

So your battery assuming is 4s4p with those cells should be capable of 14V / 0.28mOhm = 50kA but this excludes all the connections resistance, cables, shunt and fuse. So yes you will need a very capable fuse for your particular battery.

The battery in that example diagram was 4s2p with EVE cells so I assumed they are the same as mine.

0.5mOhm DC resistance per cell means ideal case (0.5 /2p )* 4s = 1mOhm there are some connection resistance and buss bars that I did not even considered

Then there where two shunts in series then the ANL fuse and all of this have resistance plus there was at least some length of cable to connect all this.

I mentioned that of the total short circuit resistance was around 2mOhm (not impossible in that diagram) then max short circuit current will be limited to around 6kA and so the ANL fuse will be able to properly protect that path.

It was already at the limit of what an ANL fuse can do so using a better fuse is not a bad idea.  The fuse was also two large 250A for what it was meant to protect as the PV shunt was just 150A meaning max 100A continues and that means a 150A fuse will have been appropriate.

I can not provide advice about fusing as the requirements are different for every application and also different between countries.  I just explained how the fuses are sized and what they are meant to protect.

In that particular example the fuse was protecting the wires and connections. So all buss bars, the cells, the wires and shunts need to handle the same current as the fuse that protects them.

And fuse fault current rating will need to be above battery voltage divided by short circuit resistance.

[Egbert Jager]

Retyping this as it seems not have been posted... Lucky for you all my memory is poor so this will be short.

I'd like to add an element to the discussion that has not been said out-right: 

"On a sailboat,  ̶s̶h̶i̶t̶   Shorts happen." The moisture, the salt, the vibration, the need to run wires through inaccessible locations, routing from outside to inside, through fiberglass, wood or steel bulkheads, plus the heat, all contribute to the increased likelihood of faults. Our fusing represents this and is an attempt to protect BOTH the main conductors and the little wires inside our equipment.

Given that a short could occur anywhere, does this change where you would recommend fusing, and what size?

I'd also like to know how everyone on a boat has dealt with the ABYC rule around fusing with 7" of the power source:

     11.10.1.1.1 Overcurrent Protection Device Location - Ungrounded conductors shall be provided with
     overcurrent protection within a distance of seven inches (175mm) of the point at which the conductor is
     connected to the source of power measured along the conductor.

[Dacian Todea (electrodacus)]

"Given that a short could occur anywhere, does this change where you would recommend fusing, and what size?"

You already provided the answer to the question

"11.10.1.1.1 Overcurrent Protection Device Location - Ungrounded conductors shall be provided with
 overcurrent protection within a distance of seven inches (175mm) of the point at which the conductor is
 connected to the source of power measured along the conductor."

So fuse will be as close as possible to the source and will protect the conductor from both overload and short circuit.

If that conductor is going in to a buss bar and continue on the other side of the buss bar with same conductor specification no fuse is needed for that conductor but if one or more of the conductor exiting the buss bar has smaller cross section so lower current caring capacity than what the initial fuse is rated for then you need to add another fuse within those 175mm from the buss bar capable of protecting that wire.

A fuse will not be able to protect from a short circuit with large enough resistance that is not producing a large enough current. So if you have a 400A fuse and wire shorts to some salt water puddle or some grounded stainless steel part where total short circuit resistance is over 30mV (12V battery) then current will not be large enough to melt the fuse thus fuse will provide no protection.

As a general rule you will want large loads like say inverters to be as close as possible to the battery. And for low power DC loads that are far from battery you may consider an isolated DC-DC converter assuming those are allowed.

[sailingharry]

Egbert,

The ABYC rule for 7" is a challenge, for sure.  There are exceptions in the rule if you sheath the wire (or other listed criteria) that allow certain longer runs, but I still subscribe to the 7" as a best practice.  In particular, older boats that weren't built with this in mind are very difficult to retrofit -- but in that case, putting a fuse into a previously unfused cable, but only being able to put it on, say, the battery switch 3' from the fuse, is a HUGE improvement over the original build -- and I suspect that most surveyors will give you a pass on the rule for making a big, but less than perfect, installation.  If you really don't want to fuse at all, there is even an exception allowing no fuses on an engine cranking circuit, and since most older boats have an A/B switch and both batteries can be "engine cranking" no fuses are required at all -- not a good idea, but compliant!

Major rework is a different story. On my last boat, a '79 Sabre 34, I did some major surgery, built a much larger custom battery box, and crammed a lot more battery into it.  Fuses were mounted right on the outside of the box, and while maybe not 7" were well under a foot.

For lead acid batteries MRBF are a great, but expensive, solution -- if you have the inch or so headroom to install them.

But, this is a LFP forum.  LFP is a new can of worms.  I'd really try really hard to meet al the requirements of E-11, if only to make sure your insurance doesn't get grumpy.

As a practical matter, I'm not entirely sure I agree with your assessment that "shorts happen."  On my current boat, the factory install (1998) has a run from the battery to the fuse of about 4'.  Not compliant, for sure.  But as I look at it, I ponder the risk.  If I replaced that nice insulated (ummm.... oh... non compliant welding cable.....ooops) cable with a piece of bare copper wire, there would still be ZERO risk of a short.  There is nothing it could touch that could cause a short.  Nothing.  As Dacian points out, salt water is a path to ground, but a long way from a cable melting, fire causing "short."  (As a curious aside, I do electrolytic rust removal on rusty stuff using a big 12V power supply in a vat of very salty water, and if I get 2A it's a big day).

[Egbert Jager]

Further to the discussion about using the 7713 as a SBMS0 controlled "type 5" shut off. This was the wiring diagram sent in the package.

Has anyone successfully used this switch on their boat?

[Egbert Jager]

Sailing Harry,

I was a home inspector in a former life. I've learned to never say that something stupid can't happen. It apparently doesn't just happen by accident, sometimes its on purpose!

When I say "shorts happen", I'm taking that from the history of mankind. Some village somewhere is missing its happy citizen... and he's ready to throw his stuff in all the spaces when he comes aboard.   We can't make enough rules to protect us from everything. As they say, the ABYC standards are a baseline to build up from, not a milestone to achieve. - Otherwise expressed as the ABYC standards (or home building codes) are the cheapest, most unsafe, the builders are allowed to get away with.