Relay and Wiring Externally Regulated Alternator for SBMS0 Control

[Dave McCampbell]

On my boat, besides PVs and a shore charger, I also have two small older 60a alternators, externally regulated by smart regulators.  These are little used as the solar is normally sufficient for daily loads.  But they are useful for additional charging should there not be enough solar for more than a few days while we are underway.  I currently have a on/off switch in the field wire between the regulators and alternators so that they can be disconnected when not needed and the solar charging is on.  There can be up to about 10a flowing in the field wire during charging.

I have looked back through several months of posts and have not yet found a good answer on how to use the SBMS0 to disconnect charging should the alternator/regulators try to over charge my LiFePO4 bank when switched on.  As I understand this I could disconnect the field wire or the ignition wire. 

Options I have considered include wiring IO plus and minus outputs directly to a small on/off switch, using some sort of small optocouplers, SSRs, or DSSR20s.  Anyone already doing this with minimal ma required from the SBMS0?

Also, what is the max ma available from the EXTIOs?  I have read 50, 100 and 150ma in various places on the forum and website.

Many thanks

Dave

First what is the max ma capacity of the SBMS0 EXTIOs?  I have seen 50, 100 &150 ma written in various places on this forum and the ED website.

  

 

[Oberon Robinson]

Hi Dave, most people use an isolated DC-DC charger for alternator charging - something like the Victron Orion-Tr or Sterling B2B.

I looked up the datasheet for the opto-isolators in the SBMS0, and they have an absolute maximum on-state current of 110mA.  Dacian recommends keeping it to 50mA.

[Dacian Todea]

Dave,

Max current for EXT IOx on SBMS0 is 50mA and that is more than sufficient to control any remote ON/OFF capable device that requires less than 10mA and also the same si true for any solid state relay control.

What model of smart regulator do you have ? They normally have an enable input that will not require much current just a logic level. Also are the alternators just directly connected to LiFePO4 or is there a Lead Acid for starting the engine ?

[Dave McCampbell]

Hi Oberon.  Thanks for your input.  Are you suggesting I replace the alternators with a DC-DC charger?  Since we are on a boat with engine driven alternators already I would prefer not to do that, especially since this charging source is little used, mainly for backup to the solar.  I just need a simple solution to disconnect charging if there is a high voltage event.  Thanks very much for that info on the capacity of the IOs.  So absolute max, but not recommended 110ma, and working max 50ma.  That leaves a bit of room for operator error.

Hi Dacian.  We have 5 year old 'VSR' alt regulators, which are the predecessors to the WP-500.  Both designed by same person.  It does have a convenient enable/ignition input.  Maybe that is a better relay disconnect location than the field wire?  If I use that, what device would you recommend to disconnect the enable wires to the regulators?  Alternator charge outputs run to a charge buss and then direct to the LiFePO4 house bank.  LA start battery and its charging is separate.

The SSR you suggested for the shore charger HVD needs only 7ma to activate, but the optocouplers we have take 41ma each to activate, 4ma at standby.  And then there are the two DSSR20s in the PV-MPPT wiring.  If I have to use EXTIO4 for them all in parallel, which I want to do as they can all be set for the same HVD, that puts me over 50ma.  Is there a better/more efficient device, or optocoupler, to use in place of the optocouplers I have?

Now that I have been using it for about 10 days, I am liking the 2P4S battery configuration better than the two 4S batteries in parallel.  The wiring is much simpler and there is some balancing advantage. I can still see our weak/leaking cell, although only at half voltage loss compared to when it was separately monitored.  I have also run across some interesting cautions in the Orion literature about parallel strings.  Their wording includes this:

The use of parallel strings with lithium ion batteries presents many inherent risks and challenges that must be overcome for safe deployment. The use of this functionality by non-authorized persons or institutions is not permitted.

So it appears you are right to caution us all on using this configuration.  Although not 'illegal', 'not permitted' is pretty strong wording from them. 

Thanks again for your patience with us amateurs.  The learning curve is steep but worthwhile.  Dave

[Oberon Robinson]

Dave, an isolated DC-DC charger would go between your alternator and LiFePO4 battery -- in my case, I'm going with a 24V battery, so I'll be using a Victron Orion-Tr 12|24 which will take care of both voltage conversion, and charging on/off.  But if your VSR can perform that function for you, there's no need to add any more equipment.  You'll just need to figure out the voltage & current requirements for its enable/ignition input, and wire accordingly.

Remember that the SBMS0 has 4 available EXTIO options, each of which can be configured for either charge control or load control.  So you don't have to combine all your inputs into one.  Have you come across FilterGuy's I/O summary chart?  https://diysolarforum.com/resources/electrodacus-sbms0-i-o-summary-chart.112/  I found that helpful, in addition to Dacian's manuals.

Agreed about the learning curve!

[Oberon Robinson]

Also here's another resource I came across that might be helpful since you have a weak cell: https://www.repackr.com/#/pack-builder

[Dave McCampbell]

Hi Oberon.  Thanks for that useful info about the DC to DC charger.  My smart regulator can handle the charging and charge termination without much help as long as nothing goes wrong inside it.  I am just trying to find a suitable relay that the SBMS0 can use to disconnect it from the alternator or turn it off without requiring too many ma while the circuit is NC.  Someone on this thread must have a solution for this problem.  What relay are you using for the SBMS0 to control HVD for your alternator?

Yes, I have a copy and have studied the I/O Summary.  It is a very helpful document.  I am also aware of the 4 independent I/O options.  I was hoping to be able to reserve 5 and 6 for charge and load buss disconnects which would be at a different voltage than the separate equipment disconnects.  Are you doing this?

Thanks for the link to the repack guy.  We are still trying to get RJ to honor their advertised 5 year warrantee for our excessively self discharging cell.  It has been 6 weeks and many emails now since we notified them of the problem.  We are still working on it.

[Dacian Todea]

Dave,

Is a bad idea to parallel Lead Acid starter battery with LiFePO4 as I guess that is what you want to do trough the relay. For small DC loads most people use the Victron Battery Protect they have 65, 100, 220A rated versions and they can be controlled directly by the EXT IOx as they only need about 2mA for remote. They are also fairly inexpensive with the BP65 usually at around $40

 

[Oberon Robinson]

Hi Dave, I'm still in the design phase, so I haven't fully decided on my allocation of EXTIO ports - I do also like the idea of having a second level of protection just in case a critical component happens to fail.

For relays, I've got some of these guys on order: https://www.digikey.com/en/products/detail/ixys-integrated-circuits-division/CPC1706Y/3077519 -- they're 5mA to activate.  You'll also need about a 1.5kΩ resistor for the activation circuit.

That's the normally-open one, the normally-closed version is: https://www.digikey.com/en/products/detail/ixys-integrated-circuits-division/CPC1705Y/7776155

If you've got 10A in your alternator field wire, and you want to switch it with these SSRs, you'd need to parallel 3 of them.  They have a max load current of 4A.  But as Dacian said, if your VSR has a logic input for on/off, it should have a much lower current requirement.  Is that what your enable/ignition input is?  Do you have the specs for it?

If I understand correctly, you have two alternators, one for your lead-acid starter battery, and one for your LiFePO4 house battery.  Is that right?  Otherwise if you were charging lead-acid and LiFePO4 off the same alternator, you'd need an isolated battery-to-battery charger.

By the way, due to your post, I was curious about your smart alternator regulator, and looked up the commercial version, WS500.  Looks like a great device, but pricey!  I think I'll stick to voltage sensing and keeping my alternator draw to a small percentage of its rated output.  I'm building a van system, and like you, the alternator charging is just a backup option.

[Dave McCampbell]

Hi Dacian.  We have a catamaran with two engines, two alternators and two regulators.  The alternators only charge the house LFP bank.  I am not paralleling my one LA start battery with the LFP house bank.  All my charging sources go through a Charging Buss to the house bank.  The isolated starter battery gets trickled charged by the LFP bank through a diode and thermal circuit breaker.  The starter battery charging will not be controlled by the SBMS0 as the diode and tcb do that.  That part has worked fine for years, and I expect it to work well with the LFP.

What I need is to find a relay with considerably less activation current than the 42ma optoisolator I have, that can be controlled by the SBMS0 EXTIO4 along with the solar and AC charger relays, to turn off the two alternator regulators, if it exceeds voltage limits.  I can install these two relays in the enable/ignition circuits for the regulators.  I will check the specs on the regulators to see how much current that wire has when the ignition is on. I expect it will be very small so the BattProtects are much larger than I need.  Based on your advice, I already have two of those for the two charge busses.  Thanks for your advice.  Dave   

[Dave McCampbell]

Hi Oberon,

Thanks for the links to the relays.  5ma input activation current and able to handle about 4a load is just what I am looking for.  Looks like they have plenty in stock as long as you don't need more than 330!  Also, will go check our local sources closer to the Philippines.

See my note to Dacian above for our charging setup on our catamaran.  I will have to research how our VSR regulators' ignition/enable wiring will work with this relay.  More on that later so we close the loop on this for others. 

We bought our VSR (Very Smart Regulators) 5 years ago before the designer got together with owners of WP-500.  At that time the VSRs were based on an Arduino like, circuit board and required some sophisticated programming and much more wiring than other commercial brands.  But they were available to us at less than $100.  

My computer programmer wife did the programming, and I did the wiring with much help from the designer and a friend that had them.  As you have seen they are very capable and all parameters, including absorption tail current, are programmable.  So now I just need to find a relay that will let the SBMS0 EXIO4 control them at the same HVD setpoint as the MPPT and AC chargers.  And I will need on/off switches appropriately placed, so that only one charging source is on at a time.  That I have under control.  Thanks again for your interest.  Dave

[Oberon Robinson]

Hi Dave, DigiKey lists the number in stock under the "Price & Procurement" heading at the top right of the product page.  I checked the Philippines division of DigiKey and they have 339 in stock, so hopefully that will cover your needs. :) 

I would love to have a smart alternator regulator, or a smart alternator, but since my van came with a 260A alternator, I don't think it will mind if we draw 40A away for charging if we need to.  I'm just going to make sure I set the starting voltage in my Victron B2B to above the alternator voltage at engine idle, since apparently that's what kills alternators, when they have too much draw at too low of a speed, so they overheat.

I'm envious of your boat in the Phillippines, we are in the frozen wastelands of Canada, but starting to see the first signs of Spring.

On Sunday, 28 February 2021 at 22:19:57 UTC-5 da...@svsoggypaws.com wrote:

Hi Oberon,

Thanks for the links to the relays.  5ma input activation current and able to handle about 4a load is just what I am looking for.  Only problem I see on your links is the 12 week mfg lead time.  Do you think that is accurate for your delivery or does DigiKey have those in stock?  Also, will go check our local sources closer to the Philippines.

[Dave McCampbell]

Hi Oberon,

Great news.  Sherry is our procurement specialist so she is on it!  I am still working to find out the enable/ignition wire load.  

Just checked the ignition wire and it needs about 30ma to turn the VSR on.  So that means this relay will work fine there.  How did you calculate the 1.5K ohm resistor?  Using a 13 volt drop from 14.2v and 5ma load I get about 2.6k ohm resistor.  Maybe my assumptions are off?

The NO relay will be open when type 0 is set on SBMS0 and closed/relay on when type 1 is set?  Then open/stop charging if a cell goes high and the BMS shuts off charging?  This means there will be a 5ma load for each ignition wire relay on the EXTIO4 added to the other PV and AC relays when type 1/charging is on.  Have I got that all correct?

Yes, I think the alternator heat issue has to do with slow idle speed not providing enough fan cooling for high current alternator charging.  Have a good spring, we don't have that here.  It is summer all the time.

[Will OBrien]

I'm curious which 'smart alternator' you have.

Also, one convenience with using a Victron DC-DC is that you also have a direct charge enable link that you can drive from the SBMS0 (preferably with an external opto board)

There's a second reason to want a DC-DC charger - to protect your alternator. 

Victron made a long, if interesting video on this topic.

https://www.youtube.com/watch?v=jgoIocPgOug

[Oberon Robinson]

@Dave those are all great questions, and I will defer to Dacian as I'm not 100% sure of the answers and I don't want to mislead you.  This is not my main area of expertise!

[Dacian Todea]

Dave,

Not sure I understand your question. Are you asking about the CPC1705 / CPC1706 ?

Those will require a 5 to 10mA on the input so 1.5kOhm will be good choice with a 12V battery but you can increase that to 2.2kOhm if you need to control more of them and you do not want to exceed the 50mA capability of the EXT IOx

If you ask about DSSR20 then that has a 7KOhm input impedance so it will be using about 2mA can be less depending on what you select as external resistor on EXT IOx+  and you will want to have at least a 5Vdc on the Batt remote on DSSR20 if you form a resistor divider with the external resistor thus you do not want more than 10KOhm on EXT IOx+ if you control a single DSSR20 from a 12V battery.

Alternators are just about 50% efficient so if you output say 1kW from them 70A at 14V then there will be another 1kW wasted as heat thus alternator becomes a good size space heater and likely not even with good ventilation it will not be able to sustain that. Alternator's are designed to charge small starter Lead Acid batteries that will quickly get to 14V and thus start requiring less current so alternator will not overheat in that sort of application as the thermal mass is large enough for it to deal a few minutes with the higher current.

LiFePO4 will not get to 14V until they are fully charged so alternator will push all the current it can even above spec tring to get to the set voltage (as alternators are just simple constant voltage sources) and since this will take hours with a discharged LiFePO4 the alternator is more than guaranteed to get damaged thus the reason DC-DC converters with constant current limiting usually 20 or 40A are used in order not to damage the alternator trough overheating.

[Dave McCampbell]

Hi Dacian,

Again thanks for your informative reply. 

Yes, I am asking about the 1705/6 relays and which I should choose, the normally open NO or normally closed NC.  They are to be used with the SBMS0 EXTIO4 output to open or close the ignition/enable wire which turns on and off the alternator regulator.  I will be using 2 DSSR20s for the PVs and one DC-AC SSR for the AC charger in the same EXTIO4 so that I can set one HVD voltage for them all.

Here is how I think it should work:  A NO relay will be open when type 0 is set on SBMS0 and closed/relay on when type 1 is set.  Then open/stop charging if a cell goes high and the BMS shuts off charging?  This means there will be a 5ma load for each ignition wire relay on the EXTIO4 added to the other PV and AC relays mentioned above when type 1/charging is on.  Have I got that all correct or should I be using a NC relay for this?

[Dacian Todea]

You will need the normal open SSR so the CPC1706.  You will need one for the ignition signal and a different one for the 2x DSSR20 and DC-AC SSR.

[Dave McCampbell]

Hi Dacian,

Thankyou very much for that reply.  That answers my question about which relay will work for shutting down the two VSR regulators with the SBMS0 EXTIO4-.

However, are you suggesting that the two1706 SSR ignition relays cannot be wired directly in parallel with the two DSSR20s and one DC-AC SSR to EXTIO4-.  And I need to wire the DSSR20s and SSR through another 1706 and then into EXTIO4-?  

If so how should I handle the value of the resistor I should use for the EXTIO4+ to battery + wire?  I am not familiar with the term 'resistor divider' you mention in your previous post.  So a resistor value for 2 DSSR20s for PVs, one DC-AC SSR for AC charger, and two 1706 SSRs for ignition regulator wires, all activated from SBMS0 EXTIO4-.

It just occurred to me that these 3 charging sources will NEVER be used at the same time.  Only one source will be charging at a time and that is normally is only solar.  So it seems I will need on off switches in the wiring so that I can shut off two sources while the other is charging.  And then maybe separate EXTIO4+ to Batt+ wires with appropriate resistors for the relays involved?

Many thanks for taking the time to help us sort this out.  Dave

[Dacian Todea]

If you connect them all in parallel then all your charge sources will be disabled when engine is OFF (no ignition signal).

The DSSR20 has the equivalent of 7KOhm resistance on the Batt remote connection to GND that means that if say you connect a 7kOhm outside between battery+ (say 12V) and Batt remote connection then voltage at Batt will be half so 6V

The Batt input can take any voltage from 5V to 30V so not a problem but you need the external resistor to limit the current trough EXT IO4 that will be in series with this (assuming EXT IO4 directly controlling the DSSR20).

Is best if you draw a diagram of what you want to do then I can point out where there may be problems. 

[Dave McCampbell]

Will.  We have 5 year old VSR external regulators which are the predecessors of the WP-500.  Much same design(William Thomason) and functionality, but no longer sold.  I intend to have a look at DC-DC chargers once I resolve the current issues around our regulators and the SBMS0.  Guess I would need two of them as we have two engines/alternators.

Just watched your Victron video link.  Interesting.  Our VSR reg does both alt and batt temp sensing and has several methods to do current limiting.  It seems as though this takes care of the overheating issues shown in the video.

[Dave McCampbell]

Dacian.  Thanks and will draw a diagram.

[Dave McCampbell]

Hi Dacian,

Below find a hand drawn block diagram of my charging system on our catamaran.  The lines typically indicate the charging wiring to the batteries (VSR regulators with field and ignition wiring the exception).  Most cruisers with boats will have charging systems similar to this using at least the same 3 sources.  So it will be worthwhile getting this sorted out.

We only want to run one of the charging sources at a time, never two or 3 at once.  I will be using the relays we have been talking about above and shown below for the SBMS0 to disconnect the active charging source in case of a high voltage or SBMS0 failure event.  Since we will only have one source active at a time, I don't mind using on-off switches in the control wiring to the relays to keep the inactive ones off.

We are currently using the solar, wired as shown and HVD control from EXTIO4 with a 1kohm resistor.

Can you advise me if this wiring will perform the above functions and what size resistors I should use and their location. 

Many thanks in advance.  Dave

[Dacian Todea]

Dave,

The Batt+ resistor on EXT IO4+ can be just a 470Ohm to protect the EXT IO4 in case EXT IO4- is shorted to GND (battery negative) Then 13V / 470Ohm = 27mA so well below the 50mA limit of the EXT IO4 thus EXT IO4 is protected.  27mA x 13V = 0.35W so any half watt to one watt resistor will work just fine even in case of short to GND.

Then EXT IO4- will be connected directly to DSSR20 and to the SSR you have on the AC input line.  The DSSR20 will each take around 2mA max while the SSR depending on model maybe around 10mA or less thus about 14mA will flow trough the 470Ohm resistor thus about a 6.58V drop on that resistor meaning  if battery is at 13V there will still be around 6.42V at the DSSR20 and SSR controlling the AC input so good enough for both.

For controlling the enable on alternator's is best to use say EXT IO5 set as type 1 and then have the EXT IO5+ connected to the ignition signal (not to batt+) trough a 1kOhm resistor as this will limit the current to about 12 to 13mA and thus good to supply one or two CPC1706.

If this alternators are not connected to any other battery and are dedicated just for charging the LiFePO4 then you may be able to control the CPC1706 with same EXT IO4- just need to add 1Kohm for each CPC1706 (so between each CPC1706 and EXT IO4-)  and on the EXT IO4+ you will need to have two parallel 470Ohm resistors so voltage drop across is not to high when it also needs to supply the CPC1706

[Dave McCampbell]

Hi Dacian,

Thankyou very much for that wealth of information!  I will need a day or two to digest it and see if I have any other questions.  That looks like it will allow me to do what I want to do, and should be good info for other cruisers with similar charging sources.  Will get back to you soon.  Dave  

[Dave McCampbell]

Hi Dacian.  Does this rough sketch look like what you advised above for my control and resistor wiring for my 3 charge sources all wired in parallel to EXTIO4?  Many thanks.  Dave

[Dacian Todea]

Seems to be correct just of course you can not connect so many wires to EXT IO4- connector they will need to be connected all together to some external point then a single 24AWG will go to SBMS0.

[Dave McCampbell]

Dacian, thanks very much for that.  Just finished up my top balance yesterday, so now I can finish up the this portion of the system.  Good idea to externally connect all the control wires, then run only one to the SBMS0.

[Dave McCampbell]

Oberon.  How are you handling mounting the small 1706 relays and attaching them to the small Cat cable wiring.  The pins on those relays are pretty small.  Also, are you including the resistors somehow in your 1706 mounting or at the SBMS0 end?  It sure would be nice if someone was to design an all in one mount for multiple 1706s and their resistors.

[Oberon Robinson]

Dave, for my application I'm building a number of circuits into a perf board: https://www.digikey.ph/product-detail/en/bud-industries/EXN-23403-PCB/377-2626-ND/5886453

Here's a quick video on how they're used: https://youtu.be/Ro0_3bzqTkk

The other option I've considered, but haven't tried, is to solder wires directly to the 1706 pins, and heat shrink each of them.  That might be way too fiddly, and it would still need some kind of mounting option.

Unfortunately I haven't really come across any decent panel-mounted SSRs that would work for most people.

[Dacian Todea]

Dave,

If you do not want to solder wires then you can use one of this MRD 060D2 https://www.aliexpress.com/i/32889473704.html  you should be able to find them in many other places.

There are also many other options they just all cost more than the CPC1706 and also use more space.

[Dave McCampbell]

Oberon and Dacian.  Thanks to you both.  Will go have a look at those. 

[Dave McCampbell]

Dacian.  I don't think the Slim SSR you sent the link to will work inside my small Lexan box where the VSR regulators are located, but a flat mounted DC-DC SSR will.  That will also be much easier to wire up with the two very different size wires for the control to the SBMS0 and larger 14ga ignition wire.  Any problem using one of the flat mounted DC-DC single phase SSRs (like a Fotek 10a) for this application?  It would be in parallel with the two DSSR20s and the AC-DC SSR to EXTIO4 described in my posts above.

[Dacian Todea]

As volume the green SSR will be smaller but yes you can use any DC SSR. With Fotek you may need to buy two or three to make sure you get a good one at least based on my past experience. There are many manufacturers that produce the fake Fotek at lower costs.

[Dave McCampbell]

Thanks Dacian.  I was wondering why some Foteks were 1/3 price of others.  The earlier one I bought for the AC charger says it is made in Taiwan and seems to work as advertised.  So I will get several of the more expensive ones made in Taiwan.