LTO Cells

[Jim Jones]

Wondering if your controller can handle LTO cells? (2.4v nominal per cell).

Why LTO cells? I need to dump as much power as possible as quick as possible for 16 x 500 wat panels into a battery and LTO has a massive C rating for both charge and discharge.

The only other alternative would be LiFePo4 cells that can do this - possibly headway cells?

[Dacian Todea]

LTO have zero advantages. The SBMS can handle LTO but since is 2.4V that means either a 12V (6 cells in series) or a 18V 8 cells is possible.

For same money you can buy 2x to 3x the LiFePO4 capacity so you can easily charge at the same rate for the same amount of money.
And 16 x 500W is not a problem but why 500W panels ? Those are likely huge and maybe those are 72 cells so not very efficient unless you spend extra money for MPPT.

But 8000W PV array say at 27V (8s LiFePO4) is about 300A

So a at least a 8s3p battery made with 280Ah cells (popular low cost LIFePO4).

For example this are the cells I got recently (will install them in a few months)  https://energiepanda.com/product/4pcs-eve-3-2v-280ah-deep-cycle-lifepo4-battery-cell-lf280k/

4 cells cost $699 that includes shipping and import taxes so 8s3p will cost about $4000 but you have about 21kWh storage capacity.

For same amount of money you can probably get less than half the LTO capacity and while it will handle the 2x or 3x charge rate it will be fully charged in an hour or less and then you just have unused solar energy.

Also while you get less than half the capacity for same money with LTO the weight will be about the same so shipping costs also about the same part of the price.

I guess you refer to the 40Ah 66160 cells.

You can get about 16 of those cells for same price as 4x EVE LIFePO4 cells.

LTO           16 * 2.4 * 40Ah = 1536Wh

LiFePO4   4 * 3.2 * 280Ah = 3584Wh

LTO weight    16 * 1.2kg = 19.2kg

LiFePO4         4 * 5.4kg = 21.6kg 

Based on spec AC impedance of those LTO cells is about 0.4mOhm so around 0.7 to 0.8mOhm DC internal resistance.

The LIFePO4 EVE cells 0.25mOhm AC so around 0.4mOhm DC

With 5 cells in series LTO you can not quite use the entire capacity due to large voltage fluctuation. But since there are 16 cells we compare say you use a 5s3p (15 cells) to build a 12V battery.

LTO battery total DC resistance will be 0.8mOhm / 3p = 0.26 * 5s = 1.33mOhm

LiFePO4 battery total DC resistance will be 0.4mOhm * 4s = 1.6mOhm

So 1.33mOhm vs 1.6mOhm not much of a difference so both of this batteries will handle the same charge rate assuming you are willing to accept the same loss as heat.

The cycle life is also not that different considering the EVE is rated at 6000 cycles but has almost 2.5x the capacity on each cycle. And in real world they will both have about the same calendar life witch is the limiting factor in most applications.

[Jim Jones]

Hi Dacian,

Thank you for taking the time to give an in-depth reply to my question.

Let me give you the back story to this. Your advice is highly appreciated. I have been following your progress for some years now but never had the need for your controller - It is a fascinating idea you have - to store solar energy in water.  

My situation is that I want to power a boat with an electric motor. The motor is 10Kw @48v. I would like to use LiFePo4 on this boat to store energy for this motor and I am considering a big bank of batteries - around 143 kWh - so about 120kWh useable. It only depends on space on the boat - weight is not an issue as it is a 40ft displacement boat. The boat weighs 11t (aluminium hull/deck). A rough calc is about 90Kg per 48v/16s battery. Each battery is about 14.3kWh , so 10 of these batteries. Should be in the ball park of 900Kg. The existing motor/gearbox that will come out is close to 300Kg, so I will be adding approx 600Kg of extra weight to the boat.

So a battery made of LiFePo4 280Ah cells at 10P16S =  is 2800Ah for 143kWh total capacity. So if charged at .2C means I could charge these batteries at around 500 amps. (Looking at using Seplos battery system/cases - can put a total of 16 batteries in parallel).

However the complication is that I cant fit solar panels on this boat. So I will be having an auxiliary boat following along (which I needed regardless of solar and charging or not). On this auxiliary boat I can build a canopy covering the whole deck area - so approx 10m long x 3m wide. So can use big panels. 

The rough idea for now that I am trying to figure out if it makes sense or not, is to have batteries on this axillary boat to charge from the large array covering the deck and then when that battery bank is full, pull alongside the main boat and transfer this power over to the LiFePo4 bank on the main boat. 

The 1st advantage of using LTO batteries is they are the SAFST chemistry out there. I will be on the main boat and my guys (all locals) will be on the axillary. So safety is an issue since they know nothing about batteries and would not be able to handle an emergency if something went wrong with the battery bank. 2nd advantage is they charge FAST and can discharge fast. So If I built a 48v bank of LTO at 400Ah using those 40Ah 66160 cells (so 220 cells)) , they could be charged quickly and as soon as full, the boats heave too and an umbilical cord is passed from the auxiliary boat to the mother boat and the power in the LTO's transferred to the large LiFePo4 bank. 

On the surface of it, it seems doable. The LTO bank on the axillary boat can handle a 500 amp discharge without breaking a sweat and the LARGE LiFePo4 bank on the mother ship can handle a 500amp charge rate without harming the LiFePo4's. I would like to repeat this several times a day (as many times per day that we can manage). All of this is happening on a large freshwater lake where we will be diving, not out on the ocean where all this may be very difficult to accomplish. This is in the tropics with a good 6 sun hours per day. We have an abundance of sun at this location and will only be operating in the dry season since in the rainy season the chance of a lightening strike is too great.

A 48v LTO bank is 22 cells @40Ah. So to get to 400 Ah @48v will require 220 cells. At 1.25Kg each this will be around 300ish Kg with cabling/buss bars etc. This is very manageable in terms of weight on the auxiliary boat and the space is available for these big LTO cells.

One problem I am not sure of how to overcome yet is how to transfer the power - possibly DC to DC charger? Can I get a DC to DC charger that big ? If not then I could possibly use an inverter to send out the power from the LTO bank as AC to the Inverter/Charger on the mother ship - but there are nasty losses in that type of system. I am open to any ideas on how to do this.

So how could I possibly use your system to manage all this?

[Dacian Todea]

So you will have a 10m x 3m = 30m^2 of solar panels on some auxiliary boat (not sure if this is always connected to the large boat or it will move independently some area around the large boat).

30m^2 * 1000W/m^2 * 0.2 = 6000W max PV array and so a full sunny day maybe 30 to 36kWh

To me the battery seems way to large if this is the only energy source and it is sunny every day.

Charging a battery from another one is extremely expensive and you may be worst of that using diesel or gasoline.

It will be useful to know what is the original engine power and what sort of fuel consumption you had in order to estimate the energy needs before converting to electric not to significantly oversize the electrical system.

Your consumption should stay below 30kWh/day if all you have as energy source is a 6kWh PV array in a sunny place with no shadows.

With this in mind a 143kWh battery will not make much sense.

[Jim Jones]

Thee Auxiliary boat will be powered by a small Yanmar diesel engine. This aux boat will be carry diving gear/compressor and divers/food supplies etc. Sometimes it will move independent of the main boat (main boat will stay moored at home and not be used) This aux boat will be happening no matter the outcome of what we do with the main boat.

The main boat has a Volvo 55 HP engine. Approx 4.2l/Hr of fuel at 2000 RPM. It has a 115amp 12v alternator fitted but this is to charge the start battery only - NOT for charging LiFePo4 batteries.

The 55HP needs an overhaul - about $8K USD. If I wanted to charge a 48v LiFePo4 battery bank I could install a 48v/100amp alternator and  Wakespeed 500 Regulator. This means a new 48v alternator at apprx $3500 USD, and a custom set of pulleys and brackets - at least $2000. The WS500 will be approx $700. Wiring, breakers/fuses and labor to do all this will take me to around 10K USD to install an alternator charge source to charge the LiFePo4 batteries.

De-rated to around 75% output the 48v/100 amp alternator should put about 3.5kWh of charge into the batteries at 2000 RPM cruising speed and take 4-4.5 litters of diesel per hour to do this. The life expectancy of the alternator is around 1500 to 2000 hours of use. All up this is an expansive way to charge batteries.

I have shore power where the boat is moored and so will leave the dock fully charged. The reason for a big battery bank is for x days of autonomy away from a charge source. It is a yacht after all and the plan is to sail as much as possible. Several of the places we visit are 70NM away and have charge points at these destinations, so will charge from mains at arrival and while there. There is several hundred NM of coast with no charging facility - hence the idea to build a PV platform on the aux boat. We often stay at a given dive site for 2-3 days - sometimes 4 days. So there are days of little engine use but can harvest solar charge while anchored at these sites. These dive days at a site can be used to get the bigger LiFePo4 bank back to full. Plus we need power on the main boat for refrigeration/lights at night, laptops etc.

Having a large LiFePo4 battery bank allows longer times away from any mains charge source so that the refrigerator and freezer can stay cold all the time and still have enough power in the bank to power an electric propulsion motor. Diesel is difficult to get in these places and if it is found is always in 210 ltr drums and is suspect at best. Propane cant be found in this region at all. So all cooking has to be electric/charcoal BBQ. So we need refrigeration/freezer/electric cooking/lights/instruments (radar and IP cameras are most important) and laptops/charging cameras etc. All of this has to come off a house bank and I would like about 5 days of autonomy. Thats how I get to the LiFePo4 bank size. As mentioned, while anchored at a dive site for a few days the PV system will be able to recover the LiFePo4 bank to almost full.

I can get a nice 48v 55amp DC charger for around $2500 USD. https://dcautogen.com/

This could be useful to put some charge back into the LiFePo4's on days where the batteries are run down and we cant harvest enough PV.

We could keep the Diesel engine and just spend the 10K to recondition it and refit it back into the boat and then spend another 10K to fit the LiFePo4 alternator charge source. It seems like now is a good time to go electric if we are ever to do it. A big attraction to the electric motor is little to no maintenance. The diesel needs servicing every 100 hours and this is expensive where we are. Then there are the heat exchanger issues and the cost of maintaining this system. Electric seems to be a good way to get rid of mechanical issues. No engine/gearbox to fail or service or maintain.

its an interesting thing to ponder for sure.

[Jim Jones]

48v DC genset.

https://www.youtube.com/watch?v=aT0qkicuDug&t=67s

[Dacian Todea]

I have zero knowledge about boats and have almost no info on your use case.

It seems is not just about propulsion but also electric cooking and refrigeration but not sure for how many people or what you use currently in propane as you can convert to what you will need as electricity.

It will have been more relevant to know the fuel consumption per distance traveled rather than how much the engine uses per hour at 2000rpm that means nothing without knowing the load on the engine.

But such an engine is at best about 20% efficient so with 9.7kWh/l * 0.2 = 1.94kWh * 4.2l = 8.148kWh sy rounded to 10kWh needed to do the same sort of work with an electric engine.

I do electric cooking for two people and have a fridge/freezer plus LED lights and computers and I average 4kWh/day for all those things and only have a 4.5kWh battery.

A typical propane tank here contains 8kg of propane and that has about 100kWh worth of stored energy (cooking with that may be 60 or 70% efficient) so equivalent with 60 or 70kWh of electricity it is just more expensive as here is about $20 USD that means about $0.2/kWh similar to cost of storing energy in LiFePO4 so it will not be more cost effective to directly use energy from a LiFePO4 but if you could use PV solar directly that is an order of magnitude less at just $0.02/kWh thus the reason I heat my house with solar PV but I do not use LiFePO4 for heating as that will make it as bad as heating with propane gas in therms of cost.

[Jim Jones]

Sure - understand all you have said.

We have propane on the boat but have to go 2500 Klms round trip to go fill the propane tanks up! So we tend not to use it very much. We do a lot of charcoal cooking on a BBQ, and also for heating water for tea/coffee etc

I just spoke with the electric motor people. They say thier 20kW motor is a better fit for my hull. They estimate about 4 to 5 kW to push the boat at around 4Kts and about 2kW to push the boat at 3Kts. The slower we go the less power used. 

Anyway, what I am wondering about is, how can I transfer the power from the Aux battery bank to the main boat bank and are your devices useable in my scenario?

I need to stay at 48v because of the electric motor requirement for 48v. Is it possible to use your devices with 48v at all ? Do you think you will ever go to 48v devices?

[Jim Jones]

also, forgot to add. The current diesel pushes the hull to about 4.5 Knots for approx 4 ltrs an hour (normally sits at about 2-2200 RPM to do this).

I do get that this is way way off track for what you normally do. The interesting aspect is using a PV array on the aux boat to charge a battery bank on the aux boat and then transfer it to the main boat. I need to charge batteries. The aux boat could be a 24v system so your system could work there. moving the power from 24v to 48v is doable with a DC to DC convertor - I just dont know how much power can be moved like that and how fast or slow this would be.  

The thing about the LTO batteries was charging them fast so that we could get several charge cycles a day out of the system - that and the safety aspect. LTO's contain no carbon and so cannot burn no matter what. 

Doesnt apply to me as I am in the tropics and we never go below about 16c at night in winter and average 24 to 26c at night in summer. Daytime is always hot - 35c. But for you in Canada - LTO's can be charged at up to -50c with no damage to the batteries. That could be useful to some people.

[Dacian Todea]

The SBMS can not be used for 48V systems and I do not have any plans for a 48V BMS.

If your diesel requires about 4 liters for 4.5Knots then about 8 to 10kW will be need from an electric motor to get the same. (it depends on how efficient the Diesel engine si but the smaller ones are likely not above 20% all included so maybe around 8kW).

The problem with using an intermediary battery is that the price of energy will be double.

Best case scenario (realistic) for any LiFePO4 or LTO battery over usable life will be $0.2/kWh

So say you need 4 liter of diesel at $1.5 per liter for one hour it will cost you $6 total

With electric if you need 10kWh it will be $0.2 * 10kWh = $2 just for the battery amortisation but if you need two batteries so you charge one from the other that doubles to $4 so you are getting very close just with the batteries then when you add amortisation for electric motor and controller plus inverters and solar there may not be any financial advantage.

The main problem is adding an intermediar battery for charging as that will just double your energy storage cost.

You proposed a 20kWh LTO or something like that with a 5 or 6kW peak PV array that will produce best case about 30kWh per day thus you can not even charge the LTO twice a day with the amount of solar available from that PV array.

Especially if the aux boat requires also some of that electrical energy, then it may just be one charge cycle per day.

If that aux board was connected to the large boat then you could charge directly from solar and since solar PV panels are already constant current source you also do not need any DC-DC conversion and the cost is significant compared to your proposed high power DC-DC converter.

Also about cost you need to consider that with electric is like you pay in advance so is like purchasing now all the fuel you need for the next 15 to 30 years.

Regarding battery charging below freezing all types of lithium batteries including LTO will be affected. But in most cases battery is inside a climate controlled room like it is the case for my battery witch is just a bit more than 1m from my computer inside the house where temperature will not drop below +18C

For mobile applications an insulated box with small electric heater 10 to 15W is sufficient to keep the battery above +10C and you sure prefer a battery that for same weight has 2 to 3x the capacity so LiFePO4 will easily win against LTO in all applications I can think off.

And yes safety is slightly better for LTO but LiFePO4 is also fairly safe and if protected by a proper BMS it will be perfectly safe.

There is a reason why LTO has such a small market share compared to LiFePO4.

In any case my SBMS can handle any type of LiFePO4 battery including LTO (there is even a preset for LTO) but max 8s.

[Oberon Robinson]

Jim, it sounds like you've done a lot of creative thinking about what would work for your situation.  I'm wondering why you wouldn't just connect your solar barge with a DC umbilical cord, and keep all your battery and control equipment aboard your yacht.  That would be a lot more efficient both for time and power than having an intermediary battery that you have to dump in batches into your main battery, which will take a significant amount of time per batch, and also increase your electrical losses.

It also sounds like cost is not really a concern.  I'd suggest you look into Batrium BMS for your 48V system.  As much as I love Electrodacus, it doesn't seem like it's an ideal fit for you.

Oberon

[Jim Jones]

Some really good points you have made. This give me food for thought - I will have to engineer this a different way. Not sure what I will do at this point as there is a lot involved in all this. Its not just dollars and cents. Its about living the lifestyle one wants and out in the boonies far away from civilisation its hard to put a price on that.

For not though I need to re-read this thread a few times and take some notes to mull over.

Thank you for your deep insights into this topic.

[Jim Jones]

Hi Oberon Rob,

Yes, I have a lot of years of being out there doing this the hard way - so there has been plenty of time to read, study and think about it all. 

Thanks to Dacian's input i have come to the realisation that moving DC power from battery to battery (in a meaningful way - ie, lots of amps) is not going to happen. I do get your point about the umbilical cord between boats. It fraught with issues though and thats why I am trying to avoid it. Its not impossible - just lots of things that can go wrong. There are certainly times when the aux boat can be moored alongside the main boat and in that situation the umbilical cord to move power from the solar panels to the main battery bank works fine. At other times the aux boat is out and about by itself while the main boat remains at anchor in a protected bay or cove. At still other times, the main boat will remain at home and only the aux boat will move. So it just wont work out very well.

I am not sure yet but I am thinking that it may make sense to build a 24v LiFePO4 battery in a pelican style case that can be connected to another such 24v case and so on in parallel to get enough amp hours. By staying at 24v its less batteries in a case and so more manageable in weight to move around. The idea being that after a string of "24v cases" are charged by the solar array on the aux boat, they can be disconnected from each other and moved to the main boat for direct connection to the inverter for discharge. As Dacian points out, with only 6kW being produced in an hour a LiFePo4 battery can easily handle this input - I still prefer the LTO's but they are big and heavy batteries - so not ideal for the pelican case idea. 

I am looking at TAO BMS for the main boat BMS system. I like Dacian's BMS for the aux boat. By coming down to 24v because of weight issues for a battery in a case, it becomes possible again. I dont know yet.......thinking about many ideas on how to do this - I listen to everything and rule nothing out. Sooner or later a solution will be found. Problems are just opportunities in work clothes.

[Richard Bewza]

Jim,

I have been thinking about your electric boat project and I have a suggestion.

Calculate the maximum battery weight after installation of electric motor and a 70kw diesel generator and fuel. Example: 20 x 48v 280ah batteries would give you 50v x 5600ah = 280kw of energy. 

Leave the dock with a full battery and come back to the dock with an empty battery using the 70kw diesel generator to recharge when away from the dock. In order not to overtax the 70kw generator you could charge the batteries at around 50kw and that would be an acceptable rate for your 280kw battery Bank. 

You could also add 2kw or 3kw of solar panels to your flybridge and bimini for use at anchor.

Rick

[Richard Bewza]

Sorry, I wanted to add that the 280kw of batteries would weigh about 90kg x 20 = 1800kg or 4000lbs

[JFA_in_Montreal]

If solar energy is only a minor addition to the overall power (say. 2kw for 6 hours vs 20 or 30 or 70kw for cruising 24h/d), if you'll be using diesel anyway to recharge the batteries,  I fail to see what's the advantage of electric over diesel.

The diesel motor runs at pretty constant output when driving the prop, silimar to what it does  when driving an generator. When you use an electric car, the electric motor is efficient because the combustion engine is not efficient when running at varying RPM and torque/load.
But a boat propeller is the condition that makes combustion engine happy (constant RPM/load) and combustion efficiency could be optimized.

So why add the electrical losses of an electric motor system?

Large cruise ships use electric motors, but their systems are different, highly optimized, and what they loose in raw efficiency they gain, size of installation, and reduced weight and navigation advantage (thus increasing their payload).

As for the weight of the batteries, maybe we should ask EVE or CALB to make cells in the shape of a boat keel... :-)

[Jim Jones]

Hi Richard,

Thanks for your thoughts. The main boat is only 42ft - no way I can carry all those batteries - although I would like too!

[Jim Jones]

yes I am coming to the same conclusion. There is a lot of energy in diesel fuel and it fits into a small space !

Of course there are pitfalls to diesel too - getting clean fuel were we are located is not easy and there is the maintenance of the engine itself.

I have to say though that it is really looking like the best solution is to simply leave the diesel engine in place and just carry enough battery for house bank duties.

[Oberon Robinson]

Jim, have you considered moving to a hybrid diesel-electric engine?  They offer a lot of benefits, including working as both a generator and electric motor, plus using either or both diesel and electric for propulsion.

I'm very curious which part of the world you're in, and what you're doing out in the wilderness for months at a time?

Oberon

[Jim Jones]

Hi Oberon,

Yes had considered a hybrid. Just cant get one anytime soon. It does seem to be the perfect solution though. Also very expensive so from a pure dollars and cents thing they make no sense at all. However sometimes its about more then money.

I am in Africa. I photograph the underwater world.