LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[OceanSeaSpray]

Originally Posted by typhoon

My 600 ah house bank of Sinopoly's (8x300ah) after one year installed , balance at .003 and .007 volts in around a one third state of charge . I charge at 220 amps .

I just want to explain again why this kind of measurement is completely meaningless.

If you want to assess cell balance, you need to do it at the SOC the cells were balanced at, which is FULL.
This is because if you measure them on the "flat" of the discharge curve for example, significant differences in SOC translate into very little differences in voltage: you can't see anything.
LFPs always look beautifully balanced at 60% SOC. You need to compare when the cell voltage is something like 3.55V almost fully absorbed, with very little charging current.

[ColdEH]

Originally Posted by OceanSeaSpray

I just want to explain again why this kind of measurement is completely meaningless.

If you want to assess cell balance, you need to do it at the SOC the cells were balanced at, which is FULL.
This is because if you measure them on the "flat" of the discharge curve for example, significant differences in SOC translate into very little differences in voltage: you can't see anything.
LFPs always look beautifully balanced at 60% SOC. You need to compare when the cell voltage is something like 3.55V almost fully absorbed, with very little charging current.

Point taken , and that is where did the initial balance before I put them into service .

I don't concern myself with the balance at that state of charge now because that is not where I use my cells , I keep them well out of the knees on both ends of the voltage curve . If I see them getting a little out , I may balance them again at 3.55v per cell But for now they are working fine and I am getting my full 400 ahs ( thats all I use ) out of my cells with none of them running astray .

Regards

[ebaugh]

I've been away from the forum for some time. I read the last few pages with interest.

The only new experience I can add...we are commissioning a catamaran with a 1000Ah bank in each hull. Normally these banks are combined in parallel. Each bank has a BMS to protect high and low cell voltages and take the bank offline if necessary.

We have found that by charging to approximate 3.6V per cell, banks in parallel, the more discharged bank takes the charge and upon reaching "full charge" of 3.5V to 3.6V per cell or string of cells, it rebalances the two banks so they are in sync.

This install has 160 100Ah cells. 80 per bank. 10 per "string".


Sent from my iPad using Cruisers Sailing Forum

[JayH]

Hi Bob. Very timely post. The cells for my catamaran arrived today and I'll be doing the same thing: two parallel banks with a separate BMS for each one.

[GoingWalkabout]

Originally Posted by OceanSeaSpray

MOSFET transistors fail in switching applications due to stresses, typically voltage spikes at turn-off and current inrush at turn-on.

How much stress they endure depends on the load they are switching, their rating and how well protected they are by additional components. The issue is that stronger, more resilient devices cost more. If you want a fail-safe design, you also need to double them up, so it is now twice a higher cost compared to a cheap board using a single low voltage transistor for each output.

Solenoids should always have a reverse spike protection diode. The more current they switch, the harder they are on the control circuit. Because the problems arise from the transients at switching, it is hard to define what is or is not within specifications. The answer is to built the control circuit to industrial strength and it is more costly.

HI OcenaSeaSpray. I have enjoyed reading your posts on this LFP discussion. Mind you I have just started following it and have worked back a few links so my question may have already been answered and therefore redundant.

Since as you point out the load balancing boards/electronics are highly problematic and can infect do more damage than curing the problem they are designed for. My question is why are a lot of boaters using 100amp systems with many individual batteries in a bank rather than say a 500amp or 1000amp system in a singular battery or in 2 or 3 batteries?

Unless I am missing something the load balancing would be so much easier on a few batteries rather than banks of say 8 or more.

i know that when engineering particularly for a boat, engineering in redundancy is a good thing. But a redundancy that could cause and on board fire is far worse than not being able to run the fridge and AC while out on a passage. I would think that having a a couple of old tech batteries for switching over to for the critical instruments such as radio and GPS etc would be far better than stringing together a whole lot of batteries that could get out of balance or its add on electronics shorting out leading to an onboard fire.

I would seriously appreciate thoughts on this.

Thanks,
Chaya

[OceanSeaSpray]

Chaya,

If I read you correctly, you might be bringing together two unrelated subjects.

When you build a lithium 12V-equivalent battery, you string 4 cells of 3.2V in series to get the voltage. Those can get out of balance for all the reasons highlighted many times earlier.
When you want a lot of capacity, you just make bigger 3.2V "building blocks" by putting a few cells in parallel in each of them, but any imbalance is still only going to be between the 4 "units" in series. There may be plenty of cells in a battery like this, but there is no "redundancy". They are all needed in the same time.

If you want redundancy, then you need two battery systems. You can split a big 12V lithium battery into two smaller ones: it is a great solution, but you need two BMS, two sets of disconnectors etc. It is a bit more costly. Then you need to decide if you run the banks in parallel, or dedicate them to different circuits.

Alternatively, you can install a small deep-cycle SLA as a supply for critical loads. Since it remains fully charged nearly all the time, it should last many, many years if treated properly. This means that if you run the lithium house bank down to the cut-off limit, essential loads are not affected.
Incidentally, this is how I have designed my system. I have 3 load circuits:

1/ Essential instruments, chart table light, compass light on the standby SLA. It is a very small load, less than 1A altogether.
2/ Nav lights, VHF, SSB, etc on a feed that is normally from the house bank, but can be switched to the little SLA if ever needed.
3/ Everything else off the lithium house bank.

The engine has its own SLA starting battery, modest and completely independent, always full. This makes it a 3-bank system.

Arguably, the safest lithium topology is when you only have single cells in series, because if a cell fails internally, it just discharges itself and you get a LV load disconnect followed by a complete disconnect. This doesn't mean that I would call a bank with paralleled cells "dangerous". It is pretty safe, but it does have a new potential failure mode. This needs to be recognised and understood.

This being said, you can build 200Ah lithium systems out of just 4 cells that are still light and robust enough to be taken to sea. With decent charging arrangements and energy efficient loads, a 200Ah lithium battery goes one hell of a long way when living board.

Several of the systems I have built have been tripped on HV or LV (mostly) for various reasons due to actions their owners took afterwards or voltage regulation failure. No big deal. This is why the protection is there. These systems need to be engineered and built rock solid, so you can afford mishaps. No matter who does what/what goes wrong, you protect the battery so it never gets abused and remains safe to charge and use.

I hope this addresses your question.

Eric

[botanybay]

Originally Posted by OceanPlanet

Very nice! For many of these Yanmar engines we have been able to fit modified American Power 42i large-case J180's into the small case position, using custom pulley/belt kits. Not always...but when we can it is very slick for charging Li banks. Here is a pic of a recent custom 24V x 160A AP 42i on a Yanmar Y3M30. This was for a custom 53ft Bieker cat by Gold Coast yachts, so with two engines they can charge at around 250A @ 27V.

For 12V boats we have done similar, for a solid 400A @ 14V (two engines).

I have been looking for something similar for a Perkins M90, however, the alternator mount is on the aluminum timing cover and I am concerned about overloading it with a large alternator.

I have researched online and not found anything which is marketed to this engine.

Any thoughts?

Thanks

[PacificGreen]

So aside from one guy on youtube that made a rotary real time lithium battery management system where he can check individual cell voltages and adjust as necessary there haven't been many choices. Granted individual balance boards try to do the same but as posted are not sufficient for many reasons.

Retrieving individual cell voltages in real time is important and if you see one going south. So therein lies the dilemma. How now will the liveabord cruiser balance his pack?

After having played around with my trial pack of 72ah calb cells I concurr with many of the stated quality control aspects. I had to replace two of the cells in a relatively new 48v pack for reasons I'm unsure of.

Splicing two new cells into that pack and top balancing again was no picnic. To say that top balancing cells according to MaineSail and Pbase is time intensive.

I used a 4 port RC charger as many have I"m sure to accomplish this. Tops them up to 3.6v and shuts them off without fail. I set the charger on 4 cells and went to work for the day. Took four days to top them up. Then whatever else I did - wired in parallel let sit for a few days then charge all in parallel. From recollection.

What I had wished for in this case was three more of the HiTec chargers. I ran this off a MaxBurton 120vac to 12v 15amp converter. You can get the ac/dc HiTec chargers.

I'm making a jump here and I've connected mine to a 48v bank on one cell when all wired up and it started and read the correct cell voltages on my trial bank. So...

Would having 4 X4 AC Plus 4 Port AC/DC Multi-Charger | HITEC RCD USA hooked up to 16 batteries work.

It provides real time monitoring of cell voltages via USB. They don't have to be on all the time and I or another as the operator can make decisions to add or reduce current to individual cells as needed.

Wiring would certainly be less when compared to having 16 balance boards waiting to corrode and trigger the unforeseen HVC/LVC that spikes your charge controller under load.

So what I have to find out and work on more is how to wire the contactor to disconnect all the eventually out of balance boards. It is just not a factor I would like to be pursuing maintaining these little boards when 32 leads from the battery posts will be more than reliable enough and not prone to failure.

I don't have the luxury of going Dual Bus with my system. From my experience with my trial bank once done right the cells do not drift. I have read all of this thread and lean heavily towards the third day deckofficer and t1terry aspect of lithium battery management.

I'm not entirely impressed with the Junsi products as they have no option to take immediate corrective action while underway to avert cell imbalance. This way I could top balance the pack but am unsure if this can be done with the batteries still hooked up as 48v or would I have to wire them all in parallel? In essence I'm looking at it like larger cell monitoring boards but these ones actually pack a punch.

For all intensive purposes I have a 48v 400ah balqon pack. When the first cell monitoring board goes I will pursue this method. I need to be clear on how to simply wire the contactor to a simple on off switch that I manually operate.

During normal operation Low Voltage alarms are two 3000w dc smart generators. Tested these generators and they auto stop auto start at 45v and 56.5 volts. They are variable load generators and quite powerful in DC charging amps.

https://www.youtube.com/watch?v=2GmMqfDkrp4

and you can find them on ebay for one boat dollar each. I've tested two so far and although the quality upon delivery is not great they do produce 40amps or more at peak output. They can be ran in parallel and I have done so during my testing. Here is one in operation:

https://www.youtube.com/watch?v=owiXuuyf7EA

We tested both the Ray Electric Outboards during this past spring and both of the smart generators. The first time out we ran with for the most part 52.5 with one bad cell in the pack and the Ray Happily accepted that voltage. The videos reflect a proper functioning 48v bank with 16 good cells. There was a marked increase in power with all 16cells.

I output the generator current to my 440HVA Coleman Air charge controller. It took me awhile to get the exact setting 57 volts for the dump load on the controller but it comes on before the warning light on my HiQap balqon bms starts to flash.

So low voltage is covered by the generators starting or trying to start as the case may be. Choke helps but I'm sure they would start after a couple of attempts. By this I mean they try to start 3 times in each starting cycle. So far as I now this continues until they start so eventually they would warm up enough to start.

I'm coupling this with a large array of solar panels 2160w of 180amp 24v panels doing 80volts more or less at 35amps possible. So mostly I'm probably going to reduce the 57v dump load when away from the boat for long periods of time. The solar is simply disconnected from the battery when dump load occurs. I wanted to get away from having to have a dump load resistor wired in and that is possible because I'm using these two small generators instead of a wind generator.

I have not tested what would happen if I removed the battery from the generators during running to simulate a LVC/HVC cutoff from the BMS. All the more reason for me to remove the infringing LVC/HVC mechanism from the BMS. I don't think allowing some failure prone balance boards to manage my system to be a good thing.

On that note on a single bus sytem if I ever suffered a HVC/LVC event and it triggered a disconnect for whatever reason and my solar was charging would it damage more than my charge controller (sensitive electronics, appliances etc)? 440HVA has a fuse that may or may not prevent damage if battery is disconnect. Thus I will carry a spare board for the 440HVA and also a fuse. Just wondering about all the other circuit protected runs and if they would be affected.

I'm going to include some pictures and I'm bracing for the worst. I've spent the better part of three years building towards a very simple system for my 8m Catamaran and I'm about to start the installation.

Nobody said Marine electrical was easy or cheap but I did eventually get the pack wired up and tested various functions only to realize a little later I used the wrong color of wire for my positive leads. ChaChing and now will redo all those connections on install.

Here is a great video of my Ray Electric Outboard on my CraigCat running from my 72ah calb 48v bank. https://www.youtube.com/channel/UC6B...1XlLYww/videos and a good video of the Ray running full out

https://www.youtube.com/watch?v=DJh6BU5wbmU

I must admit I'm a little perplexed on how to wire the shunts to look neater but thinking they will all get placed in an enclosure. I will have five shunts. EV Display shunt, 2 for the Ray Electric Outboards, one for the generators/Lestronic II input will be on the 440HVA and the one shown for the solar input - it still needs a blocking diode installed.

I did easily manage to run my incinolet from the 3000w cotek 48v inverter at 38amps off and on for a couple of hours as that is how it cycles. I did manage to charge at around 24amps from my makeshift solar mounting options. I was able to charge at idle in parallel with two of the smart generators at around 24amps no load. I was able to charge on the solar input and generator input to around 22amps with both the Lestronic II battery chargers (I'm unsure if these can be ran in parallel.).

I intend to attempt some form of capacity testing on the bank once it is onboard and hooked up to my systems as otherwise there was no way I was dropping 400ah to 20%SOC during testing.

[PacificGreen]

Here is a picture of the contactor box supplied by balqon Lithium batteries - Electric Seas so it is a kilovac contactor and can I wire it for manual on off given what I have?

[T1 Terry]

Originally Posted by typhoon

Point taken , and that is where did the initial balance before I put them into service .

I don't concern myself with the balance at that state of charge now because that is not where I use my cells , I keep them well out of the knees on both ends of the voltage curve . If I see them getting a little out , I may balance them again at 3.55v per cell But for now they are working fine and I am getting my full 400 ahs ( thats all I use ) out of my cells with none of them running astray .

Regards

Haven't been here for a long while :lol:
Be aware that under charging the batteries constantly will result in a false fully charged voltage being registered. Hard to explain is simple terms but it's like pushing a load of dirt up with a dozer, when you stop you have a slight mound but the height the other side of the mound is less than the top of the mound. Now push a second blade full up to the original mound, it will be now higher but the height past the mound is still the same. repeat the process and soon the height of the mound will stop you from getting past it, even though the height the other side is close to the same height as the base of the mound you have pushed up.
It is a sort of memory charge, not the type we are familiar with but a memory charge all the same.
Charge to this end voltage and the capacity will appear to be getting less over time, charge to 0.10v higher per cell and you will be surprised just how many more Ah go into the cells before they reach this new high voltage. A few cycles like this and then recheck the capacity, you will find most of it has returned.
The same problem occurs if you don't occasionally deep discharge the cells, voltage appears to suddenly drop off yet if you push through the cell voltage recovers.

All this has been learnt from our now over 4 yrs daily cycling 24/7, over 1,500 cycles as house batteries in normal house battery use. The first deep discharge capacity test was a little scary, looked like we had lost 20% or more of the capacity, 3 good cycles to 3.8v and down to 2.6v and all but 5% of the advertised capacity was there between the normal 3.5v and 2.8v... gotta be happy with that eh Really don't know if more would have returned if we had continued but we were happy with what we got and we were running out of time.
Fortunately the only cells I have destroyed were my own, complacency and pushing the envelope.... and just really dumb things, probably more of that than any other cause, they are tough but they don't tolerate stupid very well

T1 Terry

[senormechanico]

Terry,

Missed you around here.

I found the same thing with my home's 700 aH 24 volt system. The battery only gets use when the grid fails.

My Magnum's inverter/charger with optional control panel's SOC said the battery was more charged than it was delivering when the grid went down.
I let the battery charge up to "full" at 27.4v but when I upped the setting to 28v it went right back to bulk at 110 amps for more than an hour.

Thanks for the post, it makes sense.

[Maine Sail]

Originally Posted by senormechanico

Terry,

Missed you around here.

I found the same thing with my home's 700 aH 24 volt system. The battery only gets use when the grid fails.

My Magnum's inverter/charger with optional control panel's SOC said the battery was more charged than it was delivering when the grid went down.
I let the battery charge up to "full" at 27.4v but when I upped the setting to 28v it went right back to bulk at 110 amps for more than an hour.

Thanks for the post, it makes sense.

I have only noted this once and that was when I went 80 cycles between a full discharge capacity test. I kind of panicked when the capacity suddenly dropped off by about 20 Ah's from only 80 cycles before. After the discharge and full recharge all the capacity was still there and nothing to worry about.. I suspect because I have been capacity testing every 50 cycles that I am not seeing the false ceiling effect quite as much.

Interestingly enough I have scoured the literature and not found any white papers dealing with this...? If anyone has one please let me know.. Still I continue to charge to 14.0V or less and the bank is still producing in excess of its rated capacity when discharged at a load well in excess of our average house loads.

I would have fully expected these cells to drop off a bit by now, they are 2009 cells, but they keep on chugging...

[senormechanico]

My home's bank has a 24/7 load of 0.6 amps.

I haven't found any provision for varying the Peukert exponent for lithium on my Magnum 4kw sinewave inverter charger, although I can set rebulk voltage, time of absorb and lots of other settings.
I suspect over time the SOC calibration just got too optimistic.
As soon as I upped the charge cutoff to 28 volts from 27.8 the 100% charge went to 99% and stayed there until the 100+ amp charge finally tapered down to 15 or so.
The next time I looked (maybe another hour) it had cut off and displayed "Silent", so I don't know if the current dropped further than that.
I DO know when the next power outage happened a day later, the voltage drop under similar heavy load was a bit less.
Imho, that seems to validate my suspicion of the inaccurate SOC reading.

[T1 Terry]

One sign that will be a give away to a memory effected cell pack or battery pack is voltage drop when the charging is cut. Those that use the simple 3.6v in any cell charge cut for X mins will see the symptoms immediately, a 7 day log on a Junsi logger will tell all if you know what you are looking at. The fix is simple, virtually effortless and shouldn't be regarded as down side, more a maintenance issue.


How many cycles till 30% DoD of the advertised capacity is the equivalent to a 100% DoD of the batteries capacity..... if you should live that long the answer will be interesting to those of us who can still remember the question :lol: The figures for 70% capacity remaining is up around the 8,000 cycles for quality cells well maintained, that is over 20 yrs. I would expect the cells to have died due to an error in control well before the 20 yrs are up. Those claiming Li will die at a given calendar life rather than cycle life will not be familiar with the maintenance requirements mention recently, the age related missing capacity returns with the correct maintenance procedure. Boiled electrolyte loss doesn't come back, bulged cells capacity loss comes back... well a fair bit of it, when the bulge is again compressed and the pack correctly strapped to prevent further bulging.
The best advice I can offer, read all you can read, sort out who does know what they are talking about and follow any others who have similar views and ideas, then work out just how critical the slight differences in ideas are going to be as far as the over all operation of your system. There are very few occasions when a one size/method suits all set up will be what you really need as power usage and recharging are as different as people and boats they are fitted in.... there aren't many identical ones of those are there :lol: The other tip, look at the specs for the cells you intend to use with a mind to the intended use, a cell that can discharge at 5C has very little relationship to house battery use, 0.5CA to 1CA is about the limit so you are looking for cycle life and discharge graphs within this range. There is no such thing as cheap Li quality cells, it's one or the other and always will be.


T1 Terry


T1 Terry

[CarstenWL]

Hi,

question on the size of a fuse for a 400Ah 12V Winston LiFePO4 system ...

- How do you choose the size of 'main fuse'? Will one Class T 400A fuse be ok? I have no load needing anything close to this but once saw a diagram on a 1400Ah LiFePO4 setup where 2x 400A where used in parallel ....

- How do you choose the size of the wire from the battery/fuse to the bus bars (short run)? Seems one would need 4/0 (120mm2)?

Thanks,

Carsten