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

[andyalford]

@Farang


My thoughts and opinions

• My 4x Winston 700Ah cells have gone up and down the charge scale for a few months now, and move in such beautiful synchronicity I wonder why I spent $500 on the REC-ABMS and another $1000 on anciliary protection gizmos
  • Like many have said, (MaineSail particularly) just get a good first balance, and that will do it - see LiFePO4 Batteries On Boats
  • Hence, I don't feel a strong need for the active balancing feature of the REC, 2.5A redirection at the last 3-5% of the charge cycle - a part of the cycle that I will generally avoid
• Having said that, the CAN-bus control from REC-ABMS to Victron's amazing VENUS OS (in my case, Raspberry Pi but for many CCGX.) This part is so sweet. I am currently using a Gasoline Silent-type Inverter Generator, which alters the throttle to load. So as the batteries fill up, I can hear the generator tone reduce as the current is reduced at the top 5%.
• In summary the REC-ABMS has not missed a beat. It works superbly. The bluetooth is a tiny bit buggy, but frankly I don't look at the display more than once a week, as the Victron VRM web graphs from data sent by VENUS OS / CCGX is so much more useful

Number of Cells

• I really like having just 4 cells, and I feel certain that the less cells you have the less balancing you need. But I have no direct experience of another configuration.
  
• I wish I could say something helpful about having 32 cells, but I can't. I nearly went that way, but words from CNB and others discouraged me. But I had not committed already so it was easy for me to change my plan, and I say again, I have no actual experience of that.
• I know that CALB have not manufactured 400Ah cells for nearly 5 years, so if you had got any of those, then they have been on a shelf for a while.
• Entropy wrote an excellent article on CALB 100Ah cells, if I recall correctly. See Engineering
• I took a few days out of my life to read this entire thread, and recall that around 1/3 through there was a lot of discussion about cell design, with fuses and cross links, several attached diagrams. As I was reading though, I thought that was a couple of years ago so theories might have developed since then.
• Another source for battery configurations is Nordkyn. He talks about dual banks with dual BMS and the benefits of redundancy / switching. See Assembling a Lithium Iron Phosphate Marine House Bank
• Generally I feel there is too much anxiety about LiFePo4 batteries, and they offer a superb solution, and much less problems than you might expect. At least that is my experience, and I hope yours is the same.

[MikeFergie]

The balancers cost $18 each
I use the BMS for low voltage and high voltage and temp protect as a last resort. The BMS is rated for 250 amps draw and 120 amps charging.

I have victron MPPT solar chargers, victron multiplus 3000/12/120 for shore power , a victron Battery monitor and victron voltage and temperature Bluetooth sensors on each battery. My controlling is all via these devices

[MikeFergie]

[ATTACH]204669[ATTACH]204670

[MikeFergie]

Originally Posted by mikedefieslife

I see you've gone with the Daly BMS. Did you upgrade the pitiful 6AWG wires? I wasn't happy with them on my 200a, so crudely added 50m2 instead. Of course the way around that is to just use the BMS to control a relay instead.

I haven’t decided long term. On my positive side right at the battery box I have fitted 250 amp anl fuses and on the negative side I’ve put in 350 amp shunts with a WiFi output to the lcd

[CatNewBee]

Originally Posted by newhaul

New video just posted about a review of the renogy 50 amp dc to dc with mppt solar built in
https://youtu.be/JtAUrS4zNSA
It seems to pass the smell test now I am actually considering one over the 40 amp unit.

Not impressed at all.

[MikeFergie]

Originally Posted by CatNewBee

Not impressed at all.

Nice for small systems but if you are running 700w+ solar just stick with a victron mppt controller and balmar etc external regulators for high power alternators but hey we might just see a 200 amp one developed in a year...

[newhaul]

Originally Posted by CatNewBee

Not impressed at all.

Ok now i respect your opinions so could you let me know the issues you see with this gear ?

Keep in mind my bank size and sizes of charging sources.
Future 240ah lfp bank
200 watts solar ( potential for additional 200 as needed flex panels

75 amp alternatir to be fitted.
Running fla start battery.

[CatNewBee]

Push button preset profiles with unknown setpoints for absorption and float, alleged MPPT controller with 20V maximum input - I guess it is only a PWM controller, 500Wp only. No configurable B2B thresholds for the ACR, you could drain your start battery while charging the house.

Not the right gear for me. Also the batteries with the built in BMS have limitations in contrast to a battery made from bare cells. 1C cut off is way behind from what a LFP can deliver short term (3C for some minutes and up to 10C for some seconds e.g. start current of a motor on a A/C, watermaker or dive compressor.)

So nothing special there, therefore I was not impressed. It's a (hopefully) cheap device with little functionality.

The B2B part was also not demonstrated (step up converter to push the charge to the house with higher voltage than the source), could be just a pwm controller and a ACR.

[newhaul]

Originally Posted by CatNewBee

Push button preset profiles with unknown setpoints for absorption and float, alleged MPPT controller with 20V maximum input - I guess it is only a PWM controller, 500Wp only. No configurable B2B thresholds for the ACR, you could drain your start battery while charging the house.

Not the right gear for me. Also the batteries with the built in BMS have limitations in contrast to a battery made from bare cells. 1C cut off is way behind from what a LFP can deliver short term (3C for some minutes and up to 10C for some seconds e.g. start current of a motor on a A/C, watermaker or dive compressor.)

So nothing special there, therefore I was not impressed. It's a (hopefully) cheap device with little functionality.

The B2B part was also not demonstrated (step up converter to push the charge to the house with higher voltage than the source), could be just a pwm controller and a ACR.

I had not noticed the max voltage input of 24.5v ( had to reread the manual on that one ) thank you for pointing that out.

The unit is not actually a b2b unit it is more like a 2 bank charge converter ( alternator voltage and start battery voltage same . Converts alternator output voltage to Lfp ( if set that way) acceptance voltages. That part is only active with the alternator active.
The solar controller while limited seems to be the split charger .
I will look more into it . Thank you for your input it may just save me a battery or a lot of money.

[Farang]

Having said that, the CAN-bus control from REC-ABMS to Victron's amazing VENUS OS (in my case, Raspberry Pi but for many CCGX.) This part is so sweet.


Exactly, and leverages your already significant investment in Victron gear which is enough use case right there.

[*]I know that CALB have not manufactured 400Ah cells for nearly 5 years, so if you had got any of those, then they have been on a shelf for a while.

I wish my supplier (Evlithium) had told me that before accepting my order (and money) ;|

[*]Entropy wrote an excellent article on CALB 100Ah cells, if I recall correctly. See Engineering


Will go check it out, thanks


[*]I took a few days out of my life to read this entire thread, and recall that around 1/3 through there was a lot of discussion about cell design, with fuses and cross links, several attached diagrams. As I was reading though, I thought that was a couple of years ago so theories might have developed since then.

So much good info here but I didn’t go back far enough it seems. Will do a search.


Another source for battery configurations is Nordkyn. He talks about dual banks with dual BMS and the benefits of redundancy / switching.

I did read his excellent white papers but must have missed that. Will take another look.


Generally I feel there is too much anxiety about LiFePo4 batteries, and they offer a superb solution, and much less problems than you might expect. At least that is my experience, and I hope yours is the same.


Thanks, I’m sure it will be.

[/QUOTE]

[gscriba]

For those using them, how low do you go with your voltage? Love my 700 ah Winstons (4 cells/700 ah each) and REC-ABMS. With a typical slow draw of anywhere between 2.5-10 amps, there must be some general cell voltage "guideline" of when to recharge that others are using? At present time, I'm recharging using my Xantrex SW 3012 with a bulk and absorption voltage of 14.6v, two stage charge, no float.
As you can see from the picture, three days following a charge (Xantrex charger cuts out at 14.6 as measured by the Xantrex, which is higher than what the REC-ABMS is measures at cut off time), the REC currently measures 13.01v for the bank, 3.257v per cell. I have attached the Winston voltage curves.
Interestingly and as a side note, the Simarine monitor is anywhere between 0.14 and 0.2v lower than the REC. So REC measures 13.01v and Simarine measures 12.86v.
So, at what point with a slow draw, should I recharge? When the REC is measuring 3.1v at the cell level? 3.2v? I am considering the REC to be the most accurate due to it's measurement of the individual cells.
Thanks in advance.

[evm1024]

I would suggest that you get a Victron BVM702 or the like and measure the AH used. You can then either recharge when you reach a specific consumed AH or build a table that equates SOC with voltage.

Given a sync at full the consumed AH is quite accurate.

It will also allow you to measure the actual capacity of your cells.

Take a look at these curves which show that capacity differences are quite minimal between charging to a limit of 3.5 to 3.7 VPC. The idea being that charging to a lower voltage will give greater cycle counts over charging to a higher voltage.

https://www.powerstream.com/lithium-...ge-voltage.htm


Be aware that Xantrex had 2 different models of their SW-3012. The newer model has user settable charging parameters.

I had the older model and was always fiddling with the charge parameters (mostly the max charge current limit). I sold that and went to a Victron Multiplus 12/3000/120-50 120V which allows me better control over charging and discharge parameters.

The only thing that I really liked about he Xantrex was the ability to just do pass through I.e. disable charger and inverter. This can be done on the Victron with the Two-Signal BMS assistant installed.

I also have Winston 700 AH cells in my house bank. I did buy seconds so one of the cells limits the capacity to 500 AH. I've been running them since 2014 and also love them.

PS in my experience getting accurate cell voltages is difficult with all of the "inexpensive" cell monitors. I could not say about your bms. But, I do check the accuracy of all measurements in my boat with a Calibrated Fluke 87V meter.

[gscriba]

Thanks for your thoughts.
I have the newer Xantrex with the custom settings (as previously noted, two stage with bulk and absorption custom settings).
When the preset voltage is reached (14.6v), the charger stops so the actual resting voltage is considerably lower. I'll check next charge cycle. Good reminder to check that.
The Simarine does count amps and though the voltage is different then the REC, it is consistently different. When I randomly check the voltage at the battery, the measurement also is consistently in between the other two readings (REC and Simarine). Interesting to note the voltage curve provided for the Winstons appears to me to be pretty close to the amp count/capacity percentage.
So at what amp count do you recharge and what does your Victron read as the voltage in relation to the point you do recharge?
Thanks again.

[john61ct]

Anywhere between 12.2V at the bottom while resting, up to 13V you could recharge.

There's no real point waiting for the former if recharge energy is readily available, unless you wanted "storage mode" for longevity, knew you weren't going to be feeding loads for a while.

And no point starting to recharge at the latter higher point, unless you knew you were going to need to be using most of your capacity soon.

This assumes you wanted to optimize for longevity, lower SoC most of the time is better than sitting up near Full.

But tricky to automate, since only you know how readily recharge energy is going to be available, and what sort of loads you will need to feed in between.

Some people if not most are happy to recharge at every opportunity, even if that means the bank sits at high SoC most of its life.

They will still get many years' life from their bank, but not nearly as many as the owner making the extra effort to optimize the many variables involved.

And note the above assumes resting voltage. While loads are active, if low current, sag may sag half a volt or so, hard to guess SoC at the ideal middle ranges, so that's when a SoC meter can help.

The 12.0V limit might be say 10% of usable SoC, best to not get anywhere near that unless you really need to, and then only occasionally.

[newhaul]

Originally Posted by gscriba

For those using them, how low do you go with your voltage? Love my 700 ah Winstons (4 cells/700 ah each) and REC-ABMS. With a typical slow draw of anywhere between 2.5-10 amps, there must be some general cell voltage "guideline" of when to recharge that others are using? At present time, I'm recharging using my Xantrex SW 3012 with a bulk and absorption voltage of 14.6v, two stage charge, no float.
As you can see from the picture, three days following a charge (Xantrex charger cuts out at 14.6 as measured by the Xantrex, which is higher than what the REC-ABMS is measures at cut off time), the REC currently measures 13.01v for the bank, 3.257v per cell. I have attached the Winston voltage curves.
Interestingly and as a side note, the Simarine monitor is anywhere between 0.14 and 0.2v lower than the REC. So REC measures 13.01v and Simarine measures 12.86v.
So, at what point with a slow draw, should I recharge? When the REC is measuring 3.1v at the cell level? 3.2v? I am considering the REC to be the most accurate due to it's measurement of the individual cells.
Thanks in advance.

on my boat with my camel brand cells I keep the 100ah bank between 12.5 ( 3.125 vpc) and 14.2 ( 3.55vpc ) most of the time .( simple control via solar controller. ) push it to 14.5 ( 3.625 vpc ) once a year for balance and ah testing.

I expect to do the same when I get my new 240ah bank in place