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

[OceanPlanet]

Originally Posted by Hoopla

Most high capacity LFP friendly chargers seem to be only readily available as Charger/Inverter Combos. However people are reticent about using them as a combination as they use a common DC source/supply cable connection which renders either the BMS's HVE or LVE protection useless. In so far as Victron units are concerned there is a workaround.

This workaround can even make older model Victron Multiplus or Quatro Charger/Inverter units very LFP friendly in terms of both AC and DC surge issues and for cell voltage protection.

More modern Multi/Quatro units come with Auxilliary Sensors (potential free contacts that can be configured to operate open or closed) which are connected to your BMS, possibly via a relay(s). The BMS can then turn the Charger/AC side off in the event of a HVE (or just in advance of that if your BMS has that alternator friendly feature). It can also turn the Inverter off for a LVE. This is accomplished using Victron Software Assistant called "Lynx Ion BMS Support. Even those with older Multi's that have no Auxilliary Inputs, the Lynx Assistant can configure the Lead Acid Temp Sense to act as either a HV OR a LV Input switch for the Multi/ Quatro. Unfortunately for the older units not both.

For those with older units email the installed firmware number (chip on main board is stickered or obtain using VEConfigure) and details of your unit to Victron tech support and ask for an appropriate firmware update (which you will flash the board with) that will be compatible with VE Configure 3. Version 3 is required as it incorporates a flat LFP charge curve and is compatible with Lynx Ion Support Assistant to control the Auxilliary Input(s) and work with any sort of LFP BMS.

For older Multi units with only one Auxilliary Input/Temp Sense I advise putting the Multi on the Charge Bus and configuring the Input to enable the BMS to turn the charger off in the event of a HVE. The Multi has in VE Configure 3 a pack voltage setting to turn off the Inverter well in advance of a LVE. As an added precaution on account the Inverter could still drain the battery bank via the Charge Bus simply instal a standalone relay to the Multi that is connected to the BMS's LVE output. The only complexity is that when recharging using the Multi after a LVE, this relay would have to be manualy reset. That would not be necessary if another charge source was first used.

Hope this helps, particularly those with older Victron units.

EXCELLENT post Hoopla! ...we have been doing this with Victron Multis & Quattros for years, however never bothered to post it. You saved me the work...;-)

[SailRedemption]

I believe the regular Victron Phoenix battery chargers can also be set like the Multi can through the box or through the computer connection. At least that's what I got from reading about it. I have a 30 amp that I'll use to charge my bank. It's small but if I'm at the dock I'm at the dock long enough to let it charge up. It can also be used as a power supply so I can turn off the bank and still have power if I wanted. I didn't see the need for a larger one and I wanted a separate inverter than the charger so they are on different busses.

See more @ redemptiverepair.com

[ColdEH]

Originally Posted by exMaggieDrum

Alctel - Canadian Electric Vehicles Ltd. - talk to Randy, sales rep. Nice guy. They are on Vancouver Island north of Nanaimo.

These guys are great and Randy is right on the ball and answers his phone!

I bought my Sinopoly's from him , no trouble at all , shipped right to my door and the batteries are working excellent.

Regards

[nixsee]

Hi there,

I've read this entire thread, MaineSail's, ebaugh's and mbartosch's guides, and more and have a pretty good handle on all of this. However, a few questions remain.

I made a large post with a lot of questions previously, but clearly overstepped my bounds and got limited response. I've been able to find answers to most of them through some digging, but a couple remain.

• For the initial balancing charge, there seems to be some differing opinions. I've seen numbers like 3.6, 3.65, and 3.8VPC thrown around. Which is appropriate for CALB CA 100s/LiFePO4 in general? I intend to keep regular charging to 3.45VPC.

Also, there has been discussion (I've seen T1 Terry talk about it a fair bit) of using a high initial voltage to "condition" the cells, which will sacrifice some of the cells' maximum current capability, but lengthen their life. Is there a consensus on this idea and what voltage should be used?

• What is an appropriate LVC level? I have a HousePower BMS, like many here. It turns on the warning alarm and LVC signal at 2.9 and turns off at 3.1VPC. The Protection level is 2.6VPC, which sounds like it is well below safe discharging levels (I've seen 2.8 mentioned a number of times).

Is it appropriate to have the LVC at 2.9V open my loads contactor and then close it when it reaches 3.1 again, and use the 2.6 protection level as a last resort? Or should I just use LVC to set off an alarm (LED and/or buzzer) to allow for manual action, and then cut off the loads at 2.6VPC if I am not around/fail to act? My bias is towards cutting off at 2.9, but just wonder if this is too conservative.

Thanks!

Nick

[mcarling]

Originally Posted by nixsee

For the initial balancing charge, there seems to be some differing opinions. I've seen numbers like 3.6, 3.65, and 3.8VPC thrown around. Which is appropriate for CALB CA 100s/LiFePO4 in general?

3.65V per cell is fine. 3.60V would also probably be fine. I would not risk 3.8V per cell, but I'm sure it's not a big risk if the voltage will not be held there. The point is to be on the steep part of the curve, past the knee, and 3.60V or 3.65V will do that. There is simply nothing to be gained by going to 3.8V.

Originally Posted by nixsee

Also, there has been discussion (I've seen T1 Terry talk about it a fair bit) of using a high initial voltage to "condition" the cells, which will sacrifice some of the cells' maximum current capability, but lengthen their life. Is there a consensus on this idea and what voltage should be used?

I'm skeptical (about most things). The reputable manufacturers (certainly including CALB) condition the cells before they leave the factory. I would not attempt any further conditioning.

Originally Posted by nixsee

What is an appropriate LVC level? I have a HousePower BMS, like many here. It turns on the warning alarm and LVC signal at 2.9 and turns off at 3.1VPC. The Protection level is 2.6VPC, which sounds like it is well below safe discharging levels (I've seen 2.8 mentioned a number of times).

Is it appropriate to have the LVC at 2.9V open my loads contactor and then close it when it reaches 3.1 again, and use the 2.6 protection level as a last resort? Or should I just use LVC to set off an alarm (LED and/or buzzer) to allow for manual action, and then cut off the loads at 2.6VPC if I am not around/fail to act? My bias is towards cutting off at 2.9, but just wonder if this is too conservative.

All these options seem reasonable. If your cells reach 2.6V once in a blue moon when you have an equipment failure or an emergency, no sweat. It's not optimal but far from a disaster. Just don't do it regularly.

[senormechanico]

A friend of mine has a 48 volt home backup system with Winston 700 cells.
Due to a factory defective (and imho overly complicated) BMS, one cell went waay flat.
It did get there at low current of a constantly shunting BMS, but it measured only about half a volt when the fault was discovered.
After removing it from the bank, he charged it up at 40 amps and it recovered with no apparent damage.
It's still in his system and seems perfectly fine.

[roetter]

I am in need for a simple automatic balancing system.

I have 2P4S LiFePo Winston 700Ah cells. After one year cell pack 2 and now after 3 years cell pack 3 have some sort of internal drain. They loose voltage slowly.

The boat is stored afloat during the Summer for 6-8 months in the Bahamas. Solar with Outbacks are keeping the batteries at 13.3V.

So far I have manually balanced the cells when I return to the boat with a good length of cable connected to one cell set drawing about 25A. I have to do that for days. Now I have the problem that I have the boat delivered by a crew that knows nothing about Lithium. Leaving the cells as they are, will risk dropping cell set 2 very low as the other sets stay around 3.2V.

I am contemplating a simple balancing system that will be programmable or kick in at relatively low cell voltages - I.e 3.4V.

What can you recommend?


Rolf

[Maine Sail]

Originally Posted by roetter

I am in need for a simple automatic balancing system.

I have 2P4S LiFePo Winston 700Ah cells. After one year cell pack 2 and now after 3 years cell pack 3 have some sort of internal drain. They loose voltage slowly.

The boat is stored afloat during the Summer for 6-8 months in the Bahamas. Solar with Outbacks are keeping the batteries at 13.3V.

So far I have manually balanced the cells when I return to the boat with a good length of cable connected to one cell set drawing about 25A. I have to do that for days. Now I have the problem that I have the boat delivered by a crew that knows nothing about Lithium. Leaving the cells as they are, will risk dropping cell set 2 very low as the other sets stay around 3.2V.

I am contemplating a simple balancing system that will be programmable or kick in at relatively low cell voltages - I.e 3.4V.

What can you recommend?


Rolf

Rolf,

You mentioned this issue back in October of 2014? Have the cells been top balanced then 100% isolated/disconnected and voltage watched? If the cells are actually self discharging, when 100% disconnected, this is not good... If the cells are left at 3.325VPC this is a pretty full battery and could be damaging long term. You stated previously that you disconnected them for storage and did not float but now you seem to be floating at 13.3V??

If you have indeed left them "floating" this is perhaps one of the reasons not to float LFP but I suspect an n=1 is not sufficient data..

I would like to figure out the issue so we can prevent it in the future.. When I get time I will go back and read some of your posts on your system to see if there is something that could be causing this. Heck I have some CALB cells that have sat for 12+ months and voltages are still the same on all cells..

[mcarling]

Originally Posted by roetter

I am in need for a simple automatic balancing system.

I have 2P4S LiFePo Winston 700Ah cells. After one year cell pack 2 and now after 3 years cell pack 3 have some sort of internal drain. They loose voltage slowly.

The boat is stored afloat during the Summer for 6-8 months in the Bahamas. Solar with Outbacks are keeping the batteries at 13.3V.

So far I have manually balanced the cells when I return to the boat with a good length of cable connected to one cell set drawing about 25A. I have to do that for days. Now I have the problem that I have the boat delivered by a crew that knows nothing about Lithium. Leaving the cells as they are, will risk dropping cell set 2 very low as the other sets stay around 3.2V.

I am contemplating a simple balancing system that will be programmable or kick in at relatively low cell voltages - I.e 3.4V.

What can you recommend?


Rolf

First, I would urge you not install any sort of automatic balancing system. The cell monitoring systems are bad enough; the cell management systems are downright dangerous to the cells.

6-8 months is a very long time to float the cells. Were they ever discharged below 100% during this time? Is there a reason why the floating is needed? Is there a load which consumes continuous power?

I agree with Maine Sail. Do a top balance with all the cells in parallel and then check each cell for self-discharge over a period of time. If you have a bad cell that is self-discharging significantly, you'll need to remove it from the bank.

[OceanSeaSpray]

Originally Posted by roetter

I am in need for a simple automatic balancing system.

I have 2P4S LiFePo Winston 700Ah cells. After one year cell pack 2 and now after 3 years cell pack 3 have some sort of internal drain. They loose voltage slowly.

The boat is stored afloat during the Summer for 6-8 months in the Bahamas. Solar with Outbacks are keeping the batteries at 13.3V.

So far I have manually balanced the cells when I return to the boat with a good length of cable connected to one cell set drawing about 25A. I have to do that for days. Now I have the problem that I have the boat delivered by a crew that knows nothing about Lithium. Leaving the cells as they are, will risk dropping cell set 2 very low as the other sets stay around 3.2V.

I am contemplating a simple balancing system that will be programmable or kick in at relatively low cell voltages - I.e 3.4V.

What can you recommend?


Rolf

I remember you posting about this earlier indeed. Zero self-discharge would mean infinite resistance between anode and cathode... not achievable, but in your case the divergence between cells seems huge for sure and you wouldn't be the only one who got dodgy cells from Balqon from memory.

Since nearly all systems must eventually drift out of balance, given enough time, I find it interesting anyway.

I considered building a shunt balancing unit like you are talking about, but later shelved this idea. The key problem with dumb shunt balancers is that they react to the combination of the true "open-circuit" cell voltage (which is SOC related) and the voltage drop caused by internal resistance when current flows. Because internal resistance varies from cell to cell and it skews the voltages, if you shunt while decent current is flowing, you immediately throw the cells out of balance. If you keep charging until the current tapers down to almost nothing and the cell voltages have time to become equal, then the shunt balancers get a chance to effectively undo the initial upset they caused.
This can work in an EV application with frequent full recharges, but it can't work at all for us, so I moved away completely from this idea. None of the banks I built have needed any rebalancing so far (all Sinopoly 100Ah or 200Ah cells), but they are not many years old either. They have diverged by tiny amounts over time however.

If you want to shunt, it has to be when there is no current flowing ideally and you should shunt in an area where the charge curve has a good gradient in order to be accurate, which places strict limits on low-voltage shunting.
Addressing balance issues in a bank that is in storage is not really going to be possible.

Because online balancing is in fact something rather tricky to do and can involve back-calculating the open-circuit cell voltage, it can only be done automatically by a centralised battery management module (which is why all schemes with shunting cell boards are out). Automated balancing should only result in very rare and very small corrections when the conditions are right for them.
If you have bad leaky cells, the leakage current could still exceed the capacity of a balancing scheme.

Any rough idea of how much charge you are losing per month in the bad cells?
Have you checked if the bad cells are running warmer while charging? High self-discharge can indicate perforated separators, the top of a risky slope.

Eric

[roetter]

Originally Posted by Maine Sail

Rolf,

You mentioned this issue back in October of 2014? Have the cells been top balanced then 100% isolated/disconnected and voltage watched? If the cells are actually self discharging, when 100% disconnected, this is not good... If the cells are left at 3.325VPC this is a pretty full battery and could be damaging long term. You stated previously that you disconnected them for storage and did not float but now you seem to be floating at 13.3V??

If you have indeed left them "floating" this is perhaps one of the reasons not to float LFP but I suspect an n=1 is not sufficient data..

I would like to figure out the issue so we can prevent it in the future.. When I get time I will go back and read some of your posts on your system to see if there is something that could be causing this. Heck I have some CALB cells that have sat for 12+ months and voltages are still the same on all cells..

1. First break was 3 month with battery disconnected at about 50% SOC . Everything was fine when I returned.
2. Another 4 months break same set up. Cell set 2 was really low, about 2.8V.
3. Next season I did not dare to leave the battery disconnected, and kept the solar on at 13.0V. When I returned after 6 months cell set 2 was low, but ok to not damage the rest. Has a long time balancing ny bleeding the pther 3 sets.
4. Last season setup same as season before, but this time 9 months. Also, I had a skipper bring the boat from Georgetown to Fort Lauderdale. I emailed him exact instructions on what to do and to call with Skype so I could give hi live information on what to do. I just go an email all was fine and he set off with the boat with cell way out of balance. I would guess about 500Ah low on set 2. 300Ah low on set 3. Luckiliy I had my programmable relay set to very conservative parameters, for HV and LV disconnect. Since he motored most of the time going thorugh without stopping, I assume that set 2 did not go into very low voltage.

I will need to keep the battery actively balancing while away to keep them alive when I am gone for a long time. I have nobody in Georgetown who would be looking after the battery while I am gone and manually balance them.

I have been trying to get another 700Ah cell, but not so easy these days. Actually I will probably need 2 700Ah cells. As we go on the boat to cruise, I can not let the cells sit totally disconnected to test them out. I am somewhat limited in what I can do. If I can not get 2x 700Ah cells for end of this year then I will run these cells until I kill them and see what I do next. Probably smaller cells in the 200Ah range and about 1200Ah at 12V.

My other boat in Canada with 2x200Ah WInston was disconnected for the last 3 seasons for the winter and the cells are just as balanced as before. Never had to do anything yet.
A friends boat in Canda with 2x160Ah Winston, same age no balancing.

Another friend of mine also has 700Ah Winston cells and I had to do a balancing of about 200Ah last fall whie in New Zealand after 18 months of continuous use.

Seems like the 700Ah cells can have an internal problem that drains some of them slowly.

[OceanSeaSpray]

I was told by Sinopoly strictly not to use cells any larger than 200Ah in marine applications (I mentioned this a few times here in the past). Large cells are too heavy and don't have the mechanical strength to withstand this type of service.

The figures you are quoting suggest pretty meaningful internal discharge currents, damaged separators (chafing?)... they can only keep breaking down further and then what? There is a lot more than just electrical energy stored in there. If a hot spot suddenly formed inside and got to 200degC, the oxygen would unbind at the cathode and after that it is thermal runaway.

You could reconfigure the bank down to a 700Ah 4S configuration to keep yourself going for now by using the healthy cells from the two groups that are not discharging, but I would offload the lot ashore as soon as practical and restart with smaller cells as you suggest. Nothing else is going to fix a problem like that.
Failing cells would be a risk to keep on board even disconnected, especially if they are going to be shaken around.

[svrodeorm]

Please forgive me if what I will ask already has been covered before.

I've been following this thread on and off together with similar stuff on RV and offgrid homes forums. Together with a bunch of scientific reports and whatever ps up when using search engines in a creative way I believe I've gathered just about th konowledge I need in order to put my money wher my mouth is....

My position leans towards the KISS principle, perhaps mostly for philosophic
A reasons ;-). Since I've been pampering leads for most of my life (long term live aboard cruiser and former RVer too) I believe that pampering LFPs won't be any more trouble, just different. My intentions is to keep my future batteries between 25-75 % SOC and size the bank accordingly.

However, there are two questions I've never really seen answered anyway. As for an occasional need/wAnt to balance cells ( after the initial top balance) I wonder what's wrong with just disconnecting the whole range and hook them up in parallell until they are where you'd want them. Can take time yes!

The other issue I never seen commented is how do they like charging and discharging simultaneously as is the case on a boat?


I should perhaps mention that I am planning a smallish system 200-300 Ahr at 12 V. No electronics on battery posts, a hard LVD and HVD as disaster insurance (controller failure, shorts or whatever) our discharge rates are <15 Amps except for those few seconds when the starter And windlass runs, and our charge is in the same range from solar and a windgen.

For controller settings:

Alternator (next Step controller) 13.6V bulk then 13,2 "float"
Solar controller 13.8/13,2

Any thoughts welcome, whack. E if I got it all wrong.... the arena is wiped..

[stefano_ita]

Get this

24V-25.6V-28.8V 8 Cell-Battery Series 4A-300A Max Current UL SGS and UKAS Certified Custom Built Lithium LiFePO4 LFP Mini BMS-PCB-PCM

with the main control as this:

(i like the screen with all the data, the amp meter as to control charging and discharging current)
1-60 Batteries Per BMU EV Battery Management System (BMS) Custom Built LIGOO B51A 1-1000 Batteries

[svrodeorm]

Originally Posted by stefano_ita

Get this

24V-25.6V-28.8V 8 Cell-Battery Series 4A-300A Max Current UL SGS and UKAS Certified Custom Built Lithium LiFePO4 LFP Mini BMS-PCB-PCM

with the main control as this:

(i like the screen with all the data, the amp meter as to control charging and discharging current)
1-60 Batteries Per BMU EV Battery Management System (BMS) Custom Built LIGOO B51A 1-1000 Batteries

Im not sure if that was meant as a suggestion to me, but it's just the kinda stuff I try to avoid. A small house bank is as far from an EV as a space ship is from a Horse and wagon. With my charge and discharge currents it's a mere trickle on a 200-300 Amphr bank

Thank you anyway....