lifepo4 cell balancer issue fun

[PhilFromMaine]

Originally Posted by TacomaJoe

Looks like mine. I dropped the balance start voltage to 3300mV with a 5mV delta. Turned off balance only when charging so that balanced all the time. I set my solar float voltage so that the battery sat with the high cells just below the cell over voltage point and the weak cell slowly worked its way back up. I could bump the SCC float up 0.1V as the weak cell balanced.

This battery was offline so I could play with it while the other two ran my trailer.

Thanks for the numbers. When I get home Monday I will give them a try. So far this 10 day trip, I have made it just fine with one 200AH battery, 400 watts of solar, and truck alternator while taking side trips using my Victron battery charger and the truck's 110V outlet.

[Aussieguy]

My understanding is that the newer JBD or JK BMS have a active balancer built in

For BIG batteries you can also get large active balances that use about 5 amps

Turning OFF ... "Only Balance while charging" is good for smaller balancers
OVERKILL app allows this option ... balances anytime battery cells are above 3.3

[GolfingDave]

Since there are some folks with LifePo4 experience in this thread.

Do cells become a bit more efficient after some use? Been running some tests with my converter turned off the last week or so on some new batteries.

The last two mornings the drop overnight has been less. Nothing different in loads, basically the refrigerator and the water heater DC portion. I figure the relay for the AC portion is DC.

I know I had the maxair fan on one night and has not been on the last two nights but pretty sure it was only on for one of the nights with the more depletion. Hopefully will remember to turn it on for tonight's test.

[Aussieguy]

refrigerators are not constant loads
depending on if weather conditions change during the day / night

how HARD (load) the fridge has to work is determined by the humidity and temperature surrounding it... Plus how many times did you get out a coldie?


If you want to run tests on batteries there are cool looking load testers you can use
they will record the amps and do the calculations for you.

[GolfingDave]

Originally Posted by Aussieguy

refrigerators are not constant loads
depending on if weather conditions change during the day / night

how HARD (load) the fridge has to work is determined by the humidity and temperature surrounding it... Plus how many times did you get out a coldie?


If you want to run tests on batteries there are cool looking load testers you can use
they will record the amps and do the calculations for you.

Realize that about the refrigerator but it would be somewhat close unless a defrost kicks in one night and not the others. Pretty much stay out of the fridge after my dessert.

Ran the maxair fan all last night and percentages went up again and pretty sure the refrigerator was in defrost for a cycle which is going to be a higher amp draw for at least 20 minutes rather than just running at normal cooling amps.

I think what I was seeing just glancing thru my BMS screenshots was some days were cloudy and batteries were not fully charged. Percentage drop was the same but I was noticing the actual numbers. Put the numbers on a spreadsheet to see all at once.

Looks like I run anywhere from a high of 27% to a low of 12% draw down overnight on a pair of 100AH batteries. Readings are taken 11-12.5 hours apart.

Outside temps overnight have been consistent. Need a cold snap to come through to test them with the heater.

I am not looking for specifics but was just interested in the numbers. Camper came with AGM 75AH and the first year I would be at 45-50% overnight with the heater running.

Came back from a hike last winter(campground lost power) and the batteries were down to around 60% with just the refrigerator. Cloudy day and I was gone maybe five hours max, not sure how long power was out. Power came back on as I was setting up my generator. Knew then I probably would not make it through a night with the heater going.

Want to do a bit of boondocking this winter so making the switch to LifePo4.

[PhilFromMaine]

I have opened up the battery and checked all my connections and they are good. I have tried all the suggestions given here in this thread to no avail. Cell #2 won't charge above 3.29 while all the other cells will balance (nearly) at the top end. The BMS indicated a 100 percent charge even with the low #2 reading.

The battery under load will drop below threshold fairly quickly and shut down once cell #2 hits the lower threshold to completely shut it off. So, is it the cell or the BMS? There is no reason the cell would be damaged that I am aware of, but who knows?

I am currently thinking of switching cell #2 BMS lead to cell #3 and #3 to #2 to see if the readings change. I would think if the current readings change from #2 to #3, then the issue is the BMS. If they don't change, then the issue is with cell #2.

[TacomaJoe]

Don't switch BMS leads. It is looking at the voltage difference between the leads in cell number order and now lead 3 would have a lower voltage than lead 2.

You would have to break to battery down and move the cell.

When you say you can't get cell 2 above 3.29V is that in the battery charging? I have a power supply that I can put on a single cell to give one a charge.

[PhilFromMaine]

Originally Posted by TacomaJoe

Don't switch BMS leads. It is looking at the voltage difference between the leads in cell number order and now lead 3 would have a lower voltage than lead 2.

You would have to break to battery down and move the cell.

When you say you can't get cell 2 above 3.29V is that in the battery charging? I have a power supply that I can put on a single cell to give one a charge.

That is both with a charger and separately with a power supply. What is the brand of power supply that you have that can charge one cell? My Victron charger-power supply won't go much below 12V

[TacomaJoe]

Originally Posted by PhilFromMaine

That is both with a charger and separately with a power supply. What is the brand of power supply that you have that can charge one cell? My Victron charger-power supply won't go much below 12V

Its a DC variable power supply like: https://www.amazon.com/LWLONGWEI-Adj.../dp/B0CFLQCBCB

Used when I top balanced my cells, set it for 3.65V with all the cells in parallel and waited until they all got charged up.

[PhilFromMaine]

Originally Posted by TacomaJoe

Don't switch BMS leads. It is looking at the voltage difference between the leads in cell number order and now lead 3 would have a lower voltage than lead 2.

You would have to break to battery down and move the cell.

When you say you can't get cell 2 above 3.29V is that in the battery charging? I have a power supply that I can put on a single cell to give one a charge.

Joe,
I am not clear on what you are stating. If I switched leads and the 3.29 reading moved to another completely different cell, then that would be a function of a wayward BMS. However, I see the fallacy of my thinking since I already measured the voltage on cell #2 with a multimeter and it agreed with the BMS-3.29V

If you top balanced your cells as you stated, you must have assembled raw cells, correct? My battery was a manufactured battery in a sealed case that I cut into. Breaking it down even more to do a parallel top balance entails buying buss bars and a low voltage power supply-charger.

You implied in a prior post that you "power supplied' one cell up to 3.65V or did I misunderstand? Thanks in advance.

[nvs4602]

I did the same using a variable power supply. I did however add a 1s 25 amp bms just to insure proper charge I also capacity tested each cell with this bms too so I wouldn't over discharge them.

https://s.click.aliexpress.com/e/_mtHwgn2

I used the capacity tester which discharged cells at up to 20amp rate. Another reason for the 25amp bms.

https://s.click.aliexpress.com/e/_mr8Jliy

It all worked good together and the capacity I recorded with the capacity tester is what my shunt battery monitor tells me I have as a complete battery.

[TacomaJoe]

Originally Posted by PhilFromMaine

Joe,
I am not clear on what you are stating. If I switched leads and the 3.29 reading moved to another completely different cell, then that would be a function of a wayward BMS. However, I see the fallacy of my thinking since I already measured the voltage on cell #2 with a multimeter and it agreed with the BMS-3.29V

If you top balanced your cells as you stated, you must have assembled raw cells, correct? My battery was a manufactured battery in a sealed case that I cut into. Breaking it down even more to do a parallel top balance entails buying buss bars and a low voltage power supply-charger.

You implied in a prior post that you "power supplied' one cell up to 3.65V or did I misunderstand? Thanks in advance.

If each of the cells was 3.2V, then #1 lead would be 3.2, #2=6.4, #3=9.6 and #4=12.8 volts. The BMS sees the voltage difference between the leads. If you flipped them the BMS would see 6.4V between #1 & #2, and a -3.2V between #2 & #3. Would also see 6.4 between #3 & #4.

With the assembled battery, you can take a power supply connected to cell 2 and charge it to 3.6V while it is in series (no other charging). You can also add a lamp to a single cell to pull it down.

[nvs4602]

Originally Posted by TacomaJoe

If each of the cells was 3.2V, then #1 lead would be 3.2, #2=6.4, #3=9.6 and #4=12.8 volts. The BMS sees the voltage difference between the leads. If you flipped them the BMS would see 6.4V between #1 & #2, and a -3.2V between #2 & #3. Would also see 6.4 between #3 & #4.

With the assembled battery, you can take a power supply connected to cell 2 and charge it to 3.6V while it is in series (no other charging). You can also add a lamp to a single cell to pull it down.

Here's a wiring diagram for lifepo4 bms.

[PhilFromMaine]

Originally Posted by TacomaJoe

If each of the cells was 3.2V, then #1 lead would be 3.2, #2=6.4, #3=9.6 and #4=12.8 volts. The BMS sees the voltage difference between the leads. If you flipped them the BMS would see 6.4V between #1 & #2, and a -3.2V between #2 & #3. Would also see 6.4 between #3 & #4.

With the assembled battery, you can take a power supply connected to cell 2 and charge it to 3.6V while it is in series (no other charging). You can also add a lamp to a single cell to pull it down.

Yes, that makes sense-thanks. I had seen that in my own checks, but it completely escaped my thought process in this discussion.

So, I guess my dilemma is to decide whether to purchase the 40 dollar power supply to see if cell #2 will take additional charge, or, throw in the towel and buy another cheap sealed battery for 230 dollars and hope for the best.

I was also thinking of whether or not there is a fire danger attached to attempting to charge a possibly damaged cell?

[PhilFromMaine]

Originally Posted by nvs4602

I did the same using a variable power supply. I did however add a 1s 25 amp bms just to insure proper charge I also capacity tested each cell with this bms too so I wouldn't over discharge them.

https://s.click.aliexpress.com/e/_mtHwgn2

I used the capacity tester which discharged cells at up to 20amp rate. Another reason for the 25amp bms.

https://s.click.aliexpress.com/e/_mr8Jliy

It all worked good together and the capacity I recorded with the capacity tester is what my shunt battery monitor tells me I have as a complete battery.

nvs
Thank you for the references. I wish I had taken the battery route you took, but the knowledge about building your own systems came after I had already spent my whole budget on sealed lifepo4 batteries.

[TitanMike]

Originally Posted by PhilFromMaine

I was also thinking of whether or not there is a fire danger attached to attempting to charge a possibly damaged cell?

Fire danger is extremely remote considering the LiFePo4 chemistry and limited current from the charger recommended.

Biggest risk of fire would be severe physical damage to the cell and the resulting energy release from cell itself.

If seeking reliability I think the "cheap new battery" route would be better. Charging the single cell could well be a temporary fix and then the out of pocket replacement cost would include cost of the charger.

[PhilFromMaine]

Originally Posted by nvs4602

If you add an active balancer your delta will be 0.005 or less

This sounds like a good idea once I determine is the issue is the battery cell, or the BMS, or firstly the wiring connections. I am waiting for the rain to stop to start the checks since I do my work outside to keep the DW off my back.

[Aussieguy]

On a DIY battery and a cell becomes unbalanced you can easily disassemble battery and join the cells in parallel

They will then balance themselves
Then you reassemble battery
——————————————————
On a store bought battery
Too hard to totally pull battery and connect cells in parallel
So cut top off. Nicely

Connect a good active balancer with voltage sensing switch
The switch set at the determined higher voltage will start/ stop the balancer automatically

Put top back on battery and tape it up
Cheap battery now will work like a charm
Balancer only cost a few $$ and is a good upgrade for any battery

[PhilFromMaine]

Originally Posted by nvs4602

Sorry to hear your having problems. I went through this same issue with the battery I built. The Daly BMS I used said it had balancing capability, but it just wasn't that great of one. It only provides milli amps of current, and only did that while charging.

I now install active balancer on all my battery builds, even the small ones.
The first picture is the lifepo4 battery I built for our motorhome. The board with the yellow light is a 5 amp active balancer.
The second is 24v battery I built with 840 (18650) cells like you find in cordless tools, that runs a 4000w inverter. It has 316ah of capacity. I installed a 5amp active balancer on it as well.
The 3rd is a 12.6v battery I built for my grandsons power wheels.the circuit board on top is a 0.5amp active balancer. It has 18ah of capacity vs the 7ah lead acid it came with, he loves being able to drive around longer.
The last picture is of the 24v replacement battery I'm currently building for my mobility scooter. It weighs just under 10 lbs and has 31ah of capacity. The 2 lead acid batteries it's replacing weigh 25lbs each and are 30ah as well, be we all know you can't use the full 30ah out of them. So my range should be significantly extended.
as my next and possibly final step
So I would recommend adding an active balancer to your battery that keeps it balanced 24/7.

Amazon has them.
https://a.co/d/bpuuTuj

You can also get them from AliExpress which is were I buy them from. Takes 10 to 14 days to arrive.

https://a.aliexpress.com/_mOJ5CgU

I decided to try a cheap Daley Active Balancer as my next and possibly final step. If it solves the problem, I may invest in the Capacity Tester and the low Voltage Power Supply.

I just ordered a 10 dollar Daley Active balancer. If it works, I will buy a new case to replace the old sealed battery case. Thanks for the idea.

[PhilFromMaine]

Originally Posted by MGD1961

In my opinion it strikes me that the BMS isn’t the issue because if it were bad it wouldn’t necessarily pick on one or two cells

Strikes me as a cell issue or an issue that could develop by not cycling the battery deeply enough and then not charging with a high enough voltage. The BMMS will reset its own parameters to believe the battery is full when it sees a lower float voltage every time it is recharged. Sooner or later the empty and full parameter will get closer and closer together every time it is short cycled.

I know that in my case that could be true. I, like most RVers have neglected deep cycling. That particular battery has spent most of its life under the bed acting like a stock RV lead Acid battery. I think they call it "Plug and forget". lol


Actually someone should do a forum "sticky" (however that works) on the proper care and maintenance of lifepo4 batteries in a RV.