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How to top balance offgrid with just BMS

myersfamilyhome

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Beginning to assemble my battery setup and know I need to top balance the cells for optimal life. What I have at the moment is:
4 Victron SmartSolar 100v/20a/48v CC
1 Victron SmartShunt 500a
2 Daly 48v/16s/300a Smart BMS w/Bluetooth
32 New/GradeA Eve 3.2v/304ah LifePo4 Cells
12 Trina 325w Panels

The intended battery configuration was to do a 16s for each BMS then parallel the 2 BMS to the bus blocks that the CC's are connected to.

Is it at all possible to properly top balance the cells with just the 2 BMS's? If so how?
 

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Depending on how well the cells are balanced it could take an extended period with just the BMS. Best shot to put them in service is to note the battery voltage when the first cell hits 3.65 high voltage cut off, note the battery voltage and adjust your charging voltage to be the next tenth (0.1) lower. This will keep the battery from shutting down and allow the BMS to start balancing. In a few weeks review the situation to see if you can bump the charging voltage a bit higher.

Otherwise you can attach a 5+ amp active balancer to speed up the process. Or you could bleed off the high cell down to the low cell with a low ohm resistor. Or you can use the inverter to drive a power supply to boost the low cells up to match the high cell.

Good luck. Post your findings and progress.
 
Depending on how well the cells are balanced it could take an extended period with just the BMS. Best shot to put them in service is to note the battery voltage when the first cell hits 3.65 high voltage cut off, note the battery voltage and adjust your charging voltage to be the next tenth (0.1) lower. This will keep the battery from shutting down and allow the BMS to start balancing. In a few weeks review the situation to see if you can bump the charging voltage a bit higher.

Otherwise you can attach a 5+ amp active balancer to speed up the process. Or you could bleed off the high cell down to the low cell with a low ohm resistor. Or you can use the inverter to drive a power supply to boost the low cells up to match the high cell.

Good luck. Post your findings and progress.
The cells came in a week ago and as a prerequisite I had them send me pics of each cell being tested for voltage/resistance and had them labeled with the results. They are batch/matched to the best of my knowledge. Not sure how much of a variation between cells is safe but I'm trying to get each 16s as close as possible.
 

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I balanced my pack using only my BMS .... but,, it has 1.2A of balance current.

With the low balance current on the Daly BMS, it can be done, but is probably going to require some manual balancing techniques as well.
 
maybe an idea completely out there, but if you dont have an active balancer, but a bench powersupply and your panels hooked up...

use inverter + solar panels + 1 set of batteries ( not balanced) + bench power supply to top balance..

after 1 pack is complete, do the same for the other pack.

as long as your solar input is greater than load, you should put much load on pack 1 .
would only do this while plenty of sun, and without additional loads, so the first imbalanced pack isnt loaded into a further imbalance
 
Is there anything reasonably priced that I could order off of Amazon that would meet my needs or am I better off just trying to balance with my BMS. Now that I'm diving into this top balancing stuff I'm realizing they're active balancers passive balancers and not sure what the best investment is long-term.
 
You could bleed off the high cells manually with a light bulb or something Perhaps that would help if you don't have to many that need it.
 
Heltec 16s

I have two of the 4S and they are working fine. Still takes an extended time to do the initial balance but the battery can be in service while it goes.
 
Heltec 16s

I have two of the 4S and they are working fine. Still takes an extended time to do the initial balance but the battery can be in service while it goes.
So since I have 2 16s banks of 304ah cells I would get 1 per bank and I can assemble the 2 banks and use immediately while these actively get my cells to maximum capacity without any repercussions?
 
So since I have 2 16s banks of 304ah cells I would get 1 per bank and I can assemble the 2 banks and use immediately while these actively get my cells to maximum capacity without any repercussions?
Yes the batteries can be put in service immediately. May need to limit battery charging voltage to avoid frequent BMS shut down from cell over volt protection. This should not be any real issue and will not severely limit the capacity.

Sorry I thought I read three batteries in the bank but only two balancers are needed for the two you batteries will have.
 
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Yes the batteries can be put in service immediately. May need to limit battery charging voltage to avoid frequent BMS shut down from cell over volt protection. This should not be any real issue and will not severely limit the capacity.

Sorry I thought I read three batteries in the bank but only two balancers are needed for the two you batteries will have.
OP did mention the cells were "batched and matched" which is encouraging.
The potential issue I see is if one pack trips before the other the difference between the packs will get larger.
The pack that does not trip will keep charging and balancing.
The tripped pack will not charge or balance.

Suggest to set the bulk/absorb voltage pretty low for the first cycle and raise it slightly each cycle if warranted.
I suggest 54.4 volts bulk/absorb and 53.6 or lower float.
 
OK so I am actually in process with doing similar with two 2p4s batteries in parallel with B cells. One will cut out a bit sooner than the other if I press the voltage. Not really an issue. The active balancer continues to balance when the battery cuts off. Once the solar goes to float the cell voltage delta soon drops to about nothing. So yes while in use it is not continuously balancing. Will take some time. I am two weeks in and there is significant improvement. I am currently charging to 13.9 each day on solar as the RV is back in storage. If I hit equalize set to 14.2 one of the batteries will over volt at the cell level. By next week I think it will make it to 14.2 volts.

I took this route to get the battery installed for a trip and had no time to do the more common parallel top balance to 3.650v. Worked perfectly fine on the week trip with just solar each day.
 
For my "offgrid top balance" I pre-charged with an SCC, then a powersupply.

I have 16 cells, 280 ah each, for two 8S batteries that I first charged 8S with a BMS and SCC to 27.6, a little less than 3.45 per cell, and then put them on a 30 volt, 10 amp charger, 4 at a time. The 8S battery packs took 4.5 kw of power to charge. Once I broke those 8S into two 4S packs for top balancing in parallel at 3.65 volts and 10 amps, they were charged in three hours.

I have the DL-24P capacity tester, similar to what Will uses in his videos, and besides capacity testing, it could bleed a battery to a tenth of a volt and shut down automatically.
 
I have a similar problem, meaning I need to balance off-grid. I will have an overkill 8s BMS 100amp and eight new 280ah eve lifepo4 batteries from Amy, the reputable dealer on here. I think i will assemble the battery and charge it using my epever 40amp SCC with 1500 of panels. I will the batteries closely as they charge up and attempt to bleed of voltage with a light from those that appear to be rising fast in capacity than other. In theory, I should be able to continue this process until the BMS shuts off when one of the cells reaches 3.65. If the other cells are not near this capacity, I can bleed the voltage off the cell that has reached 3.65 to match those that havn't and begin charging again. I think I can repeat this process until I get a decent top balance.

What do you guys think? It sounds better than waiting for a bench top power-supply with only 10amps.
 
I have a similar problem, meaning I need to balance off-grid. I will have an overkill 8s BMS 100amp and eight new 280ah eve lifepo4 batteries from Amy, the reputable dealer on here. I think i will assemble the battery and charge it using my epever 40amp SCC with 1500 of panels. I will the batteries closely as they charge up and attempt to bleed of voltage with a light from those that appear to be rising fast in capacity than other. In theory, I should be able to continue this process until the BMS shuts off when one of the cells reaches 3.65. If the other cells are not near this capacity, I can bleed the voltage off the cell that has reached 3.65 to match those that havn't and begin charging again. I think I can repeat this process until I get a decent top balance.

What do you guys think? It sounds better than waiting for a bench top power-supply with only 10amps.
What voltage do you expect to charge to on a regular basis? Hopefully less than 29.20 volts. Rather than running to the top, I recommend only charging to your expected maximum. If it works, let it run. Possibly no intervention will be needed.
 
What voltage do you expect to charge to on a regular basis? Hopefully less than 29.20 volts. Rather than running to the top, I recommend only charging to your expected maximum. If it works, let it run. Possibly no intervention will be needed.
Sorry, I forgot to mention I am going to run a 8s 24v setup. I'm not sure what you mean by "running to the top....etc."
 
What do you guys think? It sounds better than waiting for a bench top power-supply with only 10amps.
If at all possible, I would recommend charging your cells 8S to 3.45 X 8 = 27.6 volts, and then if at all possible use a power supply set to 3.65 and place cells in parallel to finish the top balance. My guess based off my balance would be about 6 hours. I charged my EVE 280s 8S to 27.6 volts, and then put them in 4S and it took 3 hours to finish the top balance, so 6 hours for 8S.

Even if this means running the generator for 8 hours for a 35 watt load.

There's a reason these cells are supposed to be top balanced.

If you can't do that, I'd keep the charge set to 27.6 and a BMS single cell cutoff of a lot lower than 3.65 like 3.55. I use the BMS as a last resort.
 
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