Checkthisout
Solar Wizard
- Joined
- Nov 14, 2021
- Messages
- 4,817
I tried that on mine. Didn't work. Had to disassemble pack, purchase power supply and top balance.
Worked good.
I also added an extra inductivebalancer on top of the bms.
Gangfeng 280 Cells
- Thread starter Robby1773
- Start date
I tried that on mine. Didn't work. Had to disassemble pack, purchase power supply and top balance.
Worked good.
I also added an extra inductivebalancer on top of the bms.
Alkaline
Solar Wizard
yeah Active balancers is the lazy man's top balance, except it stays in balance afterwards too 
Ampster
Renewable Energy Hobbyist
I have had 48 of the 280s for two years and they have been great. I think there are more of those out there so the sample is skewed.
Checkthisout
Solar Wizard
- Joined
- Nov 14, 2021
- Messages
- 4,817
chrisski
Solar Boondocker
- Joined
- Aug 14, 2020
- Messages
- 5,207
There’s no code or regulations or law that tells you how to top balance, so if you can spare the weeks time to make it work, then why not? Especially if it’ll keep you up at night if you don’t.
If the pack needs to be on service now, that’s different. If you’re dead set against top balancing because of an active balancer, do that.
I spent a bit of money on my 16 x 280 ah cells for an RV build that will last a decade. I spent a week to balancing. With the flat curve, the cells can read the same or nearly voltage on a DMM, but be off a bit, which makes it more likely they are out of balance enough to trip a BMS.
How often does it happen whee they are delivered out of balance? Maybe one or two posts have people assembling cells and tearing them down.
Ampster
Renewable Energy Hobbyist
I would imagine quite often because they are not matched by the resellers. With large Amperage active balancers it is practical to let the balancer do the top balancing. One needs to set the CV setting low and increment it slowly over a few weeks to give the balancer time to work. This might be the one time that a Float charge of 3.4 Volts per cell would give the cells a low enough charge current that would give the cells more time to balance. This is not for the faint hearted and not advised for anyone without experience. A good active balance can do the same as a resistor or lighjt bulb to pull one cell down.
Last edited:
That power supply may still function well with the active balancer. Generally the supply will charge the entire battery faster in series. Then as the first cell hits 3.400 slow the charge to 1-2 amps and let the active balancer do its thing. All the while protected by the BMS.
I'm probably looking at this from a different view as I am not going to be pushing the battery bank at 100% capacity. Much unlike the baked in settings of the LiFePOWER4 server rack batteries which like to hit ~57v, this battery bank generally sees ~55.3v (3.45xxv cell). Not that much energy storage past 3.45v anyway. If you want all 100% right off the bat, then yeah, I might see doing a top balance first.
chrisski
Solar Boondocker
- Joined
- Aug 14, 2020
- Messages
- 5,207
What is 3.45? 95%?
I recently had a cell drift out of balance. Not a lot of difference voltage wise when settled. Could be as little as .005 volts. When charging and nearing 100%, would get .2 volts difference. In between there were differences all over the board. I suspected a loose connection, and sure enough it was.
I was expecting to top balance again, but after sitting 5 days on the Overkill BMS set to balance all the time when above 3.4, balance amperage unknown, appears within .015 again. I will do some stress testing this weekend to see how that goes.
Not easy to top balance a pack once assembled, but if I need to I can take the bus bars off and put a power supply.
Yeah, somewhere around 95%. At 3.4'ish, we are into the knee of the curve. Charge all the way to 3.6x if you wish, but there's simply not much power in the knees at either end. What I see is ~51v to 53v is the meat and potatoes of where the bank likes to operate, and in this range, just a small difference in voltage can be a rather large difference in power. Not so much at either end and that's why, or at least I feel that is why we either top or bottom balance. And IIRC, an active balancer such as the jk, doesn't simply burn off power from the high cell, it pulls power out of the high cell and transfers that power into the low cell. Traditional top balancing is more of a one-way
It's my opinion and take it for that, but with 2+amps working from both ends, I think we have reached the age where traditional top/bottom balancing may not be absolutely necessary for a properly operating pack. Just my $.02 and take it for that.
With that said, I can imagine scenarios where there are multiple partly cloudy days/weeks failing to provide enough power for the battery pack to reach a good state of charge for balancing, that could cause some cells to get way out of line necessitating a much more drastic approach of disassemble and top balance. Especially if the pack had runners to begin with. Agree 100%, it's a real pain to disassemble/assemble a pack, not to mention dangerous, but we are all dealing with 'grade b' cells, some with huge tolerances, which may be so far out of line the only choice is to start with a top balance.
Last edited:
I've been reading that. But alot of people say top balance and others don't. If there close I'm going to hook up and see what happens
Sam Cho TX
Solar Enthusiast
yeah Active balancers is the lazy man's top balance, except it stays in balance afterwards too
If you get good cells these are not needed, it would seem to be another device that can go wrong. I have 280K grade A cells never needed them my bank always goes to full and discharges without issue, what little charging need to happen the JBD/SFK bms is able to do.
I suggest you try out some better cells and you will see the active balancer is not needed.
Checkthisout
Solar Wizard
- Joined
- Nov 14, 2021
- Messages
- 4,817
Posts like this, criticizing what you think was our pick of "low quality" cells don't sit well with me.
You did not tell the poster what made his low quality nor did you point in the right direction of "good quality" cells nor did you offer any wisdom on how to select "good quality" cells.
Did you say this just to be mean and take a stab at the person or what?
Alkaline
Solar Wizard
It has nothing to do with cells, it simply has to do with the speed of balancing and efficiency or not having to top balance, even if you have "good cells" that simply means it would need to work less. But don't expect even "Good cells" to balance perfectly, they will too drift a bit and a small 150 ma balancer is not going to be enough, you would need to charge very slowly for a long period of time for it to perfectly balance.
Look around the forums even people with SOK batteries which are using grade GFB cells go out of balance. the AB is cheap insurance, easy to replace.
The only debate left is to turn it on / off as it charges up the cell, I'm on the fence on this but both sides have brought some good issues. The JK bms seems to have figured it out with its built in Active balancing, but I have had good luck with my heltec "flying capacitor" AB.
So don't let the myth of Good cells don't need balancing fool you, most of the times the BMS 150ma is not enough for these big 280Ah chunky boys.
The batteries are here. They look flat and beautiful. The bus bars that came with them are nicer than I thought. Battery is built and charging. Can't wait to test out and figure out hownto get solar assistant to work with JK bms. It's not recognizing it. Email solar Assistant to see what they say.
You can use the rs485 converter and rs485 usb adapter https://solar-assistant.io/help/battery/jk-bms
or go the other route https://diysolarforum.com/threads/monitor-jk-bms-with-solar-assistant.33759/page-7
Alkaline
Solar Wizard
Hey Robby,
Are they saying your 305 are testing to 283 AH? Ugh... not good! Are you sure they did not send you CATL 280?
Are they saying your 305 are testing to 283 AH? Ugh... not good! Are you sure they did not send you CATL 280?
I went with 280ah. Didn't have enough to do 305ah
