Top Balance with Cells Welded in Series; JBD BMS and Growatt?

[sailhobie]

Hello,

I have just put together my first battery using 2 x 24V batteries (48V system) from SS that are welded in series, so I cannot balance each cell individually which is typically described. I am using a JDB BMS (48v 16s 100A) and Growatt 3000 LVM TL and am wondering what would be a reasonable way to top balance them?

I don't have a 48VDC charger but could I adjust the settings (JBD and/or Growatt) to charge the batteries up so I can then use a benchtop system to top up the low cells to 3.65V per the Overkill BMS manual's suggestion (see below)?

Thanks for any advice.

 

[sailhobie]

Here is the current cell state.

 

[mikefitz]

Lower the charge volts, if possible, so that the protection does not cut off charge and allow the BMS to have a go at balance. The method using a car headlamp bulb to pull charge from the high cell does work but needs a little practice, often only a few seconds of 'bleed' will be needed to pull down the cell.
Lowering the charge voltage to 55 volts may be enough to prevent high cell disconnect.

Mike

 

[pellicle]

so I cannot balance each cell individually which is typically described.

I don't see why not ... but you will need to disconnect the battery from any load.

There have been a few suggestions so far on this site, such as by Will who uses an Amazon "charger" voltage supply that can be set to a specific voltage (just under 3.6V iirc). You can attach that or if you wanted to use it for other things you can use an IMAX B6AC charger which will allow you to clip on some clips and charge an individual cell (like I'm doing here but in this instance with a Li 18650 cell




these chargers are quite good little units.

PS: don't forget that

1. charging will take some time (with 8Amps feeding a 100Ah cell)
2. the top part of charge takes much longer than the bulk part no matter how many amps you have up your sleeve (and you should let it complete till almost no amps are flowing)

 

[DestroyFX]

I did get the same issue as my pack are used LiFePO4 that came from servers pack.

Some where top balanced, some bottom balanced and of course one of the pack I got was the "soldered" kind.

Because I could not use the power supply trick to top balance them, instead of getting a power supply, I got that : https://fr.aliexpress.com/item/1005002617607510.html



It's an active balancer. What I did is simple. Plug only one pack in your system, with the BMS and balancer. Wait until it's top balanced, then discharge a little to something like 54.6V (so it won't sit a few day at 59V while you balance others pack). Then switch for the next pack. You can use the system while one pack is balancing.

Once all your pack are balanced, you can double check there about the same voltage, like 54.6 and plug them back in parallel. Small difference in each pack total voltage will not be an issue as they will balance themself out when you get to your full SOC.

* Do NOT leave the balancer connected on one pack after you did the balance job. Once they are balanced, you're BMS should keep them balanced. Leaving the balancer connected will put the pack out of balance if you are draining the pack low.

** If you're cells are way out of balance, start by charging at 53.6V, once "charged" and the cell +/- balanced, climb to 54V, 54.5, 54.8, 55.0, 55.2, 55.5......... 59v. That way you won't constantly bump into your BMS overcharge protection cutoff. You can also find the cell that have the higest voltage and adjust the charging voltage accordingly.

*** That specific balancer, while in use, make an "high pitch noise" kind of like coil whine. It is normal.