Lithium battery packs and their charging management...

Hello.
A plain tool lithium battery pack of -say 6 series- for 24V is not being charged. It sits idle for a few days now.
Is the 'balancing' circuitry in operation ? Are the battery pack 24V terminals feeding/powering the balancing circuitry in it ?

Was the balancing circuitry in operation last time while it was charging ?.
Will the circuitry be in operation when the tool is in use ?
When is the 'balancing' taking place ?
When is the management circuit not energized if it is always connected to all the cells ?

If a cell presents an anomaly; how is it corrected by the 'management circuitry ? Charges that cell more/less than the others ?

If a cell has a lower voltage -say 3V- and the rest are 4V each; put to charge, does the charger feeds the supply of the 'management circuit' inside the battery to 'get permission' to turn-on the charging or the pack itself does not produce/conduct/allow then the charging voltage ?

Read somewhere that not all packs have the 'balancing feature' and get just power at its main terminals, when temperature sensing and identification allows the charger to proceed applying the voltage recipe.
Am mostly talking about DeWalts... Yes, I have search engines too.

Only some BMS's have charge balancing - and the clue is in the name 'charge' balancing - it only balances during charging.

The BMS/balancing circuitry takes some current all the time - although I've found a number of BMS's that actually have destroyed one of the batteries - and replacing the batteries (all of them) ends in the same battery (position) failing a short time later.

Because of this, I've stopped using BMS's, and rely on my PIC controlled charging systems to do it's job, but without charge balancing.

Externet said:

If a cell presents an anomaly; how is it corrected by the 'management circuitry ? Charges that cell more/less than the others ?

Click to expand...

OK. Asked because always hear a lot of noise that lithium pack cells must be balanced. Thanks.

If not all charge managers do balancing, does it mean a lithium pack can be charged with no balancing feature; just providing the proper voltage recipe at its end terminals ??

If a lithium pack is not balanced, and its factory recommended charger does not provide balancing feature; what ? throw away the pack ?

Generally chargers don't provide balancing features, that's built-in the BMS (if indeed it is).

First off, balancing is only for cells in series - it's not required for cells in parallel.

If you're not using a balancing circuit, then just make sure you use identical brand new batteries, and also of identical existing charges. Any new batteries, from the same batch, should be pretty identical and come partially (and identically) charged for transport.

I've had no cell failures since I removed the BMS's and just used new bare cells in series - if a cell does fail, my charging algorithms will abort the charging process after a relatively short time anyway.

You could also pre-charge cells using something like an XTAR VC8 charger, which will test and charge individual cells, we use one at work.

Nigel,
Do you have any details (algorythm schematic etc.) of your pic based charger that you are willing to share?

Mike.

It's based on various examples on-line, including this one:


Well worth a read.