Battery Tester

[Barge17]

Hi,
I am contemplating getting one of these: https://www.ebay.co.uk/itm/276537833833 ... B5Z6YV8WN:
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Mainly to fault check a Solax battery I have aquired which seems to have one dead battery pack in it and hasn't been used for a year now. Anyone else used one, please? Thanks, D

[AGT]

You will be spitting the pack, so can’t you just mark each cell and measure each cell voltage with a multimeter

[Barge17]

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OK, thanks, I am just starting on this and learning. So that indicates to me that one faulty cell could pull the whole pack down, and ultimately make the BMS shut the battery down?
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Sounds like I will most likely need to get a spot welder ready to replace cells then.
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If just one cell is faulty and taken out, would the battery function temporarily, or would the BMS not like it?
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[AGT]

My experience is with systems without BMS, but mark one eyeball and voltmeter will give good results to start with.

Maybe then a bench power supply to charge one cell to see if it takes a charge?

[Barge17]

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Thanks Agt, I have got one now and my brother has given it a trial run.
Won't be doing any more with it for a week or two now. Any suggestions for a source for a spot welder, or another way of slotting in new cells please?
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[Marcus]

Don't know anything about that battery tester or the solax battery, but as AGT says: looking and reading the individual cell voltages is the way to start.

The bms should shut down if a cell is too high or too low. If the pack is left too long and self discharges too far, the bms may not be able to function even to allow charging. I do know the pylontech bms's won't function if the pack is below 24v - you have to bypass the bms to (carefully) recharge the pack until the bms will function (34v seems to be enough), then you can charge via the bms.

If you have 1 dead cell it probably needs replacing, but to test the bms, you could substitute any small liion cell (18650 for e.g) as long as it's in the right voltage range - you won't be able to charge/discharge the pack significantly, but it should 'wake up'.

[Barge17]

Thanks Marcus

[openspaceman]

. Any suggestions for a source for a spot welder, or another way of slotting in new cells please?
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I have been looking at this to make use of various cells I have recovered from non working packs from drills and a mower.
There are various DIY designs on youtube using relays and timers but I cannot understand why it would not work by charging a super capacitor bank to a known voltage and then triggering a big relay. After all we are just after Amp-milliseconds.

[Saladin]

Hohoho...oh it'll work...the question you really oughta be asking is how do you get it to stop working after.
You can make a spot welder from a microwave transformer, or 36v lead acid (careful now..H₂) or anything above that voltage with a short circuit current in the hundreds of amps.
The reason for a timer circuit is to prevent you from welding your electrodes to the workpiece and

You shouldn't solder cells..but you can...the hotter the iron the faster you can work which is better and quench cool it asap (ahem..with a damp cloth..don't submerse it and short it).

It can be tedious but I usually check cells/batteries with a round trip charge-discharge capacity test on an Ah counting or columb counting meter. It's very accurate. Some are so dead it'll be obvious by the voltage sag once you're familiar with the discharge curve of a healthy reference cell/battery.