Li-po/li-fe? Balancer. BMS

[tdneVmoDK]

Hello.

I have got some DeWalt packs where the batteries should be fine, but i want to test them.

Some of the batteries are 3.7 and some are 3.2 nominal voltage. Why?

Which balancer should i use? I Guess that one with a charger in it is preferable

Do i need to test the cells one by one?

After this, i have to connect them together again in the right formation to give 36 or 48 volts for my eBike. How do i do this? Do i really need a tag welder? If yes, then where do i get one? Can i build one easily my self?

Which BMS should i use for this pack?

Also, when i measure the cells with a voltmeter i get weird readings. In one of the packs, all the cells are at 0.2 volts? Some other cells also got the same voltage, but some of them has gut resistance >20MOhm and some of them is around 3,5 MOhm ?!
Is it possible to revive a battery that has been discharged to 0.2 volts, and what will happen if i try charging it?

 

[cassschr1]

3.7 = fully charged. 3.2 = about 1/2 used
Yes I would test each one, BUT DO NOT DISASSEMBLE, CUT TABS between the cells with a dremel cut off wheel. You can solder easily to the tab connectors to configure your pack.
BMS, I don't know.
Readings..... .02v run a few cycles and see if they come back
30ohms = not good
3.5 ohms = good cells
Nothing bad will happen with these cells when you try to charge the low voltage one's.
I have tested a couple hundred a123 cells and built a few packs,28s5p for a 5305.
I use a cell-pro power-lab 8 charger for these tests.

 

[tdneVmoDK]

Thank you casss.

I am now trying to charge one of those with low resistance and 0 volts. I'm charging with 3.3 volts and limiting the current to 0.2. I'm almost exited

 

[dnmun]

you measured the resistance of the battery with the ohmeter scale on your voltmeter?

 

[tdneVmoDK]

Yes dnmun.

I have charged it to 3.17, and i measured it 1 hour later and it was 3.14

 

[Punx0r]

You can't measure the resistance of a live circuit with your average multimeter. The reading will be meaningless and you stand a fair chance of damaging the meter.

 

[tdneVmoDK]

I thourght it would be okay, since it was 0 V?

The negative side of the cells are connected, but not the positive side, and yet they share voltage drop. What the???

First i charged the first cell randomsly with my LAB PSU, and afterwards the second one. How can the voltages be the same?

The voltages are now down to 3.01 volts, so a voltage drop of .15 volts a day, that can't be good?

 

[tdneVmoDK]

I have just charged and discharged a pack of 5 x US15650FT dewalt cells and the imax B6 counts 957 Ah from 18V and down to 10V in discharge test. In the charge test from 10V to 18V it counted 1100 mAh dead on! They should be 1100 mAh They have been charged from 0 volt! They were 0 volt for several months. I'm curious to see how long they last.

http://peecee.dk/upload/view/386216

Now i only need a cell monitoring unit or BMS.