Need some advice recovering some batteries

[pdarnett]

So, bought a couple of batteries off Ebay, faulty, marked as do not charge. They're 36v 9Ah ones designed for Momentum bikes.

Out of the box they read about 4V, so out with the screw driver and in bits to investigate.
BMS looks undamaged and measuring via the balance leads each cell is about 0.5V.

I'm thinking they've been left to self discharge on a shelf for a few years through the BMS.

One pack has a 0v cell, so that might be a duff.

They're prismatic cells in a 10s1P configuration as far as I can see, I'm hoping I can breathe some life into them. They look brand new, never been opened(till I got there!).

Is it worth me buying an Imax B6 and seeing if I can trickle a bit of charge into each cell one at a time via the balance leads? Hopefully the BMS will come back to life at some point and then I can buy the proper pack charger and revive them.

Dave might know a bit about these packs, I'll grab some pictures......

 

[pdarnett]

Some pictures from the phone.

 

[KirstinS]

You won't be able to charge using IMAX or similar I don't think - it will just sound the low voltage alert

I have used one of d8veh tricks successfully on 18650 cells salvaged from laptop batteries. I never try if at 0 volts though

His trick is to use a charged cell to charge the very low cell - just for 10 seconds or so. This usually brings the cell up to voltage the charger will accept. Then bring up the voltage very slowly by charging at low amp , say 0.2a

It always works but when these cells
Are taken down very low (like .5v) then the internal resistance can shoot up causing issues on high drain uses like ebikes. I use them to make mobile phone chargers or ecig charger or run led lights etc

I don't know anything about prismatic cells but the chemistry is the same to presumably all the above applies ? I'd be concerned they have gone too low to recover properly though for ebike use

D8veh and others know better though !

 

[KirstinS]

To be clear you would need do the charged cell trick individually for each 3.7v cell

But again my experience is soley with 18650 laptop cells

 

[pdarnett]

I may try that, I've got some charged 18650 cells kicking about, i may knock up some leads just to give each cell a tickle one at once. If I can bring the whole pack up to say 20v then I beleive the BMS should allow me to charge properly. If not I bought some nice cases and BMS boards for my 18650's!!

 

[Deleted member 4366]

Ideally you need a charger that charges through the balance leads to save a lot of time.

It's a shame you didn't show the cells in the photo so that we can see what you've got. I' can only guess that your cells are 9aH each, in which case a single 18650 might not be sufficient to charge it enough. You need about 2.5v.

With the Imax charger you can select other battery types (nicads?), which will cause it to charge at a much lower voltage, so you can do it in stages by going Nicad, Pb, LiFePo4, LiCo. Another thing you can try is just connect the pack two main leads to the Imax (no balance leads), and tell it it's 2S, 3S, until you get to 6S. The charger won't know how many cells you actually have because it can only see the pack voltage like that, so it'llcharge to 8.4v, 12.6v, 16.8v etc. You need to monitor the individual cell voltages after each stage to make sure they rise evenly. don't do anything with the multi-pin connector to the BMS connected.

The cell that's at 0V won't come back to life. There's a fair chance the others will, but their capacity might be compromised.

The BMS won't allow charging through the normal charge leads until all the cells are above 2.5v.

 

[pdarnett]

Here's a couple more pictures, not sure if it'll help. I haven't bought an Imax yet, next on my shopping list but seems that its the best budget charger. Busy building a workshop with all the proper fire precautions as well!

BTW at the discharge end, as well as the main thick red and black leads, there a pair of thinner red and black ones that are connected to the bms board. Any idea?

 

[Deleted member 4366]

I still can't quite see what you've got. Not that it makes much difference. I think I can make out a pouch cell. What's those green boards on the top? Are they just connectors or do they have components on them?

 

[pdarnett]

No components on top, they're just to connect the cells together.
No real markings on the cells but the pack is a 36v 9ah one so I'm guessing they're 3.7v 9ah pouches as they're in a 10s1P config.

Ordered my Imax yesterday so will give charging a try. Shame my workbenches for the new workshop were completely trashed by Parcel Force yesterday, they managed to completely fold in half inch-thick mdf work tops!

 

[Deleted member 4366]

When it comes, set the current to something low like 0.2 amps. Connect the two power leads to the thick red and black leads on the top where those green boards are. Don't connect any balance wires. select 2S, which will cause it to charge the pack to 8'4v. When it gets there, which won't take long, select 3S to take it to 12.6v,and so on up to 6S for 25.2v. Then check the individual cell voltages to see what's happening. If they're even at 2.5v each, the BMS might switch on for normal charging.

To continue charging with the Imax, you need a way of connecting your 5S balance socket to the balance leads. I use a 6 pin JST male to male extension lead with some of this, broken off to 6 pins:

http://www.ebay.co.uk/itm/10-x-40-Pin-Strip-PCB-Header-Pins-0-1-2-54mm-for-Arduino-Shield-LCD-UK-/290932278467?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item43bcea44c3

Male to male extensions come free with those cheap wattmeters or any balance board, ut I've never seen them on their own. You could use one of these and temporarily solder the wires to those green boards:
http://www.ebay.co.uk/itm/Micro-JST-1-0-6-Pin-Connector-Plug-with-Wire-x-10-sets-/121235218563?pt=Radio_Control_Parts_Accessories&hash=item1c3a2ea083
Whatever you use, make sure that you connect it the right way round, and if you solder them, check with a voltmeter that the voltage rises in sequence along the connector before connecting.

Then select LiFePo4, and it should charge and balance as long as all cells are above 2v. Finally, switch to LiCo and finish off. Repeat for the other 5 cells.

 

[pdarnett]

Thanks Dave I was thinking along the same lines, I was going to get a 6S balance lead and some recycle a jumper strip off some old server boards, so very similar. If the BMS comes back to life after the initial cahrge I'll probably order the charger from Momentum (the pack producers) to see if it charges normally.

I'll document the process for anyone interested!

 

[Deleted member 4366]

The charge from Momentum will probably be expensive. Try Andrew from Oxygen. He said that he's got some going cheap, or get a Chinese one off Ebay for about £28.

 

[pdarnett]

Asked Andrew, their's is about £40, the momentum one is £35 so may as well have the one designed for the pack. But I'm going to see if I put some charge on it first!

 

[camerart]

Hi pdarnett,

If these are LI-on beware, there is a fire risk, if they are Nimh or similar, a short bust of higher voltage on the bad cells can un-crystalize them, (this can happen after bad storage) and the might come back to life, in this case, work them hard till they balance, and use a good charger. Just guidance, I'm no expert!!

Cheers, Camerart.

 

[pdarnett]

They are Li-on, don't worry I'm uber careful. just building a new workshop with fireproof worktops(up to 600c), extinguishers and sand filled fire buckets as well as individual power breakers for each socket. I'm quite new to using lithium so I'm being extra cautious, just got my IR thermometers in the post this morning as well!

 

[camerart]

You seem to have the job under control, carry on

 

[pdarnett]

I hope so! Ask me in a week when I'm bandaging my fingers!

 

[camerart]

And sifting through the embers.

 

[camerart]

Hi again pdarnett,

I occasionally need to connect cells of different types into a pack, and usually solder them. Obviously this isn't a good plan! some have steel strips, that won't take solder, and must be spot welded. I was wondering whether I could 'knock up' a spot welder for this task. Any ideas?

Cheers, Camerart.

 

[Deleted member 4366]

Normally the strips are very solderable. Are you sure you're doing it right.

You can buy a Chinese spot welder for about £100 or you can make your own:
http://endless-sphere.com/forums/viewtopic.php?f=2&t=2633