Balancing a 4S lipo pack with a Turnigy Accucell-6 charger ?

[eHomer]

I can't seem to balance the cells in my 4S 5000 mA lipo packs from Hobbyking.

Last year I assembled a 30 ah 12v battery pack with six of these packs connected in parallel, using the correct 6 way balance lead connectors and voltage alarm etc.. I carefully ran it between 4.2 volts and 3.6 as recommended.

It worked well for a few months, but now the first bank of cells is showing a voltage difference of 0.2 volts, and I can't find a way to balance it out, so that they all reach the same voltage level.

I then disconnected all the external coupling wires, and tested each 5000 mA pack individually.

One pack seems to be shot, with the first cell (in the order that the alarm tests them), showing 2.5 volts.

My accucell-6 charger refuses to charge that pack, telling me it's a 3S, so I guess I'll have to replace it.

I'm still having problems with the other five packs. Connecting them individually to the charger, they are recognised as 4S, but I can't get them to balance so that each of the 4 cells is the same. The first cell is always 0.2 volts less than the other three. I guess the faulty cell in the duff pack has pulled them down while they were all connected in parallel.

I've tried charge, balance, and discharge with the charger, but the first cell always stays at 0.2v less than the others.

Do I have to buy a charger that can charge through the balance leads instead ?

Sorry about this rambling post,

Any ideas appreciated...

 

[awol]

There are youtube videos about repairing similar problems.
To get the 2.5v low cell to charge you have to charge the pack slow for a while using nimh mode until the low cell gets about 3.2v or basically high enough for the lipo mode to recognise it. Then balance charge on lipo mode at 0.1a for hours and hours.
Hope this helps

 

[Deleted member 4366]

You could try a 5v charger on the single cell, but you need to moniyor it carefully. I prefer the chargers that charge through the balance leads because they always get it exact.

 

[eHomer]

Thanks for the prompt replies Awol & Dave.

I can understand the tips about using the NIMH mode and directly charging just that cell very slowly (presumably through the balance lead ?).

I suppose I was surprised at the balance mode being so ineffective on the Accucell, though I do remember Dave mentioning before about the advantage of some other chargers being able to charge individually through the balance leads. I would have thought (maybe naively ) that was the only way it could be done.

I think I'll bite the bullet and look for a charger that can genuinely balance through the balance leads.

 

[Deleted member 4366]

BC168

http://pages.ebay.com/link/?nav=item.view&id=251671796036&alt=web

 

[jimmyhackers]

http://www.ebay.co.uk/itm/New-SKYRC-iMAX-B6-Mini-Professional-Balance-Charger-Discharger-for-RC-Battery-/131299456836?pt=LH_DefaultDomain_3&hash=item1e920eb744

this the charger i use. (i have two they're that good)

might not actually be a charger issue. id figure after a few years one cell might degrade quicker than the others. either through impact damage (outside cells) or heat degredation (inside cells) and no matter how good the charger, it just wont get better if its shot or on its way out.

you any good with a multimeter?

you really need to see the individual cells voltages under a load to test if they're shot (big voltage sag and no capacity).
or if it is just a duff charger balence issue. i had a fake imaxb6 that was awful at balance charging and even puffed up one lipo destroying it. so your charger could be on its way out. but that seems unlikely as you have batteries it works fine with

the balance wires are essentially power supply wires but with a much smaller ampgauge wire rating.

try charging the single "dead cell" at a small amp rate on the single cells charger option (3.7)v through the balence lead instead of the power lead.

see if it will reach it optimum volts this way. if it does its good. if it doesnt it might be an indication the cells bad but possibly still usable.

you then need to monitor the voltage sag and usable amp hours when draining this cell. the imax charger i have has an "empty" setting where can can set an amp load upto 5amps(depending on voltages) and at the end it tells you exactly how many amp hours it took draining down to the "end volts" you specify.

granted this wont put the same load on as your ebike, but you can still test this load as voltage sag in "the field". and compare it to the other cells performances.

if you cant charge the cell to max volts it isnt the end of the world but only if...

you can test mah, and they are accetable comapred to a healthy cell.
and when the voltage sag under full load isnt much lower than other healthy cells.

you then need to decide if you want to replace the cells or your charger.

dead cells...if your feeling adventurous can be removed and if you have enough left over good cells a soldering iron and some tape.....you can salvage them.

 

[eHomer]

Thanks for the link Dave.
Yes, I remember you suggesting the BC168 before, it looks a much more sophisticated than my Accucell-6, albeit much more expensive.
Despite me often being a tight git, I'm definitely weakening now, it looks like the best and most versatile long term solution for anyone tinkering with Lipos.
It's a shame there are no UK suppliers though, I always seem to get knobbled with the customs and VAT charges from China, topped off with another chunk to Fedex for "admin"...

 

[eHomer]

Thanks for the very detailed response and ideas Jimmy, I'll work my way through your instructions carefully on the single charge through the balance lead and report back.
My initial reading of the Accucell-6 was that I couldn't get it to charge at all though the balance leads, but I didn't try any mode other than Lipo.

 

[Deleted member 4366]

Thanks for the link Dave.
Yes, I remember you suggesting the BC168 before, it looks a much more sophisticated than my Accucell-6, albeit much more expensive.
Despite me often being a tight git, I'm definitely weakening now, it looks like the best and most versatile long term solution for anyone tinkering with Lipos.
It's a shame there are no UK suppliers though, I always seem to get knobbled with the customs and VAT charges from China, topped off with another chunk to Fedex for "admin"...

The BC168 is very versatile. It's really useful for repairing batteries with a BMS too. You can work on any number of cells at a time up to 6.

The box isn't very big. Small items often slip through the duty net. I just ordered two controllers that came in a small box. They were delivered by the postman, so I must've got away with it.

 

[eHomer]

.......
try charging the single "dead cell" at a small amp rate on the single cells charger option (3.7)v through the balance lead instead of the power lead.
........

I can't seem to find that option on the Accucel-6.

The instructions and online info on it is fairly limited, but I am sure it doesn't allow charging through the balance leads, because whenever the main connections are not clipped on it shows a "disconnect" error.

The SKYRC iMAX B6 charger you gave a link to looks good, but can it charge via the balance leads, like Dave's BC168 ?

I'm focusing strongly on that feature as I can't see how any charger can possibly balance a pack without doing it through the balance leads, (without physically opening the pack up, which seems very tricky with these sealed Hobbyking Lipos.)

 

[awol]

+1 on the BC168 recommended to me too by d8veh.
It is so simple to use as you only need to connect the balance wires and set the charge/discharge voltage to whatever you want within the allowable safe range and set the charge amps.

 

[eHomer]

I'm now fully convinced....

BC168 now ordered....

Thanks for the advice.

 

[awol]

however I don't think the BC168 will allow you to charge the pack with the 2.5v cell so that cell needs bringing up over about 3v first using one of the above ideas.

 

[eHomer]

The cell in that pack is now showing 0 volts on the Hobbyking alarm meter, so I guess it's now a bin job anyway.

Hopefully the BC168 will balance out the 0.2 volt difference in cell 1 of the other five 4S packs though. It looks as though the rogue cell in that one pack is what originally put the other 5 packs out of balance, when they were all connected in parallel, (using the correct output and balance lead harnesses).

 

[eHomer]

The BC168 arrived after only 6 days from HK.
Great service from eBay seller rcecho-uk

The bad 4S pack refuses to get above 2v on cell one when very carefully using the Accucel charger in NIMH mode, so not enough for any of the Lipo chargers take over.

The other five packs are now balanced very accurately, within .01 volts, thanks to the BC168. I'll persevere with my outboard 12v Lipo battery as a 25 ah, rather than the previous 30 ah.

Thanks for the helpful advice on getting the BC168, a simple to use and much more reassuring way to charge Lipos.

Here's the readings before I balanced and then charged the pack, showing the imbalance in cell 1 which had been drawn down by the faulty cell in the bad pack.