longuylander

iTrader: (7)

I went to charge up one of my 2S lipo batteries for a fun romp with my old Tamiya TA02 rally car. When I connected it to the charger (a cheap Duratrax Onyx 150), it started beeping wildly, indicating the battery was not charging. I tested the voltage of the battery to find it was at 4.9V!!

So there are two questions here:

1. What could have caused the battery's voltage to drop so low? It had been stored at room temperature for around two months and around 7.2V.

2. Is there any way to revive the battery? I tried charging it at 1A, 3A, and 5A with no success. It's not puffed. Would attempting a charge without the balancer plug work?

scirocco14

iTrader: (5)

I've had some success reviving lipo batteries that have gone too low in voltage by charging them SLOWLY on a NiCd or NiMh setting. WATCH THEM CAREFULLY while you do this, in case the battery has an internal short.

Once the voltage is high enough for the balance charge to work, switch over.

Good luck!

Mark

SWTour

iTrader: (9)

can you check the voltage on each 1/2 of the balance? if you can you may find that 1/2 of your pack (1cell) is dead or extremely out of balance -

If so - try charging that 1/2 or that cell to bring it up to the other one.

Skiddins

Stick the battery in strong salt water solution to completely discharge it, then recycle the battery when completely dead.
Buy a new decent battery.

Having gone below voltage the pack will almost certainly have suffered some internal damage, and if it self discharged that quickly when not connected to anything it was a dodgy pack already.

Dave H

7.2 volts is too low of a storage voltage for a 2S, at least for an extended time. The pack was essentially fully discharged, not much margin for error/slight self discharge.

A typical resting voltage vs capacity table, based on discharging at 1C to 3V. Of course this will vary some by cell but most tests I have seen over the years are fairly close.

4.20v = 100%
4.03v = 76%
3.86v = 52%
3.83v = 42%
3.79v = 30%
3.70v = 11%
3.6?v = 0%

3.8 to 3.85V per cell, or 7.6 to 7.7V for a 2S, is a much more reliable storage voltage best I can tell.

D.a.v.e

iTrader: (8)

Toss the pack. It's not worth messing with. You might get it to work but there is something wrong with it. Think of it as a time bomb you caught early.

I have tried bringing one back and it went up in flames about 6 hrs after I thought I had saved it. Luckily it was in a corningware bowl in the middle of my garage so no real damage other then smoke.

rc car freak

never do the salt water method instead plug it into a low amp light bulb till completely dead then use salt water

Skiddins

No, the salt water will discharge it so it's completely dead.
It also does it very slowly, reducing the chances of a fault trying to cause a fire etc.

longuylander

iTrader: (7)

Thanks for the advice all; I think I'm going to play it safe and not try to charge the battery with an NiMH charger. I'd still love to know why it drained though. Perhaps it was too discharged (I had always heard around 7.4V was a good storage value), or perhaps it was just a poorly constructed battery.

Geezatec

Gunna ask you, What lipo charger you use? Does it use a storage charger and individual cell voltage? Abalance charger? Is it a combination lipo & NiMh charger?

1) Probably when you discharged it by running it down, and didn't put a storage charge on it.

2) Have to know what charger you use. Then I'll though it with you.

Dave H

Unless the salt water corrodes the connections before the cells are discharged, which several guys have experienced. If the connections are good the light bulb method seems to work well. Using a safe location is wise with either method I think.

Geezatec

With the Onyx 150 its not good enough. You need a charger that does both lipo's and NiMh, function to read cell voltage, Balance charger, and to storage charging. Storage charging charges 1/3-1/2amps in lipo's for storage. Full amps for storage will weaken the lipo's. There is a way to revive lipo's from low voltage cell errors. If lipo's are not puffed out you can revive.

alcyon

iTrader: (8)

Charging with nimh mode works. You cheat the charger into thinking its a nimh. You monitor the voltage as its charging. Set it to 6cell nimh. As soon as voltage rises to 6.3v you are all set. Stop the charger n switch to lipo mode. It works trust me.

ShadowAu

iTrader: (7)

Did exactly this, this past weekend, and battery seems to be fine now...

longuylander

iTrader: (7)

O.k., I went back on what I said earlier and busted out the old NiMH charger. Set on 0.8A, I hooked up the battery. When it started charging, the voltage reading was already 6.85V (I'm not quite sure how that's possible... it definitely read 4.9V prior when hooked up to a Speed Passion ESC). After less than two minutes and 25mAh of charging, the voltage read 7.05V. I hooked the battery back up to the lipo charger, and it started charging, which it is currently doing.

I'll comment when it finishes, if it finishes, and if it doesn't puff or burst into flames. Well, I'll post if it does burst into flames too, but only after I put the fire out.