rcobject

I have 2 packs of lipo. I tested them with voltage buzzer tester and got the following result:

lipo 4200mah 2s:
all 6.24v
2.36v
3.84v

lipo 350mah 2s:
all 6.34v
3.05v
3.27v

are these lipos still good or bad ? is it possible to fix them? Thanks. I used them for playing r/c with brushed motor.

chuckk2

The 4200 likely has a bad cell. With careful low current charging, it might be usable as a bench test source if full current and capacity are not needed.
The 350 may be ok with proper charging. Again, expect less than rated capacity to be available.
Numbers to remember
Cell Voltage
4.2 full charge for most common lipos
3.7 at rest voltage for properly used lipo waiting to be recharged
3.0 3.2 do not go below under load.
3.8 3.85 safe storage voltage

rcobject

I charged it with 4A for a while and stopped it. Now the reading are 7.86v/ 3.78v, 4.08v. What currents I have to charge it with? <1A? Or I got to discharge it first?

nitrosportsandrunner

ive had a lipo with cells reading 2.8v that I charged for a minute or 2 on NIMH setting. This put just enough juice into the pack so that my charger would charge in lipo mode. If you try this, do not walk away from the lipo!

The first pack is poorly balanced. I would try balancing it before charging.

The second back should charge just fine.

If charging ANY lipo that you suspect may be bad, always charge at a low amp rating. A 4000mah lipo can be safely charged at 4amps normally. With a possible bad cell, I would use 1amp. Make sure you chargers is in balance charge mode. charging at 1amp may cause your charger to time out before it fully charges the pack, but charging it slowly will help it. a 2s lipo should be 8.4v fully charged with each cell being 4.2v (4.1v is fine as well)




With the 350mah pack, 0.2-0.3 amps is best.

rcobject

After finished charging 4200 with 1A , the reading of the cells are (8.09v| 3.87v,4.20v). I think that was why one of cells was over discharged. Do I need to cycle to balance it? What current to discharge with?

nitrosportsandrunner

I have a separate "blinky" balancer which can read each cell's voltage and balance cells. usually I can put a lipo on that and get the cells closer. With the difference you are seeing, one cell is indeed damaged and may not recover fully.
Ive never used my charger to discharge a lipo. Id discharge at low amperage. Actually, to be honest I would just run the pack for 5 minutes and then put it back on the charger. A lipo with a bad cell shouldn't pose a risk if you don't strain it...IE, you run it for only a short period or use it in a old RC or one that wont draw much amperage.

You might get a few more used out of that pack, but its on its way out either way. Even if you try balancing it I doubt it will get all the way there and the bad cell will continue to degrade with each use. Eventually the pack will begin to swell.

If you are new to lipos, your safe bet is to toss it and buy a new one. I have run packs with readings like yours...sometimes I got a good number of uses out of them and other times they began to swell right away. A lipo fire can be a nasty thing. Ive never had one...yet.

rcobject

Yes I m new to lipos. The lipo pack has had bad number since the beginning. It was just used indoor for 2-3 times on my brushed motor rc car. May be it idle for too long. After I played it a while, the car stopped running. The voltage has already dropped to the danger zone. It was already too late when I checked the voltage tester.

nitrosportsandrunner

do you know if your brushed RC's speed control has "low voltage cutoff"? That is needed in order to run a lipo. NIMH batteries can be drained to the point where the rc will hardly move and then charge right back up.
Lipos cannot be allowed to drop below 3.0v per cell...though 3.1 or 3.2v is safer. Most speed controls meant for running lipos cut power to the motor when they detect cell voltage to be around 3.2v
But older ESC's don't have that.

But a lipo used and then left un-charged for some time will drop in voltage as well. Fully charged they can hold their charge very well, even for a couple of months. But if left uncharged for a long period of time a cell can go bad.

But at least we live in a time when many 2s packs are as low as $25! Back when I started a decent NIMH battery was at least $35...and those packs are crap compared to a cheapo 2s lipo we have these days.

rcobject

I use futaba mc230cr esc on 1/10 rc and the little lipo pack is used on losi micro r/c. I don't know these brushed esc have low voltage cutoff feature or not. Does all brushless esc has low voltage cutoff feature?

And my charger fixed discharging voltage ( 3v for 1s , 6v for 2s). Is it too low?
"But if left uncharged for a long period of time a cell can go bad." <-- I think this is my case . What is the different between $25 and $35 lipo?

I have a dead lipo which is less than 1v because I left power switch on overnight . How to dispose it?