I'm going to try recharging the best of a set of cells I got out of a shot laptop battery, two cells were at .9volts I'm sure this is well bellow absolute death for a lithium ion cell, the rest are between 1.4 and 1.9 volts (noload voltage) Anyone ever tried this before?

 

Nope, but put them somewhere fireproof, like a metal coffee can. There are some impressive YouTub videos of them going up.

 

As I said on the other website, your low voltage Lithium rechargeable battery is destroyed because its protection circuit failed to disconnect the load when its voltage dropped to less than about 3.2V per cell.

 

That's one theory AG, but it's more than likely the age of the pack, two of the cells went bad and developed enough series resistance to drain the rest of the cells even with the protection circuit, probably a common failure mode for larger packs that can't individually cut off each cell (I doubt many systems do that)

Although upon the notice that the absolute base cutoff is close to 3.0 volts I'm not going to even attempt it, I have four other cells that still hold a full charge and were never misused, I probably could have saved some of the cells if I'd gotten to it sooner, but it's been in this state for over six months.

I've seen the YouTube videos but I also know how it happens, if the battery is dead as in my case it's nearly impossible to get them to go up in flames like that, all the ones you see on youtube are when a relatively healthy pack is overcharged past it's critical temperature and then all the energy of the fully charged pack is released in one big go. The cells I have if they're that bad off will at worst exhibit really bad ohmic resistance when I try to charge them smoke and possible burn but not burst into flames.

 

I would be interested to see if this is successful. My idiocy left a 2S 7.4V LiPo connected to an RC plane for a week. It was completely discharged by the time I got to it, and the charger wouldn't recharge it. It reads about 6V. Any chance of resurrection?

 

I would say you have a better chance than I do, but RC vehicles abuse their cells pretty bad. What's each cells voltage after it's been left sitting for a while?

3 volts per cell is low. but mine are at 1.4-1.9 That's not just low as AG said in the other forum the chemistry will passivate at that point and can't be recovered. Your cells were only discharged for a bit, mine were MASSIVLY discharged for a huge perioud of time.

Do you have any variable fixed voltage sources that are current limited? Chose something that has a MAXIMUM voltage of 4 volts that is current limited to approximately 1/10th C, and let it try to recharge it for a few hours, watching the voltage of the cell on a multimeter and the heat.

Once you get the voltage on each cell up to low 3's you should be okay, but if the floating voltage on the cells right now is too different the 'pack' is dead, you might be able to use one cell by itself but it'll never be part of a proper safe battery ever again. Mind you the clock is on, I don't know what it takes but as AG said the cells will plate out their electrolyte components if they're too low in voltage, it's the time at those low voltages that are critical.

Manually charging Lithiums is actually really easy if you know what you're doing, a mistake on a fully charged cell will cause those fireworks show Bill mentioned that you can watch on Youtube.

 

I would say you have a better chance than I do, but RC vehicles abuse their cells pretty bad. What's each cells voltage after it's been left sitting for a while?

3 volts per cell is low. but mine are at 1.4-1.9 That's not just low as AG said in the other forum the chemistry will passivate at that point and can't be recovered. Your cells were only discharged for a bit, mine were MASSIVLY discharged for a huge perioud of time.

Do you have any variable fixed voltage sources that are current limited? Chose something that has a MAXIMUM voltage of 4 volts that is current limited to approximately 1/10th C, and let it try to recharge it for a few hours, watching the voltage of the cell on a multimeter and the heat.

Once you get the voltage on each cell up to low 3's you should be okay, but if the floating voltage on the cells right now is too different the 'pack' is dead, you might be able to use one cell by itself but it'll never be part of a proper safe battery ever again. Mind you the clock is on, I don't know what it takes but as AG said the cells will plate out their electrolyte components if they're too low in voltage, it's the time at those low voltages that are critical.

Manually charging Lithiums is actually really easy if you know what you're doing, a mistake on a fully charged cell will cause those fireworks show Bill mentioned that you can watch on Youtube.

I had not used the battery before except to test out the motor for a few seconds. Apart from being completely flat the battery should be good as new.

It's not critical, it was only a 300mAh pack which is about £5.99 on eBay. I don't have a constant current source available at the moment (CV/CC power supply is on my wish list), is it possible to get by with just a resistor and a 4V supply? I could also use an LM317. This is a project for me to try, because then I can have two packs, one spare. After resurrecting it, will it have lost capacity? I'm willing to bet so, but...

I also have a 12V SLA from a UPS that I'm trying to resurrect, it was down to 6V but now reads about 11V so I'm hopeful.

 

I saw a pretty big RC model airplane catch on fire during its first flight. The brand new Li-Po battery burst into flames. The pilot landed the airplane quickly, removed the burning battery and placed it in a bucket of sand. It burned for about half an hour. It cost $500.00.
I think the current of the motor was too high for the battery but the pilot says it was a defective battery.

 

I saw a pretty big RC model airplane catch on fire during its first flight. The brand new Li-Po battery burst into flames. The pilot landed the airplane quickly, removed the burning battery and placed it in a bucket of sand. It burned for about half an hour. It cost $500.00.
I think the current of the motor was too high for the battery but the pilot says it was a defective battery.

This is why you should always doubly overrate your current requirements. I am surprised he managed to land when the battery burst into flames. It is of my understanding that the voltage would drop quite considerably (i.e. to zero) during this reaction, unless he had a second battery.

 

RC model airplanes don't crash like a brick when their power runs out, they glide.

 

RC model airplanes don't crash like a brick when their power runs out, they glide.

Yes but without control surfaces your plane will just crash, especially if they are in different positions from neutral.

 

Tom, many typical RC setups have different power and control battery packs. The electronics powering the receiver were probably standard NiMH or NiCads.
AG, no the planes don't crash but the chemistry of the packs is trashed. The kind of packs you're talking about are operated OUTSIDE of manufacture typical profiles, in series you're gambling unless you're an electronics god, or play it so safe you'll forget 50% of the usuable power in the pack. Lithiums aren't hard to charge safely, but the discharge is... dangerous. You can't just floor the gas pedal on a new pack watch it go up in flames and blame the cell maker, whoever that happend to was a freegin moron.

 

My RC airplanes pulse the main motor when the battery voltage is getting low then it shuts off the main motor when the battery voltage is too low for the battery to survive. The receiver still works fine at its low current and the servos also still work fine at their low current. The airplane can glide with full control for a long time to a perfect unpowered landing.

The airplane with its main battery on fire had a second battery for the receiver and servos.

 

The airplane with its main battery on fire had a second battery for the receiver and servos.

Okay that explains a lot. A lot of RCer's are moving to single batteries and a battery eliminator circuits.

 

Not higher power RC stuff. Larger scales require some significant voltage for the power system so the servos/receivers are run from a separate battery pack, a BEC is just another failure point. If your power battery suddenly chokes in flight even if it's on fire you can land it using the receiver/servo battery. Even if you used a Lithium battery as a secondary power source for the receiver it's a better idea, lithiums handle the currents required by even high torque servo's much better than the ones that are stressed out to the makes for high performance brushless motors.

 

Not higher power RC stuff. Larger scales require some significant voltage for the power system so the servos/receivers are run from a separate battery pack, a BEC is just another failure point. If your power battery suddenly chokes in flight even if it's on fire you can land it using the receiver/servo battery. Even if you used a Lithium battery as a secondary power source for the receiver it's a better idea, lithiums handle the currents required by even high torque servo's much better than the ones that are stressed out to the makes for high performance brushless motors.

Ah well, you know. Either way the plane is not going to be flying well after an explosive battery failure.

Any luck on getting your cells recharged?

 

No, after AG's reminder of the lower voltage limit I won't try. As I said 'in the other place' I was mistaken about the lower discharge limits of Lithium cells, by almost a volt and a half =) Those cells are going into my recycle bin, I have four other cells from a healthy pack with cells of the same type that I have no trouble working with.