Recovering LiPo batteries

[PedroR]

Hi all

I have new information from Robobuilder which I found interesting and decided to share:

We had a customer who experienced over discharge with his LiPo and the Smart Charger refused to charge it again.

There is a way to recover LiPo's that were over discharged and get them to work again:

You need a variable regulated power supply (one that is able to supply continuous DC power) and _not_ a charger.

Please follow these steps:
1) Read the voltage of the LiPo (let's say the reading is X)
2) Using the regulated power supply, apply "X+1V" to the battery for 1 minute.
3) Keep repeating steps 1 & 2 until the battery reaches 11V (or whatever voltage is in the LiPo spec).

Now the safety part: Power Supply Charging Voltage - Battery Voltage < 1.5V !

This needs to be respected (as well as the maximum time of 1 min applying power) or otherwise the LiPo might explode. (they can also explode if overcharged or over discharged)

I've actually learned a lot about LiPo's and finally understood why they need a microprocessor for charging: you need to be supplying power in in small increments of voltage. (there are probably other things to consider in addition to this though)

Please remember to always use the Smart Charger when charging your LiPo and also use the modified firmware for LiPo users (which sets the low battery threshold at a higher voltage to protect the LiPo).

Regards
Pedro.

[StuartL]

Without current limiting this technique is properly dangerous. With the risks involved and consequences of overcharging a LiPo there's no way I'd risk this approach and instead I'd rather spend the money and replace the pack. Obviously this is more expense but I'd consider it equivalent to paying for fire insurance.

LiPo damage is almost always internal and can fail weeks or months down the line. A failed LiPo will burn hot enough to set fire to most things, including carpet and most textiles. If you damage it by badly charging it then it fails when you're not expecting it you could be in serious trouble.

Just my two cents, etc...

[ries]

i'm the one who had the problem Pedro is mentioning.

The first time i used firmware without the Lipo update so my lipo overdischarged. With the above solution from Pedro the battery came back to life and with the correct firmware the red led is flashing when the lipo was at 9V.

But the problem didn't dissappear. Currently the cell that's was overdischarged is giving me problems and when empty i have to do the aforementioned procedure to get it back to 'normal'.

Does anyone have experience with lipo's and can tell me if a cell of the lipo is broken down or....

Thanks in advance.

[Meltdown]

After dealing with lipos for almost a decade with competition rc car racing i know one thing.
Don't mess with broken lipos ever.
It's highly dangerous.
Get rid of it and buy a new one.

Lipos get seriously damaged in three ways.
Overcharging them or draining them under 2.5v per cell and If the pack was punctured or physically damaged.
If either of them happened, forget it, toss them away.

[Ketchup]

Ries,
I'm assuming it's a 3-cell pack. Does it have a "balancing tap" on it as well as the normal power connector?

The issue with a multi-cell LiPo pack is that all of the cells need to be very close in voltage to work safely. If one cell in the pack is lower/higher than the others, during the process of charging or discharging, that cell can get into the dangerous over or under charge state and cause a failure.

Sometimes a LiPo pack will give a pre-fail indicator by puffing slightly. If you have a puffed pack, get rid of it.

With my radio controlled aircraft, all of my multi-cell packs have a balancing tap that the charger plugs into. It makes sure all of the cells are within .02 volts of each other. This is the only safe way to charge them. Also, they really need to be charged in a fire-proof container. I have a special ceramic container for this with a twist-lock lid that can vent the gasses and smoke should one fail. ( http://www.batterybunker.com/ )

Do not risk your personal property to save a bit of money. I have seen the aftermath. It's not good.

Also, LiPo chargers apply the CC/CV method. Constant Current/ Constant Voltage to charge. As the pack nears the full charge state, the current will taper off. The voltage will always stay the same (4.2V per cell).

There are a lot of resources on the 'Net for LiPo safety & charging tips.

I hope this helps!