charging lithium battery

[herbwhite59]

Is there any danger of fire when charging lithium batteries? Is it O K to leave the charger hooked up overnight in an enclosed garage? It would be a 12 volt lawnmower battery. Thanks for a reply. Herb

[trader_4]

Probably depends on a lot of things. Like the particular battery and charger. Quality battery from a known, credible company or Chinese no name junk? Suitable charger, good or Chinese junk? People charge hundreds of millions of cell phones every day, very few catch fire. People were charging those little scooter widgets that kids stand on, enough of them caught fire and blew up, some burning down houses. Boeing found out their batteries were catching fire when they rolled out the 787. So, it depends. You could certainly reduce the risk by making sure there isn't anything easily combustible near it.

[Hawk]

Yes, unless you're using the manufacturer's charger that came with the batteries. Otherwise read below from

These remarks apply equally to lithium ion and lithium polymer batteries. The chemistry is basically the same for the two types of batteries, so charging methods for lithium polymer batteries can be used for lithium-ion batteries. Charging lithium iron phosphate 3.2 volt cells is identical, but the constant voltage phase is limited to 3.65 volts.

The lithium ion battery is easy to charge. Charging safely is a more difficult. The basic algorithm is to charge at constant current (0.2 C to 0.7 C depending on manufacturer) until the battery reaches 4.2 Vpc (volts per cell), and hold the voltage at 4.2 volts until the charge current has dropped to 10% of the initial charge rate. The termination condition is the drop in charge current to 10%. The top charging voltage and the termination current varies slightly with the manufacturer.

However, a charge timer should be included for safety.

The charge cannot be terminated on a voltage. The capacity reached at

4.2 Volts per cell is only 40 to 70% of full capacity unless charged very slowly. For this reason you need to continue to charge until the current drops, and to terminate on the low current.

It is important to note that trickle charging is not acceptable for lithium batteries. The Li-ion chemistry cannot accept an overcharge without causing damage to the cell, possibly plating out lithium metal and becoming hazardous.

Float charging, however, is a useful option. The safety issue with keeping the battery on constant charge is that if the charger should somehow go haywire and apply a higher voltage there could be problems. And, so the logic goes, the shorter the charger is turned on the less likely the charge will go haywire while connected to the battery. However, there is another safety method, the battery protection board, which should be included either on the battery or in other circuitry between the battery and the charger. The BPB (also known as PCB for "protection circuit board") or other battery management circuit will stop the charge if the voltage gets too high.