Help with charging conversion please?
 

I recently got into micro RC cars for indoors and I am using a Thunder AC 6 charger. My batteries are tiny 2S that say 400mah and 3.0WH. I don't want to cause a fire. How should I charge these? What amps and ? I have the 2S part figured out but thats about it.

Charge Lipo packs at 1C rate, where C is the capacity of the pack. For your micro packs, use 0.4 amps.

Ok, I don't see anything that says "C" but I will throw it on at 0.4 amps and see what happens. Thank you

Simple, all LiPo's are rated to charge with 1C and thats a current number equal as the capacity. So 400mAh -> charge with 400mA
All LiPo's can go a bit over it, 1.5C (in your case: 1.5x 400mA = 600mA) is still safe to use.

2C and higher is at own risk or the manufacturers says it can be used.

move decimal point three spaces to the left
 

OP's 400mAh pack charged at a 1C rate = move decimal point three spaces to the left of mAh capacity = .4 amp setting on charger.

If you don't see a charge rating on a LiPo, it's best to stick to a 1C charge rate for the safety and longevity of the cells.

To calculate the charge rate of a LiPo pack:

mAh (capacity) divided by (/) 1,000 = Amp hour of pack (Ah)
Amp hour (Ah) x 1C charge rate = charging amps to enter on charger

For example:

A 4,000mAh pack, that does not state a charge rate, revert to a 1C charge rate.
In you head, move the decimal point three spaces to the left ...
4,000mAh / 1,000 = 4.0 Ah
4.0 Ah x 1C charge rate = 4.0 Amps (set charger to 4 amps)
The 4,000mAh battery pack should be charged at 4.0 amps.

If a 4,000mAh pack is rated for a 2C charge rate, the 4,000mAh pack can be charged at 8.0 amps (4x2). If 4,000mAh pack is rated for a 3C charge rate, the 4,000mAh pack can be charged at 12 amps (4x3).