Battery charge rates

[darwin-t]

How fast can you charge batteries of 20C and 35C? By that I mean, at what amperage can they be safely charged?

Also, you are not supposed to store Lipo batteries fully charged. Would it be okay to charge them with only the main plug, store them and then finalize the charge but using the balancing plug?

 

[rilot]

Store LiPos are 50% charge. Any more and you do risk shortening their life span.
I tend to charge batteries at 2C to be safe.

 

[OI Photography]

the 25C and 30C and others you're seeing on the battery labels or descriptions refer to the maximum discharge rate the battery can deliver. The maxium charge rate is sometimes listed as well but not always. Unless the battery specifies a safe charge rate you should keep it to 1C or 2C at max like rilot mentioned. Some quality batteries will let you charge at 5C or even more, but don't try charging that fast unless they're clearly specified for that

The formula to use is this:

For any battery, "1C" = <mAh capacity>/1000

for a 2200mAh battery, 1C = 2.2A
for a 5000mAh battery, 1C = 5A

So the safe Amperage to use also depends on the size (capacity) of the battery.

Btw the formula is the same regardless of whether the battery is 3S, 4S, etc.

 

[darwin-t]

Store LiPos are 50% charge. Any more and you do risk shortening their life span.
I tend to charge batteries at 2C to be safe.

How do you charge to 50%?

The battery only loses a couple of volts during use. So let's say fully charged is 12 volts, and your settings are set to auto land at 10 volts. The battery is at 83% charge. Or would 10 volts be equal to 0% and 12 volts equal to 100%?

Sorry I am being dense, but lipo batteries confuse me. Everything about them seems counter intuitive to me.

 

[darwin-t]

The formula to use is this:

For any battery, "1C" = <mAh capacity>/1000

for a 2200mAh battery, 1C = 2.2A
for a 5000mAh battery, 1C = 5A

So the safe Amperage to use also depends on the size (capacity) of the battery.

Btw the formula is the same regardless of whether the battery is 3S, 4S, etc.

Thanks for the explanation. It makes sense to me now.

 

[rilot]

Store LiPos are 50% charge. Any more and you do risk shortening their life span.
I tend to charge batteries at 2C to be safe.

How do you charge to 50%?

The battery only loses a couple of volts during use. So let's say fully charged is 12 volts, and your settings are set to auto land at 10 volts. The battery is at 83% charge. Or would 10 volts be equal to 0% and 12 volts equal to 100%?

Sorry I am being dense, but lipo batteries confuse me. Everything about them seems counter intuitive to me.

For a 3S battery. My 0% is 3.5V / cell = 10.5V
But, and this is a big but, voltage drops aren't always linear. To know whether you are flying to 20% monitor your charger to see how many mAh you are putting back in to your cells. Most decent chargers will tell you this. Once you get to a voltage for that particular pack that you measure 80% going back in, you have your 20% voltage. It take a lot of flying, testing and writing down numbers.

On a P2 of course it's easy as the iOSD tells you exactly.