Charger question
 

I knew all this stuff when I was researching chargers but the formula slipped my mind. How do I determine what the charger can do for a charge current (amp)per channel? I have a x2 400 hitec which is 400 watts per channel (x2) capable of 20amps per channel but I am only using a 20amp Trakpower power supply. So I know the charger can do 20 amps but I also know that 20amps per channel is limited by the power supply I am using and the size of the battery. Say for this calculation I am charging a 4s/6500mah/65c lipo. Can someone write out how to calculate it.

Sorry I forgot but here's a bump for ya because I want to know also

Volts x Amps = Watts (power)

I think the TP supply is a 13.8 Volt or so output:
13.8V x 20A = 276 Watts of power supply

Chargers consume some power, 80% efficiency is a safe estimate:
276W x 80% = 220.8 Watts of charge power.

A 4S lipo goes up to 16.8 Volts, work backwards:
220.8W / 16.8V = 13.1 Amps (rounded off)

The 13.1A can be used on one channel, or split across both for about 6.5A on each channel.

P.S. I always recommend not pushing power supplies to full power for best reliability for a variety of reasons. Some can handle it, but not all.

Thank you... So the charger is 400w/channel. But that is limited because my supply is only 20A, is that right? I am guessing that is why the charger actually says to use a min 60A supply. But using a 25A supply isn't hurting the charger is it? It is just limiting it?

Also, the supply has a dial that goes from like 11v to 18v. I have it set to around 12-15ish but I can't tell an exact number because the dial doesn't 't show all the numbers. Should I leave it around 12 or should I crank it all the way up?

If I happened to enter in a charge rate higher than the charger can do, it won't hurt the charger will it? It just won't go to the value I entered it will just do what it can right?

Yep, you got it.

As long as you remember the limits and don't ask for too much, then it won't hurt anything.

As long as you don't have other devices being powered that might have voltage limitations, then I'd crank it up, as long as it stays within the charger input limits (remember to consider the power drain of any other devices). This charger appears to also be rated for up to 18V input, but because of tolerances they may not match up exactly. I'm not sure but I don't think you will get any more power, but high Volts/low Amps should let it run a little cooler.

One thing to be aware of, avoid setting the power supply in the range of pack voltage while charging. I.E, leave it at 12V or get it well above 16.8V for a 4S pack. If the pack crosses the input Voltage while charging the charger must switch from buck to boost mode, which can lead to a bit of instability. Usually not a big deal, but makes sense to avoid if practical.

A charge rate higher than the charger can do isn't the possible problem, the charger will self regulate itself (at least every charger I've messed with will anyway).

It might be a problem if you go higher than the power supply can do though, at least it's far from ideal. The power supply would be overloaded, brown out, might go unstable, shut down, etc, all hard on the charger. There isn't any connected intelligence for the charger to avoid this.

Some of the high powered chargers do have power supply settings available to avoid exactly this issue. I don't think this charger does though. Just remember the limits and you should be fine.