50W versus 100W battery charger

[Honda]

This is the way I understand it. A 50W charger has a maximum output of 5 amps. A 100W charger has a maximum output of 10 amps. When charging a 4200mAh LiPo battery, the charger runs at 4.2 amps. So, a 50W charger is all that is necessary to charge the battery. The 100W charger is also going to charge the 4200mAh LiPo battery at 4.2 amps. Is there any reason to buy a 100W charger when only charging one battery?

[Jimmie Neutron]

Wattage is not a direct correlation to amperage.
There are three parts to the equation... voltage needs to be considered as well.

Say you have a 6S 4200mAh battery and a 10 amp 50 watt charger and you want to know what amperage you can charge at:
Watts / Voltage = Amperage
50 / 25.2 = 1.98

So, even though the charger is capable of 10 amps, it will not be able to charge a 6S batter at more than 2 amps due to its wattage limitation.

[Honda]

I need to charge a 2S 5000mAh battery. I don't know the voltage. Where do I find that?

[Jimmie Neutron]

2S = 2 cells in series.
4.2 volts per cell when fully charged.
4.2 x 2 = 8.4 volts.

[Honda]

OOOOH! That's where the 25.2 number comes from. 50/8.4 = 5.95 Amps... so, a 50W charger will almost charge a 6000mAh 2S battery. I need to charge a 4200mAh battery. 50W will be plenty. I wouldn't need a 100W charger until I have a 2S battery over 5900mAh or a 3 cell battery over 3900mAh. 4.2 X 3 = 12.6. 50/12.6= 3.968

[Jimmie Neutron]

I am impressed!
You caught on to the concept and the math very quickly!

[Honda]

This is the way I understand it. A 50W charger has a maximum output of 5 amps. A 100W charger has a maximum output of 10 amps. When charging a 4200mAh LiPo battery, the charger runs at 4.2 amps. So, a 50W charger is all that is necessary to charge the battery. The 100W charger is also going to charge the 4200mAh LiPo battery at 4.2 amps. Is there any reason to buy a 100W charger when only charging one battery?

Jimmy, thank you very much for the clarification. A 100W charger will charge a larger battery. For my needs; LiPo 2S 4200mAh or 5000mAh battery, a 50W charger is all I need. The larger charger won't charge it faster either because the charge rate is the same.

[mike-susieq1]

I like to charge at 2c when I am in a hurry only so I need the extra amps to do that at least 8amps. There are some good chargers like the traxxas ez peak plus that has 6amps 80w that's good but I just need more.