Amps, Watts and more...
 

Watts is equal to voltage multiplied by amperage.

Watts x Amps = Volts
Volts x Amps = Watts

Is that right?

If I know the KV of a motor and the Volts I will be using, then how can I figure out the amps or watts?
Example...: 5700kv and 11.1v = watts or amps???? Is that possible?

And KVs are equal to RPMs, yes?

Ray :D

kV is the RPM's per volt going in to the motor, so in your example a 5700 kV motor on 11.1 volts will give you 63,270 RPM at best efficiency. It won't give you power output.
The power ratings seem to be getting more guarded by most brushless motor suppliers now. Don't know why, it's always been the best way of guaging motors along with peak RPM and peak Torque.

Watt does volts x amps, but volts = watts / amps. Watts varies with rpm, so you're really asking for a curve, not one piece of data. Some companies quote maxx watts, which I assume would be at some peak rpm, but they're usually not given together, so you really don't know for sure what rpm or other conditions the maxx watts occurs at. There are no industry standards for testing BL motors so there's really no standard available for comparison.

The first is wrong.

Watts / Amps = Volts
Volts x Amps = Watts

Which watts and amp? Input or Output?
Is not possible to calculate the Input or Output power (in Watts) of a motor simply by KV and Volts. You have to measure it using instruments, or you can try to calculate it but you'll need more data.

5700 are rpm/v
5700rpm/v x 11.1v = 63327 RPM

Thanks guys, I learned about that today.

Watts
___________
Volts X Amps


Volts x Amps = Watts. However Watts / Amps = Volts. You have to divide watts by amps to find volts (or divide watts by volts to find amps).

I didn't even know this until today. I seen some motors that just have kv rating and I wanted to see the specs with a given voltage but all the motors has was kv rating so thats why I asked that question.

Is there a way to get a fixed number on the amps only instead of seeing differnt numbers?

For example...

Traxxas Velineon 3500 Brushless Motor (Sensorless Brushless)

Watts: 481 on 7.4v, 721.5 on 11.1v, 917 on 780 on 12V
RPM/volt: 3500 (10-turn)
Max RMP: 50,000
Current Ratings: 65A constant / 100A peak/burst

Lipo
25,900 RPM on 2s Lipo 7.4v - 65 Amps @ 481 Watts
38,850 RPM on 3s Lipo 11.1v - 65 Amps @ 721.5 Watts

AND

Novak Ballistic Spec Brushless Motor 13.5T

Watts: 195 on 7.4v,
kV: 3,300 RPM/volt (unloaded)
Maximum RPM: 50,000

Lipo
24,420 RPM on 2s Lipo 7.4v - 26.3 Amps @ 195 Watts
36,630 RPM on 3s Lipo 11.1v - 17.5 Amps @ 195 Watts
48,840 RPM on 4s Lipo 14.8v - 13.1 Amps @ 195 Watts

The Velineon amp numbers are fixed where as the Novak amp numbers are all different. How do I reverse this on these numbers? How can I get a fixed number on the Novak motor amps and get different amp numbers on the Velineon?

Ray :D