How to choose suitable ESC for particular motor

[hwsv07]

hi guys, i'm new here and grateful for this forum to share ideas.

i have a question. how do you guys choose the suitable ESC for your particular motor?

for e.g. i have a motor which a maximum current rating of 18A. does it mean that my ESC should have a current rating of more than 18A? is this the only criteria?

thanks.

[MacDream]

On the safe side, the rule of thumb is to choose an ESC 1.2 times the max current drawn rated by the motor. Hope this helped. Cheers!

[MeePokMan]

More Lipo = more RPM?

Hi Macdream,

I am quite new to electric RC. I wanted to get more out of my in-runner motor. Will adding more Lipo cells increase the performance of the motor? I have a 4900 Kv motor installed on a 36" Zagi (350gram total weight) using a 4.75" APC pusher propeller. I used a 30A ESC and a 2-cell lipo (7.4V, 20C, 1300Mah) and also a 3-cell lipo (11.1V, 20C, 1400Mah) - it gives a lot of power. What happens if I install a 4-cell lipo (14.8V, 25C) battery? Will it gives more RPM and hence more speed?

I think I have already accidentally fried 2 motors and 1 ESC literally caught fire while flying. Maybe I should invest in a watt meter to investigate.

[Adrianli]

More cells, same motor kv, same ESC = more amp draw. U will be frying another ESC.

[MeePokMan]

Just bought a Watts Up

I bought a Watts Up meter from Hobby City and tested all my electronic setup. Quite a lot of surprises!

For my Zagi, my setup:

Motor: KB20-40-12L, Max Amp: 20A, 4800kv
ESC: 30A
Lipo: 1300Mah, 2-cell, 7.4V, 20C
Prop: APC4.75x4.75 pusher

The results of the test:

Max Amp drawn: 38A!
Power: 260W

Yes, I am frying my motor and battery!! I will switch to a 25A ESC for another test.

[Tomahawk]

Beside using a Watt meter, is there any manual calculation to determind the amp draw and power??

[Babylon5]

I bought a Watts Up meter from Hobby City and tested all my electronic setup. Quite a lot of surprises!

For my Zagi, my setup:

Motor: KB20-40-12L, Max Amp: 20A, 4800kv
ESC: 30A
Lipo: 1300Mah, 2-cell, 7.4V, 20C
Prop: APC4.75x4.75 pusher

The results of the test:

Max Amp drawn: 38A!
Power: 260W

Yes, I am frying my motor and battery!! I will switch to a 25A ESC for another test.

Looking at your motor is high KV you so 2 cells LIpo is the way to go.
If the ESC or motor permit higher Lipo cells count setup , the rule of the thumb is to reduce the size or choose a lower pitch prop.
I have seen some guys who simply up the lipo cells count without reducing the size of the propeller with predictable disastrous result!

General safe rule

High KV motor=smaller prop size & lower cells count setup
Lower KV motor = larger prop size, number of cells count is more flexible.

just my two cents....

Cheers

[tomato]

Hi Macdream,

I am quite new to electric RC. I wanted to get more out of my in-runner motor. Will adding more Lipo cells increase the performance of the motor? I have a 4900 Kv motor installed on a 36" Zagi (350gram total weight) using a 4.75" APC pusher propeller. I used a 30A ESC and a 2-cell lipo (7.4V, 20C, 1300Mah) and also a 3-cell lipo (11.1V, 20C, 1400Mah) - it gives a lot of power. What happens if I install a 4-cell lipo (14.8V, 25C) battery? Will it gives more RPM and hence more speed?

I think I have already accidentally fried 2 motors and 1 ESC literally caught fire while flying. Maybe I should invest in a watt meter to investigate.

more cell = higher voltage = technically higher rpm...but that is only if your motor can take more cells. also remember that your esc has a certain capacity it can take so you might have to change that too. go find out more information on your motor as to how much voltage it can take =) should be able to find out such info easily

[MeePokMan]

Thanks for the advice! After knowing that I am pushing the motor beyond its 20A max load (the reading according to Watts Up is 38A), i am still enjoying the Zagi with the overload. The motor cost US$14 from United Hobby, I think I don't mind frying it! I get more bang out of my money!

Now, I am trying to find out why my glider started a small fire with the ESC totally burnt! Another case of poor matching of motor-ESC-battery!

Thanks!