Hey Guys,

Please help, I'm a newbie.

Can I use a 40-50 ESC for Floater-Jet EPO Motor 2100KV?

Here is the detail for the motor I've found googling:
AX-2208N 2150 KV Outrunner 27.7x31.4mm (DxW), 3mm shaft, 40 gram, 18A with 5x5 prop 3s.

Here is the detail for the ESC I got from Hobby King:
Cells: 2-4S
Max Current: 40A
Burst: 50A
BEC: Opto Only
Timing: 1/7/15/30 programmable
PWM: 8/16K

Here's my thinking so far:
- If I give full throttle, the ESC will push 50A to the motor.
- If I give zero throttle, the ESC will push 0A to the motor.
- If I give half throttle, the ESC will push 25A to the motor.

Is my thinking true? Please do correct me if I'm wrong.

But if it is true, does it mean that I have to limit my throttle at only 36% in order not to give the motor more than 18A?

Please help because I really don't wanna fry my motor at the first time flight experienced. It would be a discouraging accident for a newbie.

Thanks a bunch,
Beruang.

Originally Posted by Beruang

Here's my thinking so far:
- If I give full throttle, the ESC will push 50A to the motor.
- If I give zero throttle, the ESC will push 0A to the motor.
- If I give half throttle, the ESC will push 25A to the motor.

Is my thinking true? Please do correct me if I'm wrong.

Thanks a bunch,
Beruang.

Your thinking is wrong.

The ESC doesn't "push" anything to the motor, it only passes on from the battery what the motor demands so, in this case what you have is:

1. A hugh safety margin because the ESC can handle 40 amps but your motor, with the setup you quoted, should never demand more than 18.

2. A slight problem in that the ESC does not have a built in BEC so you will need to buy a seperate one to power your reciver and servos when you reach Low Voltage Cutoff for the motor.

A few beginners have mistaken what the Amps figure on an ESC means.

As Pete pointed out, it doesn't 'give' 40A no matter what is connected to it.

The 40A is the manufacturers figure that that ESC should safely work at and survive for quite a while, or 50A but for usually only 60 seconds max.

The ESC can also get hot, so cooling helps it survive longer as well.

Another mistake is that you can use a 20A ESC on a 40A load if you only use half throttle. Totally wrong.

An ESC is basically a switch, it's just that it switches on and off many times a second. So every time it switches on it still 'sees' that load that requires 40A, but because it also switches off for a period, (on off on off on off, just very very fast), an ammeter/wattmeter etc, only shows the lower average current. (See the picture below).

The 'load' is actually the propeller. It 'loads' up the motor, so that it needs more current to turn that prop. No prop = low current, bigger props = bigger current, (amps).

Fitting a prop that is too big, (usually the diameter more than the pitch), and the motor and ESC will demand more current than the manufacturer recommends. The result, something overheats and burns out.

So also don't just fit a bigger prop than recommended, with the idea it will make the plane go faster. It may, but not for long, (just until the 'magic smoke' escapes).

I should add that you can't fit an ESC that is 'too big' when it comes to its amp rating, the higher the amp rating the greater the safety margin.

The only slight disadvantage might be its physical size, or weight, (perhaps in a very lightweight plane).

Hi Pete Miller and Eflightray, thanks for your full explanation. I go with it then, and keep the prop no bigger than APC 6x5E. Many thanks.