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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Dennis Toth on February 05, 2009, 02:14:26 PM

Title: ESC size selection?
Post by: Dennis Toth on February 05, 2009, 02:14:26 PM

Guys,

What criteria is used in selecting the size of the ESC? I have used the CC45 with the AXI 2826-10 and had no problems. I know we need to have a unit designed to handle the expected amps being pulled my question is if you have more capacity (say going up to a CC60) does it hurt anything other than increase in weight and cost?

Best,          Dennis

Title: Re: ESC size selection?
Post by: Mark Scarborough on February 05, 2009, 02:40:08 PM

Dennis,
I played with Motocalc a bit, and it appears in some cases, that you can gain a marginal amount in the currrent draw by using a larger speed control, I think I noted a few percentages reduction in current using a larger rated controler. That is of course just on the motocalc program, havent tried it in real life.

Title: Re: ESC size selection?
Post by: Alan Hahn on February 05, 2009, 03:03:34 PM

Dennis,
Mark is right. The only thing that hurts is the size and weight (a little) and cost  ~^.

Title: Re: ESC size selection?
Post by: Crist Rigotti on February 05, 2009, 05:33:46 PM

ESC should be sized to the continous amp draw of the motor.    If a motor has continous amp draw of 45 then you should be using a 45 amp ESC.  Reducing throttle only reduces the average current, it does not reduce the maximum current in the current-pulses. A controller is always full-on, and at part throttle the current is chopped in smaller chunks. (Taken from an RC Groups Electric Forum thread.)

Also consider the fact that the rating of the ESC should closely match the motor because if you have an accident, the the ESC would be able to shut down and not keep going possibly cause more damage or even a fire.

Title: Re: ESC size selection?
Post by: bfrog on February 05, 2009, 06:37:44 PM

Just had to add one point. Be careful of the ratings game. The well known brands tend to be accurate about ratings. Some of the off brands tend to be "optimistic" about how much current they can draw. I have only used Castle Creations ESC's and trust them to be accurate. When in doubt get one that has a little extra headroom.

 

Title: Re: ESC size selection?
Post by: Dean Pappas on February 05, 2009, 10:08:26 PM

Amen Bfrog!
By the way, please use your full name or put your name into a signature line at the bottom of all your posts. You can do that in your profile.
Dean P.

Title: Re: ESC size selection?
Post by: Igor Burger on February 06, 2009, 01:56:04 AM

Throttled motor runs in PWM mode and it means that the current peaks are high. That means that IIR loses are higher than at contiguous current, plus more switching loses because PWM frequency is higher that commutation. Additionally those peaks must continue via diodes in switching transistors back to battery, and it makes extra IIR loses. And we fly all the time on motor, we never give chance ESC to breath like RC guys, so it definitely means we need ESC rated little higher.

Regarding security – I am not sure if ESC can switch off quickly after crash. I do not think so, I think transistor can explode earlier then ECS can react, but fortunately ESC can recognize locked motor as lost synchronization, and it is power (current) independent.

Title: Re: ESC size selection?
Post by: Dean Pappas on February 06, 2009, 04:11:57 PM

Sorry Bob! I must be getting blind in my old age: I didn't see the signature.
take care,
  Dean P.

Title: Re: ESC size selection?
Post by: bfrog on February 06, 2009, 10:26:04 PM

Dean, your eyes are fine. I added the signature after  you suggested it!!!

Bob