Hot Brush ESC at half speed

[Leo]

Is it normal? My ESC get hot (not warm) at ~ half speed? I notice that heatsink is only warm at full speed. This happen after I did some soldering to the MOFET just want to be sure the ESC is ok.

[Babylon5]

ESC gets hottest at half power is normal.
On the other hand ,ESC get cooler at max power and at lowest power.

Reason: When the power stick(throttle) at TX is change from low to high power, the internal resistances of the ESC will vary from high to low resistance(inverse law).
Maximun power occur at the ESC when the ESC resistance is equal to the load(motor dynamic resistance) and this occur somewher in the middle of the throttle position.

This is as simple as possible I can explain in layman's term.

For further understanding you need to read on topics such as electrical power transfer or maximun power dessipation on semi-conductor and how they occur.

Babylon5

[Leo]

Thks for the quick reply. This was what I thought too in the old mech speed controller with resistor, but isn't that the modern ESC with MOSFET is to switch on and off as to control the motor speed? Hence I thought they will consume very low power otherwise the battery will last the same regardless high or low speed BTW, this everning I tested the ESC with 380 motor instead of motor 550, the ESC was not hot at all, so I think the heat is from the high current drawn from motor 550.

[Babylon5]

Hi Leo, although the ESC uses switch mode and are more efficient than linear method,there is still an "averaging effect" of resistance and current.

When you uses a higher motor and drawing more current , the maximun power transfered priciples to the ESC still applies. In this case the ESC will run hotter when you use a bigger motor than a smaller motor.
In anycase do not use half power or maximun power throughout your flight.
When you are at half power the ESC will be the hottest.
On the other hand, when you are at max power, the batteries and motor will be the hottest so vary and manage your power. This will prolong the life of your ESC, Batteries and motors.

Enjoy your flight.
Babylon5

[Ghostfit]

Thks for the quick reply. This was what I thought too in the old mech speed controller with resistor, but isn't that the modern ESC with MOSFET is to switch on and off as to control the motor speed? Hence I thought they will consume very low power otherwise the battery will last the same regardless high or low speed BTW, this everning I tested the ESC with 380 motor instead of motor 550, the ESC was not hot at all, so I think the heat is from the high current drawn from motor 550.

Sounds like your Lipo's rating is too low for your Motor !

Should you have this setup in your plane and fly it, the motor will reach max power at half throttle, push the stick further up and the power will be intermittent as the ESC stores the power then releases it.
It's difficult to explain without knowing your Motor's Max Amp draw, Your ESC's max constant Amp output and more importantly your batteries max discharge Amp.

Example: Your Motor max at 20A, ESC max at 18A and your Lipo are rated 15A

At half throttle, the motor draws 15A and the ESC is squeezing every drop of electric from the battery (ESC get hot from the constant 15A throughput)

Increasing the Throttle to full bring the motor draw up to 20A but as the battery can only deliver 15A the ESC's capacitors stores up the energy until it can discharge at 20A and the motor's output sorta goes up and down (ESC only gets warm from the half on half off 15A throughput)

Sorry, that is in as simple terms as I can put it. Hope it's makes sense to you

You are right, Your 380 motor did not heat up the ESC as it's Amp draw is well within the limits of the ESC and Lipo

[Babylon5]

Hi Ghostfit, you could be right about the low Lipo rating but then again Leo mention the ESC was HOT at middle throttle position and warm at MAX position. This is normal.
As I mention again , the ESC is the hottest when the throttle is somewhere in the middle because the ESc average resistance will vary with the position of the throttle stick. This occur when the ESC average resistance reaches a value where it is equal to the average resistance of the motor.
There is a mathematical equation but it is outside this scope of discussion.


Babylon5

[Ghostfit]

Yep, Okay ! .....but the funny thing is that on my models with a perfectly "setup" system, the ESC is ambient at mid throttle and warm at full.