ESCs ratings vs failure

I’m fairly new to efoils, but have built a few eskates and scooters and I’m in process of starting an esurf build. The topic of ESCs are ever present in every e-vehicle forum. The most common observation is that cheap ESCs can’t handle their rated max current, that you need to go 50% or even 25% of its rated max.

I came across this video, where this guy tests 2 ESCs (a castle 160HV and kosmik200) at full throttle, at 50% of their rated max current, the castle at 80a and kosmic at 100a:
They pretty much handle it with ease.

But then, he continues with a second test at partial throttle, at merely 25% of their rated max current, the castle at 40a and the kosmic at 50a:

It was a complete surprise to me, but both ESCs heated up far beyond their full throttle test and the castle 160HV actually failed and went into thermal shutdown protection.

A quick google led me to this post:

Basically, FETs don’t like to be turned off and act as resistors when they do. So at partial throttle due to the PWM of motor control, the FETs are turned off longer and thus act as resistors, and heat up and the more they heat up, the more they act as resistors, in a feedback loop.

This would explain why so many ESCs fail. That 400a Flier is probably capable of 400a at FULL throttle. But at partial throttle, even 100a will probably cause it to overheat. That 130a Seaking, sure full throttle at 130a, but at prolonged partial throttle, will probably overheat at only 25% of its rated max, 33a. Maybe this is old news to you guys, but it was an eye opener for me.

TLDR: partial throttle hammers your esc WAY more than full throttle. 25% or less of max rated current at partial throttle can kill it.


Thanks for this, counterintuitive and therefore extremely helpful. So what should we do in sizing our ESCs? Should we get the lowest rated we can, then put massive heat sinks in? Previous advice was to size at 4 x expected draw.

Who gave you the advice to size it at 4x expected draw?

Some esc, like the yep, have a bult in function to handle this. Yep call it freewheeling, might be other names for it to.

Watch this video.

active free wheeling can be hard on the gearbox as i tested it unsrewed the motor from the gearbox twisted the wires and burned
yes i saw this test before, and partial load is harder on the esc
in my opinion the best way is the size the motor and kv correctly in order to run most of the time full throttle

I don’t know how to do the hyper link, so this is a copy and paste:

Apr 21

ESC recommendation

Electronics (ESC, remote, batteries)

Well that’s just it Jezza if you use a proper heat sink/watercooling you can get away with lower max amps and its fine.I cruise at 55A with my jet and wing combo, and I’m 255lbs and can get away with a lower AMP ESC also but the heavier duty ESC just gives the average builder so much more wiggle roo…

Apr 21

Propulsion System - Motors, Gears, etc

Propulsion System (Motor, Gears)

Completed all new jet propulsion system for efoils where the water intake opens and closes automatically with the throttle. Key features: Intake will not open out of the water so you cannot access the impeller when on the beach or transporting. So if someone touches the triggler the impeller is …

Apr 21

ESC recommendation

Electronics (ESC, remote, batteries)

Almost everyone struggles with an ESC overheating or not handling the current they are running and I don’t fully understand why so many opt to buy an ESC with low Amp rating 120A - 200A when you can buy something like the Flier 400A waterproof and watercooled ESC for only $285 which is like $85 more than a 130A ESC. Trying to save $58-100 on a en ESC is backwards, you should spend the most on it that part because its the brain/heart of the entire efoil. You’ll spend more buying 2-3 esc’s and waste months of time only to look back wish you just bought something heavy duty the first time.

Overkill with your ESC and wiring (6-8 awg) and eliminate 80% of the issue everyone is having so you be out there foiling! :slight_smile:

This is the conclusion I’ve come to also. So many interdependent components make this a fun project.

That is not the freerun, what he mean…
ESC with aktiv freerun means Fets /PWMs Curve he not works ans so no high Temperatur have.

Sorry my bad English