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Originally Posted by zeropointbug
LOL, okay now I know... are you sure you know what your saying?
The physical resistance is only PART of the heat output. Most of the power loss is the design of the motor, and how well it transforms the power input to it.
What is 2.7Watt? That would be barely warm to the touch....
The esc I am guessing is somewhere between 92 - 97% efficient. Couldn't tell you, it's probably about 10 - 25 watts of heat, which is alot for these little FET's to dissipate, that's why they can get so hot because of insufficient heatsinking. With a proper heatsink, 25 watts of heat is a piece of cake to keep the temps down (~15C Delta).
Is there a misunderstanding here about motor efficiency.
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Thanks, but I think you need to work harder before you can corner me :)
Well, FET dissipates heat during switching when it is in analog mode, defined by rise and fall time plus capacitance and inductance of load. Which means that load (motor) can influence and does on ESC efficiency as well. Well if you integrate over time then you can calculate power loss on ESC, would be difficult to do that over each individual FET. And yes ther are lots of them in parallel, so 10W over n-FET's with 23.4cm^2 (70mmx34mm) heatsink surface area would be great. Old rule of thumb 1cm^2 per 1W good for 50C.
Do not forget to drive those FET's you need some power too, FET's are field driven but speed cost power, current in this case. In addition do not forget about built-in diode and it's temp dependence, I am assuming you know what this diode does in pair with caps, right.
Brian, for motor to be sensitive to rise and fall of FET's switching motor system (motor and inertia of drive train) must have response time in microseconds at list if not nanoseconds. Our motors without load maybe have ms of response time.
For me it looks like Quark 125A controller might have problem with some component on board, based on Leroy's comment about his low temperature runs with 80A. Does anybody have a clear picture of 125A PCB with FET's control part?