Quote:
Originally Posted by jsr
...BTW, can you comment on how the FETs in the 80A seem to come out with higher current capability than those in the 150A? 62A x 3 = 186A vs. 26A x 6 = 154A. Seems strange unless I'm looking at it wrong.
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Actually, the 150A has 24 FETs, so it's 26A x 4. But anyway, you can't look at just the current ratings. The RdsOn, switching speed (or slew rate), and power dissipation have to be taken into consideration as well. Even something as seemingly innocent as gate capacitance can (and does) have an effect on switching speed. An FET might have a higher raw current rating, but if the slew rate is slower and/or the RdsOn value is higher, there will be more heat (power dissipation) and might exceed the safe value. So, they may be derating the current more than usual on the 150A to compensate.
And all electronic hi-power devices need a certain amount of cooling surface area to function effectively, be it PCB traces or heatsink. These ESCs are VERY small considering the amount of power they can funnel to the load. So, if an FET is spec'd at a certain current rating, but the actual amount of cooling area is below the recommended value, then they have to derate the current even further.
Just looking at FET specs is one part, it is also important how the circuit is implemented. Short of reverse-engineering the entire ESC and taking a boat load of measurement with meters and o-scopes, it is all just speculation. The best we can do when we look at the specs is to see if the advertised spec is even possible.
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