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Originally Posted by Finnster
...I know what you are saying about the amp spikes, but on the other hand I don't know why BK would have used 4 small caps for that. It seems easier and more reliable to have used 1 large cap. The caps are only 220uf, so they aren't really that large at that. When one of the caps was bad, the esc did not work properly at all.
I'm concerned about the heat build up, something is casuing a high amp draw.I don't see it being the setup. It got warm even whenI tested it in a 2 min drive in my rusty. Worst case would be some internal short Would a bad FET do something like this? Dunno, I don't see a whole lot else there. Nothing smaoking or burning, so not a whole lot for me to go off of. I have a feeling there is more power there too which is not getting to the wheels. I would think the 8xl/16 cells could break 40. Its still off that by a bit. We'll see what Monday brings I guess.
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Actually, several smaller caps in parallel have a better transient response (charges and discharges faster) than a single large cap. Plus, multiple smaller ones are usually cheaper and easier to mount, but may take up more physical space than one would. Those four 220uF 50v caps have the same capacity as one 50v 880uF cap, if in fact they are all wired in parallel.
As to your heat question; FETs have an "on" resistance. Having several in parallel (like these ESCs do) effectively decreases this total "on" resistance. If one FET has, say, 0.1ohm of resistance, then ten of them in parallel will have 0.01 ohms of resistance. Higher resistance creates more of a voltage drop which, combined with the current, generates heat. Less resistance, less heat. The point to this "lecture" is to say that if you have one or more burnt out FETs, then the total resistance goes up, creating more heat for the same current. I don't know if this is the case in your situation, but it is a possibility.
Something like the Eagletree system would record your battery current for you and tell you if you had too much amp draw.
Could be one or more phases on the motor itself is bad but I doubt it's that since it ran perfectly fine with my Bk 12020, and I really didn't use it all that much anyway. If you had a meter with a "conductance" mode, you could get accurate readings of the windings. With a regular meter, the winding resistance is so low that it will look like a short when it isn't. The most you could do here is check the resistance from each terminal to the motor case - it should be an open circuit for all phases.
An interal short would definitely blow something, but how would that happen? Even water doesn't short electricity unless it is very high voltage, it's the corrosion that gets ya. Most semiconductors usually open when they give up the ghost as opposed to shorting. Kinda like a fuse; too much current will burn up the small parts inside the devices.
Sounds like the ESC to me, hopefully the new cap will help. While you are at it, you might want to replace all of them. If they are all in parallel, what happened to one happened to them all. Maybe only one totally crapped out, but the others may be weakened.