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Re: New Talon Speed Controller
Tom,
That is a static resistive test. You are most likely testing the current carrying capacity of the FET bond wire. The thin wire that connects the FET leads to the chip die. Most recent heavy duty FETs are current limited by the bond wire. The die can carry more current than the bond wire. It's a one shot thermal fuse. Hook a FET up to a direct short and watch the case pop. The bond wire vaporizes and blows the case. To really test the Talon you need a dynamic test to stress the die. You need to have the H-bridge coping with switching transients. A good test would be to but a cim into a gear box with a fly wheel attached. Say like a AM pneumatic wheel or a little heavier. Test by applying full power till it is up to speed and then reverse the direction. Wait till it gets up to speed reverse direction. This will stress the FET die in addition to the bond wire. Again with modern power FETs This repetitive avalanche condition affects the FET thermally. It's more like a real world FRC condition. My robot goes forward my robot goes backwards. Especially in this years game. If a Fet is allowed to heat beyond Tj max they fail fast. However if they are subjected to high temps close to Tj max they will have a shortened life. High energy switching transients tend to damage the structures around the gate. For these reasons teams should monitor the talons heat sink temp and a small fan would be a good idea in most drive train applications. Drive teams tend to go hard on the robot way beyond the 2 minute match time. Andy Mark has a IR thermometer on First Choice. A wise purchase for Talon running teams.
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