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Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
Is possible to determine the pulse rating (ballpark values) of power resistors.
For example a couple of 1ohm 5W resistors in parallel can survive a 200A pulse for 100us?
I ask this question because I obtain strange phenomena when usin power resistor (RC snubber) for coilguns. In particular scr latch in the previous stage when the igbt draws back down the scr cathode. In particular i programmed the device to fire a 500us pulse on the IGBT driver, stop the pulse and remove the scr gate drive, then wait 600us and pulse again 500us the igbt, but this time without the scr gate drive (it should not latch) but it latchs again. This doesn't happen if i wait 1000us. The scr turn off time is 20us. So probably the problem is the emf of the coil, even if the calculations show that the voltage doesn't exceed 500V . Maybe the resistor core is heated up and the heat doesn't have time to dissipate resulting in 3-4x the nominal resistance.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I don't know if I understand you, but are you trying to acheive some kind of forced commutation over there? I don't think it's going to work the way you described.
Maybe it would be nice if you posted a schematic. :p
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Power resistor pulse rating
