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Thermal dissipation.
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sureshot:
I'm putting together a resistive load for testing purposes. I want to incorporate a crowbar for any likely over voltage scenario that could accrue. What I'm stuck with is the heatsink for the SCR or it's size to be more specific. My maximum load testing won't exceed 22 Amps at a maximum of 14 Volts. More topically testing around 220 Watts at 12 Volts. I know the SCR only heats up if it's fired (I think) So was hoping to get some idea of what size heatsink I might need. The SCR I'm thinking of using is the VS-40TPS12APBF 1200 Volts 35 Amps. This might be overkill I'm not sure yet.
Any help appreciated and thanks for reading.
T3sl4co1l:
That seems like a lot more risk to your DUT than to your resistors?  Resistors are chunks of metal, they hardly need protection!

Tim
David Hess:
SCRs used for crowbar circuits do not usually require any heat sink.  The SCR is suppose to fire and blow a fuse and while the peak power is high, the total energy is low and the event happens so quickly that the heat sink is too far away from the SCR's junction to matter.
sureshot:
Thanks for the reply. Yes it is a power resistor construction, I was only looking to save the unit if a power supply went high for some fault reason. As you say the power dissipated is brief, so I might be able to get a modest heatsink in the case. It would save the meters and unit also. It's only for 12 - 14 Volts power supply testing.
sureshot:
It's these inside the case. The crowbar would save these also, dam expensive.
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