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Changing Scr


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#1 Seyvert

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Posted 19 May 2009 - 09:22 AM

Hello,
I have a prolem here.I am repairing an AVR for a Slipring Generator
This AVR use a pulse transformer to trigger the SCR (BT152).Now I want to change the SCR into a bigger one (500A 1200V). But the gate won't open. . . Will increacing the winding of the pulse Transformer will help ?



#2 marke

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Posted 19 May 2009 - 06:51 PM

Hello Seyvert

Welcome to the forum.

To control an SCR, you must apply sufficient gate voltage and gate current.
If the SCR is much larger than the original, it is quite likely that the transformer and/or the driver are no able to pass sufficient gate energy.
Increasing the secondary turns will increase the trigger voltage, but may reduce the trigger current depending on the driver circuit.
Another problem is that the latching and holding currents of the larger SCR will be larger than the SCR that you are replacing and it is possible that the SCR may not latch quick enough to provide a reliable operation.

You need to verify that the SCR is able to latch and hold the current inot the load within the period of the gate pulse, and then ensure that the gatge drive circuit is capable of producing enough energy to trigger the SCR. If you ttrigger current is marginal, you can damage the SCR, even on low current as it will only partially turn ON and under this condition is very sensitive to di/dt which can be very low compared to normal operation.

Best regards,
Mark.




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