Puck Thyristor Understanding

roro36

I just started working on a furnace that uses the puck type thyristors for the main power switching. Every now and then, one of them blows and we replace it. We ususally use a mega tester to test wheteher they have blown or not i.e. put 250V across and short the gate to the anode. A zero impedance means its working fine. I am however not too sure how accurate this is for testing? In the data sheets of these thyristors it says they need to be clamped with 500kg of force in some cases. Now by running 24Vdc through these thyristors is this test being performed adequately? Does the device need to be clamped and does the amout of current running through it matter. If its rated for 1300A and I run 1A through it and t works, doees this mean it ill work for high amps or not?

Thanks

Fish4Fun

roro36,

Yes. SCRs and TRIACs work or don't work, no middle ground; so if it works @ 1A, it should work @ rated current. Make sure when replacing one to clean the heat sinks & use a good quality heat sink paste. Use a torque wrench to get the clamping pressure as close as possible.

Fish

roro36

How important is the clamping? If testing without is fine, what is the importance of the clamping in the machine?

Fish4Fun

Maintaining proper thermal and electrical conduction.

Fish

roro36

Sorry, stupid previous question, meant for testing? Is it not necessary to have the SCR or Diode clamped for testing?

Fish4Fun

roro36,

AFAIK, the only reason for clamping during testing is to ensure proper electrical connection. If it works "unclamped", you should be good to go, if it does not, you may want to clamp it and re-test it. These devices have a large contact area between the metal ends and the silicon that may not perform properly unless clamped. In most cases a "new device" will work just fine w/o clamping, but mechanical and thermal stresses may prevent older devices from operating properly w/o pressure.


Fish

roro36

Thanks.