How to Test SCR?

Looking for some help here on a SCR we have in a regen dc drive this is the exact model in question http://www.irf.com/product-info/datasheets/data/irkt71.pdf. What is the best method of testing this? All i have is a Multi-Meter and a 12v DC power supply with some spare wire and light bulbs.

I have found that most of the time a SCR fails shorted. You can test for this with a multimeter by checking the resistance from anode to cathode and from cathode to anode. The resistance should be very high, in the meg-ohms region. The following circuit can be used to check if the SCR turns on properly.

g_4key said:

Looking for some help here on a SCR we have in a regen dc drive this is the exact model in question http://www.irf.com/product-info/datasheets/data/irkt71.pdf. What is the best method of testing this? All i have is a Multi-Meter and a 12v DC power supply with some spare wire and light bulbs.

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In the style of "isolated" SCR pack that you show in that link, all you need do is check the resistance across the anode and cathode, the "line and load" if you will, the big screws on the top. There are two SCRs in that pack (assuming you have the 2 SCR version vs the SCR + Diode version) and you won't know which one it is, but that's irrelevant because they are together anyway. So two of the screw terminals will be common (the anode) inside of your assembly, meaning there will be a jumper bar or wire connecting them, the other one is the cathode. Polarity is irrelevant (unless it is the SCR+Diode version). Anything below 10kohm is bad, meaning shorted.

If the andode-cathode resistance checks out, then you put your ohmmeter on the gate terminals, the little push-on tabs. You want to look for between 5ohms and 90ohms of resistance, and polarity is important, so if you don't know which way it is, swap your + and - leads on the VOM to make sure. Any reading below 5ohms or above 90ohms means a bad gate. It's usually a good idea by the way to test the gate circuits by using the OTHER end of the gate lead wires, where they plug into the board, because that picks up a defective wire or connector (at the SCR) as well.

If it's neither of those issues, it's likely in your firing board circuitry.

By the way, POWER IS OFF on these tests!!!!!

Thanks guys! It is the two SCR version the IRKT91-14/1651 +35 is whats written on it. I will build the circuit provided and take some measurements and let you guys know. I'm pretty much a "ID101T" about electronics but hey thanks again!

So i made a circuit with a 120V ac to 12V DC power supply with the positive side containing two 6V DC bulbs in series and a alligator clip at the end and a simple wire for the negative side with a alligator clip on the end as well. I then proceeded to connect the positive lead to screw 1 then the negative line to the tab 5 the cathode and finally shorted the tab 4 the gate to the positive screw 1 and the lights came on . Switched it around for the other SCR positive to screw 3 and negative to tab 7 and shorted the gate tab 6 to screw 3 same result. It passed on all SCR. Now when i try to measure anode to cathode screw 1 to cathode screw 3 i get infinity . I believe i have my probes on the wrong terminals where should they be? For gate to gate (tabs only) gate to gate tabs 4 and 6 nothing, from what i can gather that's because they're not connected so that makes sense unless I'm wrong. From gate to cathode tabs 4 to 5 and 6 to 7 i get on average 14-17 ohms. To me i think these are good SCRS let me know of any feedback, what i did wrong, should do, or your thoughts. As always again thanks!

If you put your multimeter on the megohms range and place it across anode and cathode, you will get a high restistance. While keeping them in place you briefly short out the anode and gate the multimeter voltage will be sufficient to turn on the SCR. Once on it will stay on as long as the multimeter is connected, and the multimeter will now show a low restistance if the SCR is functioning correctly. Of course this is done with no power connected.

Steve

Check out these links

http://www.ab.com/support/abdrives/documentation/fb/1012.pdf
http://www.circuitstoday.com/how-to-test-an-scr