How To Test an SCR

In this video I will test three different power SCR's. We will determine which one is bad! I will go over the methods I use to successfully determine if they are shorted, and also if they are turning on. These devices are usually the main power switching devices in DC motor drives/amplifiers around the world! SCR is commonly also known as the thyristor. This video does not cover SCR theory but rather methods on testing an SCR.

Remember, this can not determine if the "latching" of the SCR is working. This failure is very rare, but possible. Always consult a spec sheet of an SCR before you test it. Damage can be caused to the device if you are not aware of its allowable voltage and current specifications.

Warning: Please do not attempt any electrical testing or troubleshooting if you are not an experienced electrician or technician, well trained with electrical voltages/currents and the damage they can cause. You are responsible for your own actions.

Credits -

[johanlundh]

Excellent video. You got yourself a new subscriber today! 😊True pedagogy is such a rare trait and you truly are one of those precious few. Cheers from Sweden and happy new year!

[MrBtdobie]

The pressure requirement is what landed me here. Works great now. Thanks 😊

[sadhunikul]

thanks for SCR explanation, it helps a lot

[onefixitman]

It would be great to see the resistance from anode to cathode while the gate signal is turned on and continue reading while removing gate signal. It should conduct until reverse biased. Thank you for the video.

[-_Grind]

Thanks, this helped me identify defective thyristors in welding machines.

[shamanking]

Hello.
would recommend apply voltage with the battery to test the SCRs while they are still mounted on a soft starter ???.
or is this done only when SCr is been removed ???
are you familiar on how to do voltage drop test to verify contactors health on soft starter???
I been told there is formula to calculate the expected milli volt reading, but cant find much info.

[inversionesalucel]

Great, it is clear, however not so when you consider enough or too high resistence values. How do you decide what is enough or high? has this criteria rounding the Thyristor size? Please help us to understand better, Appreciated

[markd.nightingale]

Great video! Very informative thorough presentation!

[syedzakirhussain-sbwe]

Great video. Sir, please make the video on IGCT testing

[DrHarryT]

I always viewed "OL" as Over Limit meaning the resistance is beyond the range of the meters current setting.

[Jose-twbl]

The preassure required for these hokey puck diodes is stated in the datasheet, but how the heck do i verify the clamping force? I just tighten the bolts on the heatsink but i have no idea how much force i am applying... Any ideas?

[brucemansfield]

I have a puck scr that is reading resistance without any pressure on it. Does that mean it’s shorted?

[VincenzoGenovese-rj]

hello and congratulations, I have a question, I often deal with 24 to 80 V DC-powered handling systems driven by SCRs of 200-300 A and above managed by the relevant logic/controller. Let's assume that I have an anomaly elsewhere and the SCRs don't come into operation, how can I energize them manually to test them without dismantling them? Let me explain better, the systems control motors, if these do not turn usually the technician energized the first SCR to make them turn, the second SCR which charged a capacitor and then a third SCR which with a sort of countercurrent turned off the first (usually they are disk st333 as in the video, by doing so he was certain that all the power was ok, and he could move on to troubleshooting the auxiliary part, the driving, safety devices etc., therefore what voltage and polarity should I give to the gates always taking into account that some machines are powered by 24v, others by 48, others by 80 and so on. Thank you.

[robertgraham]

Is 1.6meg ohms to low on the SCR anode to cathode? The new ones we have are 20 meg ohms

[tlsatlsa]

Liked and subscribed! Had to test some puck SCRs today.

[montygore]

Thank you for this video. I have been retired for a very long time and was checking a battery charger I have that quit. I could not remember if I should get a reading between the anode or cathode and gate. I looked everywhere and could not find the answer I needed. Thank you for this video. Excellent info.

[HolyDiver]

Hey man, I have a mini lathe with a brushed dc motor driven by SCR’s (A69154) and cannot for my life find a data sheet for. Do you possibly have the resources? I’ve got 76ohm b/t outside leads but not sure which is gate or cathode.

[SabaM]

If I have dag in one of my current phases from thyristor whuat could cause it?

[PaulusPanjaitan]

bro, how about resistance Kathode to Gate? is it should the same resistance with Gate to Kathode?

[jacksonwilson]

Great.

It was so helpful to me.
Thanks