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SCR testing

SCR testing

(OP)
Okay guys, I know I don't know what I am doing but I am trying to test a hockey puck SCR. I have a flashlight taken apart. I have the neg from battery going to negative of the light. I have the red wire from scr going to the pos of the light. I have the positve of battery going to the plate connected to the anode of the scr. I then take the white wire of the scr and touch it to the anode and the light lites up. I take it off and it goes off. This isn't the way I seen the test done online, but I couldn't get the light to do anything that way. I have several SCRs that I know some are good and some are bad. Also putting pressure on them doesn't seem to make a difference.

RE: SCR testing

First of all: you need to put some pressure on the puck. It is very common that the contact between anode silicon and housing doesn't exist before there is a certain force across the puck.

Use a piece of flat metal and a weight or a drill press to apply enough force to make a reliable contact. Then run the normal test (negative to cathode and positive to anode plus a resistor from positive to gate). Size of resistor is not critical 47 ohms will usually work. Large pucks may need a lower value.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: SCR testing

I have some big hocky pucks and their mounts. Seems to me they take over 1,000 pounds. When you say flashlight I think there may not be enough voltage. The device itself may drop more than a volt. I'm thinking a vice and at least a six volt battery. Haven't used one in 20 years.

RE: SCR testing

There is a min amount of current to maintain conduction with an SCR. The bigger the SCR the higher the current. More than likely the current of the light bulb is too low to maintain conduction. This current could be in the excess of several hundred millamps or more.

RE: SCR testing

(OP)
That's kind of what I figured and found out. Thanks guys. Anyone use an actual SCR tester from like Amps Abundant?

RE: SCR testing

If you use a vice then make sure you provide thick spreader plates between the vice jaws and the puck. Last time I had to test big SCRs I used a 110V DC supply and a halogen floodlight as a load. The gate was triggered with a momentary 'dab' of a wire to the positive supply through a few hundred ohms.

RE: SCR testing

Generally I just looked at the resistance. <10k ohms, bad, >10k ohms, good. I was only wrong once.

Still had to clamp the hockey pucks though. I had a pair of C-clamp type welder's vice grips that worked for everything I had to test in the field, which was up to around 800A. Put a couple of big "fender washers" on the faces of the puck to protect them, then set the clamp to where I could just barely get it to squeeze and snap over to lock. Unlocking it was often an event, I learned the hard way to wrap something like my jacket around it so everything didn't go flying off and breaking things... my forehead being the first thing that clued me in.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

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