I design and test high power equipment that uses large SCRs (silicon controlled rectifiers). Sometimes one will go out.  I use 6 in a three phase bridge configuration and if one goes out, its difficult to find the bad one without taking them all out. You can make a "in circuit" tester out of a flashlight.

Step 1: What Is an SCR?

An SCR is a Silicon Controlled Rectifier.  They are used in power supplies, welders, inverters and other equipment for controlling power. The one below can carry 350 amps of DC current with a rating of 2400 volts.  Think of them as a diode that can be turned on with a small current to the gate.  Once turned on, they stay turned on till the current flow is interrupted or below the minimum current. Large SCRs like this one requires 150 milliamps at 3 volts to turn on. The SCR behaves like a solid state latching relay.  The large base at the left is the Anode and attaches to a heat sink.  The "pigtail" end at the right is the Cathode and the white wire is the Gate. The additional skinny red wire is connected to the cathode and is used with the gate when connected to a triggering circuit.
It your photos it looks like the anode and gate leads are soldered to the same polarity as the cathode. The outer ring at the head of the flashlight is a contact surface for the switch that bridges the negative from the battery to the bulb. Or am I missing something?
Nevermind. I'm an idiot. I get it now.
<p>Hello ,<br>I made a tester about 30 years ago using resistors for the load and LED's for the indicators . Mine used 4 &quot;C&quot; batteries to get 6 volts , had a normally open switch to trigger the gate , a normally closed switch in the anode/cathode circuit , also a normally open switch with a load resistor and LED for a battery test . To use the tester , connect the 3 leads to the SCR , press the GATE switch and it should turn on . press the other switch to turn it off . I used it many years doing industrial electrical maintenance . I retired a year ago and as far as I know the electricians at the plant are still using it .</p>
I have a quick question I follwed your instructions but once i ge to the stp about removing the gate once removed the bulb turns off. And also if I touch the cathode lead to the anode it produces a bright blinding light. It should not do this. Help?
That is normal for the SCR tester. It is as if you are closing the switch on the flashlight.
That's a great experiment! i have a 3W 160 lumens <a href="http://www.gadgettown.com/Flashlights/">LED Flashlights</a>, is it suitable to experiment?
You can also test Mosfets and IGBTs if you add a 9 volt battery inseries. I have instructions at this <a href="http://home.comcast.net/~botronics/TestingSCR.pdf">link</a>. You can test leds too. Its a multipurpose tester and even a flashlight!<br />
I recently obtained a couple large SCRs that look just like the ones inyour instructable. They're labeled &quot;GE C55B&quot;, but I couldn'tfind any information or datasheet for them. Do you have a similar model,and if so, do you have or know where to obtain datasheets for these?<br /><br />Thanks for any help you can provide!<br />
I don't know about the GE SCR, but here is a <a href="http://www.pwrx.com/pwrx/docs/t700.pdf">link</a> for he datasheet on the big one shown. You can get the Powerex scrsfrom Galco.<br />
Thank you for a well-done, useful Instructable; even though I do notwork with large SCR's.&nbsp; <br />
Thank you.&nbsp; Here is a youtube video of it working.<br /><object height="344" width="425"> <param name="movie" value="http://www.youtube.com/v/zxIu1KIUZMk&amp;hl=en&amp;fs=1&amp;" /> <param name="allowFullScreen" value="true" /> <param name="allowscriptaccess" value="always" /> <embed allowfullscreen="true" allowscriptaccess="always" height="344" src="http://www.youtube.com/v/zxIu1KIUZMk&amp;hl=en&amp;fs=1&amp;" type="application/x-shockwave-flash" width="425" /></object><br />

About This Instructable




Bio: I like to tinker and experiment with electronics, robotics, programming, and photography. Along with my latest interest in Steampunk.
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