How to test a triac.
Testing triac using a multimeter.
A multimeter can be used to test the health of a triac. First put the multimeter selector switch in a high resistance mode (say 100K), then connect the positive lead of multimeter to the MT1 terminal of triac and negative lead to the MT2 terminal of triac (there is no problem if you reverse the connection).The multimeter will show a high resistance reading (open circuit).Now put the selector switch to a low resistance mode, connect the MT1 and gate to positive lead and MT2 to negative lead. The multimeter will now show a low resistance reading (indicating the switch ON).If the above tests are positive then we can assume that the triac is healthy. Anyway this test is not applicable triacs that require high gate voltage and current for triggering.
Circuit for testing a triac.
This is another approach for testing a triac. Almost all type of triacs can be tested using this circuit. This circuit is nothing but a simple arrangement to demonstrate the elementary action of a triac. Connect triac to the circuit as shown in circuit diagram and switch S2 ON. The lamp must not glow. Now press the push button switch S1.The lamp must glow indicating the switching ON of triac. When you release the push button, you can see the lamp extinguishing. If the above tests are positive you can assume that the triac is healthy.
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I agree with the previous comments. MT2 label should be at the top and MT1 label at the bottom side with the gate. Trigger voltage in phase with MT2 (at top) to allow triac to operate in the first and third quadrants when AC is normally applied.
Eric, MT1 and MT2 have to be reversed, as you say. I just tested it on an actual part..
Thanks for pointing out.
Aren’t MT1 and MT2 reversed in both this drawing and the test description? I’ll admit that I’m brand new to understanding triacs, but every other book and website I’ve found shows MT1 and the Gate on one side and MT2 on the other side. I’ve only found one other description of testing triacs, but it described joining MT2 with the gate on one probe and putting the other probe on MT1. I’d really like to know how to reliably test triacs. Are there triacs configured in different ways regarding MT1/MT2 designations, or was this just a typo? Thanks for your help!