triac / relay output

A triac is a solid state device that only works well with AC (needs the zero cross to turn off). A relay is a electro-mechanical device that will handle both AC and DC. Relays also do have a somewhat limited life span and speed. Relay cards generally have limited current capabilities. For small DC loads, use a transistor output card.
 
Relays are mechanical devices which will get destroyed if you run them to often and to fast... but they could survive a short circuit ... Triacs are not mechanical devices, will switch fast and often but will be dead with just about any over current.

You will not use a relay outputs to make a Christmas light show.
 
A relay is either all on or all off
A triac never entirely turns off as the attached load is part of the circuit still passing a minute current in order to pull the circuit to the off state of a few volts, when the on state will be 10, or 20, or 50, to 100 times greater.
 
As a troubleshooting hint too, a 120VAC triac will show 120VAC on a meter with no load. I've had many electricians get screwed up here.
 
Thanks for the replies , i almost got caught up in it last night.
had 95 volts when in off state and 110 when on
card seems fine, found defective reversing starters
 
Ron,

We're going to have to make a book out of all your posts here. Pure pleasure ind humbling info. Thanks
 

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