Triac low output problem

  
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The circuit is two separate 3023 optoisolators driving two separate triacs, each one powering a large 3-phase contactor. One contactor is engaging fine. The other one is rattling badly because it isn`t getting full power to pull in. The top photo shows trace from the good triac circuit, working fine. Bottom photo shows the bad one. It looks like t
Triac low output problem - schematic

he triac is dropping out right after hitting peak positive voltage. Thanks for any help. I`m a first time poster who is in over his head on a repair - really more of a mechanical guy than an electrical expert. (I`d be happy to trade mechanical advice!) The triac should only turn off when the current passes through zero. Since you are driving a coil, maybe the current passes through zero where you see the voltage drop. To be sure you would need to measure load current too (on a scope). As you can see from the attachment I can simulate something very much like the result you are seeing. The problem arises from too short a gate pulse. If you are applying a pulse (y/n ) to the triac gate you may need to make it longer - say 90% of the AC cycle in duration. As you can see from the attachment I can simulate something very much like the result you are seeing. The problem arises from too short a gate pulse. If you are applying a pulse (y/n ) to the triac gate you may need to make it longer - say 90% of the AC cycle in duration. The load voltage. The PSIM schematic used is attached. I guessed the circuit values. With a control duty cycle of 0. 7 I obtain the waveform indicated earlier. With the duty cycle increased to 0. 8 the problem vanishes and the load has the full sinusoid imposed. One would have to know the actual circuit parameters to correctly advise the OP. The load voltage. The PSIM schematic used is attached. I guessed...



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