Re: Project Help Pool Motor
Posted: Wed Nov 08, 2017 12:05 pm
@roland_vs While that would undoubtedly fix the power dissipation problem I have a doubt. I assume the purpose of using a SSR is to avoid the issue of contact wear. With an inductive load the worst potential for contact wear occurs when the contacts open at a time in the cycle where current is a maximum. There is then a risk of arcing with transfer of material between the contacts. With a parallel SSR, the SSR will have zero volts across it when the contacts open, so the triac will be off. Unless the triac is immediately forced into conduction it won't help with this problem.
The conventional solution is a snubber network to limit the dv/dt in the hope that the contacts open sufficiently quickly to prevent an arc being established. I think you'd still need that, because the triac control circuit is probably designed to turn on at a zero voltage crossing.
I'm not entirely sure what the SSR is bringing to the party compared with a properly implemented conventional relay circuit. My recollection of the theory of induction motors is rather corroded with the passing years. Is inrush current a problem?
The conventional solution is a snubber network to limit the dv/dt in the hope that the contacts open sufficiently quickly to prevent an arc being established. I think you'd still need that, because the triac control circuit is probably designed to turn on at a zero voltage crossing.
I'm not entirely sure what the SSR is bringing to the party compared with a properly implemented conventional relay circuit. My recollection of the theory of induction motors is rather corroded with the passing years. Is inrush current a problem?