I recently ran into a similar problem in a design class I was teaching. As a mechanical engineer, I have to admit that I don't always think these things through, and I can guarantee that an undergraduate mechanical engineering student isn't even going to suspect that there is going to be an issue. What I realized is that I know how to deal with a collapsing field with a DC relay, but not with an AC circuit. Seems to me that your application would be better off with cascading a mechanical relay after the SSR. Even then, there is a missing protection circuit, and I haven't tried to figure out what that is.
The students blew a SSR that turned a power supply on and off. We solved the problem by replacing as needed. Not sure what shorts the power side of the circuit, there is probably a gate/collector max voltage violation or something like that. On Mon, May 2, 2016 at 7:17 PM, andy pugh <bodge...@gmail.com> wrote: > The PSU on my lathe is something I made myself. On the input side are > two SSRs, one for power on/off and the other switches-out a soft-start > resistor. > There is also s discharge capacitor that is switched in when the main > input SSR is switched off. > > Today things went a bit strange, blowing the breaker and then the > discharge resistor. This was with the PSU powered up, but not turned > on. > > It turns out that I have an unanticipated failure mode, if both input > SSRs fail closed-circuit. > > I have tested the SSRs on the bench, running a light bulb, and they > both light the bulb with nothing connected to the control terminals > (And with the control terminals shorted together). > > So, I am wondering if there is a problem running a rectifier input > with SSRs. I found something in an Omron document suggesting that > turn-off might be unreliable, but that doesn't seem to be the issue > here, the relays are now incapable of turning off a (filament) light > bulb. > > Did I get unlucky, or are SSRs a bad choice for this application? > > -- > atp > "A motorcycle is a bicycle with a pandemonium attachment and is > designed for the especial use of mechanical geniuses, daredevils and > lunatics." > — George Fitch, Atlanta Constitution Newspaper, 1916 > > ------------------------------------------------------------------------------ > Find and fix application performance issues faster with Applications Manager > Applications Manager provides deep performance insights into multiple tiers of > your business applications. It resolves application problems quickly and > reduces your MTTR. Get your free trial! > https://ad.doubleclick.net/ddm/clk/302982198;130105516;z > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Find and fix application performance issues faster with Applications Manager Applications Manager provides deep performance insights into multiple tiers of your business applications. It resolves application problems quickly and reduces your MTTR. Get your free trial! https://ad.doubleclick.net/ddm/clk/302982198;130105516;z _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
