On Tuesday 03 May 2016 04:54:32 andy pugh wrote: > On 3 May 2016 at 02:51, Jon Elson <el...@pico-systems.com> wrote: > > You should very conservatively derate the SSRs > > in many circumstances, but especially where capacitive > > inrush surge is possible. > > The PSU is powered through a 20A breaker and the SSRs are rated at > 40A. The anticipated peak motor current is about 12A total. > Would you suggest a hiher rating than that? > > > Do you know what the ACTUAL inrush surge is? > > I did, until the relay with the job of switching-out the > inrush-limiting resistor failed. It should be much less than an amp. > (240V AC through a 620 ohm resistor) > > > Also, is it > > possible that a momentary power dip caused a surge while the > > SSRs were in the turned-on mode? Possibly, there was a > > voltage spike while the SSRs were off, and it caused them to > > catastrophically break down. You might think of getting > > some MOV surge suppressors to put across the input mains. > > Also, maybe get SSRs rated for higher input voltage. > > The SSRs are rated for 380V and are running on 240V mains. I have not > previouslyhad any problems with mains voltage spikes. > The PSU seems to have failed either when turned off, or at power-up. > This is on a lathe that is not, as yet, working. I only found that the > PSU was dead when I came to try to set up the X axis motor having > finally finished the mechanical assembly and wiring. (I did not get as > far as enabling the servo amps)
You may need higher voltage rated devices, Andy. Without ANY switching spikes, or the EMP from a nearby lightning strike, they are seeing the RMS peak voltage of 338.4 volts (240 * 1.41) 100 times a second. Here, the common $10 one is 480 volt rated, somewhat better than your 380 devices, but on a 240 volt circuit I'd use this one from mpja.com: <http://www.mpja.com/50A-660VAC-Solid-State-Relay/productinfo/32171+RL/> at $30 a copy. You could probably remove the heat sink shown. You need at least 600 volt rated devices, and some MOV's across the line that will absorb the stuff above 400 volts. I don't see any such critters on the mpja site though. The higher the joules rating, the better, with 100 being a recommended minimum from grandpa Gene. They will need to be fused in the event they get too hot and fail of course, but you could just let the circuit breaker handle it in that event. I would install them someplace where they won't do any further damage should they explode, and where they are easily seen if you want to check them for any discoloration or damage. On this side of the pond, most, but not all of the commonly available multi-outlet switched strips that sell for more than a 15 dollar bill have at least a 50 joule device in them, and here in the coyote.den I have a big one that ties power, cable tv cable and telco lines all to a common point with a 250 joule rating for the whole works. I haven't blown anything that was plugged into that "master strip" in about 15 years now. Its on a 1500WA UPS but my brother color laser printers power up inrush was too much for the UPS so it was plugged into the wall, and it got blown about 6 weeks back. I just replaced it with a MFC inkjet, that seems to be permanently set in super ink saver mode, black never gets any darker than about an 18% grey card. Photos WILL be washed out. But thats another story... Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ 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
