If Solid State Relay SSR happen to be a thyristor it will only allow a limited dv/dt or it will fail to turn off. A common source of dv/dt is inductive or maybe capacitive load and it happens because a thyristor turn off at zero current although a reactive load do not have zero voltage at zero current. Problem is circumvented by a properly sized capacitor in parallel to limit voltage rise during turn off.
Nicklas Karlsson On Tue, 3 May 2016 09:54:32 +0100 andy pugh <bodge...@gmail.com> 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) > > -- > 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
