> On 03.05.16 11:42, andy pugh wrote: > > On 3 May 2016 at 10:41, Nicklas Karlsson <nicklas.karlsso...@gmail.com> > > wrote: > > > In other words i/C should be less than maximum allowed du/dt. > > > > I am not sure how to determine the i for this calculation. I guess I > > can find the dv/dt from the component numbers on this page: > > http://www.instructables.com/id/The-inner-workings-of-Counterfeit-FOTEK-SSRs/ > > The servo drives have so far been limited to 4A, but whether that > > translates to 4A at the input to the rectifier I am not sure. > > Section 6 on page C-343 here: > > https://www.omron.com/ecb/products/pdf/precautions_ssr.pdf shows a > > square-wave with zero time at 0 current. But I don't understand how > > that is possible with a sinusoidal input voltage. Surely the current > > is zero for all the period of the cycle where the input voltage is > > less than the capacitor voltage? > > Spot on, but the circuit in section 6 doesn't include a capacitor, that > I can see. > > > I wonder whether I would be better with DC-rated SSRs on the DC side > > of the rectifier? > > The link to SSR precautions indicates that the SSR already includes a > snubber. But page 3 of the notes says that is often not sufficient, and > suggests a 440 - 470 volt varistor (MOV) as protection in a 200 - 240 > volt application. That clearly assumes the use of e.g. a 600v SSR, not a > mere 400v unit.
The way to find out if snubber capacitor is large enough is to make the calculations or simply measure at turn off. I make assumption SSR is a thyristor/triac or similar. Varistor protect against overvoltage but do nothing against dv/dt. If SSR turn off at zeror current there should be very little voltage snap. For resistive load both current and voltage are at zero at the same time. For reactive load there are voltage at zero current and dv/dt depend speed of turn off or how fast snubber capacitor is charged. ------------------------------------------------------------------------------ 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
