On Tue, May 3, 2016, at 09:34 AM, andy pugh wrote: > On 3 May 2016 at 14:27, Erik Christiansen <[email protected]> wrote: > > Yup, a MOV goes across the triac, to clamp voltage spikes. > > When you say "Across" do you mean across the output terminals of the > SSR, or between the live terminal of the SSR and neutral? > > The former is easier, and I doubt that there would be much trouble > caused by dumping the spikes into the main capacitor as long as the > rectifier wasn't too upset.
A MOV across the SSR protects the SSR (only). A MOV across the input protects everything. However, the MOV across the SSR can potentially do a better job of protecting the SSR because the lead length is shorter and thus inductance is lower. At decent power levels (tens of kW and up) the main cap and rectifier can clamp most transients, so only the SSR is at risk. But small rectifiers can be destroyed by the peak currents that happen when the cap clamps an incoming transient. At a former employer they had to beef up the rectifiers on a sub-kW class drive for exactly that reason. As an aside, here is a blog posting about the power supply I built for a CNC project. There is a link to the complete schematic early in the text, and photos of the completed supply. http://jmkasunich.com/cgi-bin/blosxom/shoptask/power-input-01-11-07.html Note that the EMC filter and inductor after the rectifier are not absolutely required. I had them in my well-stocked junk box so I used them. The contactors and relays also came from junk. I think the only thing I bought was the disconnect switch (from Automation Direct). This particular supply is a bit unique in that I designed it to work as a voltage doubler on 120V, or as a bridge rectifier on 240V. -- John Kasunich [email protected] ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
