On 3 May 2016 at 12:41, Erik Christiansen <dva...@internode.on.net> wrote: > > 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.
Part of the reason for this arrangement of relays is that I could not find an NTC device with enough current carrying capacity to work as a surge suppressor. Until I googled just now I thought that this was what was meant by MOV. The data sheets for Varistors seem to specify an activation voltage and a power dissipation, but no off-state resistance measurement to calculate the power dissipation. Or is the resistance so low that this can be ignored? > IIUC, there's also a bridge rectifier between the SSRs and the capacitor. > But the inductance being switched is the power transformer on the input. This PSU is connected to the mains without an isolation transformer. > It is tempting to move to the DC side, and use a 600v DC SSR, or just a > high voltage MOSFET. (N-channel, in the -ve lead has lower RDSon, and is > easier to drive.) The section 6 that you mention recommends using a > MOSFET SSR on the DC side. Do you see a 600v one of those on ebay? The closest is a 400V unit, only 20A and £135 http://www.ebay.co.uk/itm/SSR-20A-400VDC-Part-DC400D20-/351592581782?hash=item51dc8d0a96:g:S9EAAOxyd8NSa8CE -- 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
