Hi Colin, Good information here:
http://www.epanorama.net/circuits/semiconductor_relays.html#triacselect HTH Dave On Jan 13, 2008, at 11:41 AM, Jon Elson wrote: > John Kasunich wrote: >> Colin MacKenzie wrote: >>> I have a simple relay board I made using >>> grayhill solid state relays. These relays are opto-isolated. >>> Because my >>> relays are 3A 140v rated and my rotozip is 5am motor, I used 3 of >>> them >>> in parallel to comfortably run the rotozip with lots of amp >>> headroom. >> >> >> Not sure solid state relays can be paralleled or not. I bet if you >> measured the current through each one you'd find it is NOT evenly >> distributed. Might even be flowing through only one of them. A 3A >> relay will handle "5A" at least for a while, and under light load the >> rotozip probably draws less - maybe even less than 3A. So you >> might be >> running on one relay right not and not know it. > Colin, > > When paralleling transistors you have current sharing problems, > and need to use ballast resistors. Assuming these SSRs are > SCR/Triac type, due to the nature of those devices, I suspect > one relay is ALWAYS carrying all the current. Unless you use > significant ballast resistors in series, I can almost guarantee > that one relay has the lowest on voltage, and the other two drop > out as soon as that one turns on. You are living on "borrowed > time", and one of those relays will almost certainly short out > eventually. I'm just amplifying what John is saying here. > > If in doubt, do a little google searching about paralleling > SSR's, I'm sure anyone who knows says it won't work. > > Jon > > ---------------------------------------------------------------------- > --- > Check out the new SourceForge.net Marketplace. > It's the best place to buy or sell services for > just about anything Open Source. > http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/ > marketplace > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
