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
