Kirk Wallace wrote: > On Sun, 2009-04-12 at 22:04 -0400, John Kasunich wrote: > ... snip > >> Regardless of the type of turn-on, once the Triac is on, it won't turn >> off until the current through it goes to zero - even if the LED is off. >> That's why SSRs only work for AC - in a DC circuit the current won't go >> to zero. >> >> Hope this helps, >> >> John Kasunich >> > > Thanks John. Did you mean "That's why _SCR's_ only work for AC"? > > Oh, boy! I sure did mean SCR and Triac-type SSRs, the ones marked for AC output. > I was looking at two devices, both datasheets looked the same to me > except: > > S108T02 has > "Zero crossing functionary (VOX : MAX. 35V)" > > S108T01 has > "Non-zero crossing functionary" > > I just want to turn a 24 VAC transformer on and off for my weathercam > antenna rotor, so I suspect either one will work. > > Actually, zero-crossing SCRs are not real good for this. With little transformers with high winding resistance, such as in this case, either will work fine. With bigger power transformers, turning on at the zero crossing causes the transformer to be saturated every time it turns on, with a big "HUMMMmmmmmm". A random-turn-on SSR will only do that when it happens to be turned on near the zero crossing. Best is a 90 degree turn-on, where it turns on at the voltage peak. I haven't seen that they sell such a device, but a PLC could do it for you.
Jon ------------------------------------------------------------------------------ This SF.net email is sponsored by: High Quality Requirements in a Collaborative Environment. Download a free trial of Rational Requirements Composer Now! http://p.sf.net/sfu/www-ibm-com _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
