A solid-state relay can accept much lower input currents and voltages to turn it on and much longer life. Here are the benefits I found: -opt coupled for protection (eliminates signal noise onto data line and protects digital components) -high current surge capabilities -small size -low current consumption -longevity of life (much longer) -reliable switching -quiet (silent) -less bounce at output (usually caused by reed) bad: -usually low current (though high current is available but expensive) -killed by over voltage spikes (just requires protection (Caps to ground)) -when they die, they die closed (on, but some have protection) -cost a little more -require heat sinks for high current (increases life expectancy) The opt coupling allows superb isolation. All you need is a LED, a light detector, and a high current triac if you want to build one yourself. Looking at some datasheets, I found that some operate at 3 to 30v with 7 to 16ma input current. The specific one I am looking at now allows a switching speed from 25 to 70Hz. "SSRs have some disadvantages. Their output is quite easily damaged by over-voltages, they are restricted to single-pole, normally open, configurations and they have much larger on-resistance than conventional relays. If SSRs are not driven properly or become damaged, they can act like rectifiers, resulting in a half-waving AC supply to the load." (Electronic Times, http://www.electronicstimes.com/story/OEG20010829S0014) well, that s all I care to find. If you have relatively low switching speeds for a non critical application (you can replace the relays easy), then I would say use contactors. These allow much higher currents and all you would really need would be a buffer at the output of your digital device and maybe amplify it to drive the relay. You can find them at almost any auto parts store. -----Original Message----- From: Madhu Annapragada Date: Fri, 2 Nov 2001 09:58:14 -0500 To: PICLIST@MITVMA.MIT.EDU Subject: [EE]:Contactor vs. SSR > Hello: > If one wants to remotely turn a 48VDC, 10A inductive load on and off using a > logic level control signal (as opposed to putting a switch in series with > the load) is it permissible to use a solid state relay as opposed to a > contactor? For that matter, from a regulatory point of view , what does a > contactor do that a solid state relay doesn't? Forgive me if this question > sounds naive, but I have been unable to track down the answer in any of the > books on my desk. > Thank you > Madhu > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > > -- "If you wish to make an apple pie truly from scratch, you must first invent the universe." Carl Sagan _______________________________________________ Sign-up for your own FREE Personalized E-mail at Mail.com http://www.mail.com/?sr=signup Have you downloaded the latest calling software from Net2Phone? Click here to get it now! http://www.net2phone.com/cgi-bin/link.cgi?157 -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu