Hey, don't power it from the regulated supply that is running your processor... use the unregulated DC and connect the controller to the relay via a semiconductor like a transistor, mosfet, etc...
Buy the book "Noise Reduction Techniques in Electronic Systems" by Henry Ott.
There is a section on relay contact protection, which details the exact failure modes, the different circuit protection topologies, and even design equations to determine the right component values, like R and C in a snubber. It is a treasure on this subject! Thomas McGahee wrote:
Why not use a dual approach?: Have the MT1 and MT2 of your triac connected ALSO to the contacts of a Normally Open relay.
When you want to turn on your 2.5kW load, FIRST turn on the triac and wait about one cycle time. THEN turn on the relay. Keep both activated until you want to turn the load off, then FIRST turn off the relay, **wait long enough for the relay contacts to fully open**, and then turn off the triac. Easy to do with a PIC.
The triac can easily take the initial turn on load. Then when the relay kicks in the voltage across the relay contacts AS THEY CLOSE will be only a volt or two, since the triac is on. But then the relay will conduct the load for the several minutes the load is on. When turning off, the triac will ensure that there is no arcing of the relay contacts. Then the triac turns off.
I have been using this method for cutting down on the wear and tear of a heavy duty relay I use to control an electric room heater. The triac needs only a fairly moderate heatsink, as the relay ends up handling the ON current for all but the turn-on and turn-off transition times.
My unit (which is not PIC controlled, but rather controlled by some logic gates and timer circuits) has been running since 1975 without a problem. Oh, yes, I use a snubber network to ensure the triac does not get re-triggered at turn-off.
That's brilliant! Nil contact arcing for the cost of a cheap triac that is hardly ever on...
|file: /Techref/io/relays.htm, 6KB, , updated: 2010/12/21 08:28, local time: 2013/5/24 01:19,
|©2013 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?|
<A HREF="http://www.piclist.com/techref/io/relays.htm"> Relays</A>
|Did you find what you needed?|
PICList 2013 contributors:
o List host: MIT, Site host massmind.org, Top posters @20130524 RussellMc, IVP, Bob Blick, alan.b.pearce, John Gardner, veegee, Sean Breheny, Isaac Marino Bavaresco, Carl Denk, Josh Koffman,
* Page Editors: James Newton, David Cary, and YOU!
* Roman Black of Black Robotics donates from sales of Linistep stepper controller kits.
* Ashley Roll of Digital Nemesis donates from sales of RCL-1 RS232 to TTL converters.
* Monthly Subscribers: None at this time. on-going support is MOST appreciated!
* Contributors: Richard Seriani, Sr.
Welcome to www.piclist.com!