At 04:03 PM 3/31/2007, Peter Todd wrote: >I have a few projects that I'm using cds-type photocell resistors in >them. Specifically they are all digikey #PDV-P9001-ND > >I mentioned this to someone who said that photocells are unreliable and >won't last more than a year or two. He said they all fail due to light >exposure within a few years. He may in fact be thinking of early failure in street-lamp usage. Early street-lamp photo-cell units were notorious for failing after only a few years. My limited experience with these failures is that the failures were caused by excessive power dissipation within the photo-cell while driving the relay coil in low to moderate light levels. Seemed to be much more of a problem in northern areas because of the slow change from bright to dim and vice-versa. As far as I know, those problems don't exist on modern street-lamp photo-cell controllers. I do think that you may be running your photo-cells a little hot if you are operating them at their maximum rated current. Depends upon the voltage across the cell. Hope that helps! dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 22 years of Engineering Innovation (1984 - 2006) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist