On Fri, May 30, 2008 at 9:16 PM, Gerhard Fiedler wrote: > David VanHorn wrote: > >>> The device in question is this : http://www.sekicon.com/eng/product/st-22.html >>> Which mentions 'Min current 50mA'. >> >> This is called "Wetting current" and operating the contacts with less >> than this current will result in intermittent opens. > > Isn't the "wetting current" the current that is needed to make the contact, > while operating the contact (after applying an initial wetting current) can > often be safely done with lower currents? Or, the other way round, often > the current that is enough for maintaining the closed contact operational > is not enough to safely close the contact? The wetting current is, indeed, the minimum current needed to make sure the contacts create a safe electrical path on initial contact. The data sheet, however, says "minimum current" and not "wetting current" It is entirely possible for a relay to have both a wetting current and a different minimum current, and that relay operation below minimum current (even if properly wetted) is not guaranteed. The automotive industry has decades of experience in this area, and that experience is one of the reasons relays are used widely even in today's cars - it takes a long time to get that kind of reliability and knowledge out of any particular technique. -Adam -- EARTH DAY 2008 Tuesday April 22 Save Money * Save Oil * Save Lives * Save the Planet http://www.driveslowly.org -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist