Yes, flyback diodes on the relays. Using Tants due to space on SMD board. The Tants fried not on the 5v coil side, but the 12v contacts side of the relay. The load at the time was another PIC driving leds, not relays. No high inductances around there. Thanks for everyone's comments - I intend to replace 16v caps with ines rated at 25v or better, Stuart Meier -----Original Message----- From: Tjaart van der Walt To: PICLIST@MITVMA.MIT.EDU Date: 01 May 1999 11:23 Subject: Re: [OT]Tantalum capacitor failure Stuart Meier wrote: > > Following a topic here a while back, I have several 1 and 10u tantalum > capicitors on boards where the PIC switches a couple of relays. The 5v > relays are switching 12v,and a cap on the 12volt line has just fried. It was > rated at 16 volts. > > I thought this was a defective component, but another one has just gone... > > I'll be uprating them in future, but surely a 16v cap should be satisfactory > on a 12v line? > > Stuart Meier Are you using flyback diodes on the relays? The coils can easily induce a few hundred volt peaks. Unless you are using SMD components, steer clear of tantalum caps. They have a nasty way of failing in a short. Kabooooom. If you have to use them, use at least a double rating (25V caps on a 12V system). Remember the usually-forgotten diode between the negative side of the relay coil (on the collector) and GND. This way you guarantee that no excessive - voltages get on the GND line. -- Friendly Regards /"\ \ / Tjaart van der Walt X ASCII RIBBON CAMPAIGN mailto:tjaart@wasp.co.za / \ AGAINST HTML MAIL |--------------------------------------------------| | WASP International | |R&D Engineer : GSM peripheral services development| |--------------------------------------------------| | Mobile : tjaart@sms.wasp.co.za (160 text chars) | | http://www.wasp.co.za/~tjaart/index.html | |Voice: +27-(0)11-622-8686 Fax: +27-(0)11-622-8973| | WGS-84 : 26¡10.52'S 28¡06.19'E | |--------------------------------------------------|