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          |
|--------------------------------------------------|