Stuart Meier wrote:

> 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

Are you using the relay to control to power of a circuit? Is the design of
the circuit such that energizing the relay can cause a high current pulse
of current to flow into the capacitor. If so this is a known failure mode of
tantalum capacitors. They have a finite current surge capacity. I have had this
problem in a design that was hot plugged. Even using capacitors with a voltage
rating of many times the input voltage does not always solve the problem.

Some manufacturers are now making tantalum capacitors with higher
surge ratings. AVX's TPS series is an example of a high surge capacity
tantalum. Other options are to use Sanyo's Oscon series or high value
ceramic capacitors. which don't have this particular flaw.

If the operating current of the circuit  is low enough a simple solution would
be to place a resistor in series with the contacts.


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