On Sat, 15 Nov 2008 20:39:00 -0500, Wes wrote:

Bruce L. Bergman wrote:

If you add a relay to a transistor drive circuit and you aren't
absolutely sure how well the device was engineered, put a back-EMF
diode or a neon lamp or other snubber across the coil leads.

Generally a 1N40001. I always wondered why many common relays like the Omron octal and 11
pin dc relays didn't have the diode installed already with polarity marked for coil.

Waitaminit!! The 1N4001 is only 50V - you want to use a 1N4004 or
better (1N4005 or 06) to get above 400V. That spike can easily go
over 50V and the diode won't live forever.

And the dumb things are under three cents each in bulk, so you have
no excuse for cheaping out.

As for pre-installing the Back EMF Snubber on stock products, they
never know what type or voltage relay you're going to use with that
relay socket. But it would be a cool and useful factory option if you
are ordering production quantities of relay sockets.

-- Bruce --