On Fri, 25 Dec 2009 09:45:32 +0000, Jim Lesurf wrote:

snip

My experience is that almost any type of conventional relay will end up
causing problems if the unit is used for many years. Avoid if at all
possible. Solid state relays would be much better if you can find one
that suits your purpose.


For goodness sake don't tell the thousands of small generating stations
that have been using relays for generator control continuously for the
last 40 years or so... They might get suspicious if they find out that
their technology is so unreliable. ;-)

Providing relays are specified correctly (and not run at too high a
temperature) they can be very reliable indeed - often better than solid
state switching as they aren't affected by moderate spikes on either the
coil or contact circuits. When that is coupled with the very simple plug-
n-play maintenance (which is often all the systems get) it makes them
ideal for use in remote generation plant.

The main problem is wiring. They are very labour intensive when a lot are
needed, not to mention the space needed for relay racks. I've yet to find
a 4-pole SSR with changeover contacts... :-)

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
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