Yup, relays are fine as long as you put a substantial current through them
and use them when you need them. When you don't, you need to be really
careful about what you use. The point isn't really that relays are evil,
it's that you shouldn't add complexity that you don't need, and when you
do, you should make very sure that you've been careful enough about the
specs to compensate for the added complexity. One more component to fail,
one more set of contacts to get fouled or intermittent.
The standard approach to switches (more capacity for the contacts is
better so you size them two to five times the likely current) doesn't
apply to relays because the contact pressure is so light. Low current
across relays were the bane of phone systems and the reason why your phone
connection used to be so variable. Call it a personal thing--I built a
computer when I was 13 that used hundreds of relays as flip-flops. It
rarely worked. I tend to avoid the little buggers in favor of a directly
switched circuit with adequate switches.
-----Original Message-----
From: TeriAnn Wakeman [mailto:twakeman@cruzers.com]
Sent: Thursday, April 03, 2003 7:42 AM
To: Friends Friends of Triumph
> Relays, push buttons. There's a reason why these kind of systems were
> not commonly added to cars until there was solid state electronics to
> fail all as one monolithic molten mess. Reliability.
<<SNIP>>
> Bang it around in a race car and you're asking for trouble.
My 1960 Land Rover has been rewired with relays on high and low beam
headlamps, the auxiliary driving lamps, on board compressor, winch, a
relay for isolating the second battery, and even the complete switched
electrics are on a relay.
I can not imaging any race car taking more banging about than a leaf
sprung Land Rover that sees serious long range expedition travel. I have
yet to experience relay failure from the after market automotive relays.
Any off roader running higher than stock wattage lamps, and auxiliary
electrics that draw high power are using relays with great reliability.
I used to own a 1970's Saab. That vehicle had relays on everything. i
suspected they used relays to activate the relays. Other than a hiccup in
the Bosh fuel injection system several factory trained technicians were
never able to find the electrical problems were repeated failure of the
radiator temperature sensor and German style fuses burning out where the
metal of the fuse contacts the fuse holder. It the 5 or 6 years i owned
that car I never experienced a relay failure.
Personally I have found automotive relays to be quite reliable over time,
long drives on deeply wash boarded roads and rock crawling.
TeriAnn J. Wakeman
Marigold Ltd.
www.marigoldltd.com
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