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I'm trying to work up a rational eurolights wiring harness, and my feeling
is that it is time to go away from using relays to switch the power on and
The problem is this: To turn the lights on, we are energizing the relay. To
keep the lights on, we keep the relay on. My suspicion is that the
automotive type relays we are using are not rated for continuous duty - a
four hour ride at night means four hours "on", and if the relay overheats
and fails, the light goes out.
As a compromise, I came up with a four-relay system which is quite simple
to wire. Each relay works ONE filament, so in case a relay goes pfft, you
only lose one light. (Power goes to each relay from jump-start stud, old
headlight wire - white or yellow - energizes correct relay, relay then
turns on appropriate filament. Remember to add solid ground from headlight
bulb to chassis. Duplicate system for other side of car.) This also should
have the advantage of not needing any changes in the autocheck system since
both sides are loaded equally and the autocheck senses the *difference*
between current draws to figure out a bulb is gone.
But I'm still not happy about the relays. Would it be possible to switch
the filaments on and off using a large, heat sinked power transistor with
the white and yellow wires providing the "on!" and "off!" signals to the
base of the transistor? I know that 30 amp 2N3055's in a TO-3 package can
be bought for a buck or two, and it strikes me that with a few resistors
and an anti-spike diode or two we could have a really reliable
no-moving-parts system for turning the lights on and off. As an additional
benefit, it could be set up so that even when the lights are "off" there is
a small bit of power flowing which would greatly reduce the starting surge
which is what frequently burns out light bulbs in the first place.
Any EE's out there in lister-land want to comment?