RE: Eurolights wiring

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

Many relays _are_ rated for continuous duty.  Take a look at the load
reduction relays ... think of the catastrophic effects that you would have
if that failed ... and I don't think I've ever heard a report of one being
replaced.  By far the largest effect is going to be the pitting of the
contacts from being switched on and off.  

I found that the load reduction relay in the 5k fusebox is actually rated
for 60 amps!  While I'll probably still go with double pole relays each for
the highs, lows and fogs it is awfully temping, knowing that the single pole
relay is so small.  I guess the big thing would be finding a connector into
which the relay could be plugged.  

What are you planning to do for the burned out bulb indicator?  I've pretty
much convinced myself to relocate the module to be with the relays so that
it will continue to operate correctly, installing some sort of jumper in the
socket in the relay panel.  As I posted some time back, I'm pretty sure I'll
be able to fit everying into a sealed box that was once an ABS controller
from a 5k.  I have yet to try to determine where to mount the thing ...
probably somewhere behind the radiator ... I'd hate to have a high current
connection to the battery in a place where a minor to moderate frontal
impact could cause a meltdown!

> 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
> off.
> 
> 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.
> 
> 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.
> 
Remember that while this idea might work, it would only tell you that the
relay coil has burned out ... :-)

> 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.
> 
... I suppose that this could work, but I worry about the reliability of
transistors far more than that of relays!  You will always have a small
voltage drop across the collector/emitter too.  Hey, if it is attractive to
you, it definitely can work.  Rather than switching the hot lead in an
emitter follower mode (which would guarantee that the headlight voltage was
0.6 volts lower than the voltage into the base ... and the possibility of
higher internal power dissipation), I'd recommend that you use the
transistor to switch ground to the filament.  Also, rather than having a
constant current through the bulbs when the lights are off you can fashion a
"soft start" circuit with an RC network on the base.  

HTH!
Steve Buchholz
San Jose, CA (USA)