Well, the harness could be the culprit, definitely. It could be intermittently
shorting somewhere. I will have to look carefully. I might even hook up my
DVM set to "continuity" so it will beep at me while driving if it sees a short.
The harness was out of the car for restoration a few years ago, and it had no
insulation problems apparent then. Things could have changed.
I have certainly smelled no hint of smoke, but a relatively brief or high
resistance short could fry the stabilizer without melting wires.
Regarding electronics, I was planning on using something like a 1N4007 diode.
I believe that it the 1000V/1A type. I have some 27V bidirectional TVS's
around, and I will use one. Do you think the 1000uF cap adds anything to the
protection vs a 0.1uF that the regulator needs routinely? It seems as if you
think that there is no other component that I should add to the power supply to
further protect it? I am not too concerned about maintaining a super-regulated
voltage, I just want to avoid blowing the regulator. I am not experienced in
the design of power supplies in general, expecially not for such a nasty
environment as the car. I would love to see what an oscilloscope would show in
the power in the car. I have no scope, however.
The beauty of the linear regulator is that it is reasonably hard to destroy it
if it gets shorted, and it will not deliver enough current to smoke the wires
downstream.
-Tony
-------------- Original message --------------
From: "Dave Connitt" <dconnitt@fuse.net>
> Hi Tony,
> It sounds to me like your voltage stabilizer is the victim, not the cause..
> Especially since you are on our second stabilizer in a short period of time.
> I think your problem is a short somewhere to ground. Is a wire rubbing
> somewhere against metal? Also, you might want to consider carefully checking
> the harness for smoke trying to jump from wire to wire! If the wire harness
> looks OK, do you have a extra fuel gauge or temp gauge you can swap in?
>
> If you build a solid state replacement definitely use a diode of some kind
> on the input. Even a 1N4001 rectifier diode would be better than nothing.
> They are 1A, 100V parts but it sounds like you may already know that.. A TVS
> on the input would be better still. I use TVS parts all the time to protect
> communication circuits and they work great for transient protection. But, I
> still wonder if the stabilizer is the problem?? I am suspicious of the 38
> year old wire harness myself.
> Best Regards,
> Dave Connitt
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