Wednesday, November 14, 2018

Report Card Time

 If you like reading what I write about resistance wire, then you're in for a treat.  Kinda.  While some people spend years and careers working on and writing about many types of vehicles, nearly none of them ever end up writing about resistance wire.  Despite that, I somehow have managed to make the subject a recurring feature -- and I have a feeling this probably won't be the last time it comes up.

Today I'll be covering how I dealt with a segment of resistance wire that is used in the factory harness, what it does, and considerations to have in mind when planning a new harness and/or alternator upgrade.

The original harness used a run of resistance wire unrelated to the starting circuit I covered previously.  It is spec'ed to 15 Ohms, and links the wire that delivers battery voltage to the ignition switch with the wire from the alternator to the idiot light.  The functions of this wire are current delivery to the light when the ignition switch is in "RUN", and a redundant source of resistance in the event that the bulb burns out.  The reason the latter is important is because the alternator's voltage regulator isn't designed to receive full battery voltage on that pin, and can end up getting cooked if run for very long in that state.

I've personally yet to find a local source of resistance wire that doesn't include a junkyard, so I planned on using a resistor I had laying around to get the job done.  Before I could hop to it, I needed to do a little research on what resistance value I should aim for, on account of the upgraded alternator I'm using.

The factory alternator was a model 10si, which allows for a pretty simple upgrade to a CS130, which has a rated output of 105A, is usually cheaper than a 10si, and will charge at lower RPM.  Another difference appears to be the light circuit resistor value needed to keep the alt from scrambling it's insides.  I found  a million opinions on what size resistor is needed, but the Delco service manual for the CS130 clears that up a little in the section on bench testing.

"Use a resistor of any value between 35 ohm, 5 watt, and 500 ohm, 1/2 watt between battery and "L" terminal.”

So now we're looking at a 15R value in the factory harness, while the CS130 needs 35R, minimum.  Since I'm not tied to the factory harness, I decided to go ahead and change the resistor value to something inline with the Delco manual.  All I had in my immediate vision was a 50W 150R resistor, so I figured I'd cut it open and trim the resistance down a little.


This is pretty much the same as what I started with.  First thing I had to do was peel it.  To do that, I sawed the base away from the bottom, then sawed from as close to the top side as I could, through the aluminum, down to the outer edge of the black circle.  Couple of hammer taps to a cold chisel later, and I was able to strip the aluminum away from that black core of epoxy.

The epoxy was surprisingly easy to remove.  I just gently clamped it in my pliers a few times and it crumbled away.  It's worth mentioning that this didn't take much force at all, which is great in avoiding damage to the wire the epoxy covers.

After shelling the epoxy, I cut the wire away from one end of the resistor core and stripped the wire away, periodically checking the resistance of the wire still wrapped on the resistor frame.  I got tired of dealing with tiny wire after a while and called it good at 41R.  Here's what it looked like at that point:


Then I wrapped the free end back around the post at that end, dropped a dot of super glue on it to hold it in place, then stood it up in a plastic tube and potted the whole shebang in some 2 part resin I had handy.  No pictures of that, but you'll see the finished product in a future update.

So with that, I finished doing what was required to be done with the base electrical system.  I've now got all wires to start and run, so here's where things are at now:


Gotta get up in 3 hours to get back at it, so I hope you'll excuse me ending this abrup

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