Internally Regulated Alternator Trivia - Bootstrap Current?

[Zed Head]

Thanks for the confirmation.  I already picked up a dual action (NC and NO) Siemens/BMW relay with base, at the wrecking yard.  Purple.  100 ohms across the solenoid.

 

Since then I wondered if the fuel pump control relay could have been used instead.  It seems to be the only NC relay in the 1978 car.  Only wondered because I have one.

 

Did you look at that picture in #31?  That's the worry.  Maybe the water it was submerged in was cold and oxygen-free, and that's why it still works.

[Captain Obvious]

Oh yeah, I forgot to talk about your current relay. It certainly looks like a water line on the relay, but what has me confused is that it doesn't look level. So unless the car was parked on a very steep slope or the relay wasn't bolted into position and was hanging at some off angle by the wires, it may not be a water line?

 

Is that simply a trick of the surrounding reference points and the rust line IS actually level?
 

And I don't think that submerging it would really prevent it from working. The resistance of water is way higher than copper and the vast majority of the currents down there would still go where they were supposed to even while submerged. Not to say I would recommend it, but just saying I don't think that would kill it right away. I think a mechanical failure would occur before an electrical one. In other words, I think the internals would rust up solid before the coil would fail.

 

That's definitely gruesome though. Thanks for sharing!

[Captain Obvious]

And one more thing... At 100 Ohms coil resistance, that wrecking yard relay will draw less than half what your original is pulling. A little over 1 Watt being dissipated inside the case of that one compared to close to 4 W for your original.

 

I know 4 Watts doesn't sound like a lot, but put an empty soup can over a 4 W nightlight plugged into the wall for an hour. Then pull the can off and grab ahold of the bulb. 

[siteunseen]

I know 4 Watts doesn't sound like a lot, but put an empty soup can over a 4 W nightlight plugged into the wall for an hour. Then pull the can off and grab ahold of the bulb. 

You've done this! 

[Captain Obvious]

I'm always grabbing stuff I shouldn't be....

[siteunseen]

...and things you should!

[Captain Obvious]

Sampler flights!! I'm in!  

[Captain Obvious]

I got some pics of my 77 style brake warning relay. Four position connector, three populated positions. Here it is in it's natural habitat:

I took it out of the car and discovered that I had left myself a note from the last time I was in there:

 

Pull the guts out of the metal case. Note the black crispy areas on the coil windings:

 

Looking it over, I was actually able to see the break in the coil wire:

 

Also, being the curious type, I measured the resistance of (what is left of) the coil and I got 10 Ohms, which is way too low. It does, however explain the balled up melted blobs of copper on the ends of the magnet wires where the wire melted back... Tells me that it didn't go peacefully. When this thing went open circuit, it went with gusto!

 

So with all the above info, here's my forensic analysis...

 

The coil ran hot from day one and eventually degraded the varnish insulation between coil windings until it shorted internally somewhere. It may have gone from it's original starting resistance is to the current level of 10 Ohms in one shot, or it may have shorted out just a couple turns initially which would reduce the coil resistance, draw more current, and get even hotter (avalanching to it's ultimate death). In any event, eventually one coil turn shorted to another and greatly reduced the coil resistance to the current 10 Ohms. For a short bright instant, the coil drew over an amp until POP, the wire acted like a fuse and vaporized a quarter inch of copper.

 

I'm comfortable not using it at all. I use my parking brake religiously and it also lights the brake lamp on the dash. In other words, my brake bulb gets tested even though I don't have the relay installed.