Technical Totally frustrated...need Delco 10si Alternator help

Just now back from the alternator shop. Had a new resistor intended for tractors installed on two alternators. The one on the left has the Speedway larger pulley- and it would not kick in at idle. The one on the right has the Offy pulley which spins 1/4th turn more per revolution. That was enough to have it kick in at idle. In the middle is the stock Chevy pulley.



This solution should work. I'll have a chance to rewire tomorrow with #8 lead off the alternator post, build a good ground, hook up the warning lights, and see if the warning light and volt gauge work properly.

I'll install the one on the right and keep the one on the left in the pickup tool trunk as a spare. In a pinch it will get me home, even if it means blipping the throttle at idle.

But here's what I've learned: on a 12-volt conversion on a flathead, taking a stock 10si and an aftermarket pulley and hoping it will work isn't the solution. Unless you also change the resistor, the alternator will only function at moderate to high speeds. The rest of the time (idle and low speeds) you are running off the battery.

Look again at the difference in pulley sizes....

 

1. Don't do this on a 10SI. OK on an externally regulated alternator, but on an internally regulated one it's not a true test.

2. I'd be interested in knowing where they put this "resistor". Never heard of this before.

3. The purpose of the sense lead is to tell the alternator how much voltage/current to put out to properly charge the battery. All this talk about parasitic and accessories needing to be considered is of no consequence. The absolute best place to connect the sense lead is at a point where there is no voltage drop between it and the battery and the second best place is where there is minimal voltage drop between it and the battery. Therefore the best place is at the battery post, and the second best place is one of those "heavy wire" locations, such as the horn relay, starter, etc.

 

I said resistor...meant to write "regulator." There are a variety of regulators available that "kick in" at higher or lower rpms. The rebuilder wasn't certain what rpm this one turned on, but it was what he used for tractor conversions of the 10si. The regulators are available for both 3 wire or 1 wire applications. Installing it is a matter of splitting the case and swapping out parts. It took the tech less than 10 minutes to complete the job and test the new unit.



The regulator tells the alternator how much output is required for both recharging the battery and meeting electrical demands from lights, windshield washers, electric fans, etc. Isn't that correct?

I plan on pigtailing the sensing wire from Terminal 2 to the alternator output (B+) post. The reason is that the wires are very short in a '34 pickup with the layout of my circuitry. I rarely if ever run the truck at night. It was no electric radiator fan. Very few demands on the electrical system, not even a radio.

We calculated out the potential voltage drop (Ohm's law) in various scenarios and situations, and the difference in putting the sensing wire at the battery post vs. somewhere on downstream was so insignificant, it just doesn't seem to make a practical difference (and saves me having to run another wire).

I'll run another wire if someone can give me a compelling reason, but otherwise, it just seems much cleaner to go the pigtail route.

In a bigger car with more electrical demands, I understand that the decision is more critical. It just doesn't seem the case here. But I stand to be corrected.

There seems to be some disagreement as to best protect the wire from the battery output to the battery with a fuse (75amp) or a fusible link. I will use #8 wire on the output post (and #8 on my alternator ground). Some say to use a fusible link (#12 wire) as it is most dependable. Others say that the jumbo fuses are fine.

Any thoughts? Thanks again for the help and guidance here. I've learned a ton in the past week.

 

Had the day off, put everything back together, rewired correctly. Just now fired the truck up, and everything works the way it is supposed to, volt gauge and warning light! First time ever, and I am so happy. It operated incorrectly for the better part of 3 years. About time it got wired right.

Thanks for the help, everybody. What a great sense of accomplishment working on this stuff yourself, but it wouldn't have happened without the brain trust. I am in your debt, guys.