GM alternator conversion

[esmeby]

I have been searching the 311 site and forum a bit and have a few questions that I can't find the answer for.

Installing a 60 amp alt in my 69 u20 converted car. Alt is in, no problems, but wiring questions are the issue.

http://www.311s.org/phpBB2/viewtopic.ph ... alternator

Based on the above thread, I am lead to believe that I could hook up the white wire to the output of my new alt, and hook a larger (8ga) wire directly to the battery. I have a 30a fuse on the white wire already. This would allow the stock ammeter to work, but leads to question #1

Question 1: If the alt kicks in full charge, will the 30A fuse blow, or will the current take the path of least resistance and go to the battery (if that is the least resistance).

Question 2 My new alt came from a junkyard and I do not have any idea which of the 2 wire terminals is for the "sensing" part of the regulator. Anyone know if it is the top or bottom as they both point to the right side of the car. (the 311.org image wasn't clear enough to tell)

Question 3: Can I hook up the sensing wire to any accessory wire just like a volt gauger?

Question 4 I hook the alt case to a ground according to the 311 tech page. Is the ground on the alt case from the large bolt on the rear that held the stock GM mounging spacer?

After I get this done I will put up info on my site with some images.

Thanks much.

[S Allen]

Erik,

I am not sure about the amp gauge part but the rest is a pretty easy hookup. One wire from the battery to the alternator. On the 81 chevy camaro alternator I use the the very top connection which is the sensing wire. It gets connected directly to the BAT terminal. That top I speak of is standing above the alternator looking down. The field terminal second from the top is not connected. I just tape it off. The alternator still charges fine but you have to blip the trottle once to get it kicked in. The cases on the camaro alternator have a bolt on the back that is meant to connect a ground from the case to the frame. It has nothing to do with the mounting hardware. How many amps does your alternator put out? The camaro one I use is a 60 AMP output which is plenty for a roadster and all of the accessories you want to add. When you get the write up done I would like to put a copy on the 311s.org website if that is okay with you.


Steve

[S Allen]

Erik,

I went back and read that thread you had in your original post. It looks like if you would rather use the old amp gauge and not put a volt gauge in you can hook the WHITE wire coming out of the original wiring harness to the battery terminal on the GM alternator and forget the wire coming directly from the battery. You should still protect the old wiring with either a fusible link or an inline fuse.

Steve

[esmeby]

All hooked up like you suggested. Factory wiring to alt output, sensing terminal hooked directly to alt out.

No charging, Volt gauge shows 12 with nothing on, 10 with lights on.

The write up says blip throttle to charge, but it also says high enough RPM. How high? I didn't have time for a drive, and I didn't want to really rev it in the neighborhood as it was already past 10 when I started it.

Thanks again.
Erik

PS: the large bolt on the rear held a steel bracket/spacer for the alternator mount on mine (81 camaro) It came from a used parts store with this attached. I would have used it for the mounting, but I needed to cut a bit off it, but I really needed a bandsaw to do it correctly.

One last edit=
Looking around, Several other sites say that this method of hookup will require a rev to 3k or so to start charging. Does that sound about right? I did not go that high in my startup test.

And in regards to using the factory wiring, does it make any sence to hook it up directly to the battery and use the factory white wire? More curiosity at this point than anything.
I think it may work, but I don't know.

[TR]

I can only talk about the Subaru alt that I have, but the sensing line from mine goes to a 12V, low amp bulb, the other end to +12V. When I turn my ignition to 'on', the light comes on - the +12V flows through the bulb, through the non-generating coils of the alternator to ground...When I 'start' and the engine is running, the light goes out because the alternator is charging...and the bulb has +12V on each side of it, or zero voltage across.

Do the units you have work the same way? Dunno...TR

[S Allen]

Erik,

I have to blip my throttle to around 2,000 RPM to get it to start charging. TR, we could use a sensing light but it works fine with out it. You only have to blip the throttle if you are sitting after starting at idle. I do not think runnning the wire coming directly from the battery to the alternator when you are using the white wire out of the original charging system will hurt anything. The white wire routes current through the amp gauge and then back to the battery I believe. I wish one of the people that has done a high windshield would chime in and tell me if I am full of -hit because I do not know this to be 100% true. I guess I will take a look at the wiring diagram to see what I can see. You are definitely on the right track.

Steve

[Marky510]

On my '70 and my '68, the big white wire from the alternator goes to the amp guage then back out to the battery terminal on the starter, hence form there back to the battery. So if you have good flow through your amp guage, it should show charging (or not charging). You could leave this hooked up stock and also run directly to the + battery terminal, but probably won't make any difference in the charging ablilities.

Mark

[S Allen]

It is just as Mark says. Power routes through the amp gauge back to the starter and to the battery. You should be fine except for maybe putting an inline fuse in for the power going into the amp gauge. A 30 amp fuse should be plenty of protection for the old wiring.

Steve

[esmeby]

Sucess.
Charging like a dream.
Short version
60A Gm alt from 81 Camaro (I am growing my mullet out again)
69-ish U20 conversion
Alternator mounts to smog mounts,
if you have already moved the alternator to the "cool side", everything you have likely will already work. There is only about a 1mm difference in the alt case between the two.

Alt output is running through factory wiring, protected by a 30A fuse. I have AutoX class this weekend, I will let you know if I start blowing fuses, or melting wires.
#2 wire is hooked directly into output.
#1 wire may be hooked up to a warning light in the future.

Lessons learned.
Apparently the #1 and #2 wire may be in different order. My junkyard alt did not have the markings, and I thought #2 was the top one as Steve said in an earlier post. No charging.
Not knowing this I thought my alt was bad.
Pressed for time, I bought a $35 rebuilt from NAPA, and had them throw in the factory plug. #2 wire was on the bottom, and much heavier. Did a little research to verify this and hooked it up, viola. A charge.

Lights are brighter, shows a slight charge on ammeter. 14 on volt gauge (I have both). Takes just the slightest blip of throttle to begin charging.
Yipee.

Other notes. Tried hooking up both the factory wire, and a wire to battery as per earlier questions. Worked, but ammeter read low (makes sense now).


I will be writing up details and instructions on my site soon (and giving Steve a copy for 311.org) geared towards dummies like me.

This should be painless, but for me, it was not. Next time it will take me less than an hour.

Now, about those pesky oil leaks......

[S Allen]

Erik,

Great! Glad to hear you got the bugs worked out. I guess it goes to show that not all alternators are created equal. Looking forward to the write-up. Roadster on and good luck in the Auto-X class. I am sure you will have much too much fun!

Steve

[esmeby]

All is in and my site as a page on the swap. Running through the factory wiring, I have put in about 120 miles and one AutoX with no problems.

I added a link to my sites main page to the alternator area.
Not my best work, but it may help a novice mechanic with this project.

[S Allen]

So Erik, do I have your permission to grab the alternator stuff from your web site and publish it here on the 311s.org site? It looks good to me.

Steve

[esmeby]

Yessir you sure do.

All I require in return is a U20 timing set.

Just kidding, in case you couldn't tell.

[S Allen]

Erik,

I knew you were either out of your mind or joking about the 2 liter timing set. I bought my whole SR20 setup for what you will pay for that! Not for me that is certain. Any how, I will grab the stuff from your site and post it on the main site. Thanks for sharing. Glad to hear you are having way too much fun auto-xing. Enjoy!

Steve

[S Allen]

Erik and all,

I put your write-up and pictures here http://www.311s.org/tech/electrical/gmalthigh.html
I tweaked on the write-up a bit. Great job and again--thanks for sharing.

Steve