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3 Wire Alternator

9K views 21 replies 7 participants last post by  rdobbs77 
#1 ·
I'm active on one other forum, and posted a question about a 3 wire alternator's wiring, but am not having luck or am not understanding so thought I'd post it here. I've attached a pic of a diagram I drew out and was curious to know if my wiring is acceptable for this alternator? This is not a car. Alternator is on a 350 that I have on my homemade test stand.


Backstory: I recently disassembled the pushbutton/toggle switch set up and installed a turn key/fuse block set up. Biggest thing I noticed was that on Sunday, I routed the Term 2 wire onto the battery post of the alternator. Turned the motor on and idiot light came stayed on (at that time I had it routed to IGN of fuseblock and not IGN post on turn key). Yesterday I go to tinker with it more and found the battery dead! Charged it up enough to start, did not hook up Term 2 and ran idiot light to IGN post on turnkey. Light did not come on which was good. However, I'd like to hook up the Term 2 wire. So on what I drew out, should the Term 2 wire be 'spliced' into the alternator battery wire? I will note I tried running Term 2 wire to 'an always hot terminal' on the fuse block and my volts seemed to drain, which did not make sense...
 

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#2 ·
Man, it's been a long time since I played with GM alternators but I believe you need the #1 terminal (field) connected to the accessory side of the switch to prevent feedback to the ignition.
The #2 terminal is the sensing terminal and it should be connected to the load (battery positive post). If my memory is right you can leave it disconnected as long as it is for the engine stand but it can be connected to the alternator "battery terminal" too. Remember to have a good ground from the alternator to the battery negative.
Use a test light between the disconnected alternators "battery" post and the wire that connects to it. If the light is on with the engine off then you have shorted diodes.
 
#4 ·
Yeah I drew that diagram this morning and thought I'd try it out when I get home. Thanks for taking the time to look at it to let me know if it looked right or not:) This alternator only has the two exciter terminals and batt post. I don't have an external regulator mounted anywhere so thought this was the way to go, would that logic make sense? Thanks Joe
 
#7 ·
Thanks Joe. It looks like I've got the internal reg alt by looking at the location of the tabs. I'll rewire this anoon based on the diagram if I have time and see what happens. Since I don't run the motor often, I know I've got less than 12V at battery right now but figure I've got enough to start it. Should be able to put my Volt meter on battery before I start and meter on there after its running to see if I've gained a Volt or two and know if the alt working.


Out of curiosity, if I wanted to run it as a one wire alt, I could simply not use either of the two exciter terminals, correct?
 
#8 · (Edited)
Ok Joe, EOD Guy, and forum members need help. Had time this afternoon and wired it according to this diagram I have posted. Here were my results and observations:

Note: Battery was not fully charged, had charger on it for a few hours. When Disconnected Charger:
1. At rest, Multi meter showed 11.74 volts. Interestingly, Volt guage showed around 9.3 volts. ???

2. Start the motor and its running (only ran it for about 3 minutes): Idiot light stays on. Multi meter shows 13.40 volts. Volt guage shows around 10.3 volts. So, I figure alternator must be doing its job because I've got a rise in Volts regardless of the device I use to test the volts with. Just don't know why guage and multi meter show different readings??!!

3. Shut the motor off. Alternator EXTREMELY HOT, you could fry eggs on it. I figure, I've got the exciter wires crossed. I don't. Exciter 2 going to battery, Exciter 1 to the idiot light.

4. With motor still shut off, i put multimeter on there. It shows 11.7 Volts and progressively goes down every few minutes, like 11.70V, two minutes later 11.69V, etc. So i disconnect main alternator wire from battery. I disconnect Exciter wire 2 from the battery and put the Multimeter on there. It shows 11.76 Volts and held there everytime I checked it.

This is a test motor on an engine stand, not a car. I only have a simple 5 fuse fuseblock of which one of the fuses I'm not even using. I will note that I do not have the Alternator grounded as I did not think it necessary since i dont run the motor very often and its just a test motor, but I need some advice to tell me where I'm going wrong. Thanks for reading!!:D
 

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#9 ·
Not an electrical guru, but doesn't the idiot light need to go to ground? The idea being that it creates enough draw to generate the magnetic field to get the alternator to charge?

Another item, why not use a CS130? More amps, if needed, and less parasitic draw when less amps are needed. Couple that with they are dirt cheap and I cannot see a good reason not to use one.

The alternator being too hot is a dilemma - something is not correct.
 
#10 ·
Alt getting hot after shut down and the constant drain on the battery indicates a mis-wire or a bad alt.

I included a basic alt wiring diagram, a terminal pic etc....

Your #1 terminal (idiot light) should go to the accy side of the ing switch not the run side.

#2 terminal can go straight to the battery pos post or the starter lug where the pos cable hooks to

You must hook the #2 terminal (not the #2) to make a 1-wire alt, but why would you want to?

The idiot light get power from the ign switch on one side and the other side of the idiot light goes to the #1 terminal on the alt (power on both sides of the light. How it works..... when you turn the key on, the idiot light gets pwr from the ign switch, the other side of the light is connected to the #1 terminal on the alt and is grounded by the internal regulator.....light lights. When you start the engine, the ground is removed from the internal reg and the light goes out because of the lack of a ground, juice flows through the bulb filament and excites the alt field and the alt starts producing juice. The #2 terminal is the sense wire and tells the alt how much juice to produce, dependent on the demands of the electrical system.

Hope this helps
 

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#11 ·
I'm definitely getting more of an education with alternators than I'd like:) My current guesses as to why its getting hot and fast is: 1. since there was not a full 12volt at battery the alternator was working hard. 2. the alternator is bad, maybe diodes inside it no good. I have read these things can get hot fast but what's funny is i have virtually no load on it other than a 1000 rpm idle and the battery which again, was not a full 12v. i might just take alternator into a parts store on Friday and see if they can test it, would assume they can. At least that be one more thing to rule out.

Other than originally hooking my igit light to IGN instead of ACC, I'd say the wiring looks to be in order. Guess i'm going to have to tinker with this thing some more:(
 
#12 ·
print and learn to perform this test.

http://i.imgur.com/Mo57rdb.jpg linked to make it pop up full screen..







have a look at how GM wired up the 10SI alternator in the early 80s..

http://i.imgur.com/U8qP580.jpg linked to print full screen.



the brown wire goes to a 194 bulb and then to the IGN1 or ACC position on the ignition switch..


if you note.. the output of the threaded stud goes thru a 14 gauge fusible link at the starter.. but the red wire that plugs into the side of the alternator (Sense wire) also goes thru a 14 gauge fusible link..

be sure to read the top of the page.. the Dashed line goes to the Head light switch... and a few fuses.. the solid red line goes to the ignition switch B1 and B3 positions.. also to some fuses..

i am not saying you need to wire your alternator like this.. but gm did it and if you pass the voltage drop tests.. especially 1 thru 4 and 6.. 5 would go to the threaded studs usually found on the firewall of gm trucks.
 
#13 ·
It's on an engine stand, doubt he'll have much use for the voltage drop tests.

Looks like I had fat fingers (again) ....lol..... To turn a 3 wire into a 1 wire..... run a jumper from the #2 terminal (not the #1) to the charge lug on the rear of the alt, but again why?
 
#15 · (Edited)
The question about the one wire rig up was a side question. I've got a drag car that is almost built and should see its first fire up in a few weeks. I wanted to run a one wire alternator for it. So just so I understand, your saying I can simply run a wire from Terminal 2 spade right to the alternator lug (no splicing), correct? Also, what if I don't run anything from the spade, on a one wire set up, and simply have the alternator main lug wire running direct to 12V--would it matter
 
#16 ·
Converting an SI-series alternator to a one-wire configuration requires changing the voltage regulator to one designed for that application. Simply running a wire to the BATT post with a conventional three-wire regulator will not do this. Now, the CS130 alternators have this function built in and can be run as a one-wire with no issues.
 
#18 · (Edited)
I know I've got us switching gears from the alternator on the test stand, to a different alternator I'll be using for racing. The one I've got on my race motor is from Summit: part no SUM-810344. Its a 140AMP internal reg alt and states its one wire or 3 wire capable. So with that being said on this particular alternator, I'd just need to run the one wire from alt lug to 12v and not use either of the exciter terms, correc? Just trying to understand thanks:)
 
#20 ·
Exactly right. #1 does not require a bulb as it just needs to see voltage above a certain level to turn on.
#2 is for voltage sensing.
A 10 or 12si will work with a jumper from the battery stud to the other 2 terminals in a pinch, not recommended for long term.

My guess is you have some sort of internal short that is both heating up the alternator and drawing down the battery.
 
#21 ·
I checked parasitc draw on my 'test stand motor.' Found Parasitic draw with the alternator's Exciter 2 wire hooked at the battery. So I took the alternator off and took it a part. Set the multimeter to 'diode' setting and ran the tests. They all came back at readings of around 500 which to my knowledge is what they're supposed to come out to. For kicks, switched multimeter to test for OHMs. Ran the tests, and one diode refused to register any OHMs on one particular test. Bad diode here? thanks,
 
#22 ·
As luck would have it, I had another alternator in my shop. hooked wires up, tested for parasitic draw, and encountered NONE.:) Tmrow, will install it, with idiot light and all, and see what happens. So far, things are looking good but will know more tmrow,
 
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