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Old 12-23-2004, 08:59 AM
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3 Wire Altenator Help.

I am going to replace my old externally regulated altenator with a newer 3 wire internally wired altenator. I was checking out Speedway's catalog and found this item. My question is, do I really need this? It looks like this just hooks the sensing wire up to the battery post negating the benefit of the 3 wire system. I also assume that the line from the ignition switch has a diode in it to prevent back feed.

If you're hanging a common internally regulated GM alternator on your ride, you had better cough up the bucks for this problem solver. If you just wire-up the alternator with any old "parts store" plug you will have a nasty little surprise in store for you..the engine won't shut off!


Also, please check my rational here.
-The Batt line goes to the main junction of my electrical system.
-One of the spade terminals goes to the same location as the Batt line to act as the sensing unit. QUESTION: Which terminal is this?
-The other terminal goes to my dash mounted ignition switch. QUESTION: Which terminal, on the ignition switch, do I hook this up to?

Is this correct?

Thanks for your help

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Old 12-23-2004, 09:01 AM
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Guess it would help if I attached the picture.
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Old 12-23-2004, 09:27 AM
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It costs a little more...

You might want to check this out:
http://www.madelectrical.com/catalog/alt-1.shtml

Although the item you referenced will work, the Mad Electrical item is much better - it includes everything you need and has excellent documentation.

The diode is needed for some ignition systems, but not all.

One of the main differences between the cheap kit and Mad Electrics is it includes longer wire so the alternator gets a more realistic sensing voltage based on the voltage drop at a central location a few feet away instead of 6" away. The cheap kits just loop the output back to the bat terminal. The documentation gets into this a lot better than what I can remember. Read this for more info: .http://www.madelectrical.com/electri...esensing.shtml


I can check my ride later today or tomorrow to get the answer to your other questions.
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Old 12-23-2004, 06:30 PM
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66Caprice,
Thanks for the note. I have spent quite a bit of time reading all the forums on MadElectricals website. I have done searches for other postings here. My problem is that people have said one of the terminals goes to the junction and one of the terminals goes to a switched hot. I have not been able to find anyone that says, which terminal it is that goes to those locations. That is, looking at the back of the altenator is it the left or right terminal that goes to the switched hot?

Thanks again. I have tried to do my homework on this, but I just can't seem to find the answer.
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Old 12-23-2004, 07:25 PM
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One large wire says Batt and your plug will have two wires, a red and a white(in your case yellow). The white goes to the warning light in the dash(is not required) and the red wire is looped back onto the Batt terminal. The stories of run on after KO is bologna unless you have an electrical fan, in which case the problem is not in the charging system anyways.

So:
Small red> Batt terminal

Batt Terminal> Battery

White wire> dash warning light.
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Old 12-23-2004, 08:45 PM
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WONDERFUL!

Thanks NXS!
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Old 12-23-2004, 09:31 PM
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Thumbs up

Anytime!
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Old 12-24-2004, 07:14 AM
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Quote:
Originally posted by NXS
One large wire says Batt and your plug will have two wires, a red and a white(in your case yellow). The white goes to the warning light in the dash(is not required) and the red wire is looped back onto the Batt terminal. .
[color=yellow]Although the above will work, it's not the right way to do it.[/color]


Quote:
Originally posted by NXS
The stories of run on after KO is bologna unless you have an electrical fan, in which case the problem is not in the charging system anyways.
[color=red][size=4]This is just plain wrong.[/color][/size]


First, for reference when looking at the alternator from the back the left terminal (the #1 terminal) is where the alternator exciter wire goes. This wire should go to either a warning light in the dash or if you don't have one to a 12 volt power source that is on when the ignition switch is turned on. This wire MUST have a diode installed to allow the engine to shut off if it's not wired to a warning light. A diode must also be installed if you're using an aftermarket ignition system. Also if a diode is required since it's a one way "valve" so to speak it must be installed with the stripe toward the alternator for it to function properly.

Second, the wire to the right on the two wire terminal (the #2 terminal) is the voltage sensing wire for the internal regulator. If you loop this back to the BATT terminal you are in essence bypassing the remote voltage sensing capabilities of the three wire alternator. Although it will work this way, you might just as well install a one wire alternator for what good it does you. You need to run this wire to a remote location like the BATT terminal on your starter. This will allow the system to sense the voltage the system is actually running. When you simply loop it back to the BATT terminal on the alternator it just senses the voltage the alternator is putting out and not what the system is actually running. The internal regulator can't provide the proper voltage if it is always thinking that the system is fully charged which is what happens if this wire is looped to the BATT terminal. By running the wire to a remote location the regulator can sense what the system needs and the alternator will then put out the proper voltage to keep your system fully charged.

Centerline
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Old 12-24-2004, 07:52 AM
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Centerline,

i am most certainly correct. If it is wired exactly as I wrote there will be no problems presented. As YOU wire it back into a hot wire it will send voltage back...but why? What is the point for running the warning light wire BACK into +voltage?
Quote:
This wire MUST have a diode installed to allow the engine to shut off if it's not wired to a warning light.
[color=red][size=4]This is just plain wrong.[/color][/size]
That wire does not even need to be hooked up. So wire it into either a light OR don't hook it up at all.


Quote:
You need to run this wire to a remote location like the BATT terminal on your starter. This will allow the system to sense the voltage the system is actually running.
You can do that but the voltage will be virtually the same in either place and it just clutters the engine compartment. Are you trying to confuse the guy or sell your one wire alternators?
==========================================

http://www.oldengine.org/unfaq/10si.htm

I want to know why you would run the warning wire back into +voltage with no light. If the alternator "dies" you will provide a short to ground.

Last edited by NXS; 12-24-2004 at 08:39 AM.
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Old 12-24-2004, 08:06 AM
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Thanks Centerline for your post.

I would assume that the idiot light is put in series with the 12v switched source. Would a LED with appropriate resistor work?
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Old 12-24-2004, 03:18 PM
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Quote:
Originally posted by NXS
Centerline,

i am most certainly correct. If it is wired exactly as I wrote there will be no problems presented. As YOU wire it back into a hot wire it will send voltage back...but why? What is the point for running the warning light wire BACK into +voltage?.......That wire does not even need to be hooked up. So wire it into either a light OR don't hook it up at all.
The wire is run back to an idiot light or a 12 volt source because that's the way it was designed. The three wire alternator has three wires for a reason. The exciter wire provides a signal to the alternator which turns the internal regulator ON. Although it will work the way you have suggested, you are not taking full advantage of the internal regulator or the alternator's ability to keep your system charged.


Quote:
Originally posted by NXS
You can do that but the voltage will be virtually the same in either place and it just clutters the engine compartment. Are you trying to confuse the guy or sell your one wire alternators?
This is not true. If hooked to the BATT terminal on the alternator the regulator will only sense the output of the alternator. The regulator will not be able to tell if the system is running below 12 volts. If hooked to a remote source it will be able to sense the voltage at that location which will be in most cases something less than 12 volts. This will be a much more accurate reading and it will allow the regulator to modify the alternator's output so it can provide more than 12 volts when the system needs it.

As an example, when you have the AC, lights, heater, and wipers on the system requires more than 12 volts from the alternator to keep up with the demands of all the accessories. Without remote sensing the alternator will be putting out 12 volts (because that's what the regulator is sensing) and this will not be enough to keep up with system requirements. With remote sensing the regulator will read the drop in voltage due to draw of all the accessories and will modify the alternator's output to compensate. This is much better than making the system draw the extra current from the battery which is exactly what will happen if the voltage sensing wire is hooked to the alternator's BATT terminal.


Quote:
Originally posted by NXS
I want to know why you would run the warning wire back into +voltage with no light. If the alternator "dies" you will provide a short to ground.
To begin with, it's not really a warning wire and because that's the way it was designed. Again it's a three wire system that is designed to have all three wires utilized in order to perform up to its potential. The exciter wire is required because it provides the signal which turns the internal voltage regulator ON. When it comes to warning the driver if the alternator quits, when there's no idiot light in the system (from the factory) then there is a gage for the driver to monitor the systems performance.

Like I said before the system will work your way (providing the vehicle is using a factory ignition system) but it won't perform up to its potential unless it's hooked up correctly. When wired your way the system is functioning the same as if it was a one wire alternator which is not adequate for a vehicle with a lot of accessories.

Centerline
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Old 12-24-2004, 06:52 PM
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I would assume that the idiot light is put in series with the 12v switched source. Would a LED with appropriate resistor work?
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Old 12-24-2004, 07:42 PM
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Yes.
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