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Old 01-13-2014, 05:12 AM
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Default GM 3 Wire Alternator

I put a GM 3 wire internal regulator alternator on my Kubota and am having some problems getting it to charge and use the idiot light. I have no problems using it without the light.
It is hooked up like the first diagram. Light will stay on, alternator is not charging. If I momentarily give the sense terminal 12v it will charge and keep charging. My thought is the bulb has too much resistance and can not break the threshold to start charging but once it does its fine.
The second diagram shows a similar system with a resistor added to prevent this(and charge with a blown bulb). I cannot find the value of the resistor or a minimum resistance to start charging.
I have found a lot of references to using a diode, but since this is a diesel I really don't have to worry about electrical run-on
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Old 01-13-2014, 07:48 AM
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Sounds like your field and sense wires are reversed (1 & 2).
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Old 01-13-2014, 07:50 AM
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I always used a diode when hooking a alt like that to prevent feedback when the key is off, Wouldn't using a diode instead of a resistor in the second drawing work?
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Old 01-13-2014, 09:41 AM
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Quote:
Originally Posted by Walker View Post
Sounds like your field and sense wires are reversed (1 & 2).
2 is to +12v, 1 is to the switched +12v
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Old 01-13-2014, 10:09 AM
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I have used a lot of them in there various ratings and configurations. The pick up rpm where they starts to charge seems to vary a little with the selected ampere rating in a given frame.

The test is to rev the engine to 15-1800 rpm if the alternator starts charging the wiring is fine and the pulley needs to be smaller.

These alternators are designed to run at 6000 + rpm all day long in cars that run 2000 - 2500 rpm at 60 mph in top gear and 5500 at red line with a 3:1 pulley ratio driving the alternator.
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Old 01-13-2014, 11:15 AM
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I think I seen the light/resistor setup in a Nova.
Looks looks they used a resistance wire (Ni- chrome Wire), not a resistor.


10-SI Delcotron.
Series 100

I'll keep looking, the book I have uses a 10 ohm 6 watt resistor for bench testing no idiot light shown.
I cant say if that is the value used in the car with the light.

whatever you do also measure the charging amps with an amp clamp, that is just in case the resistor sets the charge current/rpm ratio.

Edit: Fig 5,
http://vintage.mitchell1.com/PClubDa...2/V2823012.pdf

http://library.worldtracker.org/Coll.../Chapter08.pdf
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Last edited by GWIZ; 01-13-2014 at 11:56 AM.
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Old 01-13-2014, 05:11 PM
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The two wires are first the reference sensing that connects to the point at which the voltage will be regulated.
The second wire is the start excitation injection point It feeds current from the battery to the junction of the internal biode trio and the field hi side. The field low side is connected to the regulator pass element and a test grounding pin visible through the D shaped hole beside the rear bearing housing.
Once the alternator starts the diode trio puts the same voltge as is on the output terminal on the injection point. This puts the same voltage on both sides of the light and it goes out.
Should the alternator fail to start the light remains on or comes on if the alternator fails or the fan belt breaks .
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Old 01-14-2014, 11:51 AM
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Quote:
Originally Posted by Cavalry View Post

If I momentarily give the sense terminal 12v it will charge and keep charging.
All alternators need a voltage to get started, then they can use the generated voltage in place of that.

What you are saying, the #2 wire is not getting any power from the battery.

Why is #2 "not" getting voltage when your drawing shows it connected to a 12 volt supply ?
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Old 01-14-2014, 01:29 PM
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Smile Alternator Handbook..

Cav

this handbook should give you enough on proper wiring of that 3 wire ...
even thoughis likely a lot more info than you are looking for at the moment..

But you might find it useful..

http://kb-kbh.dk/shipslib/el_ombord/...ndbook_ocr.pdf

120 page PDF handbook with a lot of good practical installation info .. as well as reference

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Last edited by H80N; 01-14-2014 at 08:20 PM.
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