Re: GM 1-wire VS GM 3-wire???

Posted by Bob on December 29, 2006 at 17:16:17 from (69.178.229.154):

In Reply to: GM 1-wire VS GM 3-wire??? posted by City-Boy McCoy on December 29, 2006 at 16:51:45:

CBM,

You HAVE a great alternator NOW, the standard "3-wire" Delco unit.

The alternator's #2 "voltage sense" terminal AND it's large output stud CAN have battery voltage to them, even with the tractor shut down, but the #1 terminal CANNOT have voltage to it with the engine shut down, or the battery will be drained.

IF your setup DOES shutdown the voltage to the alternator's #1 "switched excite" terminal when the engine is stopped AND the alternator is causing the battery to drain while the engine is "OFF", you have a bad diode in the alternator, or a bad internal voltage regulator, probably damaged because you did NOT have an "idiot light", diode, or resistor in the lead to the alternator's #1 terminal.

Running WITHOUT a lamp, resistor, or diode in that lead is a CERTAIN recipe for alternator failure, sooner or later.

The reason WHY is shown in these 2 diagrams, if you care to take a look at them:

My suggestion... Check to see if the #1 terminal is actually powered down with the engine shut off.

If so, try completely disconnecting the alternator overnight (tape up the wires for safety), an verify that the battery stays up. If so, you have proven the alternator is draining the battery.

Have it repaired, or replace it, and use the "idiot light", diode, or resistor method of protecting the voltage regulator and diode trio, and you'll be in good shape.

WHY replace it with a goofy "one-wire" unit that needs to have the engine "revved" to make it excite????

MAD Electrical has LOTS of information on their sire, linked below.

One thing you will notice there is that they suggest taking a wire from the #2 "voltage sense" terminal all the way to the (+) battery cable. That is a GOOD idea, especially on a car, with a more complex electrical system, and can be done on a tractor, too, but is NOT necessary on these simpler systems, unless you want to take the extra trouble.

Also, for the systems they are concerned with, IIRC, they always use an "idiot light". However, rest assured the "idiot light", the diode, or the 10 Ohm, 20 Watt resistor may ALL be directly substituted for each other in the "switched excite" circuit.

GOOD LUCK!

• Get MAD

Replies:

• Thanks, Guys! City-Boy McCoy 18:13:01 12/29/06 (0)

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