Alternator issue

David G · Apr 7, 2017

I just got this tractor running after 20 years, so have no history on it, the alternator charges but the light does not go out.

I am posting a picture.

Thanks,

Janicholson · Apr 7, 2017

One of those terminals (inner I think "L") is the same as the #1 terminal on a Delco, it attaches to ignition voltage through a marker light or diode or 10 ohm resistor. All of these prevent the ignition from getting enough current from the alternator (from that terminal) to stay running when shut off.
The outer terminal "S" senses battery voltage. it can be attached to the output terminal (Big stud) or most correctly, to the Pos battery terminal. The second way "measures" actual battery volts more carefully. Jim

David G · Apr 7, 2017

I have it hooked up that way, works fine, so how does light stay on?

Janicholson · Apr 7, 2017

If the system is working as it should, the regulator in the Hitachi acts as follows:
When the key is turned on, the ignition voltage goes to the L terminal through (small light, 10 ohm resistor, or Diode. This voltage is sensed as excite voltage and causes the field to turn on. The voltage going to the regulator is sufficient to light the light bright because the regulator acts as a ground in this condition. As the engine starts, the Hitachi (through the regulator) supplies charging voltage to that terminal. The bulb now has full voltage on both sides of the bulb, and it goes out because there is no ground. If the regulator fails, or the brushes on the rotor fail, or it is wired wrong, the light can be flickering, on steady but dim, or bright. If the source to ignition is on the coil side of the ballast resistor it can stay lit as well. Does this help? Jim

Bob · Apr 7, 2017

"If the regulator fails, or the brushes on the rotor fail, or it is wired wrong, the light can be flickering, on steady but dim, or bright."

Jim, might as well add a shorted or open phase winding or a shorted or open rectifier diode to that list. Under certain circumstances the alternator may even charge at reduced current under those circumstances.

James Howell · Apr 8, 2017

Thanks for the description.

RodinNS · Apr 8, 2017

I think.... but I'm not directly familiar with that alt... but I think it's basically the same as the Delco 10si.
What I would do is get an ohmmeter... and pull those two wires from the plug connector. One of them should be the indicator terminal and the other should be the reference voltage terminal. So the reference terminal I think will not show you resistance when you measure it against ground. The indicator light terminal will. Or you could just flip the wires on the terminals and see what happens...
What I'm thinking is that the wires are reversed... and it will charge, and charge quite hard the way it is right now.
Otherwise you probably have a fault somewhere in your indicator wire circuit.

Rod

Alternator issue

David G

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Janicholson

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David G

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Janicholson

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Bob

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James Howell

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RodinNS

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