4020 Excite Resistor

Mike in Nebraska · Dec 21, 2012

My 67 4020 that i converted to 12v has never started charging until full throttle. At idle the light will come back on. I read somewhere about putting a resistor in parallel with the light but can't remember the correct resistor. (I wrote it down but can't find the note) I believe it was a 10 ohm? I have tried several different alternators with the same result, so I know thats not it. Thanks

oldtanker · Dec 21, 2012

Mike need more info. What alternator? If it's a GM one wire you need a different pully to overdrive the alternator. I think they are available on this site. If it's a GM SI10 is it wired right? But you have me guessing here. I don't know what you used as an alternator. It came fromthe factory with a Motorola alternator and 12 volt system so just what did you convert?

Rick

LarrySTN · Dec 21, 2012

Mike, it would be helpful to know what alternator you used. My experience is that when
the alternator needs lots of rpms to start charging something isn't right with the alternator. If it were a one wire alternator that would be cloce to normal but since you are using the charge indicator light I know it's not a one wire. And for Rick below the 67 4020's came 24 volt with a generator not an alternator.

John T · Dec 21, 2012

What did you do, convert a diesel from 24 to 12 volts or what??????? What alternator you have??? You at 12 volts Neg ground now???

Unlike in a gas engine where an idiot light or resistor or diode is used to prevent ignition feedback and run on when ignition is off, such isnt obviously a concern in a diesel.

In the gas conversion some used a resistor in paralell with the idiot light so the alternator could still be excited even when the light burned out.

If its a 10SI family of 3 wire alternators it needs excitation current and an incandescent idiot light or a 10 ohm resistor either one would allow enough current to flow HOWEVER if it was an LED lamp its resistance may be too high and theres insufficient excitation current!!

If its a 10SI 3 wire and the idiot light is an LED you might try a 10 ohm resistor instead.

Not knowing what you have or what was done I just cant whats the problem or how to cure it.

John T

Mike in Nebraska · Dec 21, 2012

Its a 67 so it was 24v. It was converted with a Deere kit. It is a Delco 10SI three wire. I've tried alternators off of other tractors and the problem stays with this tractor.

Heat Houser · Dec 21, 2012

Delco 10SI
Batt to switch to one leg of the charge light. The other leg of the charge light to Pin 1 on the alternator. This circuit needs to be switched for if not, your light will always burn as it is grounded thru R5 in the regulator. This will drain your battery.

When charging
Alternator output from the diode trio is fed into the circuit between the light and R5. This output is more than R5 can dissipate so voltage rises. Via pin one and the wiring, as this voltage rises, it finally becomes equal to battery voltage. Once this occurs, you have equal voltage on both sides of the light and it goes out. Equal voltages means no electron flow.

BTW, once the alternator starts to produce, it becomes self exciting via the diode trio.

Take a digital volt meter and watch if battery voltage steadly climbs after starting. It will bump up by a tenth of a volt or so as the batt is recharged. It should finally settle out at the regulator's voltage setting as it becomes fully charged. If it does this, you have a wiring problem, not an alternator problem.

Heat Houser · Dec 21, 2012

BTW, you need batt voltage in on pin 2 as this is where the zeiner diode gets its signal from. The ZD controls the base of transistor 2 and transistor 2 controls the base of transistor 1. Transistor 1 controls the field circuit. Diode trio, to brush, to slip ring, to field coil, to other slip ring, to transistor 1, to ground.

oldtanker · Dec 22, 2012

(quoted from post at 06:33:44 12/21/12) Mike, it would be helpful to know what alternator you used. My experience is that when
the alternator needs lots of rpms to start charging something isn't right with the alternator. If it were a one wire alternator that would be cloce to normal but since you are using the charge indicator light I know it's not a one wire. And for Rick below the 67 4020's came 24 volt with a generator not an alternator.

OK the only info availble to me on JD is from this site and tractordata. Tractordata says the the gassers used one battery and I was guessing that the diesels were 24 and the gas 12.

Learn something every day.

Rick

4020 Excite Resistor

Mike in Nebraska

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oldtanker

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LarrySTN

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John T

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Mike in Nebraska

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Heat Houser

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Heat Houser

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oldtanker

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