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John Deere Tractors Discussion Forum
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Re: 4020 Excite Resistor

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Author  [Modern View]

12-21-2012 04:30:13

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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?


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Mike in Nebraska

12-21-2012 06:12:15

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 Re: 4020 Excite Resistor in reply to oldtanker, 12-21-2012 04:30:13  
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.

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Heat Houser

12-21-2012 14:38:01

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 Re: 4020 Excite Resistor in reply to Mike in Nebraska, 12-21-2012 06:12:15  
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.

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Heat Houser

12-21-2012 14:46:54

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 Re: 4020 Excite Resistor in reply to Heat Houser, 12-21-2012 14:38:01  
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.

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