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Polarity of model b

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Dr. Bill

04-08-2003 11:42:34




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I just received a 1952 A-C Model B from my son. It runs on the battery as the charging system is not working. What is the polarity of the ground?
Currently, the ground is negative but I have been told that the correct ground should be positive. If positive ground is correct is the charging system destroyed !!!?????




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steve

04-08-2003 16:12:19




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 Re: polarity of model b in reply to Dr. Bill, 04-08-2003 11:42:34  
generators dont normally "destroy". to test the generator, remove all wires and connect a jumper from the "F" terminal to the frame mounting bolt (ground). start the tractor and then measure the voltage between the "A" and "F" terminals. with no regulator a 6 volt system will put out about 15 volts. a 12 volt system might put out 30 volts. as you can see it might be possible to put a 12 volt regulator on a 6 volt generator and regulate for a 12 volt system. If you have an alternator with an internal regulator and connect it backward, it will be "fried".

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Dr. Bill

04-09-2003 06:44:51




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 Re: Re: polarity of model b in reply to steve, 04-08-2003 16:12:19  
Steve: Thanks again for the reply. The generator has two terminals; both are on the top, by the rear of the unit. The lower terminal has a wire connected to the underside of the regulator. The other terminal has a wire running to the regulator. Which is which????

Dr. Bill



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Ray Barden

04-09-2003 18:34:10




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 Re: Re: Re: polarity of model b in reply to Dr. Bill, 04-09-2003 06:44:51  
To Dr. Bill I have a 1950 Allis Chalmers modelB
My grandfather bought it the same month I was born
It has a 6 volt system with a generator and it is positive ground. It still runs like a top.



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Dr. Bill

04-09-2003 17:50:22




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 Re: Re: Re: polarity of model b in reply to Dr. Bill, 04-09-2003 06:44:51  
Steve: I scraped a little paint and found an "A" on the lower generator terminal. No other markings on the generator. This current system has a regulator mounted on the top (3 terminals) and one terminal on the underside that the "A" terminal has a wire running to it (fourth terminal.) I believe that I will be able to figure the rest out based on your testing recommendations from yesterday.

I have one other question ... Has this reversed polarity hurt the magneto in any way? I have changed the battery cables around to reflect the positive (+) polarity for the ground but I am concerned about the magneto. The tractor seems to start OK since the change.

Thanks again,
Bill

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steve

04-09-2003 18:56:53




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 Re: Re: Re: Re: polarity of model b in reply to Dr. Bill, 04-09-2003 17:50:22  
Bill, you need to check the generator with a volt meter and see if the "A" terminal is + or - when running "F" grounded. IF F is + then you are positive ground. THe tractor did not have a regulator in the beginning, it apparently does now. You need to connect it correctly and it must be designed for + or - ground. Some are both and can be changed by "polarizing" or touching the B and G terminals together after all wires are connected and motor is still off. But first you need to decide if you are going to go + or - ground. I assume by your post you have 6 volt and want + ground like "original".
I will send you a diagram off a D14 which shows a 4 post regulator with 6 volt + system. The 4th post is for power from the key switch.- may not need.

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steve

04-09-2003 15:07:40




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 Re: Re: Re: polarity of model b in reply to Dr. Bill, 04-09-2003 06:44:51  
the terminals on the generator should be marked "F" and "A" for foeld and armature. I can check which is which on mine if needed, but they should be marked under the paint. The F on original tractor went to the light switch which was the current regualtor (resistor). The A terminal went to a cutout relay and the other side of the relay went to the amp meter- then battery. This cutout took the place of the voltage regulator as you know it. It has only one coil inside. IF you have a voltage regulator with 3 or 4 terminals on it, they should be marked with F, G (which is the armature-generator) and B which goes to the battery by way of the amp meter. I can send yo a print of a 6 volt positive ground system, and a drawing of mine which is a 12 volt generator with a voltage regulator, negative ground. If you wnat a alternator, i can supply another drawing.

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Steve in N.J.

04-08-2003 12:29:53




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 Re: polarity of model b in reply to Dr. Bill, 04-08-2003 11:42:34  
Bill, the OEM style electrical system is 6 volt Positive Ground. Now, unless your son has a 12V conversion w/alternator, then it would be a 12V Negative ground. If it's the OEM 6V system, if it wasn't hooked up for to long reversed, it may be okay. If your not sure, ask your son if he changed it over to 12V. We have the correct service parts for either system if you need any, once you find out what you have.....
Steve/B&B Custom Circuits

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