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Allis Chalmers D15 electrical

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David Newman

05-11-2008 15:55:34




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I have inherited a 1962 D15 and was told by my late uncle that the battery was to be hooked up in reverse i.e. ground strap to the positve post and neg. cable to the pos. post. Looking in the operators manual I have found a ref. to a positive ground electrical system. I have never heard of this before and would like to understand the reason for this. Is this the way old tractors are wired because it has a generator instead of an alternator?

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JMS/.MN

05-11-2008 20:19:37




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 Re: Allis Chalmers D15 electrical in reply to David Newman, 05-11-2008 15:55:34  
Many older tractors, cars, trucks, were positive ground- well into the 60s, including Allis-Chalmers. Ground strap went from the positive battery post to the frame, negative went to the electrical system. They used generators to charge the batteries, and they were positive ground generators. You can get generators rewired to run a negative ground system, thus maintaining the "original" look, but having negative ground. Many mfgrs switched to negative ground when they switched to alternators, instead of generators. Yes, with a generator, you need to "polarize" it whenever the battery is disconnected from the system. Polarizing tells those little electron guys, which way to run. Not rocket surgery- simplest explanation is--- touch a jumper wire to any two of the three terminals on the generator cutout momentarily, and if you get a spark- it is polarized. You don"t damage anything if your first two contacts do not spark. Do this with the battery connected, engine off. When you start the engine, it should charge the battery.

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John T

05-12-2008 06:27:13




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 Re: Allis Chalmers D15 electrical in reply to JMS/.MN, 05-11-2008 20:19:37  
Actually theres no need whatsoever (i.e. its simply NOT done/required, they dont have seperate or different Pos or Neg ground generators) to as you stated "rewire" a standard tractor DC Generator to make it charge at either Positive or Negative ground, it will work fine at EITHER Polarity. BUTTTTT TTT for sure there are different configurations required for an alternator (if thats what you meant) to work at Pos or Neg ground as they have polarity sensitive diodes.

As far as Polarizing in order to make the genny work at the tractors polarity (Pos or Neg) all it does is to impart a certain degree of residual magnetism in the soft iron field poles in the correct North/South MAGNETIC Polarity such that she begins to generate electricity in the corresponding correct ELECTRICAL Polarity.

Hope this helps, yall take care now

John T Retired Electrical Engineer

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JMS/.MN

05-12-2008 08:58:12




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 Re: Allis Chalmers D15 electrical in reply to John T, 05-12-2008 06:27:13  
Had one done at a local shop last summer for my AC WF- was the guy talking about a different type of relay, then, if he asked if I wanted it set up for pos or neg? I don"t remember what the original voltage was on the gen- maybe he switched a 6V to 12V for me.



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John T

05-12-2008 09:43:52




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 Re: Allis Chalmers D15 electrical in reply to JMS/.MN, 05-12-2008 08:58:12  
JMS, He may well have been referring to a Cutout Relay or perhaps a Voltage Regulator of which THERE CAN INDEED BE A DIFFERENCE AS YOU REFERRED TO IN POSITIVE VERSUS NEGATIVE GROUNDING !!!!! !!!!! On the later solid state two terminal diode "Cutout Relays" they can work at either Polarity buttttt ttttt t they simply have to be reverse wired if polarity is switched and many have the Pos or Neg directions right on the label and indeed the shop dude would need to know your configuration cuz it wont work if wired in reverse !!

If its a full fledged 3 or 4 terminal Voltage Regulator instead of the 2 wire Cutout Relay, some are labeled for EITHER polarity, some are labeled specifically for Pos or Neg, so again the shop dude needs to know your configuration!!

Its NOT the Generator that matters, they work regardless of polarity if polarized correct as described above, buttttt I certainly agree a Voltage Regulator and/or Cutout Relay can make a difference..... ...

I doubt he converted 6 to 12, that can be done by changing out the gennys Field Coils, but that conversion requires the gennys changes plus the VR plus the ignition system (unless a magneto) so unless you requested it I dont see wwhy that would have taken place?????

Fun discussion, yall take care John T

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Bob

05-12-2008 10:02:34




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 Re: Allis Chalmers D15 electrical in reply to John T, 05-12-2008 09:43:52  
Don't forget to mention that the difference in generator-type voltage regulators between(+) ground and (-) ground is the material the contacts are made from. Some regulators work fine for either ground, some have different materials in the lower and upper contacts having to do with how they "wear" from arcing, and the materials are "swapped" from the top contact to the bottom and vice-versa between (+) and (-) ground units.

A mechanical regulator made for the opposite polarity WILL work, but (supposedly) contact point life will not be as long when used on the polarity opposite what it was designed for.

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John T

05-13-2008 06:39:17




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 Re: Allis Chalmers D15 electrical in reply to Bob, 05-12-2008 10:02:34  
Good point Bob, I agree and maybe thats why the ones labeled for "Pos or Neg" ground might be more expensive due to having to use extra (and that stuffs expensive) contact point coatings versus if intended only for one ground??? Another thing that would affect polarity sensistivity is if they used any sort of suppression diodes in the relay circuitry.

One advantage of retaining the tractors original ground is purchasing electrical parts may be easier or cheaper and youre more likely to get the correct polarity part from aftermarket vendors..... .....

Take care all, I gotta mow grass before more rain

John T

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John T

05-11-2008 18:53:33




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 Re: Allis Chalmers D15 electrical in reply to David Newman, 05-11-2008 15:55:34  
David, Based on some historic literature Ive read (no warranty, just what Ive read) prior to the standardization of the Neg ground system, some (Chrysler and Ford n others) believed corrosion between automotive frame members would be less in the Pos ground system. Many early farm tractors (as well as some autos), especially 6 volt, used Pos ground while the later and some 12 volt models began the conversion to the now standard Neg ground. A Generator can charge at either polarity if polarized while most alternators require Neg ground. If you swap polarity the coil needs to be wired to match the polarty, the ameter leads need corrected, and the genny needs to be polarized.

Best wishes

John T

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Bob

05-11-2008 16:25:00




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 Re: Allis Chalmers D15 electrical in reply to David Newman, 05-11-2008 15:55:34  
For some companies, (+) ground was "convention", and for some, (-) ground was the "norm".

Generators/regulators can be made to function either way, as can alternators.

This has been discussed to death on a variety of Boards, and there is really NO reason, except for "that's how we do it around here" for a company to favor one system over the other.



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