Tractor generator question

I'm always messin around with stuff and most of the time it works like I think it should, but this one isn't. Here's the deal, I have an old tractor that was 6 volt + ground converted to 12 volt - ground and using the 6 volt generator to charge the battery. Have a relay hooked up to carry juice from the arm terminal to the ammeter, energized by the key and a oil pressure switch for ground, that works great to break the circuit when engine is off. I have a light switch from a WD with the resistor hooked to the field terminal so that it won't charge too hard, the problem is it charges full bore, even with the field terminal unhooked. It's a two brush autolite generator 6 volt 14 amp. Hooked on 12 volt it charges 28 amps at about half throttle, I was thinking it would charge about 8 to 10 through the resistor and be good enough. I have continuity from the arm terminal to case and also to the field to arm and the case, What gives?? or am I trying to do the impossible.Thanks for your thoughts, I know I should put an alt on it, I'm just messing around.

Some Autolite generators may have been B circuit types. Those require voltage to the field, and the field windings are internally grounded. Most are A circuit and have voltage connected to the field internally and the field windings are grounded externally to make them charge. Assuming yours is an A style system, it has a internal short to ground from the field windings to the case. If it is eliminating some of the windings, it can produce dramatic field current, and output with no control. Seems like what you have. Jim

You are headed for a blown up battery.A 55 chevy exploded 2 12 volt batteries when a 6 volt generator was put on by mistake.I got a reading of 60 amps at fast idle.

GREAT possible catch by my friend Jim there, when I read your words AUTOLITE I also wondered if it may be a Class B Genny???

Some Fords used the Class B system while most other old tractors used Class A Delco systems. AND THE VOLTAGE REGULATORS AND CHARGE REGULATION CIRCUITS ARE DIFFERENT !!!!!!!!!!!

Okay ifffffffffff it a Class A Genny (may NOT be since its Autolite) and she full charges allllllll the time even if theres no connection to FLD post its possible the post nut got overtightened (broke insulting pass through) and is shorted to case frame ground. That would make them alwaysssssssssss full bore max charge!!!!

Buttttttttt if its a Class B genny the other end of the internal field coils (NOT end where post is) is dead grounded to case frame so full voltage on the post makes them full bore max charge.

Sooooooo to lower the charge if its a Class B the current limiting resistor like light switch controllers use must be between the hot voltage source and the gennys FLD post. Its max charge if full voltage on on FLD but its less if theres a resistor between hot voltage source and the gennys FLD post.

One you determine if you have an A or B genny its not rocket science to reduce the charge rate, it just depends on how/where the resistor is placed. On an A it between FLD posy and ground,,,,,,,,,if a B its between hot voltage source and FLD post.

Got it???????

John T

Nice possible catch., Autolite caught my attention also, I think some Fords (but AFTER 8N) and some Massey Harris used Class B??

John T

Thank you John T and Jim, It's on a Massey 44, so your saying I might need to run 12 volt + through the resistor to the field terminal to get what I'm looking for, I will try that. I have a barrel full of Autolite generators off Masseys and they all have continuity between all posts and case, so does this one. I learned something new, thanks again.

Ima thinkin (no warranty) some of those old Masseys were indeed Class B systems, maybe Jin knows??

If it is Class B the other end of the field is grounded to the case frame so to lower the charge rate you put a power resistor (3 ohms at maybe 25 watts???) between hot 6 volts and the external FLD post as it reduces field current.

John T (hope Jim weighs in here also)

(quoted from post at 09:12:28 04/04/12) Thank you John T and Jim, It's on a Massey 44, so your saying I might need to run 12 volt + through the resistor to the field terminal to get what I'm looking for, I will try that. I have a barrel full of Autolite generators off Masseys and they all have continuity between all posts and case, so does this one. I learned something new, thanks again.

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ontinuity between all posts & case does NOT tell you whether it id type "A" or type "B".

I cannot tell from here, but if you put a piece of plastic sheet under all brushes, and disconnect all wire at the terminals, a B series will have grounded firld terminal with less than 6 ohms.
an A circuit will be open to ground, and conductive to the third brush (if 3) or conductive to the Arm terminal if 2 brush.
If the field is shorted to ground, all terminals will show connection to ground when the brushes are Up on an A type. Jim