300 12v conversion

Hi, does anyone know the best way to convert a Farmall 300 from 6vdc to 12vdc? Are the original starter and points and condensor still useable? Also the voltage regulator? If the 12v alternator has a built in reg. can the original be eliminated? Thanks

Sure. The issue is extremely well covered. Below are the diagrams to do it and more. The use of an idiot light is a good idea with a marker lamp as the bulb. Do not use a LED for the bulb, it needs to pass current for excitation. The use of a Hitachi Alternator from a Mid 1980s Nissan is easier and smaller to mount. JimN
Bob M s fantastic solutions to wiring farmalls.

I will ad to the post above that the use of what is called a one wire SI10 Delco system is not recommended Some of them work, some require high engine speed to excite, and some drain the battery when not being used. Collectively the folks on this board are probably 90/10 on the one wire system. JimN

"Are the original starter and points and condensor still useable?"

YES, the points are more of a current switch and their and the condensors voltage withstand rsting is wayyyyyyyyyy higher then 6 or 12 volts anwyay.....The starter will work as is although it can be tougher on starter drives and I wouldnt let it crank a longggggggg time

Also the voltage regulator?

NO, If you use a generator, it and the new Voltage Regulator need to be 12 volt

If the 12v alternator has a built in reg. can the original be eliminated

YES If you go with an internally regulated Alternator, the old Voltage Regulator IS NOT USED

NOTE Most alternators require Negative ground so in cases where you have to convert from Pos to Neg ground (not sure on the 300, if 6 volters were Pos or Neg) the ammeter leads need swapped so it dont read bass ackwards and the coil leads need swapped so + gets switched ignition voltage and - leads to distributor. HOWEVER if shes already at Neg ground none of that needs done

Jim n Bobs diagrams ought to cover the rest

John T

Yo Jim, a friend sells the 3 wire to 1 wire adapter plugs for the Delco 10 SI that fit on the lil No 1 and No 2 terminals and all it does is use a 147 ohm resistor from the hot terminal to the lil No 1 for excitation and of course, jumps the hot to the No 2 for voltage sensing. They excite fine but there is a small current draw (12/147)through that resistor when the tractor sits.......I still prefer a 10 SI excited via the coil/ignition with a series 10 to 50 ohm current limiting resistor or an idiot light versus only the diode

FWIW John T

My best take is that Delco's engineers made it such that it would operate as designed, Idiot light etc. I also believe in putting a Fuse link of appropriate size in the main feed from the Pos bat cable to limit smoke emissions. JimN

THANKS, the tractor is a pos. ground so I will switch ammeter and coil voltage. I am also taking for granted that a Delco SI 10 alternator is pretty easy to come by. I did scan the diagrams in the link you guys sent and was not able to find a 300. I am sure the wiring on a 300 is a little more complex than an H or an M but should be "basically" similar. I just picked up the tractor yesterday as a non-runner and figured now is the time to switch it as if it is 12v I can run my sprayer off it instead of a aux. battery. I got the head off and to the machine shop already this morning so now the wiring starts. THANKS

The 10SI is indeed "easy to come by". It was used in virtually every GM car and light truck from the mid-70's through the late 80's.

Regarding the 300 wiring you are correct - it is only a little more complex than an H/M. The most significant difference is the 300 has a key ignition/start switch - thus the addition of a solenoid to the starter circuit.

Thanks, i did notice the solenoid attached to the starter when removing it. I have been looking more closely at this tractor and am wondering if I should leave it original as it is pretty nice the more I clean it.

maybe your charging issue is merely the regulator, generator brushes, a broken wire, or the need to be polarized. your generator and regulator can be tested by a competent repair shop that specializes in rotating electrical for auto/industry. Usually a ma and pa type operation.

If you want 12v and original look, have 12v field coils put in the generator (or find a 12v generator of similar design), and use a 12v regulator.

karl f

If the electrics in good shape and properly maintained your 300 will start/run very reliably on the stock 6 volt system.

So unless your tractor is gonna be a daily worker I'd lean toward leaving it original!

Well, now I am really going to have to think...My generator is stuck tight so it will be dropped off at the repair shop this week. I guess I will know about regulator after I get gen. back, usually 2-3 days with this shop. I know of no way to check regulator except gen. running. As this will not run everyday I am torn as if to leave it original or convert it, although I do like the sound of the 12v gen. instead of an alternator. Sounds like that would look better with less alterations. Is there a certain generator that works well? This is really getting interesting, I have a lot of fun with my H,M and SM but this is my 1st experience with a 300. I think Im going to like it!!

One more question. If I go with a 12v gen, does tractor have to be switched to neg. ground? Thats not a problem, just wondering. Thanks

If you go with 6 volt generator I'd highly recommend installing a new voltage regulator at the same time. (VR's do age and wear out. It'll be $45 well spent - trust me!)

Any generator can be set up to operate either positive or negative ground. However if you elect to go with a 12 volt generator I STRONGLY suggest you run it negative ground. This is because it lessens the chance of making a cable connection error should you ever need jump start your 300, saving perhaps both your 300 and the jumping vehicle from serious electrical damage.

Some regulators (6 and 12v) that are of new internal design use diodes and or Voltage control circuits which are very polarity specific. These cannot be polarized for either grounding system, do not let the smoke out. (I know you know this Bob, it is for Makin,Hay)

Good point Jim - thanks for the reminder!

OK, so if I am listening properly, I do not polarize a new 6v {assumung I stay 6v, pos.gnd} voltage regulator when rebuilt/new 6v. gen is installed? Or only if it is not "polarity specific?" So if the new reg. is as the old ones, I would do as always and polarize it to pos. gnd. I am assuming I can get a "polarity specific" reg. and then no polarization would be needed.

Well, not the case at all.
Polarizing is a function of having full current pas through the field windings such that the field pole cores (steel pieces in the center of the windings) become magnetized. This process (on a "A" type generator like the ones in Farmalls) just passes battery current through the Armature post by bypassing the regulator.
The field is attached inside the Gen to the armature post on one end, and the F terminal on the other. The F terminal is grounded through the regulator, thus when Battery voltage is applied to the armature terminal on the VR, the voltage also goes through the field windings polarizing the field poles.
The voltage regulator is not polarized ever.
The voltage regulator is just the most convienient place to jump the battery voltage to the Armature post, by jumping from BAT to ARM at the regulator.

Many regulators do not care which polarity they are working on. they just do the job of regulating the amount of grounding that takes place while generating voltage to charge.
Some more recient Voltage regulators have internal parts that are polarity specific, and will not work, and will be dammaged by being used on the wrong polarity system, or a battery put in backwards.
Thus it is advisable to choose the polarity you want to run, select either a VR that does not care, or a VR that matches that polarity. Then with the tractor off, polarize the generator as above. Do not polarize a Ford style "B" circuit generator this way!! JimN

Ive got it. That was my fault, I did not mean "polarize" the reg. I meant generator after the new reg. was installed. So basically the reg. works as a resistor with a variable amount of ohms/res. to ground directly related to how many vdc pass thru it? Or does it read vdc off battery and then close if they drop below a certain amount? I am sorry for asking so many questions but I sure like knowing what I am doing and why. So for instance, lets say I have a 6vdc negative ground tractor that has a properly working charging system and I am going to take the gen. off and put it on this 6vdc positive ground tractor. I would just need to polarize it to pos. gnd? assuming the reg. is correct polarity. Thanks

Conventional VR internal workings consist of at least two, if not three components that do the controlling.
The first is a cutout relay. It is a normally open magnetically closed switch. It has two windings around the metal core of the unit. A pull in winding, and a hold in winding. This Cutout relay disconnects the generator from the battery by opening a heavy set of contacts. It is always open when the generator is not spinning. It will close when the newly spinning generator makes enough voltage on its own from residual magnetism in the field pole steel, to generate enough voltage to pull in the contacts. (Pull in winding).
The hold in winding is heavy wire made to handle full gen output and more. It is of few turns, and holds the contacts closed firmly when the gen is putting out charging voltage. The cutout will disconnect the generator if the generator output (at idle for instance) drops below the charging voltage of the battery (less than bat volts).
It does this so that battery current is not sent into the gen armature and then to ground. The battery would discharge rapidly in this case through the gen windings because it would be higher voltage than the gen. Electrons running the wrong way. The Cutout is also set to open when the tractor is shut off (again so the generator is disconnected and not sucking battery voltage to ground. This is super important, because the battery will drain in just an hour or so, and the generator will overheat and smoke will come out of the openings. Because it is not rotating and being cooled by the rotation and position in the airstream of the tractor fan.
If you idle it down the amp gauge will show less and less charge. until it is discharging. at about 3 to 4 amps discharge, the Cutout relay will open and the discharge will be limited to the ignition draw, (adding any lights if they are on). The cutout is not connected to anything but the Gen terminal, and the Bat terminal, except that the pull in winding is grounded to the VR frame so it has a place to sent pull in voltage.

The Voltage regulating relay system is either one or two additional coils and contact systems. It is a voltage chopper. It is a vibrating set of contacts that have charging voltage (from the Armature terminal) running through its fine wire coil. This voltage goes to ground at the far side of the coil, to the VR frame. The voltage tries to open a set of contacts. These contacts are in the field circuit. There may be double contacts in this relay with two or more resistors connected to ground (usually under the floor of the VR). These resistors go to the contacts, and adjust how much the field windings in the gen are grounded. The more they are grounded, the higher the output voltage of the gen, and the more charge goes to the bat. This set of contacts is held closed by a spring that adjusts the exact amount of voltage allowed to go to the battery.
As the voltage rises, the relay contacts stay poen longer (they vibrate remember) and this chopping of the ground circuit regulates the output voltage. It is very crude and electrically noisy making and breaking current that makes magnetism. it actually makes high quality static, and radio interference. It is also why many digital meters cannot be used with an older vehicle while it is running. It is such a noisy environment, that the meter reads AC voltages instead of DC, jumping all over and giving false readings.
There may be that third coil in some regulators. It is a current limiting relay (also in series with the voltage control just mentioned. It is set to have all of the Gen out put pass through its thick wire coil. (it winds around both the Cutout relay, and the Current limiting relay on its way to the Bat terminal) Its contacts also are normally closed until the gen begins charging beyond its rated amps. (generators are not self limiting in current, and will smoke if charging into a load that is too heavy, alternators are self limiting) The heavy current opens the contacts again chopping the field ground path so that the gen output is regulated as to Amps.
I have simplified this believe it or not.

I hope it helps JimN

I believe it, and believe it or not, I understand it. When you put it that way it makes perfect sense, albeit somewhat fascinating to think of. I cannot thank you enough for your time explaining this to me. It would have taken quite awhile just finding the proper reference containing this information, not to mention the time to study it. A DC generator is like an electric motor as when one is overloaded it will simply draw more amperage to continue working, hence the application of overload relays and such. As my practical knowledge of A/C controls and drives has gotten me this far I am eternally grateful to have learned this to help me when I am not getting paid! THANKS AGAIN

(quoted from post at 08:17:13 03/17/09) Some regulators (6 and 12v) that are of new internal design use diodes and or Voltage control circuits which are very polarity specific. These cannot be polarized for either grounding system, do not let the smoke out. (I know you know this Bob, it is for Makin,Hay)

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"polarity specific" also applies to many old vintage relay type regulators. My understanding is that some replacement regualators were "universal" and that the difference was in the makeup of the contacts. Evidently it was a tiny bit cheaper to make contacts that would put with arcing "on one side" for a certain ground polarity.