:Model B, C 12volt conversion, how many amps?

On a Model B, C converted to a 12 volt system how many charging amps are needed?

Depends on the auxiliaries and how long you intend to run it each time you start it. Applying 12 volts to the 6 volt starter is going to increase the cranking amps some.

Most use an alternator because it comes with a solid state regulator that treats batteries right while the older vibrating magnetic regulators didn't always do so well. Their precision of voltage regulation was generally poorer tending to cause poorer battery performance if low and poorer battery life if high. In the 60s SAE standards allowed a regulator to be acceptable from 13 to 15 volts. While a 12 volt battery capacity is seriously reduced if only charged to 13 volts and battery life is cut seriously if constantly charged to 15 volts. The overcharging makes the battery lose water and then if not regularly refilled, it looses plate area and capacity as if it was undercharged.

A solid state regulator (and I've built a couple) for a generator can make it work as good as an alternator. First one was when I put a 1500 CC VW engine in a '64 bug that was 6 volts. The generators and generator mounts wouldn't interchange so I built a 6 volt regulator for the 12 volt generator and it charged at low engine speeds like an alternator. I also used a diode for the cutout so there wasn't the reverse current of the magnetic regulator and cutout at low engine speeds which improved the charging efficiency at low engine speeds. But there are few solid state regulators on the market for a generator though Steve offers solid state (e.g. diode) cutouts. And new magnetic regulators tend to be set even poorer than SAE standards used to allow. My first farm size tractor came with a nearly new regulator, but didn't charge like it should. I took the cover off and adjusted (by bending a part) it for proper charging voltage and that tractor gets a good battery life even though the generator only charges at 20 amps maximum. So long as I run it long enough to get the battery current tapered down towards zero and its been 22 years since I made that adjustment. A 60 amp alternator would charge three times as fast if the wiring was sturdy enough. I help that tractor with a battery maintainer after running the tractor. That tractor drives the tachometer off a gear box on the back of the generator making an alternator a difficult replacement.

Then today more people know an alternator than a generator.

For certain the correct police would prefer a generator to an alternator on a vintage tractor. But on my 4020 when i found the regulator bad after replacing a worn out pulley and adding an ammeter, I bought an alternator for just a few bucks more than a JD regulator and get much improved battery life. Changing the battery away from JD's long skinny battery also helped battery life and cost.

For that matter the correct police would prefer it was left 6 volts, after all, it has started for more than 50 years on 6 volts, maybe more than 70 years, so long as the battery cable connections get cleaned more than once a year.

Gerald J.


Edited by Gerald J. - 21 Sep 2012 at 12:38am

Since you are striving for a politically correct look, I assume the B/C is still a magneto sparker. In that case all the generator does is charge the battery after the starter discharge. There is no high current required to do this so I assume just about any auto generator will do the job.

EdK wrote: Since you are striving for a politically correct look, I assume the B/C is still a magneto sparker. In that case all the generator does is charge the battery after the starter discharge. There is no high current required to do this so I assume just about any auto generator will do the job.

No actually it's been converted to a distributor.

BTW you will need a resister to cut the coil voltage back and 12 v light bulbs.

sent PM

a 6 volt generator will put out about 14 volts when not connected to the battery. A 12 volt generator will put out about 30 volts when not connected to a battery.. So Yes, you can use the 6 volt generator to charge a 12 volt battery. Best to use a 12 volt regulator n the system. Possibly not the best solution, but it will work. ... ALso you should use a new 12 volt coil. THe resistor with the old 6 volt coil will eventually cause problems.

Man this is neat stuff, I wish I could absorb it all!

Yeah, most electrical stuff other than the very basics is still a mystery to me.

If I test the bat. terminal on the regular with a multimeter is that reading I get what the regulator is putting out or is it the reading from the battery?  Because it read exactly the same as what I tested on the battery itself.  Can I read directly off of the generator terminals what it's putting out?  I tried and couldn't get any reading.  I may of just not had a good ground.  It started raining and I didn't hardly get any chance to mess with it.

What needs to be done to switch the tractor back to positive ground?  Switch the wire from the coil to the distributor around to the positive one?  And of course hook up the battery positive ground.  Is there anything else that needs to be done?




Edited by briwayjones - 22 Sep 2012 at 4:23pm

A sulfated battery refers to the plates in the battery being sulfated?  Which is what eventually causes a battery to go bad?

Since you don't have a true restoration, I would suggest changing to a one wire alternator and solve all your problems.

Sulfate is the normal product in the plate active material from discharging a lead acid battery. Its normally in very small particles, which charging converts back to the plate active materials. And that is good because sulfate particles are larger than the active plate materials and so when sulfate accumulates it pushes active plate material loose which falls to the bottom of the battery and that's amphours permanently lost. But if a battery sits discharged the particles will gather into big crystals displacing more active material and those crystals are resistant to charging. Then the battery, even with a normal charging voltage applied, will draw current all day but not run a load very long the next day.

Some say repeated charge and discharge will break down the sulfate crystals and some chargers do that at a rate of 120 cycles per second. I thought I had a sulfate problem in a battery in one of my tractors and so devised such a charger and it had no effect. It had no effect because the battery was fine, the starter brushes were worn out which I found when one of the brush leads broke off while I was commuting from farm to home and had stopped at a gas station. I was able to find tools in the station (without the owner's permission) to get it to start and that starter was still warm when it hit the counter in the town's auto electric shop for rebuild. That tractor was impossible to start by pulling. Some of the maintainers claim a desulfation operation.

Gerald J.

L is for lighting loads where the lamp current increases the generator output a bit.

Gerald J.

Well, I still don't know if the regulator is working.  And that's because the generator is not.  The generator produces 4 volts at best.  That was determined by grounding a multimeter on the "F" terminal on the generator and reading on the "A" terminal.  That's correct right?  If I tried it the other way it was showing discharge.

If you need help with your 12V conversion, give me a call. Be happy to help ya out and walk ya through anything. Been doing this stuff for 40 years. Some make this more complicated than it really is....
Steve@B&B    (973) 632-5596