(800) 853-2651
SHOP NOW

6 Volt vs 12 Volt

J

John B.

Well-known Member
I just replaced the starter and battery in my Farmall H the old battery and starter were junk. It is still factory 6 volts positive ground. It starts and charges just fine.

Why are so many changing their old tractors to 12 volts and installing alternators? Is it something they don't understand about generators or am I missing something here??

Just Curious!

John B.
 
My grandpa changed his WD (which Dad and I now have) because he had no other 6 volt stuff, say if he needed a jump. Also, chargers are harder to find that work on 6 volt stuff. Don't know for sure, but wonder if his generator quit, making it more economical to install an alternator. Greg
 
Those that convert are not willing to go the extra inch to keep the battery cable connections clean that 6 volt system demands twice a year compared to once every couple years for 12 volts.

Gerald J.
 
because they don't keep them in good working order so they think 12v will fix all there problems. have 6 tractors that are 6v and all will start at -30. two of mine have 6v alternators that are positive ground . yes you can have a + ground alt.
 
Hi Greg,
I have to agree if you have to jump a 6 volt but it can be jumped very easily with a 12 volt battery, you just have to make sure you have everything else turned off and best to jump it while trying to crank it. I've jumped many a 12 volt vehicle with 24 volts with out any problems. Usually a jump start position on a battery charger is double the voltage but limited to the amperage it can put out.

Between a 6 volt dead or low battery and trying to crank the engine with a low battery the two will absorb much of what a 12 volt will put out if jumped with a 12 volt battery.

I haven't seen hardly any battery charger that doesn't have a 6 volt position on it!
 
Hi Marlowe,

Yes I have seen the six volt positive ground alternators also. They are pretty rare though I must admit.

John
 
Yes you are very right!!

We had twelve volt positive ground tractors with generators at home for years and never had any problems with them.

Never had any problem with the 6 volt tractors either.
 
I've seen some sloppy conversions over the years. I rip off all these sloppy mods and install fresh new 6v wiring and fat 0 gauge cable.

Ta da... fires right off. Meanwhile Mr. Fat Jim on his 12V farmall H wonders why his conversion didn't make his tractor start any better with the 30 year old plugs and distributor cap.
 
I change them to 12 volts because cost to keep them 6 volts most of the time is 2 or 3 times that to change them to 12 volts. But most tractor I work on have seen better days and I bring them back from the dead to be put back to work. I just did a Farmall M today and have almost nothing in the change over
 
My John Deeres were all 12 volts, but positive ground generator machines. I installed alternators, negative ground, because they would adequately charge the batteries for my particular use. I used them for feeding cows at night in the winter months, after I got home from work. The generators would almost, but not quite recharge the batteries. About once a week, I had to either charge or jump the tractor to do the feeding. The alternators made them trouble free.

I replaced my first alternator last summer, after about 20 years of use and minimal maintainance.

The heck with generators.

Paul
 
The starters need rebuilding and bad cables and the list goes on so quick fix just go to 12v then they post everyday having trouble forgettinh that the system worked for many yrs just have to modernize and go with 12v.
 
12 volts will spin a six volt starter a lot faster than it will spin at six volts, even when everything is perfect.

My Ford was converted before I bought it. If it had been original I would have kept it that way, but it's not and I see no reason to go back. It starts easily in sub-zero weather; I use little or no choke in all but the coldest weather.
 
I have everything else at my house 12 volt, so my tractors are too.Plus 6 volt batteries are expensive here, when you can find someone who stocks them. Not to mention, a good rebuilt alt. can be bought for less than the price of a new, quailty regualtor around here!.
 
If the starters need rebuilding and the cables need fixing you would have to do that to convert to 12 volts also, so what's your point. The cost to do that work is the same to fixe these itmes wether it's 12 or 6 volts.
 
Well yeh the starter is going to spin faster since the voltage has doubled. But remember the amperage has been cut in half when you go to 12 volts on a 6 volt starter.
 
It may be cheaper to put a 12 volt battery in place of a 6 volt, only because 12 volt batteriers come in more selection of sizes than the 6 volt batteries do. So you can go with smaller battery on the 12 volt than the 6 volt.
 
In my experience if the tractor is kept in good working order (good enough to be hand cranked) the 6v system will work fine. If you aren't willing to keep things up, or it doesn't get used often, or you want standardization, or do a lot of cold weather starting, 12v is probably the way to go.

All of my antique tractors have a magneto ignition and 6v charging system. On principle I won't upgrade to a distributor or 12v.
 
Some of the larger tractors of the day, like the Farmall M and oliver 88 were pushing the limits on how much cranking power the average 6V system had at the time. Then later on these tractors were fitted with oversize, higher compression pistons and suddenly the 6v system couldn't cut it anymore, no matter how good the starter and cables were.

Like others said 6v works fine on smaller tractors when the system is kept in good shape, as it always should be anyway. Jim
 
12V is often a bandad cure for starting problems to compensate for worn/dirty/undersized wiring.
Judging by the amount of people baffled, smoke and flying sparks.With the quick,easy and cheap alternator conversion. It's not much of an advantage.
Most of the time the alternator becomes a belt tightener. And the 12V battery gets charged in the shop from a 120V charger. Lights and instruments rarely work either.
A generator works fine if the driver isn't putting around with the engine only at idle speed.
And if they would fix the brakes so they don't stop the engine everytime they get off the seat. As they put the tractor in gear to keep it from rolling away.
 
Yes, tell me how fast it cranks at below zero.

How many 6 volt diesel starters have you seen? Ever wonder why they didn't work? There was enough trouble with early 12 volt diesel starters; thus the reason many were 24 volt.

Sounds like you never owned and drove a car with a generator and the headlights on at low engine speeds?

Also, tell me how well it charges when you run it at night with 10-20 amps worth of lights hooked to it, at low engine speeds.

It's a matter of improved technology. Many if not most older 6 volt systems, when all is perfect, will not crank over the engine at zero degrees or below, as well as some newer 12 volt systems. It's not because 12 volt is automatically better than 6, it's more because as technology shifted to 12 volts, more cranking-amp capacity was also added along the way. Also, there is much less chance of loss along the circuit as the voltage gets higher.

In addition, take a starter designed for a 6 volt system and intended to crank on 4 1/2 - 5 volts DC, it will do much more hooked to a 12 volt battery cranking a 9 or 10 volts.

Then there's the old generator. Regardless if 6 volt or 12 volts, it basically only uses 1/2 the power it makes. Instead of using diodes to recitfy AC into DC, it just selects a small portion of power from the commutator to keep things DC, and does not use the rest. So, an alternator is much more efficient, powerful, compact, and lighter.

One more thing. Much easier to find deals on 12 volt batterys and accessories.

I've got several old tractors still original, with 6 volt systems. I don't have to start them up when its 20 below, and I don't need headlights on them either. A couple of Case VACs, three Case DCs, a few Deere two cylinder crawlers, a Shaw R12, Oliver Cletrac HG and OC3, several Ford Model AA trucks, etc.
With any, if I have to start them in extreme cold, things go much better if I unhook the 6 volt battery, and temporarily stick in a 12 volt. Night and day difference.
 
With twice the voltage across a fixed resistance, you'd have twice the current. Not half the current. And if the starter locks up, that's exactly what you'll get.

Starters, like all DC motors, produce a back-EMF proportional to the speed of the starter. As the starter turns faster, less current flows through the windings than when it is stalled or first starting.

So hooking 12 volts to a 6 volt starter results in double the initial starting current. As the motor spins up, the current through the motor drops. The final current depends on the final RPM of the starter, which depends on the load the engine places on it.

The starter will spin faster with 12 volts than with 6 volts. If it spins twice as fast, current will be approximately THE SAME at 12 volts as it was at 6 volts (because the starter is producing roughly twice as much power). If it spins maybe 50 percent faster (typical), the current will be more than half, but less than the same as it was at 6 volts.
 
It's actually been cut more than that. With the 6V starter, you are running it closer to stall than with 12V.
 
Quote "The starter will spin faster with 12 volts than with 6 volts. If it spins twice as fast, current will be approximately THE SAME at 12 volts as it was at 6 volts (because the starter is producing roughly twice as much power)." Unquote

Not really. If you are pushing twice the normal current through the 6V motor at 12V. The motors is not running at twice the power. It's running at four times the original 6V power level.
 
Current doesn't even apply here. The only common denominator when discussing mulitple voltages is wattage (or KWs).

The Farmall H used either a Delco 1107427 or a 1107448. Either one is rated at 65 amps at 5 volts (normal 6 volt system cranking voltage). That is 325 watts of rated cranking power. Same starter (basically) cranked at 10.3 volts (normal 12 volt system cranking) is rated at 75 amps. That's 772 watts of cranking power which greatly exceeds the 325 watts when run on a 6 volt system.
 
We are thinking the same thing here but expressing it differently.
What I'm saying if the 6V starter on 5V drew 500amps, that's 2,500W.
Apply 10V to that same starter, current can double depending on rpms, back emf, load etc. That would be 1000amps X10V for 10,000W. Four times the input power.
Of course output power on the pinion to the flywheel will be less than 4X due to magnetic path saturation etc.
The problem with 6V systems is getting enough voltage across the coil when cranking. With the battery terminal voltage dropping to 5V while cranking. Then voltage drop on the cables, switches, conenctions and chassis return path. The coil may see only 3V, no wonder the engine won't start. There isn't enough voltage built to jump the gap on a wet plug.
Now taking a look at the typical system. A 6V battery from bargain bob's,dusted off from the back of the rack a few years ago.Walmart 4 gauge discount bin cables. Some high resistance cable conenctions becuase everything wasn't truely buffed down to clean metal. A chassis return path through sheet metal istead of bolting directly onto the starter's mounting bolt. Plugs gapped a little wide with some soot on them and wet from being flooded. High resistance automotive plug wires instead of solid core, resistor plugs too.
Now try to start a worn out machine on a cold day with summer oil in the crankcase. And old gasoline in the tank.
Odds are she isn't going to start.
 
No disagreement here. Considering that many farm tractors sit outdoors and get rained and snowed on - just that factor alone makes a 12 volt system more reliable because the connections and amp-carrying capacity are not usually as critical as in a 6 volt system. In fact, to the converse of this discussion, that's why the Deere 12 neg-12 pos - 24 volt crank systems were so problematic. At 24 volts, current traveled easier and found it's way to areas it did not belong. The bulk of problems with those sytems was the groundless starter motor developing a ground due to damp brush-dust.

I like 6 volt systems, but recognize them for what they are. Slow, steady, and reliable except in cold weather. Just like me.
 
On smaller motors like the 113s, can/would a 6v starter being driven with 12v spin fast enough to spin out the impulse coupling on a mag, so that you're trying to start it with an advanced spark?
 
If the starter spins the engine twice as fast, it is delivering twice the power. Not 4x the power.

I said (and you quoted) that I expected the current to be about the same (when spun at 2xRPM) at 12 volts as the starter drew at X rpm at 6 volts. Thus the input power would be double (not 4x). Back EMF increases with increasing RPM, limiting the current.

With the starter STALLED the starter delivers no power but consumes 4x the power at 12 volts as at 6 volts.
 
The current is greater at 12 volts. The current would have been reduced if the starter had been rewound for 12 volts but in this swap it usually isn't and the starter current is higher.

Gerald J, Electrical engineer.
 
If you get a mag spinning so fast that the impulse coupling gets disengaged, it's also fast enough so you no longer need it anyway. That's the nature of the design of the centrifugal cut-out.

That being said, all my older tractors with mags, 6 volt starters, and 12 volt batteries, still have the impluse clacking away when-ever I'm cranking. Even my Shaw R12 tractor with a Wisconsin TF-D which really zings over on 12 volts - with a Fairbanks mag, still has the impulse catching.
 
You kind of lost me a bit on two things. First, there is not a perfect linear progression of RPM versus power needed to make that RPM. I.e., twice as fast takes a bit more than twice the watts.

Also, a stalled starter - certainly IS doing work if it's trying to rotate. It's creating X amount of force, but not enough to overcome the "interia of rest" of the unit it's pushing against when in "stall" or "lock" position.
 
If I had a 24V Deere. There would be a solenoid installed between the + battery and the post on the side of the starter.
 
Ever try working after dark with a 6 volt Farmall with the original lights? You better know your fields pretty well. My Ford with 12 volts and the delco alternater looks like it has airplane landing lights compared to our farmalls. Really nice for plowing snow at night. Or if you need to pull up to something and jumpstart it you have a tractor that can easily do that. I have used my 9n to charge batteries on bigger tractors that were dead and hard to get to. Like a mobile charging station!
 
Well, John, you should have known better than to use "voltage" and "amperage" in the same post on this board. This place is so overloaded with electrical engineers you can't swing a cat without hitting one. Anyway, while those other guys argue about how many electrons can dance on the head of a pin, I'll throw in my own two cents.

First, can we agree that when it comes to starters, faster is always better? If so, then current is really immaterial. The faster starter wins every time.

Second, less current isn't necessarily bad. Less current means less voltage drop between the battery and the starter and that means more volts to the starter.

That said, I can show you that under every condition, the twelve volt battery will deliver MORE current to starter than the six volt battery. Let's consider three data points: The starter at zero rpm, at the steady state cranking speed at six volts, and at the 12 volt steady state.

Zero rpm: When you first hit the starter button, the starter is essentially a dead short. The current is only limited by the internal resistance of the battery and starter, plus any resistance in the cables, relay and connections. So even if the internal resistance of the 12V battery is double that of the 6V battery, it's still going to deliver more current to the starter than the six volt battery. Ohm's law.

Steady-state six volt cranking speed: When the starter has wound up to full speed, it's reached an equilibrium where the starter torque equals the torque required to turn the engine. It can't turn any faster because the starter's back EMF equals the battery's output voltage minus the voltage drop through the battery, cables and starter. HOWEVER, if we could instantly crank the battery's voltage from six volts up to twelve volts, the current through the starter would increase, because now we have more battery voltage than we have back EMF and voltage drop. That's because back EMF is strictly a function of motor speed. The increased current from the twelve volt battery results in increased torque, which in turn causes the starter to accelerate.

That leaves us with the third data point: The steady-state speed at 12 volts. It turns out that the six volt battery can never get up to this speed because of back EMF. So it really doesn't matter what the current is at 12 volts because you can't get there with six volts. Back to my first point: Faster is Better.
 
If you ever seen a magneto on a magneto test bench you would see that spinning it a little faster than cranking speed you actually retard the timing!!!!! The impulse on a IH tractor I believe kicks out at 150 rpms on the mag which would be 300 on the engine.
 
You must log in or register to reply here.

Similar threads

O
What am l missing
2
Replies
39
Views
2K
Oldmantractor
O
J Hamilton
Update on 6 volt or 8 volt tractor battery
Replies
11
Views
517
Dave G9N
D
T
12 volt conversion
Replies
19
Views
594
JMOR
J
C
Magneto kill switch with negative ground
Replies
13
Views
480
rustred
rustred
J
Starting 8N problems
Replies
5
Views
246
Jim Phillip
J
Tractor Parts Tractor Manuals

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Copyright © 1997-2024 Yesterday's Tractor Co.

All Rights Reserved. Reproduction of any part of this website, including design and content, without written permission is strictly prohibited. Trade Marks and Trade Names contained and used in this Website are those of others, and are used in this Website in a descriptive sense to refer to the products of others. Use of this Web site constitutes acceptance of our User Agreement and Privacy Policy TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.

Yesterday's Tractors - Antique Tractor Headquarters
Website Accessibility Policy

Back
Top