1938 Oliver change to 8 volt

[rScotty]

I was going to do this 6-8 conversion once but instead upgraded to a 1 wire 12v alt because the battery salesman advised that the 8 volt battery would have a short life because it would never be fully charged to 8 volt by the 6 volt generator.

That's pretty good knowledge for a battery salesman. Most 6 volt generators will put out about 7 volts - just like a 12 volt generator puts out nearly 14 volts. The part about the shorter life is more debatable, because it depends on the quality of the lead alloy and acid.

There is another way to go with a 6 volt system. They can be made to work. The trick is to reduce the voltage loss throughout the starting system. People won't believe it works as well as it does until you do it You are already one step ahead of the curve by having a mag instead of a 6 volt coil.

The next step is to get a really good 6 volt battery. Lots of Amp hours. See if you can find one that weigh 50 pounds. Odyssey used to make one..... maybe still does. It won't be cheap, but everything I am going to say next beats the pants off an 8 volt system. Performance & price both.

Start with that darn good 6 volt battery and next we simply go through that 6 volt system on a mission to reduce voltage loss. Every one of these things will be a benefit

1. Now we do the new battery cables. Make the battery cables out ofwelding machine ground lead wire with lots of copper strands. Make the cables as short as possible, You may end up using much larger diameter copper wire for the battery cables as now, use flexible multi-strand (high dollar) wire you can buy it by the foot from the welding shop. Maybe you can get your cable ends there too. Get pure copper everytime you can. Clean, clamp and then solder the ends on - you probably can't solder at the battery end of each cable but make the best connection there that you can. Where the ground wire connects to the frame of the tractor you should scrape down to bare frame metal. Even run a jumper wire from the frame ground right over to the bolt that holds the starter to the frame.

Now go into the starter solenoid - it rides piggyback on the starter motor, and comes apart with a couple of obvious screws. Basically a tin can with a coil and contacts insidel Take it apart and polish up the big copper contacts inside. Leave the rest alone.

Next is the starter motor. Make all the contacts clean and bare metal. Either take it to a vintage car master starter rebuilder or do it yourself. Re-cut, clean, and polish the armature for full 100 contact with the new brushes. Bushings and renew connections everywhere. Don't forget to re-polarize it. Every vintage car club guy knows someone who does all this.

The reason to do all this detail work is simply because a connection that isn't perfect is a source of voltage loss. And you cannot afford any voltage loss when you are only starting with 6 volts. That is all the 8 volt battery system did - it simply offset the voltage loss. You can do the same by lowering the resistance througout with that level of attention to detail. Using larger battery cable, larger battery, and honest metal-to-metal connections.

It may not work. But if it doesn't going to an 8 volt wouldn't have either.

As a final touch, put a voltmeter across the battery terminals when it is running and make sure the generator is charging at somewhere between 6.1 and 7.2 volts at anything between a fast idle and full PTO RPM.
Good Luck,
rScotty

 

[LouNY]

Our Farmall 400 got the 8 volt change done back in the early 60's to help the starting,
the only thing changed was the battery, the voltage regulator was adjusted to get around 9 volts when the tractor was running over half throttle.
It did get changed to 12 volts in later years with an alternator.
As I recall I think the generator was only rated for 20 Amps maybe 25 not much if you wanted to run lights at night.

 

[ultrarunner]

I sold a lot of 8 volt batteries when working the classic parts counter in High School.

Most of the bulbs were marked 6-8 volts and most did nothing except adjust the generator third brush to boost output...

 

[K5lwq]

I have done the 8 volt upgrade on 6 volt systems several times. It works by just changing the battery. 12 volt conversion would be better yet like others have said.

 

[rScotty]

Our Farmall 400 got the 8 volt change done back in the early 60's to help the starting,
the only thing changed was the battery, the voltage regulator was adjusted to get around 9 volts when the tractor was running over half throttle.
It did get changed to 12 volts in later years with an alternator.
As I recall I think the generator was only rated for 20 Amps maybe 25 not much if you wanted to run lights at night.

I sold a lot of 8 volt batteries when working the classic parts counter in High School.

Most of the bulbs were marked 6-8 volts and most did nothing except adjust the generator third brush to boost output...

I have done the 8 volt upgrade on 6 volt systems several times. It works by just changing the battery. 12 volt conversion would be better yet like others have said.

Sounds like a number of TBNers have encountered old electricals. And for those that have yet to deal with one of those old tractors, there is some interesting mechanical history on voltage regulation.

Back in the days when generators had commutators with slots and brushes.....BTW, they used those slots and brushes to mechanically rectify AC to DC because semiconductors hadn't yet been invented yet..... very clever, those old designers were....
And it worked pretty well, so well that generating voltage was easier than regulating voltage. In fact, regulating voltage was a difficult problem. Not just for generators, but throughout the electrical industry. The problem was that as RPM go up, so does voltage.

Getting the voltage to stay constant was difficult because of the way we generate voltage. We do it by moving a conductor past a magnetic field - or sometimes by pretending to move the conductor by oscillating that magnetic field.....but however you get them moving past one another, how fast they go past one another is how many volts you get. Twice as fast is twice the volts.... No getting around that.

So using tractor motors to spin a generators was a problem. Luckily, clever folks came up with lots of different schemes for regulating voltage. The downside being that there were LOTS of different schemes. And we called them all simply "Voltage Regulators". But because they went about regulating voltage in different ways, most of those solutions required that the generator and voltage regulator be designed and used as a pair.

And that's the problem with any "one set fits all" solution to old generator & VR systems. What works for one set of generator and VR won't necessarily work for another.

You can do a lot with those old systems once you understand the one you have, but I agree that converting the entire system to 12 volts is the best way to go. Today you can buy an inexpensive "one wire" alternator at the auto parts store that has the rectifier and the voltage regulator built into the case. Lots of basic imported cars - Datsun & Toyota are common - use a common two bolt alternator driven by a fanbelt that works pretty reliably over a much larger range of RPM than tractors ever see.

rScotty

 

[ultrarunner]

It is common to adjust output with antiques depending on anticipated need by adjusting the generator third brush or increasing load such as daylight driving with headlights for all day driving.

Simple and it works but not automatic… Model A Ford.

 

[ROUSTABOUT]

I'd change it to 12 if it's not a show tractor. 12 volt batteries and machines that use them can be bought new this very hour. 8 or 6 volt, not so much. I've changed many a tractor to 12 v alternators. Put a ballast resistor on run side of switch. Straight 12v to points from start position. Will start good and won't burn your points up.

 

[fidowanttobe]

I sold a lot of 8 volt batteries when working the classic parts counter in High School.

That sounds like a cool high school job!

 

[ultrarunner]

It wasn't bad and I got discounts on parts I needed and side jobs...

 

[Shenandoah MF1760]

It sounds to me like you don't have enough battery capacity.

Most diesel trucks have two 12v batteries to increase starting ability, either get a larger battery (increased amp/hrs) or add a second 6v battery in parallel.