New Member / first post/ Why are the early JD's + ground

[Dave Holt]

Hello people, Great site. Restoring a 440 and will be starting the fresh Detroit motor in the am. Have changed over to the single wire alternator , but must go with negative ground. What problems will I run into with the guages?? Can any one tell me the advantage of Positive ground in the first place?? Thanks for your input.. Dave

[Lavoy]

Long ago, there were some perceived advantages to postive ground which in time it appears to be proved unfounded.
The gauges don't really care about which is ground, just make sure that the polarity on the gauges is correct.
Lavoy

[Stan Disbrow]

Hi,

Well, the only practical difference between neg and pos ground *was* how the points pit. Doesn't matter now, but here's the story in case anyone cares. I researched this years ago out of curiosity (why did everyone change?).....

In the early days, the contact material used for the points was silver, and they migrate less material (pit more slowly) when used with the positive (electron sink, as opposed to electron source, which is the neg terminal) side attached as common.

It's a matter of impedance to the current surge when the points operate the coil.

Don't get all confused between resistance and impedance, either. The two terms mean almost the same thing. Resistance is a steady-state, well, resistance to a constant flow of current. Impedance is the varying resistance to a varying flow of current - like when points open and close, or a starter motor is engaged.

Anyway, there's a higher impedence when the electrons come thru the wires as oppsed to heading back thru them, and that lowered the strength of the spark at the points, which resulted in their pitting less.

Materials, of course, changed several times over the decades. Silver stopped being used for point contacts durng WWII. Other, less precious, materials were found that worked well and they didn't care which side was grounded.

At the same time engine compression went up, which required stronger electric starters.

So, we now have a "don't care" on the polarity and the need to go from 6v to 12v (or even 24v) to raise the starting power. If you need more power, you need more current, which means thicker wiring. But ,if you raise the voltage you can raise the power without raising the current required and keep the smaller size wires.

Also, if we attach the electron source side (neg term) to the chassis, we can reduce the impedance to the power surge wich occurs when the starter is engaged.

So, here is the real reason why battery ground polarity changed.

In practice, we moved from 6v pos ground to 12v neg ground during WWII. Tractors were a bit slower to change, of course, so the 6v Pos Gnd systems lived on another 10-15 years.

The ironic part is that the side chosen to be ground in both cases was directly due to impedance considerations, but exactly opposite.

I found all this to be very interesting, at least way back when I was a student of electical engineering. I probably bored y'all to death with this.

Stan

[wwattson]

Us engineers sure appreciate it. Same thing that makes us boring at parties though.

[Tigerhaze]

It doesn't explain why the early diesels were also positive ground, although I would guess at that point it is for consistency and tradition.

[Lavoy]

That, and what I have read about a galvanic reaction of some sort of somthing having to do with something else. They just had a large discussion about this on another board, but I forgot most of it already.
lavoy

[Magoo1]

Upon futher review, I read (long ago) that the electorns would move easier from a "hot" surface. So if you have the center electrode of the spark plug as Positive it will produce a hotter spark as it moves toward the grounded (neg) side of the spark plug shell.

But after two years of Air Force training which way does electricity flow?

My $.02

Magoo

[shinnery]

The US NAVY always said that electric current flows from positive to negative, but electrons flow from negative to positive. Come to think of it Southern Methodist University School of Engineering agreed with them.
Bryce

[Little John]

To Dave Holt: Has this sufficently hurt your head or do you need more?

[wwattson]

You've got to be tough to hang out on this board. However, there was that rather disturbing thread a while back about the one guy eyeing the other guy's seat .

Seriously, this is the best forum for information on old Deere crawlers and a great bunch of fine folks. You couldn't do better.

[Dave Holt]

Thanks guys for the responses. I see the only advantaqe would be for point type ignition. Being a Diesel this does not apply. I will be using a single wire alternator with mechanical oil and water temp guages. The only guage left is the amp meter and I have been told to use a volt meter instead. I will go that route. Thanks again and have a good Holiday.
Dave

[Joe Iannitto]

Dave,
I have gone to an altenator on my 1010. I basically had no choice but to go to neg ground. The former owner converted the dozer to electronic ignition, and that wouldn't fire up on positive ground. A few months back I asked the group about a single wire altenator and as it turns out a single wire altenator has an internal voltage regulator and has 3 leads. I found a wiring diagram onsite can't remember the site. The only other short cut wa that I used Jason linked v belt because it was eaiser to get around the pullies.

[hunter41mag]

Hi,

I had heard somewhere (back in the 70's when I first got into the wrenching side) that you have less electrical corrosion with positive ground. This is due to the ground side (positive) is not charged with electrons as a negative ground is (with key/ignition off).

As I think back to the positive ground systems I encontered I never saw any with noticable corrosion anywhere in the electrical systems. Has anyone else noticed this with positive ground systems?

Don
Eastern PA
440IC

[ggfossen]

Dave,

I may have missed something, here, not uncommon, but are you using 6 volt or 12 volt on the 440?

The reason I ask is because I have not been able to find a voltmeter that would go below 8 volts, so I've found none for a 6 volst system.

Gary

[Dave Holt]

I am using a 12 system as the 440 is 12 volt. I bought my guages from Value-Bilt and am hoping they also have the volt meter.
Dave