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

[ggfossen]

Dave,

OK, thanks. I will stick with the amp gauge, I guess. I never did find a volt meter for a 6 volt system. It would be good to have both.

Gary

[Stan Disbrow]

Hi,

The galvanic reaction mentioned is really more of a metal migration in the presence of an electical field, although for the purposes of our discussions here we can pretty much equate both phenomenons as being the same thing.

This is referring to the movment of the silver between the contacts of the ignition points.

With positive ground, less silver would move between the points than with negative ground. So, there would be a longer service interval for the points, which is a good thing. No, this matters not with a diesel.

During WWII, silver was too precious to use for point contacts, so other materials were found to replace it. Then, the galvanic issue went away and no one needed to care between negative and positive ground.

The 440 diesel probably has a positive ground system because the gas had one, and that was to be compatible with what was already out there from the past. It would have been simply to make the mechanic's life easier.

The change to neg gnd came with the change to 12v, because that was already the standard for 12v systems elsewhere.

I'd say that when going from the generator system to an alternator one, change from positive to negative ground at the same time as long as you're doing other things in the wiring harness. Any electrically operated gauges need to be addressed at the same time, so if you're changing the wiring on the whole machine, that's the time to address the ground polarity change as well.

If you're just changing the gen to an alt, and not into anything else in the system, then leave things positive ground.

This next part gets pretty advanced, and isn't really necessary when it comes to dealing with the wiring on old tractors.

As far as current flow goes, keep in mind that current flow occurs due to the shortage of electrons and electrical flow occurs due to the abundance of electrons. The negative terminal of a battery is loaded with electrons, and the positive terminal is loaded with places for those electrons to go to.

The actual work preformed by the electricity is done by the electrons moving from one place to another.

Think of it like a tank of water that's pressurized connected to a second tank that's empty of water and unpressurized or even uder vacuum. The water itself can repersent the electrons. If you open the valve between the two tanks, the pressurized water will move to where the water isn't. That's the electron flow, and we can use that movement to perform some work for us while it's on it way.

Now, for the advanced part. You knew this was coming, right?

Stop reading here unless you like having a headache!

-----------------------------------

When the water moves from tank 1 to tank 2, there's also a relationship between the 'not water' in tank 2 becoming 'not water' in tank 1. This would be equivalent to what we call current flow in electricity.

One of the early researchers of electricity in the mid 1800's, I think it was Watt (but not sure I'm remembering this correctly after 20 some years), misunderstanding what he was measuring and deciding that it was the flow of current (he actually thought it was the motion of what he called 'positrons' as I recall) that was what was doing the work.

Of course, there are no positrons, only electrons, but I think we can forgive Watt and his contemporaries from not understanding things they could not have a hope of seeing!

So anyway, there was a concept in the beginning that led to a bit of backwards thinking that the real work was occuring due to the motion of 'not electrons' from positive to negative. So, this leads to the thought that current flows from positive to negative.

Now, how this affects us working on our old iron, is that this is probably the real reason why early electrical systems are positive ground. I'd bet real money that the use of silver for point contacts came about *because* that material migrated less when used in a positive ground system.

Watt wasn't completely worng, though. The conecpt of 'not electrons' being the things doing the actual work is exactly how bipolar semiconductors (the common transistor) operate. The 'not electrons' are called 'holes' in this case, but the concept is the same.

As a final thought, though, Field Effect Transistors, which are what make up the bulk of semiconductors used in most microelectronics (like computers) go back to using the motion of electrons to do the work.

Sorry for the headaches out there!

Later!

Stan

[jac]

Nice discussion. Some minor corrections.

The change to negative ground was not at the same time as the change to 12V. The 440 ICD is 12V positive ground.

Silver is notorious for electromigration ("metal migration" when bias is applied). While being the best conductor, silver is almost never used for electronic connectors or conductors due to issues (contact degradation, dendritic shorting, etc) with electromigration.

[bighamlin]

Question for all you Dr's of Electricity:

I have a 1010C Diesel with positive ground (real pain considering I have 6v, 12v and 24v equipment, both grounds). The Generator is dead, and will replace, along with all gauges. Should I convert to 12V negitive ground for simplicity or keep positive ground as original - please advise.

I guess what I am asking is; How much from being stock and original for tradition sake is it considered to switch to negitive ground.

Thanks
Paul

[jac]

I like to keep things original, but it is up to you. Positive ground parts are still available, but you may pay more. In a previous posting I listed part number for Stewart Warner positive ground gauges. I also purchased a new voltage regulator for my 440 which could be used either positive or negative ground.

Once you everything working, it really does not make much of a difference.

[Stan Disbrow]

The change to negative ground was not at the same time as the change to 12V. The 440 ICD is 12V positive ground.

Silver is notorious for electromigration....

I think you managed to find one of the rare exceptions to the changeover. I was thinking overall, as in cars, trucks, etc. as well as tractors. Deere was actually quite late jumping onto the changeover bandwagon in any event. They kept on with the 6v Pos Gnd for years after just about everything else went to 12v Neg Gnd.

I suspect that they went Pos Gnd on the 440 diesel because the gasser was still 6v Pos Gnd and wanted to keep the polarity the same for the sake of the mechanics that had to work on the entire lineup.

Yep. Silver does have its problems to go along with its advanatages, for sure. I have one set of original Deere silver contact points left, and they'll never actually be used.

Later!

Stan

[Lavoy]

I think Deere made the switch to negative ground in 69 when the second serial number range of the 20 series came out.
Lavoy

[Little John]

Wowsers...what a discussion...and I was under the 'false' impression that gold was superior to silver as a conductor of the 'electron'

[Stan Disbrow]

Hi,

No, silver is the best but it does have it's issues, one of which is that it likes to corrode.

Gold is quite good, and has the advantage that it doesn't oxidize like silver, copper and aluminum (all better conductors) do. It has the disadvantage of being a lot more costly.

We use it a lot in the electronics industry in the form of very thin (as in one ot two molecules thick) plating on cheaper metals (like copper).

I'd shudder to think what a set of points would cost with solid gold contacts, though!

Stan

[Little John]

Glad to be corrected on silver / gold. I suppose that since gold is reputed used on circuit boards etc., I assumed it was better....in one way, since you ahve mentioned it, I'd have to say it is ...corrosion is more important in electronics and the things that they fly/guide than on a crawler. I'll remain glad to have points to file on the JD.
As far as points made of gold...not to worry ....we always said that the JD Yellow (as well as Cat yellow) indicated what you would pay for their factory parts...gold. Thanks for Lavoy as well as the helpful hints on his site.

[lastchancegarage]

Stan,
Thanks for the flash-back! Just when I thought I'd gotten over the semiconductor manufacturing theory course I had taken years ago, you bring up things like "holes". Next willl be the relevance of mhos to ohms and hole mobility flow as it pertains to the p-n junction! It took years of intensre metallurgical therapy (aka welding)to get over all that abstract theory. Now I'm going to need even more therapy to forget it again. Where's my welder (strike the arc and go to your happy place...go to your happy place)
Seriously, the refresher was interesting. You never know what to expect when you log into this site. That's what makes this the best. Theory and knowledge from all walks of life. Thanks for the input.

Scott

[Stan Disbrow]

Hi,

Just to make other folks shake their heads even more than they already are....

Ohms are the units used to measure resistance to current flow. Most folks have heard of these before.

Mhos (Ohm spelled backwards - see we engineers*do* have a sense of humor after all!) are the units used to measure transconductance - like what happens inside of an amplifier.

To make things worse, they stopped calling Mhos 'mhos' years ago and call the units 'Siemens' nowadays. Most of our units are named after pioneers (Ampere, Watt, Volta, Ohm, etc). Siemens was yet another, and his name was not yet assigned to a unit of electrical measure, so guess what (or should that be 'guess watt?')????

Maybe we don't have a sense of humor after all!

Stan

[2010OWNER]

I remembered reading some time ago that the belief that the current flowed from the positive to the negative was in error. So I Googled electron flow and found this:

"Conventional Current assumes that current flows out of the positive terminal, through the circuit and into the negative terminal of the source. This was the convention chosen during the discovery of electricity. They were wrong!

Electron Flow is what actually happens and electrons flow out of the negative terminal, through the circuit and into the positive terminal of the source.

Both Conventional Current and Electron Flow are used by industry. Many textbooks are available in both Electron Flow and Conventional Current formats.

In fact, it makes no difference which way current is flowing as long as it is used consistently. The direction of current flow does not affect what the current does.

In general, two year technical programs and high school Physics use Electron Flow.

But three year technician and university engineering programs still use Conventional Current. Certain symbols (ex. diodes and transistors) and rules (ex. Right hand rules for electromagnets) were created using Conventional Current. Changing from Conventional Current to Electron Flow would cause a degree of confusion for old and new students and errors would occur, so Conventional Current was kept to ensure there was no confusion."

Found it at:
http://www.mi.mun.ca/users/cchaulk/eltk ... e/ivse.htm

Kind of like the qwerty keyboard, inertia keeps it going.
B.

[Little John]

It has become apparent that this discussion has nearly created it's own world and should be moved to the "OFF-TOPIC Discussions" Forum. Thanks

[Little John]

Lavoy, As they used to say 'The devil made me do it'