(800) 853-2651
SHOP NOW

Pos vs. Neg Ground Pros/Cons

G

Glenn F.

Member
Can someone give me a pro/con explanation for dummies of positive vs. negative ground. I am having my 1954 Case VAC-14 generator rebuilt. At this time my tractor is set up with negative ground, but I understand it came from the factory with positive ground. Should I switch back?

Thank you,
Glenn F.
 
1) Many early 6 volt autos were Pos ground, others negative. Later the auto industry all decided on Neg ground standard.
2) There was a theory about less corrosion where body frame members met if Pos ground was used.
3) Most early 6 volt tractors were Pos ground.
4) The generator once polarized works fine at EITHER Pos or Neg ground
5) Some Voltage Regulators are designed and labeled for Pos ground OR Neg Ground and its best if used correctly as labeled

I PREFER TO KEEP A TRACTOR AS ORIGINAL SO THE AMMETER LEADS AND COIL LEADS DONT HAVE TO BE REVERSED AND THERES A BETETR CHANCE THE VOLTAGE REGULATOR WILL WORK BEST

John T
 
Mechanically speaking one is not better than the other. The only real reason to change grounds is when converting it over to 12V and an alternator as most easily available alternators must have - grounding. Be certain to polarize it PRIOR to starting. If the rebuilder tests it with negative ground and you hook it up positive ground it will arc and burn the points right off the git go. Or be certain that he tested it with your chosen grounding.
 
The which is best went on to include points and spark plugs. Don't remember the argument but it was down to the molecule level where in one direction you had worse pitting than the other because molecules of the materials involved migrated more from one side to the other if you used this polarity or that. On the chassis thing, they solved that with ground straps, like you find on your hood to your body of your OTR vehicle.
 
(quoted from post at 07:45:03 08/10/15) Can someone give me a pro/con explanation for dummies of positive vs. negative ground. I am having my 1954 Case VAC-14 generator rebuilt. At this time my tractor is set up with negative ground, but I understand it came from the factory with positive ground. Should I switch back?

Thank you,
Glenn F.
Click to expand...
always liked this lighter side of grounds:
Here are a couple of takes: ( not ALL factual, just part)

1) Model T Ford had it right with Negative ground, then Ford "fixed" it with the Model A (Pos gnd), then Ford "fixed" it again in 1956 (back to Neg Gnd).

2) Ford was almost ready to go into production with the Model A & discovered that spark was positive...investigation revealed that the coil was manufactured wrong! Henry, being the frugal man that he was, said," take too much time & money to scrap/re-manufacturer all those coils...just reverse the battery cables". Finally fixed that mistake in 1956.

3) Had it wrong with Model T, fixed it with Model A, then made it wrong again in 1956.

4) Had it right with the Model T, messed it up with the Model A, couldn't admit mistake until all the guilty players were dead & then fixed it in 1956.

5) When lightening strikes, it is an electrical discharge from a Negative cloud to a Positive Earth, so if it was good enough for God, then it was good enough for machines. Of course the main current is in the return discharge from Earth to cloud…but the Earth is still the Positive end of it.

And FINALLY,

5) It doesn't make any difference, like left/right hand threads on lug nuts, as long as user knows how it is set up, either work just fine. It is just a convention necessary to facilitate communication.

the bottom line here is electricity could care less - as long as it has a path to follow it'll be as happy as a tornado in a trailer park.
 
While on the subject of pos/neg ground. A classic car that has been converted to neg ground and had a modern radio installed. Now you want the original radio which was pos ground, how do you handle this?
 
(quoted from post at 11:27:26 08/10/15) I think you mean from a positve cloud to a negative earth.
Click to expand...

I don't know what you mean?
I want to use the positive ground radio in the now negative ground car.
 
(quoted from post at 13:09:01 08/10/15) Use insulating washers on all the mounts & wire it up accordlingly.
Click to expand...
...but still a problem with antenna shield, and without it, noise & static will likely make radio useless.
 
Nothing good about pos ground. It's a dangerous oddball in a 99.9% neg ground world.

Most any modern solid state electronic accessory or permanent magnet motor is built for neg ground. Too easy to get the polarity wrong when charging or jump starting, so chance of battery explosion. No functional advantage to pos ground.

As to putting the original radio back in a rig converted to neg ground, if it is old enough to be pos ground, the radio has no solid state parts and is not likely sensative to polarity.
 
There are little solid state converters avalible cheap that will convert voltage and polarity to what ever you want for a radio. 12V to 6V,or 6V to 12V 6V pos /neg to 12V pos/ neg, whatever the radio needs. I used one once to put a neg ground 12V cb radio in a 6V pos ground truck, worked fine. The same unit would power an original 6V pos ground radio to work on a rig converted to 12V neg ground.
 
(quoted from post at 12:34:03 08/10/15) I would "assume" the vehicle has also been converted to 12V with an alternator.
Click to expand...

No, The vehicle was original 12V Pos. ground with gen. All that was changed was polarity from pos. to neg. ground.
 
Keep it as designed - why not?

change it and you've got to change your battery cables around - and perhaps your alt meter.

Why make more work for yourself for no reason.

If you KNOW it's positive ground, jump starting it isn't a big deal. And besides - how often does one ever jump start a tractor with jumper cables vs. just pull starting?

If you ever sell it - it'll just confuse half your potential buyers if you tell them you modified the electrical system.
 
Its that those tractor fender mount radios used in the 70 and 80 etc were for Neg ground. They could be used with modified isolated mounts but not near as handy. Those were pretty well solid state by that time NOT tube like cars of the thirties and forties.

John T
 
I haven't messed with that sort of thing in a while but IIRC the tube radios for cars used a "vibrator" to make AC current from
the DC current. The AC was needed for the high voltages. The vibrator was a mechanical arrangement and I don't know if it would
care one way or the other about polarity.

I do not remember though if the vibrator was separate from the radio or not.
 
The vibrator was in the radio. Turn it on and hear only that low hum of the vibrator as the tubes warmed up. I used to run one on the bench as a shop radio. If I ever hooked one up reverse polarity and had it work, I dont remember ???
 
It sounds like his tractor is already converted to neg ground and working. Converting it back to pos ground would involve all the wiring changes you mention plus coil polarity if it has battery ignition.

If you can guarntee that you will be the only one to operate that tractor for all time, then yes, you may remember and understand that it is pos ground.

Problem is though, if any time a cousin/ brother/ grandson/ neighbor gets on it and for what ever reason needs to charge the battery or jump start it while having no clue that it has a pos ground electrical system, thats when bad things happen. Burned out battery charger or a 24 volt dead short that will vaporize a battery post if not explode the battery when using booster cables, thats why I consider a pos ground system a dangerous odd ball in a 99.9% neg ground world.
 
The advantage of positive ground in a third brush generator system on 6V, with a coil and distributor system, is that it gives you 12V more spark intensity at the spark plugs (this has to do with spark plug electrode polarity and "pushing" vs. "pulling" spark). The 6V voltage is added to (rather than subtracted from) the ~50,000V voltage produced by the coil when the points open. This is almost completely insignificant. However, to an engineer, this 12V difference is FREE LUNCH. Some companies chose the positive ground option and others chose the negative ground option. Supposedly General Motors (electrical systems from AC Delco) mainly used negative ground because the contacts in the generator VR could be made to last a little longer in this configuration (this is also a practically insignificant concern). However, this too was FREE LUNCH when the engine utilized a magneto, since there was no extra 12V to be gained.
Things changed when alternators came out. Alternators use semiconductors (transistor diodes wired into a bridge circuit) to rectify an AC output into a DC output. The negative side of one of these transistors needs a heat sink to keep it cool. Therefore, it is a natural decision to attach the negative side of the transistor to the alternator casting in order to cool it effectively and cheaply. Since the casting of the alternator is bolted directly to ground, then this gives you a negative ground system.
 
Tube type car radios are NOT polarity sensitive - they work fine grounded either way.

Incidentally tube car radios even work on 12 volts AC.
 
(quoted from post at 20:14:19 08/10/15) The advantage of positive ground in a third brush generator system on 6V, with a coil and distributor system, is that it gives you 12V more spark intensity at the spark plugs (this has to do with spark plug electrode polarity and "pushing" vs. "pulling" spark). The 6V voltage is added to (rather than subtracted from) the ~50,000V voltage produced by the coil when the points open. This is almost completely insignificant. However, to an engineer, this 12V difference is FREE LUNCH. Some companies chose the positive ground option and others chose the negative ground option. Supposedly General Motors (electrical systems from AC Delco) mainly used negative ground because the contacts in the generator VR could be made to last a little longer in this configuration (this is also a practically insignificant concern). However, this too was FREE LUNCH when the engine utilized a magneto, since there was no extra 12V to be gained.
Things changed when alternators came out. Alternators use semiconductors (transistor diodes wired into a bridge circuit) to rectify an AC output into a DC output. The negative side of one of these transistors needs a heat sink to keep it cool. Therefore, it is a natural decision to attach the negative side of the transistor to the alternator casting in order to cool it effectively and cheaply. Since the casting of the alternator is bolted directly to ground, then this gives you a negative ground system.
Click to expand...
hope no one saves this! :roll:
 
Are you confused yet Glen? Hell I am and I knew what I was talking about when I posted,,,, I think?????
 
It is time to pay attention as when you are hooking up a charger or cables. + goes to+ and -goes to-. Makes no difference as to which ground.
 
Well I guess so! Seems the only reason to go positive ground is to stay original. My little tractor was "professionally" converted to negative ground before I got it. I think I'll leave it alone.

Glenn F.
 
very true but on the dead battery side, it's common practice to hook positive to positive - and the negative to the a ground source away from the battery to avoid explosions.

In this case, that would be hooking up the negative clamp to a positive ground.
 
you're right - I missed that.

But my answer stands - I'd personally go with whatever option doesn't require any more work/parts.

I don't see any advantages/disadvantages to either choice that can't be countered with equal advantages/disadvantages from the other choice.

So keep it simple.
 
Not so. I have a positive ground 6V antique car. When I acquired the car, it was incorrectly connected negative to ground. The radio (original) did NOT work. When I reconnected the battery correctly, it DID work. What you say may be true for SOME radios, but not necessarily ALL tube radios.
 

Would be hard on all the electrolytic capacitors that are polarity sensitive. Also cathode bias circuits would be bias to the wrong polarity, meaning that tube would either be completely shut down , or in full run-away. So reverse polarity on sensitive polarity bias circuitry would not work correctly. IN the case of running all the voltages through the vibrator , rectifying them and re- bias them, it would work.. but most manufacturers would not go to this expense. vibrators were for the high voltages needed for tubes and were current limited. Low voltage high current filaments and bias circuits did not normally pull from the vibrator circuits... Yes I know the filaments could be ac or dc. A lot of tubes had one side of the filaments tied to the cathode iirc...

Wow,, its been way too long since I worked on tube circuits.
 
Not that it is important, but just out of curiosity, I pulled out a schematic of a 1957 Buick, all vacuum tube radio, and the only thing using 12v in are the filaments and the vibrator. Only 3 electrolytics are on the output side of vibrator. All bias is derived from the 230v vibrator source. I just had it, so I had to look. Never previously thought about trying to run the radio off of either polarity. I also recognize that all radios are not likely created equal. :)
 
You must log in or register to reply here.

Similar threads

T
FORD TRACTORS - ELECTRICAL SYSTEMS 101
Replies
4
Views
1K
Mad Farmer
M
E
Wanted to change the radiator, ended up rewiring 6V 2N
Replies
3
Views
828
JMOR
J
W
Fixed 3 Brush 6 Volt Generator Motor Test
Replies
8
Views
2K
wrg4257
W
D
Vac 14 , pos or neg ????
Replies
4
Views
851
will in texas
W
C
Positive or Negative Ground - Does it matter?
Replies
7
Views
4K
steve(ill)
S
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