Rationale for 6V Negative Ground ??

[Conaway2]

I looked at a newly purchased 1930 Std Roadster today for a potential new member of the Low Country Model A ford Club in Charleston, SC, and was surprised to find that the car has a 6V negative ground electrical system. Otherwise, the car is an older, but very accurate, restoration.

I’m still trying to understand why a previous owner would change the grounding from positive to negative.

Is there any benefit ? I must be missing something.

BTW - we didn’t get the car started…the battery needs to be replaced.

Thanks - Jim

[stickshift]

My truck was like that when I bought it. I think the man I bought it from, who was selling it for a friend that passed away, didn't know that Model A's are positive ground. The battery was two months old at the time I bought the truck. I corrected it when I got home and bought some 1/0 AWG battery cables from eBay that made a huge improvement on starting. Back in the day, they believed the electrons flowed better with a positive ground, British cars stayed positive ground for a long time, believing it had better spark, etc. Most cars were switched to neg. ground when 12 volt batteries became common in the U.S.

[stickshift]

Another thought...If the battery was purposely made to be negative ground, the ammeter lugs would need to be reversed to make the needle move the right way. Also the coil wires would need to be switched so that the electrons travel from the coil to the plug, instead from the plug to the coil. There is a pencil point test that you can google to check this. Some people say it doesn't matter, but I want my model A the way it was built. In my case, the neg. ground was a mistake when the battery was replaced, so when I fixed this, the ammeter and coil flow was back the way it should be. Worth checking on yours to see it it was an intentional change.

[Tom Endy]

Here is a reference to the pencil trick.

https://www.santaanitaas.org/wp-cont...pful-Tools.pdf

Tom Endy

[rotorwrench]

If the change was recent, a person may find that the generator doesn't work properly. If it was polarized to negative ground then it will work.

There has been some contention about why they used positive ground. At this point in time, it doesn't really matter except for originality of design. The 6-volt conversion alternator that I have as a spare, has an internal jumper to allow for positive ground. A person has to keep this in mind if they change to negative ground and they want to use a conversion alternator. The alternators would need to be wired for whatever a person wanted to use as far as polarity. The generators can be polarized either way but reversing polarity on one may take a few attempts to get the proper magnetic gauss in the pole shoes.

[eystein]

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I think the reason is that some people who don't understand what's going on in an electrical circuit thinks that chassis ground has to be absolute 0 Volts, and also do not understand that the battery just puts out a voltage on one terminal relative to the other terminal. They might think that the positive terminal has to be some magical absolute +6V no matter what and since the chassis is referred to ground, it has to by some magical effect to be at absolute 0V, so that they cannot understand how a positive ground can work

I guess that they are not able to grasp that voltages are just relative, and that the direction of the current is immaterial as long as circuits like generators, motors and ignition are connected accordingly.

The reason why some people are hellbent on changing to negative ground is probably because they cannot get their heads around the basic principles of an electric circuit

[nkaminar]

Eystein,

I have been around Model A's for over 60 years and everything about the car is second nature to me. I am also pretty good at anything mechanical or electrical. It took me a while to realize that not all people, in fact most people, are not so inclined. That does not mean those people are any less intelligent. My wife is a nurse and knows a lot more than I do about helping people in hospitals. But she cannot figure out which end of a screwdriver to pick up. This is not meant to degrade you in any way for your comments which I thought were interesting.

Here is a neat video that illustrates this point (it is funny): https://www.youtube.com/watch?v=A1apPPy0vL0

[ModelA29]

All is not lost if they are running 6V negative ground. When I was a kid I remember showing me how to polarize the generator after putting in new brushes or changing the voltage regulator.


https://www.youtube.com/watch?v=PPUfQtVEJGg


https://www.youtube.com/watch?v=NV8FFgia7uU

[Conaway2]

Thanks for all the comments. The change to negative ground was intentional, as the ammeter needle deflects the correct way when the lights are turned on.

We’re going to install a new battery tomorrow. I’ll install it as the previous owner did and we’ll see how things go when we start the engine.

Thanks to all - Jim

[Conaway2]

Update - we installed a new 6V battery, negative ground, and the car started right up. What appears to be a cutout on the stock generator is apparently a Fun Projects EVR. Ammeter needle deflects in the correct directions for charging and discharging, so the changeover to negative ground was deliberate.

The new owner plans to leave it that way for now.

Jim

[stickshift]

I'm glad everything is good with the model A. Now its' time for your friend to enjoy his purchase. There's nothing wrong with just leaving the polarity this way, since everything has checked out. In fact it's less confusing when doing a jump-start. This is one of the reasons negative ground is a standard for car manufacturers now, less confusing and much safer when using jumper cables. I like mine original, but that's just me.

[rotorwrench]

John Reagan made the little regulators both ways and in both 6 & 12-volts. A lot of model T folks run a 12-volt system.