Postive ground electric systems.

[Alleyyooper]

I have a 1961 Allis D17 gas that has the postive ground as do my Masseys. Since Allis is being a baulky girl starting at the present time I need to hook up the battery charger and keep the charge up while cranking.
Since it is a postive ground system I half to (it appears) unhook the cables to charge said battery.
(1. Why did many auto and tractor MFG's. go with the postive ground?
(2. Is there advantages over a negtive ground?
(3. What would be the problems with changeing to the negtive ground other than haveing to switch poles on the volt/amp gage?
Thanks for any coments.

[old_nodaker]

Not sure why you would need to disconnect cables to charge battery.

The following is from a web site for converting positive to negative.

Reverse the wires on your ignition coil.This is very important: if you skip this step, you will lose 50% of your spark energy.

Reverse the connections to the fuel pump, since it may have been replaced with a transistorized pump at some point.

If you've ever replaced any original equipment (such as the instrument voltage regulator) with transistorized components, you will have to figure out how to reverse the polarity of each of these components.

Now, connect the battery with negative ground: attach the ground strap to the negative terminal, and the supply cable to the positive terminal.

Locate the voltage regulator. Remove the "F" wire. Now remove the "B" wire, taking care not to let it touch ground. Touch the ends of the wires together. There will be sparks, don't be alarmed. This operation polarized the generator, preparing it to operate with negative ground. Reconnect the wiring.

End of quote, hope this helps. Possible reason for positive ground, in the olden days they though electricity flowed better that way.

[freebird]

Also to add, make sure that your positive ground connection is very clean and the cable that goes to chassis ground is large enough to carry the amperage. On my 6v pos ground system I use a braided ground strap that terminates inside the battery box. I also replaced the harness leading from the neg side with 1-0 gauge wire. My starter spins much faster now.

[USN_ED]

It's too long for my feeble brain to fully explain but this is part of the crux of the matter.

Ya got positive and negative electrons. It is the negative electrons that flow in a wire and carry the power/current/volts/electronic magnetic force. Because it is the negative electrons that carry the current, they used to designate Negative as power and Positive as ground.

Jeesh!!! One of you Electical Engineers should be able to explain it better. I haven't messed with this stuff since I retired.

[Wingnut]

Not sure why you would need to disconnect cables to charge battery.


Its not an issue if you have a Generator, but with an Alternator made before 1978 had diode that were not as robust as the Zener diodes used in todays alternators. The older alternator's diodes would breakdown from excessive reverse current caused by a 6 amp+ battery charger.

The Zener is strong, but not indestructable: Negative carries the current. Jumpstarting a car if you remove the jumper cables positive first (the big NO NO! on a negitive ground system) This causes a reverse current and will burn up the Zener diodes in the alternator. Which car? Usually the one jumping the dead battery, because the car with the dead batteries alternator is cranking out more amp to charge the dead battery which cause a reverse current flow through the jumper cables and burn up the car's alternator that provided the jump.

Not sure if that was clear?

[BigAllis]

i m not much on batteries but if u keep all cables in good shape an everything u should get good connection i do no wth positive hook up you want make sure u hook it up tht way or you will mess up yer system plus we dont take battery out our ford its positive ground just make sure charger hookup is solid on yer battery terminals

[bear]

Eds got it i remembered that from tech school back in 89 they taught it to us then told us to forget about it being as i have always played with old toys a lot with positive ground it kind of stuck in my mind

[souNdguy]

(1. Why did many auto and tractor MFG's. go with the postive ground?
(2. Is there advantages over a negtive ground?
(3. What would be the problems with changeing to the negtive ground other than haveing to switch poles on the volt/amp gage?
Thanks for any coments.


You don't have to remove the cables to charge.. but do make sure that you have an isolated case charger.. or set it on cardboard... some doofus charger manufacturers tie the case to the negative cable.. and that will cause sparks if you hook it up to a pos grnd system and then set the charger on the tractor.

As another user pointed out.. current flows negative to positive.... that's called electron current... though there aren't really naturally occouring positive electrons.. the current referred to as flowing positive to negstive is 'hole' current theory.. and for allintents and purposes.. is not used in practical electronic theory...

Positive ground better? yes.. for more reading on this.. look up the 'edison effect', or thermionic emmision, and how it related to electrode wear and spark jumping.

As for the 'pre 78 diodes being bad w/ reverse current?.. I've never heard of that.. and amperage ( 6a number??? ) isn't an issue... diode's are rated for reverse current protectioon in PIV.. that's peak inverse voltage.. If a diode is safe to 100piv, then you could have 1000a source available.. and if the reverse voltage on the diode junction is less than the piv.. then there is no current flow.

I remember when they used selenium rectifiers... they were not as efficient as silicon diodes.. but were good at high current.. ... and both beat germanium dioded. Big differences of the 3 were the forward votlage drop across the pn junction... silicon was in the middle.. .. but had better current handling charicteristics than germanium.. so it's the most common used. Also pretty easy to dope....

Also.. the alternator issue about disconnecting a specific cable polarity vs another... I've never heard of that one either. As long as the 2 vehicles are not parked with their bumpers touching, once you remove either of the jumper lines you have an open circuit.. there is no magic inrush of current either way.. it just an open circuit. For instance.. you will notice that you can't jump with only 1 cable ( unless cars frames touching ).. the reason for this is no current flow.

As for jumping with one cable. I once jumped a buddies car off with a single coathanger.. we parked bumpers touching, and wrapped the coathanger between our positive terminals, and just let my car run for about 30 minutes and slowly charge his battery. it was still weak.. but was neat to see the laquer bun off the coathanger when he did start it...

Soundguy