View Full Version : 6V questions

12-24-2012, 09:29 PM
I understand 12V systems are more common than 6V, but besides adding A/C easily, a general history question, when and how did the switch to 12V in autos come about? Did someone or something spark(!) the change specifically?

Related to this, how and why did the positive/negative ground switch occur as well? As someone not electrically competent, this decision is one I have no clue how or why it would have happened.

Finally, I'd like to hear the pros and cons of 6V vs. 12V. I ask this because I've read some comments from some 50s car owners who are satisfied with the original electrics, so I'm curious what tends to motivate an owner to go through all the rigamarole to upcurrent a 6V to a 12V system.

Thanks for writing, sorry for causing writer's cramps in anyone. You're welcome if I motivated anyone to tear themselves away from holiday mayhem to actually answer all those questions.

12-24-2012, 10:41 PM
Sorry, I just realized I probably should have posted this in the Tech forum.

Mark L
12-24-2012, 10:59 PM
Someone else can respond with the automotive history portion. I think the switch to 12V began in the 1940s and 1950s.

In general: Do you know how energy usage for light bulbs is usually rated in watts? voltage x current = energy (watts). If the energy required to opeate something (light bulb, motor, etc.) remains constant, and you increase the voltage, the amount of current required to operate the device decreases by the same proportion the voltage was increased: example, double the voltage, half the current.

The fuse and wire gauge is usually sized by the amount of current the wire must carry. So if you increase the voltage, you reduce the amount of current required, and therefore, can use smaller fuses and smaller gauge wires to do the same work.

For automotive systems, my guess is that it would result in a vehicle that is less expensive to produce. In the case of aircraft, electrical systems are 28, 110, 220, and now 240+ volts on the 787. The big benefit here is that smaller gauge wire also weighs less.

Mark L.

12-24-2012, 11:09 PM
12 volt systems came about when engines got larger, and higher compressions. This made cranking speeds slower, and 6 volt systems take twice the current of twelve volt systems.
Some new cars are going 24 volts on some systems, it requires less copper (smaller diameter wires).
I'm not sure why the switch to negative ground.

12-24-2012, 11:12 PM
Thank you both. I do understand the relationship you described and how that makes sense.

12-24-2012, 11:33 PM
Studebaker's change came in late '55.
Along with the smaller gauge wires required for 12-volt, the cleanliness of connections, or lack thereof, in the 6-volt systems was a maintenance issue. Not that it is not an issue in 12-volts but...less so. Higher amps required to jump a dirty 6-volt connection. With proper maintenance of a clean 6-volt system there was no problem transporting us through the mid fifties. Many of us still feel fully confident of our 6-volt automobiles.

12-24-2012, 11:50 PM
I can tell you from memory most of the american cars switch from 6 to 12 Volt, Buick 1953,(the 53 Special may have still been 6V as they were still straight 8s, Cadillac 1953, Ford, Mercury 1956 , Studebaker 1956 Packard 1956 Chevrolet 1955, Pontiac 1955 Plymouth 1955 DeSoto 1955

12-24-2012, 11:51 PM
My Late 55 Studebaker Conestoga is 6 Volts

Mark L
12-25-2012, 12:40 AM
Now that makes sense about the higher compression engines. With a 6V system the starters and associated wires would have to progessively get larger and heavier. Switching to a 12V system, we could get more power out of a starter using the same size wires, but still have a reasonable weight in the starter.

12-25-2012, 07:48 AM
Actually, Packard went to 12 volts for the 1955 model year with the new V8, but, surprisingly, they were still positive ground.
1956 Packards were 12-volt, negative ground. :cool: BP

Skip Lackie
12-25-2012, 09:21 AM
In the 1930s, all American cars were 6v, split about equally between positive and negative ground. GM liked negative ground, except for Cadillac. GM switched to all negative ground after WWII. In 1953, GM introduced three GM limited-edtion cars: Cadillac Eldorado, Buick Skylark, and Olds (Holiday? can't remember the model name). They were the first with wrap-around windshields and 12v (negative ground) electrics. The rest of the Cadillac, Buick (except the Special), and Olds models went to 12v in 1954. Chrysler products, Chev, Pontiac, Packard (as noted above by BP) went to 12v in 55, as they introduced their new OHV V8s. Maybe Hudson and Nash, too -- can't remember. Ford products and Stude (and Kaiser?) followed in 56. Some imported cars (eg, VW) remained 6v well into the 1960s.

As to the other part of your original question:: if a 6v system is properly maintained, it will work just as reliably as a 12 v system. The downsides of a 6v system are the lack of readily available, high-quality batteries, the need for proper maintenance in order to get all 6 volts to the starter, and the desire of many owners to equip their vehicles with modern (12v) audio and plug-in communications hardware.

Mike Van Veghten
12-25-2012, 12:50 PM
Leo wrote -
""Finally, I'd like to hear the pros and cons of 6V vs. 12V. I ask this because I've read some comments from some 50s car owners who are satisfied with the original electrics, so I'm curious what tends to motivate an owner to go through all the rigamarole to upcurrent a 6V to a 12V system.""

One main thing for me is...much better lighting, and better overall power when the wipers, head lights, heater, defroster and radio are on at the same time..! The 6v generator just can't keep up well.

Even low power alternators have a tuff time.

As one who drives an old Stude as a daily driver, I want to be able to see clearly, farther down the road than the 6v system will provide.

Like you (Leo), I'm also not an electrical wizard. Mechanical stuff...no problem...electrical...Hmm..!
But I'm fully rewiring my 54 Conestoga as we speak. A combination of new (reproduction) wire harnesses and home made harnesses. We'll see how well I can follow a wiring diagram...!


12-25-2012, 12:55 PM
Even though my '54 sedan has a '64 259 engine in it, I kept the car 6 volts. The wiring harness was still quite good, as well as all the other electrics. It made sense to me to just use a 6 volt V8 starter and the earlier starter gear on the '64 flywheel. I do not regret that decision.

As to batteries, I do agree that it's hard to find a good long lasting 6 volt battery. Since my car is a driver and not a show car, it now has a 6 volt Optima battery and it really spins the engine over. There are battery 'cases' available for the Optima batteries that lool like tar top batteries, but I couldn't find one that would fit into the relatively small battery box on a '54 sedan.

Make sure the battery cables are all at least 1 gauge, or even better 0 or 00 gauge. Make sure you have good grounds, and that the jumper from the engine to the frame is in place. I added another ground jumper from the frame to the body also.

For the headlights, using a relay so all the current to the headlights is not going thru the headlight switch makes all the difference in the world as to how bright the headlights are on 6 volts.

And last but not least, be careful about using those battery disconnects with the small knob (that you simply loosen to 'disconnect' the battery) on a 6 volt system. Some of these can have a very high resistance and make a substantial difference in how the engine cranks.......ask me how I know :(. I'll post about my recent experience with one of these in the next few days.

My opinion only, based on my experiences. I know others have different opinions.

12-25-2012, 06:19 PM
I don't think Chrysler (Plymouth, Dodge, DeSoto and Chrysler) changed to 12 volts until the 1956 models.

12-25-2012, 07:29 PM
I don't think Chrysler (Plymouth, Dodge, DeSoto and Chrysler) changed to 12 volts until the 1956 models.

Right, Howard. Only the Crown Imperial had 12-volt electrics among 1955 Chrysler Corporation cars.

All others retained 6-volt, positive-ground sytems through the 1955 model year and went to 12-volt, negative ground systems for 1956. BP

12-25-2012, 08:13 PM
Agree. Less copper for 12 volts, and as of 1956 everyone had standardized to 12 V neg ground, with the exception of some trucks that year.
And those battery disconnect switches are seldom of any actual use, and just cause more resistance problems as stated. Can't figure out why anyone would put one on their car actually. Various cars have sat for weeks and months without them to no harm