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G'day all, This should be an interesting topic as I'm sure that many of us are not quite sure why US auto manufacturers settled on 6V electrical systems and why they changed to 12 V systems. I have read a number of articles in the SAE Journal over the years. Owen-Dyneto and others are sure to have some interesting facts to baffle us with. For kick -off, Battery freezing- I understand that the high current draw on a 6V starting system will not allow the battery to lower it's specific gravity to the same extent as a 12 volt battery cranking system. The result is that there is less chance of freezing a 6V battery in service than a 12 volt battery. Is this true? Best regards Peter Toet

The 12v conversion was strictly a cost issue. With 12v about half the wire can be cut out of the car as opposed to 6v. However, the 12v will conduct better with less voltage drop over long stretches of wire.

THe HP revolution brought on the push to sell the US public 4 bbls, 4 speeds and bucket seats not to mention additional accessories which would require more and more wire. Copper is expensive and always has been relative to the times analyzed.

"as I'm sure that many of us are not quite sure why US auto manufacturers settled on 6V electrical systems and why they changed to 12 V systems. I have read a number of articles in the ..."

I'm missing something here. If the US car companies "settled" on 6v or were in some sense slow about converting to 12v. THEN, what international car companies were so fast to use 12v so much earlier and how much earlier????

G'day all, especially PackardV8, I understand that the largest British manufacturers such as Austin and Morris went for 12V initially. These cars were widely exported and we got lots sent to Australia. Almost all British (and early Japanese) motorcycles were 6V but varied in polarity. Marchal in France was 12 V and to my reading, most Packards exported to Europe in the 1930's were converted to 12V Marchal or Lucas. ( Lucas, the Prince of Darkness and widely held as the inventor of the short circuit and open circuit) I have not had a chance to chase up the SAE article on 6V versus 12V systems but I seem to recall that the main reason for changing to 12V was the ignition voltage required for higher compression engines. As to the settling on 6V, I understand that the SAE in America was always working toward standardisation and as electrical systems became more prevalent on vehicles in the Nineteens, 6 V was accepted as the standard for a number of reasons. 6V lighting systems are supposed to be better than equivalent wattage 12 V systems as the filament is shorter and located closer to the focal point of the reflector. 6V bulbs were thus less prone to filament failure on the usealed roads of the time. I repeat that I am not implying that the US was slow to convert to 12V. 12v batteries are also more prone to tracking and loss of charge if the top of the battery is wet.

Did the 12v vehicles of Britain and france have TWO 6v batterys in series or one 12v battery???


Also: "I have not had a chance to chase up the SAE article on 6V versus 12V systems but I seem to recall that the main reason for changing to 12V was the ignition voltage required for higher compression engines."

I'd double check to make sure that was really an SAE article because the claim does not really make sense.

12v Points ignition systems nearly all run some kind of resistor between the coil and points to cut voltage to 6 to 8 volts. 6 and 8 v systems run no such resistor.
Most SHORT RUN racing vehicles prior to the 70's often ran no lites or very few electrical items other than ignition. They would drop the generator and often even the starter motor for weight control. Just run a small 6v motorcycle battery to power the ignition and maybe a gauge or two. Altho mags were often run too but not usually by the old seasoned pro's, well maybe they had a sticker on the side of their car that advertised some magneto brand.

I believe that the SAE article was in the vein of "the case for 12V "or similar. Please bear with me as I get the chance to dig it out. On resistors in 12V ignition systems, the resistor operates after the vehicle engine is started. The system usually has an 8V coil and when you operate the starter the 8V coil is used to give full ignition voltage during the reduced battery voltage cranking period. Once started the coil operates the ignition system at a reduced (8V) voltage using the ballast resistor. Most of these coils have a notice to say that they must be operated with a ballast resistor. I am confident that the early 12V systems used a single battery but I shall find out. Best regards. Peter Toet

It's quite interesting. In the second reply the exported cars were converted to 12v. This I've heard of. Mr. Illich who has owned many cars and museums in Aus. has a 34 model Packard and his car uses the Marchal headlights which he says are a great improvement. (but can't remember if his was 6 or 12v) This also raises another question, if the canadian exported cars had the 12v system. Why were Australian cars exported in 6volt. Does that means that when Packard built export models in canada they must have had 2 electrical installment lines, one for 6v and another line dedicated to 12volt

ok. Here's a question that only requires a general off the cuff educated guess. Let's see if we can get a concensus:

What percentage of all world wide manufactureres produced 12v units prior to the US 12v conversion ca. 1955???

Based on my limited experience with non-US cars prior to 1955 and on posts in this forum i am guessing only 10% of the manufacturers offered the 12v and probably on only 10% of thier entire production.

Am i way off base here???? Maybe so. Or was it more like 30% or 90%???

ok. I think we can answer the original question at the top of this post by even just approximate answers to the following questions:
1. Approximately what year range were the 12v cars sold in Oz????

2. Were cars sold as 6v prior to that year range ????
3. Were cars 6v AFTER the year range ???

4. What brand of 12 batteries were used in that year range of question 1 ??? (this question is not all that important to know but it mite help drive home a point).

Up until electric starters became popular it would not be correct to speak of a car's electrical system. Some had magneto ignition and gas lamps and had no battery at all. Model Ts ran off their flywheel and usually had no battery, their voltage could go up over 20 volts.

When starters and electrical systems came in they could be up to 24 volts.

It was only in the mid to late 20s that 6 volts became standard in the US. At the time a car might not have any electrical equipment other than lights and starter.

The 6 volt probably became popular because that was the cheapest battery that would provide satisfactory performance.

When they went to 12 volts in the mid 50s cars had changed radically. Their high compression V8s required more voltage for starting and hotter ignitions. Plus the many electrical accessories required miles of wire. The wire size could be reduced by half if 12 volts were used. This saved a lot of copper in a year's production of cars.

Plus, the new vinyl insulation was a lot better than the old rubber stuff. Meaning less possibility of short circuits when the wiring got old.

Incidentally many 6 volt cars had 4 volt coils for easier starting. That trick did not start with 12 volt systems.

Why English cars had 12 volt batteries I don't know. In the 50s it used to be amusing to look under the hood and see this great big battery and tiny engine. In some cars the battery was practically as big as the engine. Quote: