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12/6 Volt


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Fellow classic car friends,

 

I am wondering about one thing: in 1912 Charles Kettering built the first automotive electrical system and used 12V. Later on almost all (if not all) American cars had 6V, till mid-50s. Why did they change that? The only reason I can think of is the cheaper batteries, with 3 cells instead of 6. Byt all the wiring needs to be thicker with 6V, the reliability suffers, starter motors are weaker, etc.

 

Can you please explain it to me?

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1 hour ago, Szczepan Kolaczek said:

...the reliability suffers, starter motors are weaker, etc.

 

I don't know the reason for 6 volts, but it has been 

said often--including by collector Jay Leno--that there

should be no problem with 6-volt cars if they are 

working properly.  Reliability does not suffer, and

there is no problem starting them.

 

Others might be able to tell you about the early history.

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Posted (edited)
6 hours ago, Szczepan Kolaczek said:

 the reliability suffers, starter motors are weaker, etc.

 

Can you please explain it to me?

Yes - I can explain it. You are WRONG. Period.

 

Most of the Model A guys have 6 volt systems, and they drive them ALL THE TIME. Many 6 volt cars in the Studebaker Drivers Club have no reliability problems. You are correct - use the largest wire you can find, 00 size or even welding cable. Adding a 6 volt positive ground alternator is a good mod to help out charging issues. When I put one in my '49 Champion, the headlights became bright white instead of yellow, and the dashboard lights brightened up. It never failed to start for me - cold weather or hot. I never considered changing over to 12 volt - I didn't need to, it was going to cost too much, and I wouldn't have gained anything.

Edited by Studemax (see edit history)
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The invention of the simple spark jump ignition is what made the internal combustion engine practical. The early system consisted of 5 or 6 dry cell batteries to make up 6-8 volts with a coil to boost the voltage enough to jump a spark plug gap. Most if not all cars in the early 1900's had 2 sets of batteries. I'm not certain why 6v was chosen but that became the common industry standard of the earliest ign systems. The batteries were at first used for ignition only, lighting was by gas or kerosene wick flame. Electric lighting began about 1909 with 6v bulbs to operate off the 6v ignition batteries, although some cars were furnished with separate lighting batteries.

 

The 1912 Cadillac electrical system actually had a 24 volt starter. The original 1912 design used four, 6v batteries and a set of relays that switched the batteries in series to make 24 volts for the starter. Once the engine started, the relays switched the batteries in parallel for 6v to operate the lights only. Another relay and 6 volt regulator, switch the 24v starter to 6v generator mode to keep the batteries charged. Dry cells were still used at start up and the driver would switch the ign. to magneto. Kettering was able to improve his starter design to operate off 6v  in 1913. Most other companies added electric start in 1913 or 14 with similar 6v design. The same basic 1913, 6v design with separate dry cells and mag was used by Cadillac up through 1915, the first year V8. 1916 was the first year that Cadillac only used one 6v battery for starter, ignition & lights. 

 

I would say that the fact that 6v was the accepted standard for ignition and lights became the standard for starters at that time of development of the automobile.

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Posted (edited)

You can design the equipment for any voltage you want. Double the voltage for half the current to do the same amount of work. Why not 24v? Why not 48v?

 

Since using twice the voltage cuts the current in half. (at the same power level or wattage), you can use wire half as big.

 

The engineer has to decide how fast he wants to turn a starter, and how much power that will take. The voltages are multiples of 2 volts because a lead acid cell is approximately 2 volts. 3 cells is about 6 (6.3) volts. 6 cells is about 12 (12.6) volts. Additionally early ignition systems before starting motors sometimes used dry cells. Those are 1-1/2v. You can arrive at the same place pretty easily  4 cells = 6v, 8 cells = 12v, etc.

 

At the same power level (wattage) you need twice as many cells for a 12 volt battery, but they can be half as big, so there's not much difference in the amount of lead or any other materials. It is possible that the commonly available lead plates at the time (used in storage batteries for radio, farm power, etc.) were sized better to match up to the cranking needs of an engine when using 3 cells rather than 6. Still, in the teens and twenties there was no definite 6 volt standard. Studebaker and Hupmobile used 12 volt systems on a model or two in the teens, and Dodge Brothers used 12 volts for many years.

 

Today people seem to think that a starter has to spin really fast to start a car, that it has to go "CHE CHE CHE CHE CHE" like a gear reduction starter on a 60s or 70s Chrysler product, or something with a Japanese starter a little bit newer. 1910s and 1920s engineers had no 1960s Chryslers to listen to, so they just picked the speed they felt was needed to crank the engine they had designed. Then an electric motor would be designed or selected with enough power to do the job, and a gear ratio selected to match the RPM to whatever was needed at the crankshaft. The horsepower needed from the electric motor is directly convertible to watts. After allowing for mechanical and electrical losses, the rest is just picking a voltage for the electric motor design, and supplying sufficient current (amps) at that voltage to arrive at the necessary wattage. Contrary to popular belief, it does not matter what that voltage is.

 

Engines of that time had a much slower maximum RPM and a much lower idle speed. The camshafts of the day were designed to make good dynamic compression in this lower RPM range, and so it is only logical that the cranking speed needed to start them would be slower than a modern car. It had not been long since they were starting them with hand cranks, and a removable hand crank for emergencies was usually provided until the mid 1930s at least.

 

Any system, no matter the voltage, needs maintenance to keep working right. In the mid 80s I was driving a 51 Nash for a winter car, and it was a terrific one. I never had any trouble starting it. Some of my friends with their modern (at the time) 12 volt cars could not be bothered to maintain them and were not doing so well. For at least 2 winters I was carrying around a 12 volt battery in the trunk to give other people jump starts. It is always the first thing that pops into my mind when I see threads like this.

 

The only real, tangible advantage to a 12 volt system I am aware of (other than cheaper wire) is the "starting bypass". When a car with a charging system is running, the system runs at a voltage appropriate for charging a battery. That is about 7.4-7.6v on a 6 volt car, and about 14.2-14.7v on a 12 volt car. The ignition system has to be designed to run at that voltage. Cranking voltage on the other hand will be well below the normal 6 or 12 volt battery voltage, so the voltage seen by the ignition system will be several volts below what it is designed to run on. It might not even fire if the engine is chugging over on a battery that is almost dead. What some 12 volt cars have is an ignition designed to run on about 8 volts, and a resistor to drop the voltage. Then, while cranking, they short out the resistor and send full battery voltage to the ignition. In this way the ignition always gets full voltage or a little more while cranking, and the spark will not be weak. I have never seen this feature implemented in a 12 volt conversion yet, and I have seen a lot of them. Recently there have been at least 2 threads where people want to remove this feature from factory 12 volt cars so they can run some fancy aftermarket coil.

 

Modification of a cars electrical system, if wanted, should begin with an understanding of basic electricity, not marketing hype, advertising copy, or old wives tales.

 

 

Edited by Bloo (see edit history)
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12 hours ago, Bloo said:

Modification of a cars electrical or any other mechanical/operational/technical system, if wanted, should begin with an understanding of basics, not marketing hype, advertising copy, or old wives tales.

And this ^^ of course should be applied to any and all aspects of automotive (or any other, be it a boat, clock, fire hydrant, house, etc) repairs or restoration, especially if reasonably successful outcome is to be expected.

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Posted (edited)
13 hours ago, Bloo said:

You can design the equipment for any voltage you want. Double the voltage for half the current to do the same amount of work. Why not 24v? Why not 48v?

The Bentley Bentayga is the first new vehicle to use the 48 volt SAE standard.

 

Big rigs with the large-displacement diesels often used 24 volts to start them until the glow plug came along.  Even then, they still required two twelve volt batteries, as did the GM cars with the ill-fated 5.7 diesel.  My own Studebaker Diesel has two 12 volt batteries in parallel for cranking.   Kind of funny in a way, as the old-skool diesels don't need any electrical source to keep them running.

 

Craig

Edited by 8E45E (see edit history)
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There are still some Diesel trucks, construction machinery and farm machinery built today with 24v starting.

 

I have not had a problem restoring 6v systems to operate properly but you do need to use proper size cable and make sure all the connections are good. Copper battery cables and starter windings can be damaged by prolonged cranking cycles, whether its a 6 or 12 volt system. You do need to spend the bucks to buy the largest & heaviest 6v battery that will physically fit in the tray. You need to be sure that the battery has heavy enough lead plates to withstand the heat from the current drain but most importantly, don't over heat the system.

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Posted (edited)

Raising the voltage lowers the amperage which enables the manufacturers to use smaller gauge wire to perform the same task. Smaller gauge wire is cheaper and lowers the cost of production, thus increasing profits

Edited by John348 (see edit history)
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In the past 50 years, or so, many irrefutable facts have arisen in the automotive hobbies. One being, 6 volt is no good whatsoever. Generators are worse. You need an alternator. Drum brakes are by nature unsafe. Same for single reservoir master cylinders. You and everyone is going to die in the flaming wreckage. A 47 Buick Roadmaster cannot keep up with modern traffic and needs an LS engine swap and an overdrive automatic because pushing that extra  pedal is too tiring for the 21st century driver

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I don't know the answer of why they mostly chose to use 6 volt batteries, probably lost to time, unless there is some literature from back then that survives.

 

I suspect it was a economic decision, cheaper and easier to manufacture 6v than 12v and the supply chain was setup due to it. The savings on wiring would have been negligible compared to the difference in cost between a 6 & 12 volt battery.

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21 hours ago, Bloo said:

or old wives tales.

 

Here is one for you, though its more a vintage old blokes tale.

 

That a 6 volt battery supplies/produces twice the amps as a 12 volt battery when starting the same car with the same starter motor.

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23 hours ago, jdome said:

The invention of the simple spark jump ignition is what made the internal combustion engine practical. The early system consisted of 5 or 6 dry cell batteries to make up 6-8 volts with a coil to boost the voltage enough to jump a spark plug gap. Most if not all cars in the early 1900's had 2 sets of batteries. I'm not certain why 6v was chosen but that became the common industry standard of the earliest ign systems. The batteries were at first used for ignition only, lighting was by gas or kerosene wick flame. Electric lighting began about 1909 with 6v bulbs to operate off the 6v ignition batteries, although some cars were furnished with separate lighting batteries.

 

This is the dry cells batteries.

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1 hour ago, maok said:

 

Here is one for you, though its more a vintage old blokes tale.

 

That a 6 volt battery supplies/produces twice the amps as a 12 volt battery when starting the same car with the same starter motor.

This one is an interesting tale....  If taken literally there are issues with the comparison as the starter motor was designed for operation at either 6 or 12 volts. I have never seen a starter that can be field changed between 6 and 12 volts. With this in mind the 1/2 voltage equals twice the amperage and twice the voltage equals 1/2 the amperage rules are out the window. The only way those rules work are in relation to power or watts. Power can also equal horsepower in regard to electric motors (starters). By saying "the same starter" the electrical rules are now trying to compare apples to oranges.  I have never tried to measure the parameters, but I do know that when I jump my 6 volt car with a 12 volt battery the starter turns much faster and the amperage is much higher. With the above mentioned rules, the amperage should be much lower. The reason the rule does not hold true is because the impedance/resistance of the starter now becomes the constant and when you double the voltage to a constant resistance the amperage doubles. Now just to be fair, DC motors have more variables than just resistance, but the rules still apply generally.

 

My point is that for rules to be accurate the required variables need to be considered for the situation. I am not trying to start an argument about electrical theory, but just point out how simple things can make a BIG difference in the expected outcome.

 

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One old urban legend floating around out there is that 6 volt systems will have electrical fires more than 12 volt systems. Some people think they have evidence for this, but I believe they really only have a loose correlation that's more complicated than they think. Old 6 volt systems may (or may not) catch fire more than newer 12 volt systems, but it probably doesn't have anything to do with 6 vs. 12 volt. If it's original wiring, then a 6v system is older than a 12 v system and therefore maybe in poorer condition due to age. Also, newer 12 volt systems may have improvements like added over current protection that have little to do with voltage.

 

Not helping matters is that old school cloth wire insulation went out of production about the same time that 6 volt systems did, so those two things get conflated pretty easily.  My old cars have battery disconnect switches that get turned off when the car isn't running, so I avoid a lot of problems, anyway.

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52 minutes ago, 37_Roadmaster_C said:

This one is an interesting tale....  If taken literally there are issues with the comparison as the starter motor was designed for operation at either 6 or 12 volts. I have never seen a starter that can be field changed between 6 and 12 volts. With this in mind the 1/2 voltage equals twice the amperage and twice the voltage equals 1/2 the amperage rules are out the window. The only way those rules work are in relation to power or watts. Power can also equal horsepower in regard to electric motors (starters). By saying "the same starter" the electrical rules are now trying to compare apples to oranges.  I have never tried to measure the parameters, but I do know that when I jump my 6 volt car with a 12 volt battery the starter turns much faster and the amperage is much higher. With the above mentioned rules, the amperage should be much lower. The reason the rule does not hold true is because the impedance/resistance of the starter now becomes the constant and when you double the voltage to a constant resistance the amperage doubles. Now just to be fair, DC motors have more variables than just resistance, but the rules still apply generally.

 

My point is that for rules to be accurate the required variables need to be considered for the situation. I am not trying to start an argument about electrical theory, but just point out how simple things can make a BIG difference in the expected outcome.

 

 

Actually the reason the rule does not hold true, is that is not quite the right rule, the power equation (P = V x A)is more appropriate not ohms laws, which is what most people use. And the general rule with electric motors - voltage determines speed of rotation and amperage handles torque required.

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4 hours ago, maok said:

 

Actually the reason the rule does not hold true, is that is not quite the right rule, the power equation (P = V x A)is more appropriate not ohms laws, which is what most people use. And the general rule with electric motors - voltage determines speed of rotation and amperage handles torque required.

Even the power equation fails with the example, but you are very right, it is closer!  Well to be more inclusive would require complex network analysis including magnetic field density, magnetic pole interaction, back emf balance, actual mechanical load, and much more. Also, DC motor speed is a complex relationship between magnetic fields, field intensity and field density. Now with that said, the actual point was that way to much is blamed, confused and/or bundled with the simple misapplication of Ohms law, Watts law, power conservation and the list does on. Lets not even start on AC moving field theory. Alternators are AC devices and people think they are better than (pick your poison)!!! 😇

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I think a contributing factor to using 6v is the pitting that occurs in the ignition points with higher voltages in the primary circuit.   12v will make a stronger arc when the points open, causing the pitting.  Look at how 12v ignition systems have a resister built into the wiring to reduce the voltage in the primary circuit to stop the pitting.

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