Technical 303 Oldsmobile Starter 6volt to 12 volt Question

I have a 1949 303 Olds motor that came with the original 6 volt starter. I will be wiring my project car for 12 volt. I understand that the 6 volt starter motor can be run on 12 volt for short periods with no problem, but I would like to use a 12 volt solenoid since that appears to be the part that may not last if used with the higher voltage.
My question is, will a 12v solenoid for a later year Olds starter work. I was looking at getting one for a '53 Olds because it is listed as being 12v.

 

Mark, that's not actually true. Any time you increase voltage into a DC circuit current draw will go up. According to Ohms Law it should double with a doubling of voltage in a purely resistive circuit, but in the real world that's not true. The starter and solenoid are inductive circuits, and there's other factors at work (coil saturation, impedance to name just two) that will prevent the circuit from drawing the calculated amount of current as long as the load remains the same. These factors aren't linear and can vary by construction/design. But it's entirely safe to say that current draw will go up compared to 12V components, and with that, increased heat will be generated.

Duty cycle also enters into this heat build-up. Reduce the 'on' time and reduce the heat. So don't grind on your 6V starter supplied by 12V, it will burn it up sooner or later. But if the motor starts quickly, no harm.

As to replacing the 6V solenoid with a 12V version, I'd be careful. The 6V unit is designed for a higher current compared to a 12V one which may or may not be needed. If the OP plans on hitting the road with his car, it might be prudent to add a replacement solenoid to his 'carried' parts just in case.

 

Bcap, I agree with Mark, mostly. I changed my 1950 Buick to 12V in 2012. The starter worked well. Spins REAL fast. Kicks in hard. Finally, in about 2017 the drive gear [bendix? ] stripped. I then installed a 12V hi torque mini from Tom Telesco.

Ben

 

I have been running the 6 volt starter in my 52 Willys Jeep on 12 volts for 30 years with no problem. Since it may sit for a week or more at a time I have to crank it a lot to get fuel up to the carb. I am still on the original starter.

 

I run a 6v starter on a 12v model A. Awesome cranking speed. Most 12v solenoids are made for very heavy duty use so should be fine.

 

I have used 12 volt batterys in my 6 volt flatheads and oldsmobiles for many years with out one failure . don,t worry , after 10 or more years you can buy another 6 volt unit .

 

Thanks guys, I guess I'll be using the starter and solenoid that I have. I bought a modern mini starter with an adapter plate that is made to work on my 303 Olds that I had planned on using. But since I won't be running a hood on the 32 Ford Coupe I'm building, after seeing how the mini starter kind of doesn't look quite right, I started thinking it would be better to use the original starter instead.
I'll carry the mini starter with me as a spare in case the original starter quits.

 

The way I've always looked at it is that it takes X amount of work to turn the engine over. The amount of work required remains constant regardless of the voltage applied to the starter.

Let's say that the starter draw on 6 volts is 200 amps to start the engine. So 200 times 5 volt (actual cranking voltage) is 1000 Watts. Since the starter does the same amount of work to start the engine, let's look at starting on 12 volts. So working backwards, 1000 Watts divided by 10 volts (again real cranking voltage) results in 100 amps. The starter does the same amount of work, but only draws half the current. In my mind it is actually easier on the starter. It is the heat produced by current flow that damages electrical components.

 

12 volt heavy duty solenoids use to be repackaged 6 volt solenoids. This is back in the early 70s

 

The fly in your ointment is that using 12 volts instead of 6 results in the engine cranking faster. ie, more work is being done, so your math doesn't work.

 

I was in a similar situation with my Lotus Cortina with one of those weak Lucas starters that die as soon as you mention higher compression.
I did what Ford did with their "works" RS1800 rally cars and used 2 x 12v batteries in series [24 volt]
once the starter ****on was released it switched back to 2 x 12v batteries in parallel [12 volt]to be charged together.

2 x small Jap hatchback batteries fitted sideways/together in a plastic marine battery box.

 

I'm not sure that's true, but lets say it is. If cranking the engine faster resulted in double the amperage, then you are right at the same point as the 6 volt setup. End result, no better, no worse.

Also, like many others, have run 6 volt starters on 12 volts for years with no problem at all. I don't think it overloads the starter in any way. If the engine was locked up, the increased voltage would cook the starter faster, but that's the only thing I see.

 

You're trying to apply Ohms Law, which is only 100% true with purely resistive circuits. That's not what we have here. Motors are rated in horsepower, not watts, for this reason. And operate according to AC principles, not DC. So, let's explore the differences between a 6V and 12V starter, and I'll try to keep this as simple as I can.

Both are about the same physical size, both spin the motor at about the same speed for starting. Both will produce about 4 HP for the 'average' V8, or about 3000 watts. If you dis***embled them, you won't find much different inside either. The field poles and armatures will be pretty much the same size. Generally, the only noticeable difference will be larger wire used for the armature and field windings on the 6V unit, to allow higher current. But doubling the voltage to the 6V unit won't double the speed or power under load. You will get a speed increase (which indicates that more power is being produced) but it will be closer to maybe a 20% increase. Why is this?

The answer is the physical size of the iron field and armature poles. For a given size, there's a limit to how strong of a magnetic field that can be generated. It's the strength and interaction of these fields that produces the power output. Once the iron cores reach magnetic saturation (maximum strength), any additional power input is converted into heat. This is the reason for caution about running a 6V starter for too-long periods on 12V, it will heat up faster than the 'correct' starter will, even if the total current being drawn is less than what it uses on 6V. This effect is also the reason for ballast resistors for ignition coils.

To get more specific detail, you'll need an electrical engineer who's well-versed in motor design.