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Old 02-24-2020, 08:01 AM   #1
Flyboy1st
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Default I wish I would have waited

I converted to a 12 volt alternator and settled for 2 gauge cables instead of 1 gauge. 2 gauge were available in a lot of stores so I changed out battery cables to 2 gauge. I was in Tractor Supply yesterday and they have all kinds of 1 gauge battery cables and other tractor parts that will fit a Model A. Wish I would have waited.
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Old 02-24-2020, 08:06 AM   #2
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Default Re: I wish I would have waited

Tractor supply carries a lot of 8N Tractor parts which is basically a model A, just more
refined......
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Old 02-24-2020, 03:56 PM   #3
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Default Re: I wish I would have waited

With 12v you don't need as large of a cable as with 6v. Twice the voltage, half the amps. If you are having issues spinning a 6v starter with 12v I suggest you check your connections.
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Old 02-24-2020, 04:18 PM   #4
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Default Re: I wish I would have waited

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With 12v you don't need as large of a cable as with 6v. Twice the voltage, half the amps. If you are having issues spinning a 6v starter with 12v I suggest you check your connections.
This argument only holds true if the starter continues to produce the same power but as we all know, the starter spins faster on 12 volts than on 6. That means it produces (and consumes) more power. In fact, a 6 volt starter running on 12 volts will produce 4 times the power.
Put another way, the resistance of the starter remains the same. If it was say, 1 ohm on 6 volts, it is still 1 ohm on 12 volts. At 6 volts, it would draw 6 amps while at 12 volts, it would use 12 amps. Clearly then, the current is doubled for a 12 volt system, not halved.
Now that that is said, smaller cables are a good thing when you've converted to 12 volts because there will be a (small) voltage drop in the cables, which is a good thing here but bad if you are on 6 volts.
IMO, this half the current thing is just another myth amongst Model Aers like a restricted radiator will cause the coolant to overflow but that is a whole different subject and not part of this thread.
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Old 02-24-2020, 08:48 PM   #5
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Default Re: I wish I would have waited

For the same power, a 12 volt system will draw half the current. If you double the voltage, current is halved. Power (watts)=voltagexcurrent.

Last edited by Jacksonlll; 02-24-2020 at 09:11 PM.
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Old 02-24-2020, 09:26 PM   #6
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Default Re: I wish I would have waited

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For the same power, a 12 volt system will draw half the current. If you double the voltage, current is halved. Power (watts)=voltagexcurrent.
Quite so but it is not the whole story. it is the resistance that remains the same - not the power.
For the sake of the discussion, let's say the starter has a resistance of 1 ohm. That would mean it would draw 6 amps at 6 volts. (Resistance = voltage / current) If 12 volts (double) is connected across it, the resistance doesn't change and the current goes to 12 amps - double). As you say, the power = current x voltage. If both current and voltage is doubled, the power is quadrupled.
In short, running a 6 volt starter on 12 volts will make it run at 4 times the power - that's why they crank so fast. With 4 times the power available, a smaller cable is desirable to restrict the current, even if only a little.
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Old 02-25-2020, 12:23 AM   #7
Richard in Anaheim CA
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Default Re: I wish I would have waited

This should get interesting
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Old 02-25-2020, 12:54 AM   #8
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Default Re: I wish I would have waited

Meanwhile back at the ranch... You should be fine with the smaller (2 gauge) wires on your 12v system. I have never had a problem with them.
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Old 02-25-2020, 03:19 AM   #9
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Default Re: I wish I would have waited

Quote:
Originally Posted by big job View Post
Tractor supply carries a lot of 8N Tractor parts which is basically a model A, just more
refined......
Actually, the 8N (as well as the 9N and 2N) engine is basically half of the 239 flathead V8 engine. Pistons, rings, valves, valve lifters are identical and interchange completely. The 8N (etc.) oil pump and starter came from the little 60 HP V8.
But nothing interchanges with a Model A engine.
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Old 02-25-2020, 06:20 AM   #10
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Default Re: I wish I would have waited

If that starter was using four times the power, it would be glowing red hot. It only takes so much power to spin an engine. You can't make it use four times the power. The power used remains about the same, so at twice the voltage, the current draw is about half. That's why the world uses 20,000 volts when they transfer power over the high lines. So the current would be small and carried by small, light wires.
If you were operating a heating element, then 12 volts would let it use more power and glow like a light bulb. The starter motor puts out just so much power.
I'm done with this.
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Old 02-25-2020, 12:14 PM   #11
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Default Re: I wish I would have waited

Correct the below if I am wrong.


The math


Assume the starter draws 40 amps at 6 volts (probably not correct but used for comparison of 6v vs. 12v)


6V: R (Resistance) = Volts (E)/Current (I), 6/40 = .15 ohms
W (Power Watts) = I x E, 6 x 40 = 240 Watts


12V: R does not change, same starter as above = .15 ohms
I = E/R, 12/.15 = 80 amps
P = I x E, 80 x 12 = 960 Watts


So when going from 6 Volts to 12 volts using the same starter, Current doubles and Power quadruples


Running a 6 V starter under load continuously like a motor at 12 Volts would destroy the starter . Since it is only used intermittently for a few seconds, it does not heat up dangerously and is allowed to cool off even at 12 Volts.
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Old 02-25-2020, 01:02 PM   #12
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Default Re: I wish I would have waited

Quote:
Originally Posted by 30 Closed Cab PU View Post
Correct the below if I am wrong.


The math


Assume the starter draws 40 amps at 6 volts (probably not correct but used for comparison of 6v vs. 12v)


6V: R (Resistance) = Volts (E)/Current (I), 6/40 = .15 ohms
W (Power Watts) = I x E, 6 x 40 = 240 Watts


12V: R does not change, same starter as above = .15 ohms
I = E/R, 12/.15 = 80 amps
P = I x E, 80 x 12 = 960 Watts


So when going from 6 Volts to 12 volts using the same starter, Current doubles and Power quadruples


Running a 6 V starter under load continuously like a motor at 12 Volts would destroy the starter . Since it is only used intermittently for a few seconds, it does not heat up dangerously and is allowed to cool off even at 12 Volts.
You got it!!
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Old 02-25-2020, 01:27 PM   #13
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Default Re: I wish I would have waited

30 PU is basically right, but actually, it's more complex:

In theory, the starter will need 2 times the normal current @ 12 V, as written above.
In reality, an electric motor will try to reach it's no-load-speed. That would only cause a relatively low current and would not be big a problem. You could even operate the starter motor @ 12 V for some time like this without really damaging it.



What limits the speed of a DC electric motor is the induced voltage which works against the operating voltage. So if you take a motor with absolutely no friction that has reached it's no-load-speed, the induced voltage is just as high as the operating voltage, it cancels it out. ---> no further acceleration



Because of the load which the electric motor has to drive (compression and fricion of engine) it will not reach it's no-load-speed. It rotates slightly under that speed, and if you do not change the operating voltage, it keeps getting slower and draws more current the more load is applied to it.
I'd assume the engine is (at the rotational speed of the starter motor) a fairly linear load, which naturally increases with the rotational speed of the starter.
So yes, the starter will draw a lot more power, maybe not exactly 4 times the normal power, but certainly a lot more than under 6 Volts. I'd guess about 3 to 3,5 times as much.


That's not a big problem for the windings of the motor, the time needed to start a healthy car is not long enough to damage them because of excessive heat. The problem is the collector and the brushes. With the way higher current, the wear on them will be a lot worse than under normal circumstances. So if a starter normally lasts say 10 years, it will not even last half as long with the increased voltage.
That's the reason I'd always either stick with the stock voltage (which works absolutely fine if you have a healthy electrical system) or convert to 12 V and use the correct 12 V parts. With these old cars, it's not even much that has to be changed, so I'd personally not use the original parts with 12 V.


Please bear in mind that the above is only a really simple breakdown of the electric DC motor. For example it doesn't cover the timing of the motor (turning the brushes slightly against the direction of the rotation to increase the performance) or having different numbers of windings or poles.


tl,dr: Use the proper motor for your voltage.

Last edited by bavArian; 02-25-2020 at 02:08 PM.
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Old 02-25-2020, 02:05 PM   #14
30 Closed Cab PU
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Default Re: I wish I would have waited

In my simplified answer, I was assuming the starter was mounted creating a load, and the load did not change Also I showed in the math current is doubled not, 4x. But thanks for the details.
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Old 02-25-2020, 02:07 PM   #15
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Default Re: I wish I would have waited

Aii, of course the current's doubled and the power is quadrupled. Corrected it.
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Old 02-25-2020, 02:15 PM   #16
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Default Re: I wish I would have waited

Quote:
Originally Posted by Richard in Anaheim CA View Post
This should get interesting
there goes the Keep It Simple help..interesting enough for me to keep reading, what the heck is wrong with me?
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Old 02-25-2020, 03:05 PM   #17
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Default Re: I wish I would have waited

All that and no one actually answered the OPs question, except maybe 'The Master Cylinder' in post #8.
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Old 02-25-2020, 03:33 PM   #18
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Default Re: I wish I would have waited

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Originally Posted by Ruth View Post
All that and no one actually answered the OPs question, except maybe 'The Master Cylinder' in post #8.
Hey, I didn't read any question in the OP!
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Old 02-25-2020, 05:16 PM   #19
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Default Re: I wish I would have waited

Well. at least some of you have cottoned on. Double the voltage - double the current = quadrupled power as I said in posts 4 and 6
Four times the power from the starter spins the engine fast enough that the fan nearly pulls the car along!!!
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Old 02-26-2020, 05:58 AM   #20
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Default Re: I wish I would have waited

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All that and no one actually answered the OPs question, except maybe 'The Master Cylinder' in post #8.

Literally NO question in OPs post.
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