Electrical dummy

Sooooo if a 6 volt (3 cell) battery can deliver say 500 amps for a certain time, the energy is 6 volts x 500 amps over x amount of seconds BUTTTTT TTTT if a 12 volt (6 cell) battery has the same amp rating, it can supply twice as many volts x 500 amps over x seconds.

Due to ohms law if you apply 12 volts to a load instead of only 6 volts, the current is doubled, and at twice the voltage and twice the current youre obviously supplying and expending more energy into the starter then if you used a 6 volt battery, n YES shes gonna crank over faster DUHHHHH HH Sooooo its NOT true that a 500 CCA 6 volt battery is gonna make the starter perform the same as a 500 CCA 12 volt battery. Its true that 500 CCA = 500 CCA but 500 CCA at 6 volts IS NOT THE SAME as 500 CCA at 12 volts.

The other thing to note if using two batteries is in series the amperageg rating is NOT increased while the voltage is additive. However, in paralell the amperage rating is addtive while the voltage stays the same.

That all being said, on a 6 volt tractor I recommend the heaviest rated super duty 6 volt battery that will physically fit into the compartment and use 00 gauge battery n starter n ground cables for better cranking. If one insists on converting from 6 to 12 volts the old 6 volt starter can be used n YES it does indeed crank over faster.

Hope this helps best wishes n God Bless

John T Retired Electrical Engineer in Indiana

Understand that a DC motor (such as a starter) is also a generator. The voltage generated by a turning motor is called "back electromotive force", or "back EMF". A motor sitting still has zero back EMF. That's true whether there is any voltage applied to it or not. A stopped or stalled starter motor is basically a dead short. So when you connect a battery to it, the battery will source as much current as it can, which is more or less the CCA rating. However, the current through the starter generates torque which will cause the starter to spin as soon as the starter's torque can overcome the internal friction of the engine.

As soon as the starter starts to turn over, it begins to generate back EMF, which opposes the battery's voltage and reduces the current through the starter. If there is no load on the starter motor, its RPMs will increase until the back EMF almost equals the applied voltage and there is almost no current through the starter. But if there is a load applied, then the speed of the starter motor will increase only until its torque equals whatever is required to turn the engine over.

Now if you replace your six volt battery with a 12 volt battery, then the starter can turn much faster before it reaches the equilibrium point where back EMF reduces torque to what is required to turn the engine over.

So, the short answer is this: If you connect a 12 volt battery to a six volt starter, the starter will turn over roughly twice as fast as it does with six volts. And that makes a big difference when starting an engine.

The strength of the magnetic field generated by an electromagnet is proportional to the number of windings times the current through the windings. Inside the starter, the torque generated by the starter is a function of the magnetic field strength which it turn is a function of the number of turns of wire in the windings times the current flowing through the wire.

In a motor, the size of the wire represents a compromise. If I use a larger wire, I can get more current through it for a given voltage, but I can't have as many turns as if I used a smaller wire. For any given voltage and motor size, there's an optimum compromise between wire size and current.

A starter designed for 12 volts draws less current than a starter designed for 6 volts. Because a 12 volt battery have more voltage to force current through the motor windings, a 12 volt starter can use smaller wire and end up with the same magnetic field strength (which translates to torque) with less current. That's why starter cables for a 12 volts system are smaller than cables for a 6 volt system; the 12 volt starter draws less current and can therefore use a smaller cable.

Remember that CCA is the maximum current the battery can supply, not necessarily the current it can force to flow through the starter. A larger CCA battery will have more reserve capability, i.e. be able to turn the starter for a longer time, but won't necessarily be able to turn the starter any faster unless the current drawn by the starter is close to or above the CCA rating.

An example of this is a diesel truck, which uses either one really large 12 volt battery or two smaller ones in parallel to provide enough current to turn over the starter. If I were to take the truck battery and connect it to a Toyota, the Toyota starter wouldn't turn over any faster, since the maximum current is limited by the starter, not by the battery (the starter draws less current than the battery can supply). On the other hand, if I were to take the Toyota battery and try to start the diesel with it, the current would be limited by the capacity of the battery and the diesel would turn over slowly or not at all (the starter wants to draw more current than the battery can supply).

Clear as mud, right.

Keith

I heard that they may have changed this so don't bet on it.

To get amps divide watts by by voltage a 110 watt light bolt divided by 110 volts equals 1 amp.

A 6 watt bulb divided by 6 volts equals 1 amp
A 6 watt bulb divided by 12 volts equals .5 amps Walt

i do know a 6 volt has only 3 cells and a 12 volt 6 and my gutt tells me that 6 cells are more than 3 so more umph