6 volt starter with 12 volt system

But the attitude that 6v starters are somehow inadequate is just not true.

I ran my old 54 Chevy over 100,000 miles on 12v with no starter problems. All local trips.

All my working tractors are 12v M's and H's with 6v starters. Although I try to maintain my equipment, when the points get a little burned, a little water gets in the gas, the plugs foul, etc., they still get started and we don't worry about a little extra cranking until the batteries start getting cranked down.

The starters just don't burn up.

High amps cause wires to heat up, lower amps means cooler wires.

All starters are momentary motors, not rated for continuous output, so ANY starter will burn out if run too long under load.

The opposite case is best illustrated by well known "brownouts" during the summer on the east coast. Voltage drops because of overloaded circuits caused by too many AC being used. When voltage drops AC motors demand full wattage and get it by increasing amps and burning out AC motors.

The 6-volt starter will spin the bejeezus out of the engine, and last for as long as you'll need it if you don't abuse it. Learn to use the choke, and NEVER crank for more than 2 seconds.

Teh 6v starter is superior to a 12v starter wnd will give you many years of good service.

If you ever have to have it rebuilt, put the same coils and armature back into it.

volts = amps x resistance

or, rearranging things to better fit our purpose

amps = volts / resistance

regardless of what the resistance is (starter resistance is very small by the way) the resistance hasn't changed because, uh, you haven't changed the starter right? The volts are doubled like this

(6 x 2 = 12) so the formula simply says the amps are doubled.

Most notably, all this means is it'll spin like never before and burn up rather quickly if you grind and grind and it doesn't start. If it doesn't start right off, fix the problem. The starter will last a good long while assuming it is in good shape and you don't abuse it. The doubled amps are harder on brushes and commutator and they build heat in the armature and field coils more quickly.

Very simply back EMF is a voltage generated by the armature spinning in the magnetic field and which opposes the system voltage. Back EMF will vary from 0 volts (armature not turning) to very near supply voltage (armature spinning freely with no load).

This means that your equation is correct for predicting the initial inrush current, i.e. when you first hit the starter switch and the armature just starts to turn. However once the armature gets spinning on 12 volts, the back EMF for a 6 volt starter may be as high 6 or 7 volts. Therefore once it gets the motor tipping over, your 6 volt starter may actually draw LESS current on 12 volts than it did on 6 (yeah I know it sounds counterintuitive....)

Granted the higher inrush current on 12 volts is harder on brushes, commutator, etc And mechanically the higher initial torque surge is harder on the Bendix drive (that “bang” you may hear when you hit the button). But this is somewhat offset by the reduced current once the starter is spinning, also by the fact the engine often starts more quickly so starter isn’t required to grind on like it did on 6 volts.

Bottom line – so long as the starter spins the motor, it won’t burn out any faster on 12 volts than it will on 6, and may in fact last longer. Case in point: The first 12 volt alternator conversion I ever did (a ’56 S-180 farm truck) is still going strong and still has same 6 volt starter on it before I did the conversion – nearly 30 years ago...

However I submit rather this is an example of "great minds thinking alike"...(!)

A good rule of thumb, as posted in Bob M's page, I believe, is to not spin the starter for more than 15 seconds between two minute rests. I've never had a problem starting my tractor within that first 15 second time frame after converting to 12 volts.

Unlike light bulbs, the 6v starter is overdesigned for 12v service.

When I'm tired and mad (yes, it happens!) I grind and grind to get a tractor started and don't burn up starters. I'm much more concerned with the cranking time on my diesel Dodge.

For electrical power in WATTS

WATTS = AMPS x AMPS x RESISTANCE or for the same thing another way

WATTS = AMPS x VOLTS

Since I don't have actual numbers I'll just use words and say that the power applied to a 6 volt starter with a 6 volt battery is much less than that applied to the same starter by a 12 volt battery. If it were not the starter could not crank the engine faster as we all know it does with a 12 volt battery. The Volts we know have doubled from 6 to 12. The AMPS may even be less (than for the 6 volt case) as you say (I'm not sure) but they are certainly not near half so the power delivered in watts is much greater for the 12 volt case. It's the power that heats up the starter and can cause it to burn up more quickly. I'll stop here.

Starters, by their nature, don't see voltage. They see ampreage. Leave 'er on there and run it.

Allan