MTFCA Forum

I have had a slow cranking starter in my Model T for decades and chalked it up to it being 6V. Don't all Model T' starters crank like an old tractor with a dead battery? Recently I was helping a friend with his T and was surprised at how fast his starter cranked the engine, and assumed he was running a 12V system. Well live and learn, he has a 6V starter and a 6V battery. So I took my 100 year old starter to a starter/generator repair guy who has lots of experience with Model T starters. He took it apart, showed me the issues with it, and allowed me to help as he repaired it. Now it cranks over fast, no more hot cable terminal stud, no more hot ground strap, what a pleasure.

You can teach an old dog new tricks.

Excellent news Jeff

Now you know why so many folks ask "Why?" when someone insists they must convert to 12V to get the car started.

Measure the voltage between the starter terminal and engine ground while some one is stepping on the starter pedal for you and you will be surprised to read as little as 3 Volts and note the engine still turns over and starts.

With a good battery, 0 Gauge cables and the ground strap replaced with a short O Gauge cable and you can measure 5 to 5.5 Volts there and have the engine start a lot faster, unless your starter needs repair.

That’s the reason some will decide a 6 volt starter is just not strong enough for a good start. And again it begs the question why when 6 volt cranked Model T’s other old cars, tractors and etc for years and years. It’s amazing what you’ll find when taking the time and check the system from starter to switch.

I once caused offence to someone when I casually mentioned that if 6V can crank a great big V8, that there must be something wrong if it can't crank his Model T. One has to wonder how the American car industry survived, producing millions of defective cars for 35 years.
My experience is that many people refuse to believe their Model T has a defective starter motor, or other electrical fault, when by magic, a 12V battery seems to solve all their problems.

Packard built a number of luxury cars with 473 cubic inch 12 cylinder engines. They used a 6 volt system for all electrical functions. Packards were popular with customers who could afford anything on wheels.

If a good 6V starter can't spin an engine fast enough to start it, how on earth are we able to start it with a hand crank?

I believe that one reason manufacturers changed to 12 volt systems was the advent of higher compression, higher RPM 8 cylinder engines. With a 6 volt system, ignition point dwell time becomes critically short at higher engine speeds. The points cannot remain closed long enough for the coil to reach saturation.

Another obvious reason is to save weight and cash by using mostly smaller gauge wiring and lower current rated switches.

Yet another reason might have been the development of cheaper, lighter weight car radios that did not require a vibrator power supply.

None of the above were issues with the Model T or with most other pre-WWII cars.

I've driven junk cars all my life, from cheap Fords to Cadillacs. The most reliable as to starting have all used unmodified 6 volt systems, with the Fords generally beating out the GM systems for reliability and ability to start a car with a partly-discharged battery.

When you double the voltage and half the current, you can use a lot less copper in the wire.

Copper is expensive and the amount of wiring added to newer cars makes 12 volts a big savings.

I don't understand why the battery voltage has anything to do with dwell time. As has been said earlier, the main advantage of 12 volts is that by doubling the voltage, you cut the amperage in half. Wire size is dictated by amperage.

John Codman wrote: ↑

Mon May 01, 2023 10:13 am

I don't understand why the battery voltage has anything to do with dwell time.

As I understand it, it has to do with the "ramp to fire" time. In other words, how fast the coil energizes before it releases its spark.