6 to 12 conversion

[Restorer32]

Can anyone tell me what the amp draw of a 6 volt ignition coil would be? Any tips on converting a 6 volt system to 12 volts but retaining the original "theft proof" coil and cable ignition by using a voltage reducing resistor?

[Guest JT]

Resistance of a 6 volt coil is somewhere around 1.2 ohms.

[Guest De Soto Frank]

According to the dash ammeter of my De Soto, it is less than 5 amps, more likely 2 to 3 amps...

I will see if I can get an exact reading...I have the armored cable to work around too !

I'm no electrical engineer, but if you do this, you will need to make sure your resistor is of the appropriate resistance to drop the voltage, AND of sufficient wattage to dissipate the amount of current/heat drawn by the six-volt device....and put the little devil where it won't harm anything if it gets a bit hot...

Why not try a ballast resistor for a 1960's Chrysler as a test, and see how that does? These are easily obtainable from any jobber carrying KEM or Standard Ingition Products.

About 10 years ago, I owned a 1948 International KB-2 pick-up that someone had converted to 12 volts...there was a "voltage dropping resistor" in the power wire to the 6-volt heater fan...looked like an aftermarket porcelain heater heater switch, minus the knob. Well, after running the heater fan for a few minutes, that resistor was hot enough to give a very nasty burn if touched...( guess how I found this out... )...I think it was under-rated for the job it was being asked to do...

I'll try to get back to you with a more finite amp draw on my De Soto's six-volt Auto-lite "Solar-Spark" coil...

[Guest JT]

Frank is right on the amp draw. At idling a 6 volt coil draws about 2.5 amps. If measured with engine off you would be drawing about 4.5 to 5 amps (ohms law 6 volts divided by 1.2 ohms= 5 amps).

I have seen a ballast resistor such as this recommended for 6 volt coil on 12 volts:

http://www.napaonline.com/masterpages/NOLMaster.aspx?PageId=430&OEMPartNum=ICR-13

Also remember that most "12 volt" coils are really more like 6 or 8 volt coils using either an internal or external resistor in a 12 volt application.

[Guest De Soto Frank]

OK guys, had to wait for daylight before I could go out and check this out.

I checked the amp draw on my De Soto coil by "inserting" the ammeter bewteen the "distributor" terminal of the coil and the lead to the distributor.

Came up with the following current draws:

Switch on, engine stopped: 5.5 amps

Engine idling (450 rpm): approx. 3 amps (+ or - 1/2 amp)

Engine @ approx 2,000 RPM: 2. 5 amps

These readings were obtained using a Wiedenhoff Voltmeter/Ammeter test set (c. 1940, and pretty accurate when checked against a modern digital VOM).

The coil is the original firewall-mounted "lock-switch" Auto-lite "Solar-Spark" coil.

So, it would appear that if you can find a resistor capable of dissipating 6 amps, you should be covered. It might be well to check the amp draw of your particular coil, just to be safe. While it would be most convenient to insert said resistor between the coil and the distributor, that would leave open the possibility of the coild being subjected to a full 12-volts should the coil somehow get grounded between the disrtibutor terminal and the resistor.

Probably best to drop the voltage on the ignition-switch side of the coil.

Good luck !

[Guest JT]

Frank, thanks for the "live" test results and glad to see they match the "on paper" ones.

[mrpushbutton]

Frank, Don't ever get rid of that Wiedenhoff--that's good stuff!

[Guest De Soto Frank]

That Wiednehoff meter set was in a box-lot purchased at the estate auction of an infamous trucking garage in Wilkes-Barre, about 10 years ago...Stanley Serafin Trucking.

Old Stanley had started in the trucking business around 1920?, and had a garage in north Wilkes-Barre that had a fenced yard next to it, stuffed with 1930's & '40s Internationals, Diamond Ts, Stewarts, Dodges, an AC Mack "Bull-Dog", an AB Mack coal truck. I always wondered what was INSIDE the garage...

The city wanted to take the property through eminent domain to build a new fire station in the late 1980's, but somehow Stanley fought it and won.

He finally passed away around 1995 or so, and the heirs decided to liquidate the contents of the garage and property.

Apparently the garage contained about a half-dozen pre-WWII Mack trucks (in salvageable condition; these were supposedly snapped-up by a NJ collector), a '32 Packard (kept by the family), a '29 or '30 Dodge Bros. sedan, a '25 Brockway moving van (!), and a huge jumble or various car/truck parts, tools, furniture, junk.

An unusual feature of the garage ("modern", c 1920's brick, about 4,000 sq ft, steel-framed windows, flat roof, parapet walls w/ terra-cotta coping, front office, etc., was the most of the floor inside seemed to be dirt - I believe there were concrete pads poured inside the roll-up doors, going in about 12-15 ft, but then entire rear-half of the garage was dirt-floor!

The multi-meter set was still in its original black enameled steel box, with instructions, in a box of other dirty junk that probably ran me $5 at the public auction. When I opened the storage box, the meter looked brand-new, with its cream-colored face panel and red-wrinkle-paint cabinet.

In fact, I think it's worth taking a picture of...

The voltmeter has two scales and reads from 0-10 volts / 0-20 volts, and the ammeter also has two scales reading 0-30 amps / 0-60 amps. The selector switches are "center-off" so that you can correct polarity w/o changing the clip leads. There is also a wire-wound resistance rheostat for imposing loads on charging systems to adjust third-brushes, voltage regualtors, etc.

This set has made adjusting voltage regulators a lot easier for me...