Re: Model-T Ford coil

At 08:26 PM 12/9/96 -0700, Malcolm Watts wrote:
>>From MALCOLM-at-directorate.wnp.ac.nz Mon Dec  9 20:14:53 1996
>Date: Tue, 10 Dec 1996 08:50:53 +1200
>From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
>To: tesla-at-pupman-dot-com
>Subject: Re: Model-T Ford coil
>You can do OK with an induction-coil driven TC. I have obtained 6"+ of
>corona from a TC driven by a standard ignition coil run from a circuit
>using a power transistor for switching the coil and a variable mark-
>space ratio oscillator with a 12V supply. The primary cap was about 
>3000pF from memory.
>> >        I recently got an old Model-T Ford coil. After
>> >an hour, I finally understood how it works. Pretty
>> >embarrising to take so long to figure out something so
>> >old and simple. Anyway, I have only a couple of plans
>> >for its use in a mini Tesla Coil, wrapping a coil around
>> >a wine bottle, and wondered if anybody had used the Ford
>> >coil in a project and what they have done.
>> >
>> >Thanks,
>> >Bob Schumann
>> >
>> Ford coils are simply induction coils.  As I recall, the old Model T used
>> four of them (one for each cylinder) mounted in a box beneath the dash.
>> They are still being manufactured for sale to antique car buffs, but are
>> pricey at about $50 a pop.  They were a standby for the electrical
>> experimenters of the Gernsback era.  Their innards consist of a primary
>> wound with (I think), #22 DCC magnet wire on an iron wire core, surrounded
>> by a secondary of #40 enamelled wire.  There is a tinfoil capacitor across
>> the secondary to give a "hot" spark. Connections are brought out to three
>> terminals, one being common to both primary and secondary.  With a clean and
>> well-adjusted interrupter it will give a 0.75" spark (and kick like a mule
>> if you get across the terminals).  It was claimed that a Ford coil driven
>> Tesla coil would give a 4" spark, but none of the coils I built back then
>> ever did much better than 1"-1.5".
>> Norm
One of the problems with getting good results from Ford coils was keeping
the interrupter contacts clean, particularly if one succumbed to the
temptation of running them with more than 6 VDC on the primary.  Using
modern electronic circuitry to replace the vibrator interrupter sounds like
a great idea.  My wimpy results may have been due due to poorly tuned Tesla
circuits.  I eventually eviscerated a couple of Ford coils and reassembled
the two primaries and secondaries into a transformer which put out about 5
Kv, and would give nice crackly 4" discharges from the terminals of my
bipolar Tesla secondary, with enough power to light 40-W incandescent bulbs
(and also, on one occasion, to kick back and demolish a light socket).