In a prior post I had mentioned the venerable “buzz coil” as used in the Model T Ford and other automotive, marine, and stationary engine ignition systems prior to 1920. (the model T actually used them until the end of production in 1927, long after others had abandoned them in favor of single coil/high tension distributors)
The basic principle of the buzz coil’s operation is to have a low voltage electromagnet pull a set of contacts when power is applied. Doing so causes the contacts to break the circuit, thereby allowing spring tension to pull the contacts closed again and repeating the process. Hence the “buzz” in buzz coil. Wound with this low voltage coil is another, high voltage winding….the pulsations of current that result from the rapid cycling of the contacts causes a high voltage pulse to be induced in this winding. Something typically on the order of 10,000 volts….sufficient to fire a sparkplug in an engine of that vintage.
A close look at the construction of these is rather interesting. Nicely fitted finger jointed wood case, a magnetic core made from small soft iron rods bundled together (this was before widespread use of laminated cores) and a small condenser wired across the replaceable contacts and sealed in tar with the coils in the box. Those coils made specifically for the Model T can also be identified by the lack of binding posts for connection. The Ford Model T had a “coil box” which held four coils (one per cylinder) and used spring contacts to both help retain the individual coils and to make electrical contact with the flat brass buttons on the individual buzz coils. The “distributor” of the model T was a low tension switch that selected each coil in sequence to fire their respective cylinders.
As there were some 15 million Ford model T automobiles produced…and numerous Fordson tractors and stationary/marine versions, each with 4 buzz coils, along with the multitude of spares made since then (some very recently, btw) and a few other applications of these types of coils….the result is that these are a VERY common item that will turn up in antique shops or sales almost anywhere. Granted, some rarer variations exist. (the beautiful copper topped KW made coils, for example) …but for the most part, if you need one you will have no trouble finding one. Likely it will still be functional with very minimal effort like cleaning the points. I did have one with a bad condenser in it, this was easily remedied by carefully opening the case, digging it out of the tar and replacing with a modern capacitor of suitable specs. Once the case was closed up, you could not tell it had been worked on…I’ve used it for some small engine projects since then such as the 1908 Gray marine engine I restored in the video below. (the buzz coils and battery are in the little wooden box)
https://www.youtube.com/watch?v=EiNg_cSDYt0
This commonality has lead to many never intended uses for these coils. Uses far too numerous to list. Most were home-brew devices of the late 1920’s through 1940’s period….but some were factory made. I even have a factory built Champion sparkplug tester that has a model T coil inside of it to provide firing voltage for the plugs under test.
Companies such as LeJay provided books of plans and kits to modify automobile generators for farm lighting (this was before the REA) and even a nifty kit to convert a buzz coil into an electric fence charger to keep the cows from roaming too far. In an electric fence, you do not want a continuous flow of current–this is partly for effectiveness and partly to prolong the life of the battery that would have been used to power it and-when using a buzz coil, to prolong its life as well. The kit consisted of a glass tube and ball and a modified set of contacts. The idea was to have the ball roll down the tube, hit the contact which turned on the power to the coil–when the magnetism pulled the contact back and opened the circuit (as in typical buzz coil operation) it would also “kick” the ball back up the tube….then gravity would roll it back down and the process would repeat. This resulted in a series of high voltage pulses from the coil….perhaps one per second depending on how the tube was set (the angle dictating how fast the ball rolled back down) As long as it had power, it would sit there and go “clink clink clink” and send little pulses of 10,000 volt “don’t-cross-the-fence” signals to your cattle. But, there is more than one way to keep your herd on your side of the fence.
This example of a buzz coil fence charger was seen hanging on the wall for display in an ice cream shop in Illinois. As you can see, it has the buzz coil….but instead of a tube and ball, it has a small wheel on needle bearings that has a flat coiled torsion spring on it and a small projecting point on the wheel. Much like the watch spring used in an escapement movement, this allows the wheel to be kicked back and forth as it makes and breaks the power circuit for the buzz coil.
Obviously this was a homebrewed project from a local farm someplace. Chances are there is none other exactly like it and chances are today very few would have recognized what it was if they saw it there in the shop. (now that you know, maybe if you go in the place you can impress the owner with your knowledge and score a free scoop of ice cream…….or maybe not)
Other coils of this sort found their way into homebrew HAM radio projects of the spark gap era. Granted, a model T coil is not that powerful…but to the impoverished radio experimenters of the late teens and early 1920’s, it provided an avenue to get started and perhaps lead a kid of the era into a career path that would become a major industry of great importance in just a few years. And of course, some kids would hook one up to a spark plug welded into the tailpipe of their car–briefly cut the ignition, letting the car coast a bit to push some raw fuel into the exhaust pipe, then push the button on the spark coil and BOOM! Massive flaming balls of fire shot out of the back of the car. Great fun for cruising on a Saturday night! Well…fun until you over did it and blew up your muffler. I suspect this is why the muffler shop I used quit offering the lifetime replacement warranty.
They were also used to construct small Tesla coils, and modern variations made to run on line current were built into high frequency spark testers such as the well known BD-10 that is still used in neon and high vacuum applications.
http://www.electrotechnicproducts.com/bd-10as-high-frequency-generator/
Open one of these up, and part of the circuit used will be found very similar to that of the 100 year old buzz coils.
So, aside of providing spark to your Model T, running another antique engine, zapping those who touch your fence, or getting in trouble with the traffic cops or the FCC; what should you do with one of these if you find one today? Well, maybe build yourself a small retro styled plasma sculpture or an ozone generator?…make a fireball cannon for the 4th of July parade?….a fancy bug zapper? Or just impress your houseguests. (or deter them from visiting, I suppose)