How do electric ski boot warmers work?


I bought a set at a garage sale for $1, and one has a broken plug. If I can figure out how they work, maybe I can fix it.
The cable that goes into the boot has 8 wires; they are soldered together in three groups of 3-3-2. The power supply has three prongs. It also has a dial with 5 settings. I tested the voltage on the power supply. One setting is off, and the other four have 2.7v between prongs 1-3 and 2-3 and 0v between 1-2. So the neither the voltage nor the contacts change with the setting. (The power supply is marked 2.4v)
So, how do you think this works? What changes when you change the dial setting? What is the difference between prong 1 and prong 2? Is it reasonable to assume that 3 wires each go to prongs 1 and 2, and the other 2 wires go to prong 3?
I did contact the manufacturer and they said they don't support old junk.
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Sounds like there's multiple heating loops. The amount of heat generated is determined by how many of the loops are activated and how much current is driven thru them.
The switch may be switching between resistors (or even phase modulation) to control how much current goes thru each loop.
Try measuring resistance on the wires going into the boot, and see which ones are attached together. Then, rig the control box to feed a "common set" of wire loop. Eg: one end on pin 1, the other end on pins 3, and see what the voltage does when you switch it.
If it's modulated, it gets tricky ;-)
In one older system I saw (old Lange racing boots), there was a battery pack inside the boot sole which is charged by a wallwart (obviously not on the hill ;-). The heating elements were either full on or off.
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Chris Lewis,

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