Hi, I converted my 40 Coupe to 12 volt negative ground. Used a 30 amp voltage reducer for the heater fan. Two variable switches later they are getting burning hot. Made sure the second switch was for 6 volt. Didn’t have any problems till the conversion?
12 volts through a 6 volt heater switch in my truck makes the dash hot when on low speed on high speed no problem. I like the look of the old switches.
Thats what the switch is designed to do. Resistance slows down the motor speed, but resistance also makes heat
That's because you've effectively doubled the load through the switch and are exceeding its capacity. I'm not a big fan of resistive voltage reducers for this reason. This is basic DC circuit law. What's happening is your fan motor draws X amount of current @ 6V. In a series circuit, to reduce voltage you have to connect an additional resistance to drop enough voltage to the desired amount. To cut it in half, you need an equal resistance which presents its own load equal to and in addition to the existing one. And because in a series circuit current is the same everywhere and only voltage is dropped across the loads, you now have twice the load on the switch. You have two choices to fix it. One, just remove the resistor. Your fan motor will run faster/hotter but the load will be less on the switch. It may or may not kill the motor or switch; there are cases both ways. Two, swap the 6V motor for a 12V version. This is the best solution, although if the speed control is built into the switch you'll probably see different lower speeds.
If you install an electronic voltage regulator (there are plenty of small converters available) you will get your 6 volt supply at whatever current the converter is rated at (5 amps is plenty). The heat dissipated in the unit is minimal, and you have the option of hooking up any other 6volt equipment you have. I have one of these-LM2596 +LED DC-DC Adjustable Voltage Buck/Step-Down Converter Module Regulator | eBay Australia and run a 6volt heater fan and the original fuel gauge.
Years ago I just put a Chrysler ballast resistor in line before the switch. That was a 12 volt car with 6 volt heater and switch. Worked fine for many years.
On my 40 sedan, I took the speed coils from a 12 car and mounted it on the back of my fan so when the fan was running, it drew air across the coils and kept the coils cool but reduced the speed of the fan.
Another vote to not use resistors to do 12 to 6 volt. Ron Francis offers several regulated 12 volt supplies. Certainly, replacing the 6 volt motor with 12 volt is the most efficient.
I did the same with the ceramic block resistors for my six volt heater. I used two resistors wired in parallel, so they wouldn't get smoking hot, mounted them in the fan air stream. Used the reduced voltage to feed a variable speed six volt heater switch that controls the fan. Figured if it didn't work I'd replace the six volt fan motor with a twelve volt, but it's been working fine for several years now. Resistors used to vary the speed of the fan motor. Most factory applications have them mounted inside the air stream.
NAPA had a direct replacement for my Arvin in 12V. I ran it for a while on a charged battery, nothing got hot. Will only be better in the car. Pic of the motor/number. Spec say not reversible. It is. I think I had to nip some length off the shaft. Yes, "imported", go figure.
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