The Stovebolt Site Forums The Shop Area The Electrical Bay voltage reducer

I installed a heavy duty reducer to drop the voltage from 12 volt to 6 volt for my heater motor and when used with a three speed switch the reducer get's very hot on a slow setting, but it seems to not to get as hot on the high setting. It is mounted on the fire wall in the engine compartment.
I placed it before the switch but I can smell the odor of plastic inside the cab.

I'm not an electrical expert by any means but I think it may be fairly normal. A switch will do the same when running a 6v motor at reduced speed. The excess energy not sent to the motor is bled off as heat. If I'm wrong we'll hear about it.

why not just use a 12 volt heater motor? the resistors used to control the speeds do get really hot which is why they are usually in the fresh air ductwork.

Tinys got it!

One of the first questions I asked here was about burning my fingers on the back of the heater switch in my 53. On high, more power is going to the motor. On low, less power is, so basically the extra energy is bypassing the motor and converted into heat. At least thats the way I think of it. The technical geeks here will say thats wrong!

I burnt my fingers pretty bad the first time I grabbed the thing. Id watch it and make sure it isnt going all goofy on ya. That smell may go away now that its been used, but if it continues you may want to swap it out. Does the reducer have a ceramic part to it? Most of the reducers Ive seen have that to dissipate the extra heat created.

Jeff

Thanks everyone, The reducer is the type that has a metal case and the inside has a ceramic core. I had the first one mounted on the heater out flow but after about 15 minutes the reducer blew up. So I am going to try it again but for the price of two of these things it will be cheaper to get a 12 volt motor.

Thanks I'll keep that in mind.

Denny,
If I remember right, if you put two equal resistors in parallel the resulting resistance is only half of the resistance of the single resistor. The voltage drop across the parallel arrangement will actually be less than across the single resistor. That results in a higher voltage at the motor than the case with a single resistor. Depending on the sizes of everything, maybe that's close enough, and you do get less current through each resistor. Taking it a step further, use two equal resistors in parallel, but make each of them twice the resistance of the original resistor. That gets you back to the same circuit resistance as with the one resistor, the same circuit current, the same voltage drop, but each resistor is carrying only half the current, so less heat? I don't know if that's practical but it seems to works on paper.

Dale

The way to figure resistance in a parallell circuit is the product/sum method. Multiply your resistors then divide them by their sum.

I'm out, never should have brought it up!!!
DG

You would need some large power resistors for the heater motor to make a voltage dividing bridge. I would not go that route, and simply go 12VDC motor and resistor pack