The Stovebolt Site Forums The Shop Area The Electrical Bay Getting 2 Speeds from a 12-v heater blower. Update

I'm going to switch to a 12-volt fan motor for my heater. I had been using the 6-volt motor switched to one or two 1.5 ohm resistors to give me 2 fan speeds.

When I install the 12-volt motor can I use one of those 1.5 ohm resistors with a switch to give me 2 speeds?

Thanks, guys!!

This doesn't answer your question, but

I put a 12volt motor In my Harrison.

I used this switch
...pic...

It gives me three speeds
It's lighted also

they better be really big resistors, it's wattage that's important ... variable speed heater blower switches should be available from a NAPA - look like this

Bill

Hook the motor and blower up to 12 V and try to simulate the duct resistance.

Read the amperage.

Let us assume amps was 10 and you want to run at one half speed ie 6V - not exact but close.

So R = E/I = 12/10 = 1.2 ohm
amps should now be less than 1/2 due to affinity law. SO let us assume 5.

Watts = 5 x 6 = 30

This is not exact but should be close and a bit oversized.

This is all true if you had a pure resistive load but you have a motor driving a load whose power demand is the square of the change - you dropped speed by 1/2 so power demand by the fan is 1/8. Double check amperage at 6 V and hopefully I am too conservative.


Dan Bentler

Thanks, Dan! My thoughts exactly! I'm going use the 12-volt motor and see if I like it as is for the high speed. I'll then use a 1.5 ohm resistor (bought specifically for reducing 12-v for the original 6-v motor) on a switch to give me a low speed.

I know the resistor can get really hot but the one I bought was advertised for this purpose.

I had one of those variable resistance (fan speed) switches like Bill showed but it developed dead spots and the clamping thing would bend and get loose. 2 speeds are fine with me. That's what I had for my 6-v motor.

The resistor will be in a metal electrical conduit box inline with the driver side tubing so heat from the resistor is used on the driver side windshield.

Thanks, guys!

My '54 3104 has been converted to 12v. I put a 12v motor from a '60 Impala heater in my '54 Fresh Air heater. The squirrel cage in the '60 heater is smaller diameter than the '54 6v squirrel cage. I put the larger '54 cage onto the '60 motor - - it blows like a hurracane. Probably a lot more volume and velocity than the original blower. I assume that the 12v motor spins faster than the 6v motor. I hid an aftermarket 3-spd rotary 12v switch behind the dash with plenty of open space around it. I put an original style fan switch on the dash just for looks.

> Hidden 3-spd switch
> Original style fan switch

I bought the 12-volt motor from NAPA (#655-1020, $29.33). Turns out using one of those 1.5 ohm resistors gave a nice high speed. Papers are blown around the floor!

A second one of those resistors in series gives a nice lower speed so I used my earlier setup for 12-v supply/6-v motor in a conduit box inline with the driver's side defroster.

I've drawn in the wire that goes to the fan. The other 2 wires are connected to the 12-v supply by an On-Off-On switch. I'm really happy with it. Too bad we're unseasonably warm!

Thanks guys!

- Resistors in Conduit Box.

-

I just read the description of your truck.You converted it to 12 volt with alternator.Why not use this switch as dads50 suggested.I have been using it with my 12 volt system for over 20 years.It has three speed settings.

Tim

Tim,

I had one of those switches when I had a 6-volt supply and motor. It developed dead spots and that curved part of the mount bent when I tighten the screw so it would loosen up.

Maybe they've solved the problems with the new versions but if my resistor gets red hot when only the one is used, I kind of like it in that conduit box..