I plan to install a basic stepless control switch for my 12 volt heater fan. My understanding of electronics is quite limited. The wiring for this device is simply Red - pos. side of motor & power supply Green - neg. side of motor Black - neg. side of power supply
I presume that the motor speed is regulated by controlling the ground side of the circuit, correct? Here’s what I don’t get : why is the positive side routed into the switch? Seems to me that the motor still has a direct connection to positive, based on the joining of the red wire to power and to motor… I don’t understand what role the switch plays on the plus side.
Someone please explain this tinker toy level electrical control to me.
The red (12v+) is routed to the "switch" because the circuitry inside the box needs 12vdc and ground to operate.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
The circuitry will be switching the green lead (in this case) to ground and then disconnecting it at a fairly high rate. If you could look at the green lead with an oscilloscope the voltage would look like the attachment below. (Electronics experts: I know I've over simplified my explanation and that the chopper power supplies I am familiar with usually chop the positive voltage, not the ground.)
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
To add some detail to what Bill said, this is commonly referred to as "PWM" or Pulse Width Modulation and it is a simple way to get the same effect as reducing the voltage without needing a power resistor to dump the excess energy.
The ground is turned on/off so fast that the motor percieves it as a lower voltage instead of power being turned on and off.
A caveat: This particular "stepless control switch" will not work IF your heater fan motor only has one wire (the positive wire) and no ground wire.
Another caveat: It may induce electrical noise that is picked up by your radio, especially on the AM band.
Last edited by Bill Hanlon; 02/05/20245:19 PM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
Well , I tested the control and it works. About the possible static on a.m.radio , I suppose that would be similar to the static I’ve noticed at home , caused by a ceiling fan control. Sorry to hear that, (pun) , I’m getting ready to install a radio in the ‘54 soon.
