Dimmer switch question?

[griffdus]

has anyone ever ran a single pole dimmer switch to 2 12v 40 watt bulbs,i tried hooking one up in the fish house and can only get it to turn on and off but wont dim, tried hooking it up all different ways with same results.

[Jeremy airjer W]

Is this an a/c dimmer switch?

[griffdus]

For a house 110

[Whoaru99]

That type of dimmer switch needs AC to work, not DC. They depend on the zero crossing of the alternating polarity to turn off the circuit so it can be re-fired/re-triggered at some point later in the AC cycle. The further past zero crossing the circuit is re-triggered, the dimmer the bulb is because it's using less of the AC cycle.

With DC there is no zero crossing so the AC dimmer won't function properly.

To dim the bulbs using DC I suggest getting a PWM contoller. Something along the lines of this: http://www.amazon.com/Controller-Knob-Hi...pd_sbs_indust_4

[JohnMickish]

Use a cheap rotory dimmer switch. They use a resistor to knock the voltage down to dim the lights and will work on a DC system. Or go to your local parts store and get a multi speed fan switch for a car, they both accomplish the same thing.

[Jeremy airjer W]

Or go to your local parts store and get a multi speed fan switch for a car, they both accomplish the same thing.

A fan switch will not work. The switch either provides a path to ground or supplies power to a set of resistors. The resistor block is what drops current to allow for different fan speeds, not the switch.

Radio shack has a 12 volt variable resistor that will work and there are fairly inexpensive.

[Whoaru99]

duplicate

[Whoaru99]

The problem with a resistor is that it wastes power. The op has a load of 80W, or 6.7A. Every volt you drop wastes 6.7W of power. Granted, in the fish house maybe more heat is nice but one probably doesn't want to use the 12V battery for that.

The PWM wastes very little power vs. just burning up what you don't want to use in heating a resistor. So using the resistor to control 80W of lighting always consumes 80W regardless if all that is turned into heat in the resistor or all goes to lighting the bulbs or some proportion to each....always adds up to 80W.

With the PWM setup if you want only 40W of lighting then that's all you consume plus just a little more in the switching circuit, but nowhere remotely close to the 80W you'll always burn up with the resistor circuit.

It's time to come into the 21st century fellas.

[JohnMickish]

A fan switch will not work. The switch either provides a path to ground or supplies power to a set of resistors. The resistor block is what drops current to allow for different fan speeds, not the switch.

Radio shack has a 12 volt variable resistor that will work and there are fairly inexpensive.

Jeremy, you are thinking to new. Back in the day when cars where made out of steel the fan switches where a reostat. Used inline on the positive wire this is your dimmer or fan control. The old style headlight switches where the same way. You know, the headlight switch that you had to pull he knob out and twist it to dim the dash lights.

[JohnMickish]

Yes, resistors waste lots of power and make heat. A PWM setup won't work on a DC system, only on a AC system.

[CAMAN]

A PWM setup won't work on a DC system, only on a AC system.

[JohnMickish]

I should have read better, my bad. I missunderstood it as a VFD.

What is the cost of this PWM? Does anyone know?

[CAMAN]

$15.99 and free shipping

[Jeremy airjer W]

Jeremy, you are thinking to new. Back in the day when cars where made out of steel the fan switches where a reostat. Used inline on the positive wire this is your dimmer or fan control. The old style headlight switches where the same way. You know, the headlight switch that you had to pull he knob out and twist it to dim the dash lights.

Holy cow what are we talking here pre 1970? if so what part store is going to have to blow the dust off that box? LOL

[JohnMickish]

Jeez, I'm not that old. I know Dodge pickups used them into the late 70's. When I was in the Air Force, they would run these trucks 24 hours a day and the heater switches would get so hot they would melt the dash . Maybe there is a reason they went bankrupt-TWICE!