Can a light Dimmer switch control speed of a 12v fan?

Calibos

First off, thanks again to the guys that helped me figure out the wiring to power 2 12v fans off a single 12v battery and double light switch.

I just used an old light switch I had lying around but I was going to pick up a new double switch today when I had a thought. Instead of just getting another double switch, could I get a double dimmer switch? Would the dimmer work on a 12v circuit and be able to control the speed of the fans?

curtin10

yes it will control the fan speed. A dimmer switch is a variable resistor so you could buy 2 of these in maplin and it would be smaller than a light dimmer switch.

Calibos

Cheers mate. I was just worried that the might not work with 12v as opposed to mains voltage.

Actual light dimmer switches with the dials are actually specifically what I want. This is actually to contol cooling fans on a telescope. The switches will be mounted to the large telescope base so there aren't really any space considerations to worry about. Inline resistor dimmers on the cables going to the fans would actually put them further out of arms reach.....although???

Will dimmers complicate things though??. I can control the fans independently of each other at the moment. Both on, Both off, either on/off.

With the ordinary double switch, this is how the guys told me to wire.

Blue Neutral and Brown Live coming from the battery. Same coming from both fans. Used a connection block to join the Blue Neutral of the Battery and the 2 Blue Neutrals of the fans together. These not wired to double light switch at all. Brown Live from Battery into Com. Bridging wire from Com on switch 1 to com on switch 2. Brown Live of fan 1 into L1 switch 1. Brown Live of fan 2 into L1 switch 2.

I am wondering now seeing as wires are bridged etc, will the dimmer on switch 1 also affect the voltage feeding on into switch 2? or does the second switch/fan still get full voltage no matter how much switch 1 is dimmed. ie with the same witing scheme as I used for the bog standard double switch can I still have both fans on or off or either of them on or off...and running at different speeds independently of each other?

enmac

not too sure about dimmer siwtch - some utilise diodes or thyristors and are therefore only good for AC - if you can get one that a variable resistor type then you're OK

Calibos

I was just about to head up to Woodies for one.

Its not going to really say on the label which type of resistor it uses is it? Is there any way I could tell just by looking at the back of the switch what type of resistor it uses?

Steve

Most domestic dimmers use triacs to chop the ac wave and so will only work with AC.

Maybe you're best bet is to look for a model railway controller / power supply. Alternatively, maplin used to do some kits for dc motor control using pulse width modulation.

Bear in mind that some fans (such as are used in pc's) have built in electronics to maintain the same speed regardless of fluctuations in supply voltage.

dingding

Another option might be to get a 12 volt dimmable transformer and control the mains side of it with a standard light dimmer.

Stoner

Calibos wrote: »

I can control the fans independently of each other at the moment. Both on, Both off, either on/off.

if I understand your wiring config correctly, yes, a dimmer switch between each fan and the 2 gang switch would work. A 2 gang dimmer switch would also work (replacing the 2 gang switch altogether) with dingding's advice above.

DublinDilbert

SteveC wrote: »

Most domestic dimmers use triacs to chop the ac wave and so will only work with AC.

+1

SteveC wrote: »

Bear in mind that some fans (such as are used in pc's) have built in electronics to maintain the same speed regardless of fluctuations in supply voltage.

+1