Electronics Question.

[DogsBody]

I have a fan that is 12v and draws 0.48A, I have calculated this to be 25Ohms resistance,

What I can't work out is what size resistor I would need to reduce it to half speed.

Can anyone help ?

 

[Dunks]

Try a 25Ohm resistor.

 

[Participant]

It's probably logarithmic or something, in which case, I'm out (if I was ever in)

 

[bitslice]

Depends on what voltage it will stall at, I'd aim for 2/3 speed.

 

[Jokester]

As Robbie_G mentions, motor performance is normally non-linear, so erm yeah, I'm out!

Edit:
In fact no, what to do is start with 25Ohm (make sure it's suitably power rated) and see what that gives you.

 

[Jonny69]

Bear in mind the fan is a little under 6W, if you're aiming to half that with a 25 Ohm resistor you'll need a 3W rated resistor, which is going to be a fairly chunky ceramic thing

 

[DogsBody]

OK, lets make it more insteresting then.

Lets say I had 5 of these fans that were controlled by the onboard monitoring software and didn't run at full pace normally.
Add to that 2 x fans that draw 1.2A as well


Given the above situation, what rating of potentiometer would you buy to slow these fans down, (In fairness I probably don't want them at half speed just probably UP to half speed so that I can have a play around with the noise/temperature levels.)