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Fan Controller

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Overclocked

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I have a Fan that can run on up to 24v, but the minuim I want to use is 12v, So I want the starting voltage to be 12v, and I want the max to 24V. I want to be able to adjust from 12v to 24v

Can someone point me in the direction of were I would need to go in order to design one? Im not looking to do PMW, I just want to vary voltage.

I am getting my voltage from +12 and -12 (using +12 for vcc and -12 for ground, Yes it does work) So I was thinking it might not go down to 0v, rather it will go down to +12v
 
+12 to -12 is 24 volts so all you need is a rehostat in series with the fan motor. Measure the current thru the motor at 12 volts, then the max resistance of the rehostat is: R = V/I = 12/I.
 
On the back of the fan (its pretty hefty it blows 160CFM...) It says 24DC 145mA 3.5W. Below it it has 12-30V.

Does that current go the same for 12V?
 
Ok thanks

Can someone tell me what the 2 types of power are? Ive learned there are 2 types, True Power and Apperant Power. One of them used ohms law, while the other use I^2R
 
When you say you want to adjust from 12v to 24v, do you mean you want to adjust it with a rheostat, being able to go anywhere in between 12 and 24 volts? Or do you just want 12 and 24 volts?

If the latter is the case, a simple SPDT switch could do the trick for switching between 12 and 24 volts.
 
Be able to do it with a reostat. At 12V it is quiet, but at 24V it pushes alot of air.

The SPDT switch is a good idea, But dont forget I am using +12 and -12v.
 
Well that's just the thing, you can use the switch to select between 12 and 24 volts. You connect one of the fan's leads to -12V. The other lead you connect to the middle pole of the switch. Connect 0V to the left pole of the switch, and +12V to the right pole of the switch. Depending on the switch's position you will have either a 12 or 24 volt potential across the fan.
 
Overclocked said:
Ok thanks

Can someone tell me what the 2 types of power are? Ive learned there are 2 types, True Power and Apperant Power. One of them used ohms law, while the other use I^2R

Apparent power is relevant to AC only. AP = V * I. The actual power (ie. the energy that you pay for) depends upon the phase angle. If there are no reactive components (ie. only resistance) then the DC formulae apply if the AC is sinusoidal.

There is a phase angle if there are reactive components, ie. Capacitors and/or Inductors. It is difficult to explain in a few words. And you need to understand the maths.

With DC, P = V * I = V^2/R = I^2 * R.
 
But wait a second, If I were to use R=V/I, and since V=24 and I=145mA, wouldnt the resistance value be the same at 12v?
 
Overclocked said:
But wait a second, If I were to use R=V/I, and since V=24 and I=145mA, wouldnt the resistance value be the same at 12v?

the fan is not a resistive load, there is no R in that sense. The only resistance you'll see in the fan is whatever the wire that make up the coils offer. at least, i think that's how it goes.

here, check this out; instead of a 5 watt rheostat which is probably expensive, this solution uses less than $2 US in parts, perhaps less if you get a good deal on the potentiometer:

http://www.cpemma.co.uk/reg.html

just substitue the 0v as shown for your -12v connection
 
Thats probably a better solution, I have most of those parts in my box!

Cheap pots:**broken link removed**

Low wattage kind good for that circuit though.
 
So now what if I wanted to use 3 LEDs to tell what speed I am at (voltage dendent of course). With 12v being low, and 24V being high, and another being some where in the middle of the 2.

I was thinking zeners, but those might not work, BUT I have this special Opamp (its a voltage comprator) especialy for comparing 2 voltages. Would this work instead? I dont want it to be complicated (such as big IC's)
 
I was thinking zeners, but those might not work, BUT I have this special Opamp (its a voltage comprator) especialy for comparing 2 voltages. Would this work instead? I dont want it to be complicated (such as big IC's)

If you don't want it to be too complicated why not just use a simple switch to give the fan 12 and 24v??? It's as simple as it gets.
 
I meant on the part of using LEDs to tell what speed I was at. I wont want that to be too complicated.

The regulator circuit I dont care how complex it is
 
Overclocked said:
So now what if I wanted to use 3 LEDs to tell what speed I am at (voltage dendent of course). With 12v being low, and 24V being high, and another being some where in the middle of the 2.

I was thinking zeners, but those might not work, BUT I have this special Opamp (its a voltage comprator) especialy for comparing 2 voltages. Would this work instead? I dont want it to be complicated (such as big IC's)

Zeners will work. Use say a 8V2 zener in series with a LED and a resistor.

For the mid ranges use say a 15V Zener in series with a LED and another resistor.

For the maximum range use say a 20V Zener in series with a LED and another resistor.

This is crude, but for voltages < 11 V (approx) there will be no glow, for 11 ~ 18 V (approx) 1 will glow for 18 ~ 22 V (approx) 2 will glow and for > 22 V (approx) all 3 will glow.
 
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