My Own Fan Controller :lol:

JEN · Post by **JEN** » Sat May 03, 2003 2:04 pm

Please try not to laugh! I am going to try and make my own fan controller

OK, not that you have stopped laughing, I would appreciate all the help I can get, as I will need a lot of help

1. whats the difference between SPDT and DPDT switches?

fmah · Post by **fmah** » Sat May 03, 2003 4:13 pm

A SPDT is a single pole single throw, which means it controls 1 circuit and has two positions (which you could use for high and low)

A DPDT is a double pole double throw which has two poles, thus can control two circuits. Also has two positions (double throw).

Depending on how you do it, you get the most use out of a DPDT since you can use the other circuit or just ignore it if you don't need it.

I haven't built mine yet, but for testing I used a DPDT to be able to switch between two voltage settings (5 or 12, 5 or 7, 7 or 12, etc...) depending on how you wire it up. The black fan wire was on one circuit and the red fan wire on the other circuit. My switch also has a middle OFF position to turn off the circuit.

A rheostat, which is a variable power resistor, will allow you to turn a knob to change the fan speed. This lets you dial in the speed how you want it.

JEN · Post by **JEN** » Sat May 03, 2003 11:59 pm

Thanks

right now I am after 1 switch for 1 of the fans. The fans are panaflo L1A 80mm. The switch should be on-on. How would I wire this up to get 12v and 7v without without using the "trick" method, instead somehow using a resister to reduce one of the switch possitions to 7v?

fmah · Post by **fmah** » Tue May 06, 2003 11:16 pm

I don't have a diagram here, but a DPDT switch would have 2 rows of 3 pins. The X represent the pins on the switch.

12V+ XX 12V+ Ground
Fan + XX Fan-
7V+ XX 12V+ Ground

Here you would use 12V+ with a resistor for the 7V+ connection. The actual resistor value is going to depend on the current draw of the fan. AFAIK the calculation would be (12V-7V) / I (fan current) = R (resistor value)

cpemma · Post by **cpemma** » Sun May 11, 2003 3:08 pm

fmah wrote:...AFAIK the calculation would be (12V-7V) / I (fan current) = R (resistor value)

It's a tad more complex,

Resistor value = (12-V) x 12 / (V x I)

Where V is the voltage you want the fan to run at, I the fan current at 12v.

(steps on the way shown here.)

So to 7-volt a 0.2A fan, R = (5 x 12) / (7 x 0.2) = 43R.

It's dropping 5v, so wattage = 5 x 5 / 43 = 0.58, so a 1W is advisable.

fancontrol · Post by **fancontrol** » Wed May 14, 2003 7:41 pm

cpemma wrote:It's a tad more complex,
Resistor value = (12-V) x 12 / (V x I)

I took some measurements of a fan I wanted to slow down and found that current was not linear with supplied voltage. The equivalent resistance, using Ohm's law, varied from 40 Ohms at 12V to 30 Ohms at 7V to less than 30 at 4V. So don't expect exact results the first try.

And, definetly expect some heat. Use a high power resistor (or multiple resistors).

cpemma · Post by **cpemma** » Sat May 17, 2003 3:13 pm

There's yet another complexity I've not allowed for (ie forgot

) in the above formula. Many fans have an internal protection diode on the supply line, so the 12v fan is actually running at around 11.25v, and at 6v is down at 5.25.

This will account for some non-linearity.

edit: to add a further voltage loss inside the fan, the Hall switch is usually an open-collector bipolar device, and drops about 300mV.

scalar · Post by **scalar** » Sat May 17, 2003 9:02 pm

fancontrol wrote:I took some measurements of a fan I wanted to slow down and found that current was not linear with supplied voltage. The equivalent resistance, using Ohm's law, varied from 40 Ohms at 12V to 30 Ohms at 7V to less than 30 at 4V. So don't expect exact results the first try.

This is because higher voltage can carry more energy using a smaller diameter conductor.

Lower voltage requires progressively larger conductors to carry the same amount of power as high voltage. But since the wires inside the fan stay the same size as you lower the voltage, the resistance to power flowing through the fan increases.

This is why your car's 12v 1200-watt starter motor uses huge heavy cables for carrying 100 amps, but your 120v 1200-watt toaster has very small, thin power cables that only need to carry 10 amps.

This is also why very large power lines operate around 120,000 volts. If they were only carrying 120volts, each of the power cables would have to be huge, maybe 3 feet in diameter to transport the 100,000 amps or more of current.

cpemma · Post by **cpemma** » Sun May 18, 2003 7:41 am

scalar wrote:... But since the wires inside the fan stay the same size as you lower the voltage, the resistance to power flowing through the fan increases.

I suggest you check Ohms Law

Reasons for the non-linearity are the non-ohmic voltage losses across the protection diode (if fitted) and hall-switch output transistor, and possibly some inductive reactance related to fan revs.

JEN · Post by **JEN** » Wed May 28, 2003 3:32 am

Here's my fan controller. I know I said I was going to make it myself, but I cheated and got a friend to make it for me

Its simple, neat, does what its supposed to do:

i.e. control 3 fans at 12v - 7v. Thats it.

It only cost around £5 for the components and he put it together for free!

ruprag · Post by **ruprag** » Wed May 28, 2003 5:49 am

JEN one question, how do you get the 7v ?

JEN · Post by **JEN** » Wed May 28, 2003 6:25 am

ruprag wrote:JEN one question, how do you get the 7v ?

Dunno, I didn't make it!

I think it using zeneon???? something... diodes to reduce the voltage to 7v, but dont take my word for it

ruprag · Post by **ruprag** » Sat May 31, 2003 12:52 pm

Cool,
can you get a wiring diagram for us "electronically challenged" ??

This sounds like something I would like, I currently have 1 5/12v switch at the rear of my computer but having it in front with multiple switches would be cool.

Susquehannock · Post by **Susquehannock** » Thu Jun 05, 2003 10:56 pm

JEN wrote:Please try not to laugh! I am going to try and make my own fan controller

OK, not that you have stopped laughing, I would appreciate all the help I can get, as I will need a lot of help

1. whats the difference between SPDT and DPDT switches?

I use $3 rheostats for my fans now. No need to pay extra
for Enermax. They don't have the adjustability the
rheostats enjoy either.

What's so funny about making your own fan controller?

Susquehannock · Post by **Susquehannock** » Thu Jun 05, 2003 11:00 pm

ruprag wrote:Cool,
can you get a wiring diagram for us "electronically challenged" ??

This sounds like something I would like, I currently have 1 5/12v switch at the rear of my computer but having it in front with multiple switches would be cool.

This article has excellent guides & schematics of many types of fanbus:

http://bit-tech.net/article/52/1

That should have everything you need....... Good Luck! ......... 'nnock

My Own Fan Controller :lol:

My Own Fan Controller :lol:

Wire size vs current capacity

Re: Wire size vs current capacity

Re: My Own Fan Controller :lol: