Custom fan controller

[Riddler356]

I'm working on a custom fan controller that will take power from the wall to operate my noctua industrial nf-f12 ppc2000, and have hit a snag that for the life of me i can't seem to figure out anymore, and that is what rating of potentiometer or rheostat to get and where to get it.

 

A basic explanation without giving away the purpose (once i start ill create a thread until then im keeping quiet).

For simplicity i found a wall power brick that matches the fans 12vDC, 0.1A, and 1.2w to run at full speed, but what i am looking for is some way to be able to have voltage control to slow the fan more precisely than off and three different speeds, but more like a dimmer switch, the only other form of impedance other than what i am looking for is a fuse to help protect the fan from surges, in case the power brick fails.

 

Summary: Looking for a variable potentiometer that allows fine controls over a computer fan allowing near 100% speed down to ~50-60%.

[iamdarkyoshi]

Search through a bin of resistors and try putting them in series with the fan and PSU. Once you find one that yields the minimum speed you like, that is the value of variable resistor you want to search for. Be sure to get one rated at a decent power.

[Riddler356]

Just now, iamdarkyoshi said:

Search through a bin of resistors and try putting them in series with the fan and PSU. Once you find one that yields the minimum speed you like, that is the value of variable resistor you want to search for. Be sure to get one rated at a decent power.

unfortunately in my area i am unable to do that, and have to purchase them either in bulk (100+) or one at a time at $4ea, with no testing possible.

[iamdarkyoshi]

2 minutes ago, Riddler356 said:

unfortunately in my area i am unable to do that, and have to purchase them either in bulk (100+) or one at a time at $4ea, with no testing possible.

Standard resistors?

https://cdn.sparkfun.com/assets/c/4/a/9/d/515c7a2bce395f653d000002.png

[mariushm]

You can control the speed of the fan through several ways, from simple to more complex.

The best way would be to use PWM, to make some circuit that sends those pulses on the fourth pin in the fan connector to control the speed without adjusting the power. It's complicated though.

An easier method would be to control the voltage through some way, adjusting the voltage between 12v and let's say 5v would also change the fan speed. There's cheap AC-DC adapters that allow you to change the voltage using a slider on them, or you can buy small dc-dc converters or you can build such a simple circuit yourself.

If you want to buy a dc-dc converter, there's plenty on ebay or sites like dx.com , banggood etc.. just search for "buck regulator" or "step down regulator".

Here's for example something that's cheap and would work : http://www.ebay.com/itm/MP1584-Adjustable-3A-DC-DC-Power-Converter-Step-Down-Voltage-Regulator-Premium-/201346125234?hash=item2ee12a0db2:g:DeMAAOSw6BtVTIeZ

You adjust the output voltage by using a tiny screwdriver on that tiny potentiometer. You can desolder that tiny potentiometer and replace it with a larger one that you could control with your finger, you just have to measure the value of the potentiometer before buying one with a multimeter. It's probably 10kOhm or something bigger.

Another very common dc-dc converter easy to find on eBay is this model : http://www.ebay.com/itm/Buck-Converter-Step-Down-Adjustable-Converter-Power-Module-Regulator-LM2596-New-/262501270653?hash=item3d1e4b847d:g:uj0AAOSw3ydVxXc~

Same thing, you use a tiny screwdriver to turn that knob and adjust the voltage, but you can desolder that potentiometer and replace it with a larger easier to use one.

These allow to you to adjust voltage between something like 0.8-2v to input voltage minus about 0.5-1v, so for example you'd get something like 5v .. 11.5v to the fan, maybe more.

 

Another method, the easiest would be to just put a resistor in series with the voltage wire to limit the current going into the fan. Instead of 0.1A you'd only allow 0.075A or 0.05A.

By changing between resistor values, you can adjust the speed.

Here's a page that explains how to choose resistors for this way of controlling speed : http://www.blackfiveservices.co.uk/fanspeed.shtml

You can recover resistors from old motherboars or hardware you don't need anymore.

 

 

 

 

 

[Riddler356]

7 hours ago, mariushm said:

You can control the speed of the fan through several ways, from simple to more complex......

I know all this, the reason for posting was to see if anyone can help me find the right potentiometer ohm rating to use, since that is the one part i am missing, i have everything planned out, i just don't know the rating i need at i can't test many due to it being to expensive in my area for experimenting, and mine is not the pwm model.

 

Thanks for the long more thoughout reply though.

[mariushm]

Well, you can just desolder the potentiometer from such a board and use a digital multimeter to measure the resistance when the wiper is set to the maximum value. When you know that, you can buy a potentiometer with the same maximum value or one that's slightly larger, as long as you won't use the potentiometer over the position that would be the maximum on the old potentiometer.

 

Alternatively, you can check what chip is the board using and google the datasheet for such a chip. In the datasheet, there's usually notes which explain how the output voltage is set. For example they may say two resistors are used, and that you adjust the voltage by changing a resistor and the ratio between those resistors determines the output voltage so in this case you just figure out the resistor value for 5v and the resistor value for 12v and now you know your potentiometer much be able to be configured at least to that minimum value and to at least the value of the other resistor value. Now you can just replace that resistor with a potentiometer.