Regulate 12v fan speed with voltage regulator

SmilesRising · November 28, 2019

Hello, i have a 12v fan that ive modded to use as a regular fan, the issue im having is that the fan is constantly running at max speed, im wondering if i could solder it to this https://www.electrokit.com/produkt/variabel-spanningsregulator-1-5-30v-1a/ and then be able to alter the fan speed?

nick name · November 28, 2019

Have you considered something pre-made? Like this Noctua controller? It works with 12V fans. I have three Noctua 3000RPM fans connected to one and five Corsair 12V fans connected to another.

I guess what matters is the amperage of the fan you're using?

https://smile.amazon.com/Noctua-NA-FC1-4-pin-PWM-Controller/dp/B072M2HKSN/ref=sr_1_2?keywords=noctua+controller&qid=1574948729&sr=8-2

Man · November 28, 2019

32 minutes ago, smiles rising said:

Hello, i have a 12v fan that ive modded to use as a regular fan, the issue im having is that the fan is constantly running at max speed, im wondering if i could solder it to this https://www.electrokit.com/produkt/variabel-spanningsregulator-1-5-30v-1a/ and then be able to alter the fan speed?

You may want to use something like this instead:

The orange 4-pin goes into the mobo's 4-pin PWM fan controller (A cable is provided) whcih then sends the PWM singal to the rest of the hub hence you can control your fans' speed from the BIOS itself.

This is safer than splitters as this hub has its very own power source and much easier than soldering a DC fan controller with the fan.

It's also dirt cheap. Just a few bucks on AliExpress etc.

SmilesRising · November 28, 2019

1 hour ago, Man said:

You may want to use something like this instead:

The orange 4-pin goes into the mobo's 4-pin PWM fan controller (A cable is provided) whcih then sends the PWM singal to the rest of the hub hence you can control your fans' speed from the BIOS itself.

This is safer than splitters as this hub has its very own power source and much easier than soldering a DC fan controller with the fan.

It's also dirt cheap. Just a few bucks on AliExpress etc.

1 hour ago, nick name said:

Have you considered something pre-made? Like this Noctua controller? It works with 12V fans. I have three Noctua 3000RPM fans connected to one and five Corsair 12V fans connected to another.

I guess what matters is the amperage of the fan you're using?

https://smile.amazon.com/Noctua-NA-FC1-4-pin-PWM-Controller/dp/B072M2HKSN/ref=sr_1_2?keywords=noctua+controller&qid=1574948729&sr=8-2

The fan is not plugged into the computer. its a 12v fan that gets power from an old phone charger that plugs into the wall. so i need something that i can solder onto the cord and regulate the voltage

Hackentosher · November 28, 2019

I'm assuming you need to step the voltage down, so I recommend an LM7805 with a potentiometer. These lil guys are super simple to step a voltage down to another, and the potentiometer would let you dial in the exact voltage you want. Pretty sure EEVBlog has a video showing how to use them, I would have a look.

Quick note, the more voltage you want to drop, the more heat it will produce so look into a heatsink you can bolt the chip to.

mariushm · November 28, 2019

You can't use a 7805 regulator as that always outputs 5v.

You can adjust the voltage using a linear regulator.

A linear regulator takes some input voltage and outputs a lower voltage throwing out the difference as heat on the chip.

The linear regulators will always have a maximum output voltage lower than the input voltage by some amount. The cheapest regulators will have this "dropout voltage" equal to around 1v, and there's a class of regulators called LDOs which have a much lower dropout voltage, as little as 0.05v.

On that website you linked to, here's the linear regulators:

1. Standard linear regulators https://www.electrokit.com/produkt-kategori/ic/spanningsmatning-ic/spanningsreg/

2. LDO (low dropout) regulators: https://www.electrokit.com/produkt-kategori/ic/spanningsmatning-ic/spanningreg-ldo/

Let's pick an adjustable linear regulator, capable of handling at least 12v input voltage and let's say 0.5A ( you want at least double the value written on your fan, for safety)

So from that website, I picked these:

Linear regulators:

1. LM317 DPAK (max 40v in, 0.5A, adjustable) : https://www.electrokit.com/produkt/lm317mdt-dpak-variabel-spanningsregulator-0-5a/

2. LM317 TO-220 (max 1.5 A) : https://www.electrokit.com/produkt/lm317t-to-220-variabel-spanningsregulator-1-2-37v-1-5a/

Let's go with the LM317 TO-220 as it would be easier for you to work with (could even wrap wires around the leads if you don't have soldering iron)

If you look in the datasheet linked on that page, you will see the pinout for both formats, and you'll also see further on page 5 the minimum way to configure it, and details, and on page 6 you have a more complex circuit with lots of protections that are optional :

So you really need only the chip, a resistor and a potentiometer

So let's say you go with a common 100 ohm resistor for R1 and let's say you want minimum 6v going to the fan, and maximum 11v (because as I said, a linear regulator like this will have around 1v dropout voltage).

You have the formula there in the picture: Vout = 1.25 x (1 + R2/R1) so we put the numbers in the formula and simplify the formula:

Vout = 1.25 x (1+ R2/100)

Vout = 1.25 x (100 + R2) / 100

100 Vout = 1.25 ( 100 + R2)

100/1.25 Vout = (100+R2)

80 Vout = 100 + R2

80 Vout - 100 = R2

So for 6v we have R2 = 80 x 6 - 100 = 380 ohm

For 11v, we have R2 = 80 x 11 - 100 = 780 ohm

You can see there's a range of 780-380 = 400 ohm between minimum and maximum. This means you could use a common 470 ohm potentiometer, or a common 1000 ohm potentiometer.

To guarantee you always have a minimum voltage of 5..6v, you could add a standard 330..390 ohm resistor in series with the potentiometer. This way, if the potentiometer is at the lowest value of 0 ohm, you still have that resistor's value in circuit and if you have it set at maximum, you have that resistor value + potentiometer

Here's the most basic arrangement:

If you use 220 ohm or 240 ohm instead of 100 ohm, you can use a 1000 ohm potentiometer and something like a 820 ohm resistor instead of 330 ohm and then you'd have:

0: 1.25 ( 1 + 820/220) = 5.9v

1000: 1.25 ( 1 + 1820/220) = 11.6v

Potentiometer:

500 ohm (close enough to 470) : https://www.electrokit.com/produkt/pot-500ohm-lin-b500/

500 ohm (another version) : https://www.electrokit.com/produkt/pot-500ohm-lin-pcb-b500/

1000 : https://www.electrokit.com/produkt/pot-1kohm-lin-b1k/

1000 (2nd version) : https://www.electrokit.com/produkt/pot-1kohm-lin-pcb-b1k/

Resistors :

100 ohm : https://www.electrokit.com/produkt/motstand-kolfilm-0-25w-100ohm-100r/

220 ohm : https://www.electrokit.com/produkt/motstand-kolfilm-0-25w-220ohm-220r/

330 ohm : https://www.electrokit.com/produkt/motstand-kolfilm-0-25w-330ohm-330r/

470 ohm : https://www.electrokit.com/produkt/motstand-kolfilm-0-25w-470ohm-470r/