Very small battery powered fan circuit

[tucocaps]

Hello,

I was wondering if anyone would be so kind as to help me with some ideas about a small and simple battery powered small DC fan circuit I am trying to build. The product will hopefully go into production someday, so of course I'm trying to build something I can scale.

Essentially, I'm starting with a 20x20mm dc fan that is about the size of a quarter. The lowest voltage it's rated for is 3 volts.

The catch here is that I will be needing the fan to run at very low speeds, and want to be able to adjust the speed of the fan with something like a POT/volume adjustment.

So, looking for ideas on how best to start building this circuit. I am thinking about using one AAA battery, because I want the entire assembly as small as possible, but would be nice to use a commonly available battery. I'm also looking for other battery suggestions, but I'm trying to keep the total cost of this in terms of electronics/battery fairly low at this stage.

Thanks much for any help!

[mariushm]

Re: Very small battery powered fan circuit

i don't know where you'd get 3v fans.. they're usually made for 5v and 12v.

simple and not very efficient:

http://www.pcbheaven.com/circuitpage...an_Controller/

a npn transistor and a couple of resistors and optionally a couple of capacitors (all can be surface mount)

+ ----> resistor----> potentiometer ----> resistor ---> ground -

potentiometer wiper - > base of transistor

+ ----> collector ----> emitter ---> fan ----> ground -

more efficient, if your fan has four wires (meaning you can send a pwm signal to control rpm) then you could use a 555 IC and adjust the pwm duty cycle with a potentiometer.

[tucocaps]

Re: Very small battery powered fan circuit

Thanks mari. This is the fan I just ordered to test with. I'm thinking it doesn't have the extra lead you are talking about.

http://www.ebay.com/itm/181241465497...84.m1439.l2649

[mariushm]

Re: Very small battery powered fan circuit

The fan needs 3.7-5v to work, not 3v.

It only has two wires, ground and voltage so you can't adjust rpm using pwm signal, your choices are either restricting the current or reducing the voltage.

The current can be limited either by the method above, or by using a simple resistor in series.

If you want to reduce voltage by a single resistor you do it like this.

You see it says 5v 0.08A on it. So the internal resistance of the fan is V = I x R => 5 = 0.08 x R => R = 5/0.08 = 62.5 ohm

Now if you want the fan to run at 3v, you need to figure out the current.

V = I x R ... 3v = I x 62.5 ohm => I = 3/62.5 = 0.048 A

So now you determine the resistor that will drop 2v on it at 0.048A.

V= I x R ... 2v = 0.048 x R => R = 2 / 0.048 = 41.66 ohms so you pick a resistor as close as possible to this value. let's say you pick 42 ohms. Power dissipated is ixixr = 0.048x0.048x42 = 0.09 watts. So a 0.125w resistor will be enough, but going with a 0.25w would be better.

And now you have basically +5v --- resistor 42 ohm --- [+] fan running at 3v [-] ---- ground

I would recommend a lipo or lithium ion battery for this, they run at 3.7-4.2v. But you'll need a lipo charger for the battery.

See batteries here: http://hobbyking.com/hobbyking/store...tSortOrder=asc

See chargers here: http://hobbyking.com/hobbyking/store...tSortOrder=asc

[budm]

Re: Very small battery powered fan circuit

You can do some experimentz and find out for yourself and learn about motor control at the same time.

http://www.electronics-tutorials.ws/...odulation.html
You do not need large 2n3055, MOSFET will be better.

http://www.circuitstoday.com/pwm-mot...ontrol-circuit

http://www.analog.com/library/analog...fan_speed.html

[tucocaps]

Re: Very small battery powered fan circuit

Thanks everyone for the replies. Very informative, and I am grateful for the help. I've started to prototype and experiment with this project, and now have a few more questions popping up.

I tested my basic design with a 9 volt battery, and found that the speed of the fan , just with a direct connection to the 9 volt, is already in the range of speed that I am looking for.

What I'd like to do is devise a pot type adjustment for fan speed, as we were talking about earlier, but sooner or later I'm going to want to capture 3 or 4 speed "settings" , and convert the circuit into something where those speeds can be selected via a momentary push button type switch.

The battery type and size is quite puzzling to me due to my limited experience and knowledge in this area. Of course, I want the battery to last as long as possible, and I'm thinking I am ultimately going to want a rechargeable battery, with the recharge circuit also being on the device. It does have to eventually be fairly compact. The entire circuit including the battery, charger, and control part. What type, size and voltage battery might be a good choice for this? I think a thinner narrow battery is going to fit my design best. Something about 2 inches long , 1/2 inch or less wide, and as thin as possible.

Thanks for any further help.

[tucocaps]

Re: Very small battery powered fan circuit

The fan needs 3.7-5v to work, not 3v.

It only has two wires, ground and voltage so you can't adjust rpm using pwm signal, your choices are either restricting the current or reducing the voltage.

Actually, there is a 3rd yellow wire attached to the fan. Would this be a signal wire?

[mariushm]

Re: Very small battery powered fan circuit

No, that would be a rpm sensor wire .. it tells you the speed the fan is rotating at.