Simple question- brushless motor

[fred_b]

I bought a small brushless computer fan (12 v .12 A) that I want to switch on and off with a picaxe output.

I didn't know anything about Electronic Speed Control motors when I bought it and just want to run it at full speed when needed. Is there a simple way to switch it on and off (no PWM)?

(Plan to use a MOSFET- don't have the part number with me at the moment)

Thank you

 

[Andrew Cowan]

The easy options are:
A N channel MOSFET (logic level is preferred).
An NPN transistor.
An NPN transistor driving a relay.

Do you have any parts or a PICAXE project board? These often have inbuilt NPN transistor arrays.

A

 

[fred_b]

I may not have been clear. I (think) I understand how to switch a device using transistors and MOSFETs.

What I am unclear on is the three wires coming out of the fan. I powered it up directly to a battery with just the red and black wires. It seemed weak.

Is the third wire simply for variable speed when desired? Can it be left unconnected and then I should just use the red/black wires as for a standard DC motor?

Thank you.

 

[lanternfish]

Hi

Is the third wire simply for variable speed when desired? Can it be left unconnected and then I should just use the red/black wires as for a standard DC motor?

The third wire is a tach signal. And just use the red and black as for a standard DC motor?

Apart from the voltage/current you don't give any more details on the fan e.g. diameter.

 

[boriz]

Assuming it’s a standard PC fan...

Although it is a brushless motor, the simple drive circuit is actually inside the fan, so simple DC straight into the red+black wires is how it’s supposed to be driven. As LF indicated, the third wire is a feedback signal so the computer can monitor the fans RPM.

Newer fans have 4 wires, one for PWM speed control. The motherboard sockets are cleverly designed to accept both types. (3 wire or 4 wire)

Dunno why your fan seems weak. Maybe it’s just old, or you’re not supplying it with sufficient power.

For a peek inside a standard PC fan: http://gluegun.wordpress.com/

 

[Peter M]

12V .12A (120mA) isn't going to be a very powerful fan.
Even most PC heatsink fans draw more than this!

If you want a fan with a bit of grunt you'll need to look for something with a bit higher current rating.

And as keeps getting mentioned here - read a data sheet - these give the specs on how much air they can move, and often what pressure they can acheive.

As to driving it the answers are above.

 

[fred_b]

Thanks for all of the replies. The fan diameter is around 80mm.

I definitely read the datasheets. This one claims to move air at 27 cubic feet per minute. I estimated my enclosure volume to be less than 1 cubic foot.

Sounds like plenty but yes, the power consumption should have been a clue that it is weak.

Thanks again. I am always amazed at the timely and helpful responses on this forum.

Merry Christmas from Montana, USA

 

[SgtB]

I've used a TIP120 driven by the parralell port to PWM PC fans before. It works splendedly. You can also just switch it on and off.