Super candle heater, BLDC Fan speed control help.

[Dacr0n]

First off I'd like to say Hello!

It's an honor to be around all you fellow electro-techs!

What i've got here is a very simple project that I am 50% done with. I have large aluminum CPU heat-sink attached to a medium sized bolt and an array of steel washers equidistantly spaced to collect heat from my little 3 candle powered heating apparatus. The washers and bolt do an excellent job of transferring the heat to the heat-sink. Now what I want to do is use the brushless DC fan (that was originally used on this heat-sink) to be powered up and suck the hot air through the heat-sink when the heatsink becomes fairly hot. However, I do not really want the fan to be cranked up all the way to its maximum air velocity, unless required. That is only pumping at 100% if the heat-sink is cooking hot. I would imagine that the fan could be operating at arounf 50% of its possible wind velocity to blow the heated air into the room to get the desired effect I want, which is heating the small room.

I have a fairly decent understanding of how BLDC motors work and such. My main question is does this motor I have have its own internal control and commutation circuits? I also notice the fan has what looks like a thermistor to sense temp. It has 3 wires coming out of the motor. A black,red, and white. It says 12vDC. I would imaging if I apply 12V that it will start cranking full speed. As I mentioned earlier though, I don't really want it going that fast unless necessary.

*see attached pics*

So what would be the best way to control this puppy? Any suggestions greatly appreciated!

Thanks in advance!

 

[cowboybob]

Check these specs:

**broken link removed**

The white wire is, apparently, a tachometer output used by Dell computers.

The internal thermister cranks the speed up as temps rise (not sure if linear or simply two speed)

And it's brushless, so no commutators (if that's what you meant).

So, to answer your questions, just give it power, for starters, and see what it does for you before considering modifications.

 

[dr pepper]

These are usually 2 phase motors and will not work without the internal little pcb that does the commutation electronically.
Not sure about dell, and I've never seen a white wire on these (tacho is usually yellow), however as well as allready mentioned some have an extra wire as a tacho output and some have a extra wire as a speed control input.
Put 12v on red & black, if it runs fine, if not connect white to red and try again.

With carefull surgery you might be able to remove the thermistor (green blob) and put it on the heat sink on longer wires, then the fan speed will depend on the temp of the 'sink, but dont get it too close to the heat source.

 

[Dacr0n]

Thanks for the info doc.. Moving the thermistor.... That sounds like a good idea for what I am trying to do..

I could probably even tweak the resistance by adding some resistance or decreasing the resistance (by adding a resistor in series or variable resistor in parallel?) so I can tune the fans so called "auto temp response" to what I consider ideal for the job?

 

[dr pepper]

Yes you can do that, pull the themistor, let it settle to room temp for a bit then meter its resistance, if its say 5k ohm use a 10k pot.
The thermistor might be wrecked if you heat it more than 150 degrees so keep it out of the candle flame.