Any DC electrical fan experts in the house?


 
J

Jon V

New member
I have a home built temp controller. (Auber SSR ramp/soak)

I have an SSR output I use for various other applications. I now want to use this for a stoker too. Figure I can - just need to know a bit more about DC fans.

Now- I am well aware the "proper" way to electrically hook up this controller to a DC fan would be to get a relay output controller.... BUT- I'm cheap and I want to get the most out of my current controller.


SO- how about it with the DC fan? Can I vary the DC voltage and expect to see the fan speed increase/decrease? If so- will it cause tons of damage to the fan and kill it quickly?

I'm sure the fan wont like it when the output is less than the stall limit on the fan. I'm sure this serino will be often so please take that into consideration on your answer on fan life determination.
----------------------
Alternatively- Does anyone know of a way of changing the SSR signal into a relay on/off type signal?

Thanks in advance all! - Cheers.
 
Lowering the voltage will definitely slow the fan speed but if your controller does not limit current it could cause the fan to pull more current when running lower voltages. Normally 1/2 the voltage will result in 2x the amperage at full load.
 
Good call Paul. Perhaps this is why the fan would die. Overheating as the current would generate more heat at the windings? hmm....
 
I'm no expert, but I've run DC fans made for computers, 12V at 7 and 5 Volts for long periods of time without no problems what so ever. No additional electronics added, just connected the "wrong" leads from the PSU. The fans slow down, make less noise and keeps on working for several years.

It's a neat trick if you have to place let's say a server in a spot where the noise is a problem. It's not ideal, but it works to top up a cabinet with fans, wire them to 7 volts and let them spin slower than normal.
 
My guess is the motor will run at nearly the same speed until the voltage drops to a point where it stalls. The proper way to control the speed of a DC motor is to apply voltage in pulses that vary in length. The length of the pulses, controls the speed of the motor. You can do this with a RC circuit controlled by a variable resistor. You can use the output of the RC circuit to drive a bit of logic, and control a switching transistor.
 
@Geir- I was wondering if the computer builders out there were playing around with these..... I looked into speed control and found what V_Rocco was talking about. (pulse width modulation)

V_Rocco- SO, are you saying if I build this circuit : http://www.robotroom.com/PWM.html : The output of my SSR (I'd use a dc one and run a 5v supply on the output side) would go to Vcc and I'd basically be powering up and down the whole control circuit to then give the fan a clean square wave to the fan?

Thanks,
 
That is a very useful circuit. I've used it many times over the years to extend pulses. If I understand correctly, you are trying to vary the speed of the motor. In the circuit you linked, you do that by adjusting the value of R2, so that would be the speed control. You would need additional logic, but you could use a series of fixed resistors, and switch them into the circuit based on the value present on the output of whatever your controller circuit is. If it has a variable voltage output, you could use an A to D converter to switch resistors in and out of the RC circuit. That is just one idea. There are many variations on that.




Jon V said:
@Geir- I was wondering if the computer builders out there were playing around with these..... I looked into speed control and found what V_Rocco was talking about. (pulse width modulation)

V_Rocco- SO, are you saying if I build this circuit : http://www.robotroom.com/PWM.html : The output of my SSR (I'd use a dc one and run a 5v supply on the output side) would go to Vcc and I'd basically be powering up and down the whole control circuit to then give the fan a clean square wave to the fan?

Thanks,
Click to expand...
 
Last edited:
I see what your saying now. Wow- this build would be sweet with incredible resolution. It will be awhile for this stoker build (still gathering funds for the wsm purchase) but when I do I'll post the end results here. Many thanks!
 
You must log in or register to reply here.

 

Back
Top