# Speed Control On Computer Fan



## Smashin (23/1/09)

Hey guys,

I'm sure this topic has been posted to death but if anyone can help out it would be appreciated.

I'm building a magnetic stirrer and just put together this dick smith speed controller 

http://www.dse.com.au/cgi-bin/dse.storefro...duct/View/K3070

and am trying to run this fan from it:

http://www.dse.com.au/cgi-bin/dse.storefro...duct/View/Y8498

The fan rocks backward and forward but does not spin. I'm pretty sure the circuit is fine and the fan power source and fan are fine. Is there something i'm missing???


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## gros21 (23/1/09)

check polarity eg + is connect to the right sid eof teh board.

Also can u spin it by hand to 'jump start' it if so i dare say volts to low to run it. 
even if u can't jump start it volts may be low what teh reading from case modding back ground

7v is need to start it spinning and 5v will keep it running


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## Smashin (23/1/09)

Cheers gros21,

tried jump starting, no go. Tried high, mid anfd low speed.

Polarity - tried supply in both ways.

Output voltage = 10.7v

If i hock supply straight to fan all is ok.

Bit miffed on this one.

Does a certain type of dc motor need to be used???


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## Simon W (23/1/09)

The motors used in the fans are a single-phase brushless DC type. They work by pulsing the current on and off. They also have a Hall-effect sensor for determining where the rotor's position is to supply the next pulse, so they need a steady DC supply to operate.
Your speed controler is meant to be used with brushed DC motors (or lights). It works by pulsing the current to the motor to control the average power available to the motor.
It's likely that this doubling-up of pulses is causing your drama's.


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## schooey (23/1/09)

search "tight arse" and there's a war and peace effort on how to do it....

*counts down til LethalCorpse hits the thread*


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## Smashin (23/1/09)

Simon W said:


> The motors used in the fans are a single-phase brushless DC type. They work by pulsing the current on and off. They also have a Hall-effect sensor for determining where the rotor's position is to supply the next pulse, so they need a steady DC supply to operate.
> Your speed controler is meant to be used with brushed DC motors (or lights). It works by pulsing the current to the motor to control the average power available to the motor.
> It's likely that this doubling-up of pulses is causing your drama's.



Many thanks Simon, a nice clear logical answer off to the shops for brushed motor tomorrow. Can drink in piece now, may than ks all...


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