How to build a stir plate for less than ten quid

[strange-steve]

That's an exceptional bargain, well spotted!

 

[blawford]

I bought all the items from links near the start of this thread, wired them all up and my fan isn't spinning. There is a red LED that gets brighter and the plug makes a more intense, high pitched noise (although still fairly quiet) as I turn the knob but the fan doesn't start moving more than a small jolt, even at the highest setting.

Anyone any ideas? Here are some pictures, although there isn't much I could have done wrong (he says, before someone points out the obvious thing he has done wrong).

 

[strange-steve]

Nothing obviously wrong there, does the fan work when connected directly to the power supply?

 

[Dutto]

Nothing obviously wrong there, does the fan work when connected directly to the power supply?

Also, I suggest that you check the polarity because some potentiometers and 12v fans won't work if the 12v polarity is reversed.

 

[blawford]

Nothing obviously wrong there, does the fan work when connected directly to the power supply?

Not sure, will check tonight. Does your plug make a high pitched noise when turning the dial?

Also, I suggest that you check the polarity because some potentiometers and 12v fans won't work if the 12v polarity is reversed.

Everything is correct as the labels on things say, I will try swapping things about tonight as well.

 

[Gerryjo]

Try connecting the fan direct to the power supply to ensure its working.
Your potentiometer is basically a dimmer switch and there's some modern day technology that don't like them especially with electronic circuitry built in.

Gerry

 

[foxbat]

A 2-wire 12V computer fan is fine with a rheostat type dimmer. Spin up voltage is usually around 7V ish then it'll run down to about 2V below that before stalling.

Oh, and be careful not to reverse the polarity. If the fan is a brushless design then you could destroy the commutation control circuitry depending on how cheap the chinese designers were and believe me there is no cost that they will not cut.

 

[blawford]

The fan spins when connected directly to the power supply, so I guess the potentiometer is a dud.

 

[BeerCat]

That's an exceptional bargain, well spotted!

Lol, not really as they sent me a stopper. Its false advertising, i need to contact them just forgot.

 

[Gerryjo]

The fan spins when connected directly to the power supply, so I guess the potentiometer is a dud.

I bought one of these on eBay and works perfectly.
Look at this on eBay http://www.ebay.co.uk/itm/322440653213

Gerry

 

[Spapro]

I bought all the items from links near the start of this thread, wired them all up and my fan isn't spinning. There is a red LED that gets brighter and the plug makes a more intense, high pitched noise (although still fairly quiet) as I turn the knob but the fan doesn't start moving more than a small jolt, even at the highest setting.

Anyone any ideas? Here are some pictures, although there isn't much I could have done wrong (he says, before someone points out the obvious thing he has done wrong).

See my posts on pages 18 and 19. Had exact same, exact same issue. Bought a new fan off different uk seller and all worked. Still stumped but fan was the issue even though worked fine when connected straight to live.

 

[blawford]

Cheers for the pointers, didn't read the whole thread. Will see if I have another fan...

 

[blawford]

Cheers for the pointers, didn't read the whole thread. Will see if I have another fan...

Yep, I did and the other fan works fine with the potentiometer. Thanks for the help.

Guess it might be an idea to replace the fan linked earlier in the thread with another so noone else has the same issue?

 

[strange-steve]

Yep, I did and the other fan works fine with the potentiometer. Thanks for the help.

Guess it might be an idea to replace the fan linked earlier in the thread with another so noone else has the same issue?

Very odd that you and Spapro had the same problem, I wonder what the issue is with that fan. The one I linked to on page 2 is the exact one I bought and it works fine for me.
@Spapro could you maybe post a link to the fan you bought?

 

[blawford]

Bought a new fan and everything is now working - still stumped as to why the original fan would work direct to power but not through PWM ???

This fan I bought from a UK seller, arrived in 2 days and is 3 wire (don't connect the yellow wire to anything, just use the red + and black - wires), 90mm 3pin selected: http://www.ebay.co.uk/itm/12v-SATA-...hash=item4867741bb5:m:mft5OtN-HX3j5kYt0gQES3g

Anyway, all sorted, will post pic later

Here you go.

 

[foxbat]

The reason it doesn't work is because PWM (a digital waveform) doesn't reliably work when applied to the power line of a DC brushless fan unless you carefully (or accidentally) match the frequency of the PWM output to the internal commutation circuitry hidden underneath the center circle of the fan. When the PWM wave is in the 'off' part of the period you have cut the power to the fan's control circuitry so if it happens to be during the part of the cycle when it should commutate, it can't.

There are two solutions.

Stop trying to use the wrong technology. You could switch to a plain rheostat on the power line (analog dimming). e.g. the Zalman Fanmate-2. These are designed to not dim below the level required to power the control circuitry. The load will consume the same power at all speed levels, with the power not consumed by the fan at low speeds being burned off as heat in the rheostat.

Use a PWM fan with your PWM controller. Way back in 2004 Intel realised people wanted to use digital PWM control for computer fans so the 4-pin fan specification was released. You can apply direct PWM control to the 4th pin and the fan itself knows how to decode this and will allow speed control right down to the minimum possible.

 

[strange-steve]

Thanks for the explanation, so if a 4 wire fan is used rather than a 2 wire, connect the 12v + and - to the power supply, the pwm wire to the controller along with a +ve and -ve?

 

[foxbat]

Thanks for the explanation, so if a 4 wire fan is used rather than a 2 wire, connect the 12v + and - to the power supply, the pwm wire to the controller along with a +ve and -ve?

I doubt those ebay PWM controllers I see in the images posted here can be directly connected to the 4th pin because it's designed to accept a TTL 5V logic level and the PWM frequency should be 25kHz (see section 2.4 in the Intel spec). I've built a controller myself for 4 pin fans in the past but it's not suitable to show here because it's part of a much larger design.

 

[Spapro]

This was the fan I bought, mine had 3 cables on I think - but only connected 2 to the PWM controller.

http://www.ebay.co.uk/itm/12v-SATA-...var=610344256334&_trksid=p2057872.m2749.l2649

 

[strange-steve]

I doubt those ebay PWM controllers I see in the images posted here can be directly connected to the 4th pin because it's designed to accept a TTL 5V logic level and the PWM frequency should be 25kHz (see section 2.4 in the Intel spec). I've built a controller myself for 4 pin fans in the past but it's not suitable to show here because it's part of a much larger design.

Ok, understood. So you're saying then that if connecting a 2 wire fan to a PWM it's really a flip of a coin whether it'll work or not?