help with fan control

[1-3-2-4]

I'm building a simple fan control which only has 3 parts

NTC thermistor 10k Ω

50k Ω spindle trim potentiometer

MOSFET Power transistor (N-Channel)

The fan speed should go up as the temperature gets hotter but my fan does not turn at all.

but the funny thing is while heating up the NTC I got as high as 7.80V then it started to go back down again.

for the pot do all 3 leads need to be connected? because pin 2 (wiper) is connected to the MOSFET source and Pin 1 of the pot is connected to the MOSFET Gate.

The MOSFET drain is connected to the fan's (-) lead And the fan's (+) is connected to the NTC which runs to fan's(+)

I don't understand why it wont work

 

[ericgibbs]

I'm building a simple fan control which only has 3 parts

NTC thermistor 10k Ω

50k Ω spindle trim potentiometer

MOSFET Power transistor (N-Channel)

The fan speed should go up as the temperature gets hotter but my fan does not turn at all.

but the funny thing is while heating up the NTC I got as high as 7.80V then it started to go back down again.

for the pot do all 3 leads need to be connected? because pin 2 (wiper) is connected to the MOSFET source and Pin 1 of the pot is connected to the MOSFET Gate.

The MOSFET drain is connected to the fan's (-) lead And the fan's (+) is connected to the NTC which runs to fan's(+)

I don't understand why it wont work

hi,
Please post the circuit diagram.

 

[1-3-2-4]

it's listed here..

**broken link removed**

 

[ericgibbs]

it's listed here..

**broken link removed**

hi,
Are you using the IRFZ24N FET.?

 

[1-3-2-4]

hi,
Are you using the IRFZ24N FET.?

no the IRF510 N channel FET

*edit

I have 9omhs on the thermistor at room temp and 2 ohms heated up.

 

[ericgibbs]

no the IRF510 N channel FET

*edit

I have 9omhs on the thermistor at room temp and 2 ohms heated up.

hi,
Thats the problem , they have very different Vgs turn ON curves.

 

[1-3-2-4]

hi,
Thats the problem , they have very different Vgs turn ON curves.

Thats odd that he would say to get that part but wont work..

and radio shack does not have that other MOSFET I know for sure as i went to a few stores yesterday.

and RS lists the specs on the MOSFET here

MOSFET IRF510 Transistor - RadioShack.com

 

[danielsmusic]

I would scrap that thermister for a high ohmic one at room temprature. Then use a voltage divider.

 

[ericgibbs]

Thats odd that he would say to get that part but wont work..

and radio shack does not have that other MOSFET I know for sure as i went to a few stores yesterday.

and RS lists the specs on the MOSFET here

MOSFET IRF510 Transistor - RadioShack.com

hi,
I have the data for both types of FET.

For example:
if the IRFZ24 has a gate voltage of say 4.5V the drain current is about 2amps.
The IRF510 with a gate voltage of 4.5V has a current of 0.5amp.

 

[1-3-2-4]

I would scrap that thermister for a high ohmic one at room temprature. Then use a voltage divider.

but then I would also need to change my potentiometer as well right?

 

[ericgibbs]

I would scrap that thermister for a high ohmic one at room temprature. Then use a voltage divider.

hi daniel,
Wouldnt putting a 'higher' resistance thermistor in the top end of the divider reduce the Vgs when using a 10K pot in the bottom end.???

hi 1234,

Use a 100K pot with IRF510, see if it improves the turn on voltage at the gate.

 

[danielsmusic]

It would depend on the thermistor, but yes, you'd probably have to replace the pot.

 

[ericgibbs]

It would depend on the thermistor, but yes, you'd probably have to replace the pot.

hi,
Did you look at the two Vgs graphs I posted, the two FET's have different conduction specs.
Both in threshold and VgIds slope

 

[danielsmusic]

Yes, I did. You could vary the pot to compensate, though.

 

[1-3-2-4]

ah I made an error I had two connections backwards I had the fan 12+V going to the gate and not the thermistor connected to the 12+V

and the ground was not set to the wiper and gate it was set up as the source.

It works now

thanks for those that helped

 

[audioguru]

Your thermistor is shorted. It is only 9 ohms. The project says to use one that is 10k ohms which is more than 1000 times higher.

 

[1-3-2-4]

it's not shorted it's 9kohms

 

[ericgibbs]

it's not shorted it's 9kohms

I thought you had a made a typo, thats why I ignored it.

Lets know how the project goes.

 

[1-3-2-4]

Your thermistor is shorted. It is only 9 ohms. The project says to use one that is 10k ohms which is more than 1000 times higher.

I thought you had a made a typo, that's why I ignored it.

Lets know how the project goes.

heh I had a little too much birthday drinks

so far so good I will add the second fan a bit later when I grab a bit more rest, works really well it pretty much wont come on until around 25-30c which is good

that pretty much means on cold mornings no need to blow air on an already cold heatsink backing up for 5 seconds.

when my other 15,000 rpm fan arrives in the mail (that's the one going in) I will do some more testing man that little 40mm fan is almost 50dbA loud!

 

[audioguru]

My pc has fans that change their RPMs depending on the temperature (how hard the processor is thinking about things). They are big enough to spin fairly slowly (but still blow a lot of air) so they are fairly quiet.