why fan not running continuously?

[nishinavin7399]

i have purchased a cooling fan for my laptop and added a few more fans for extra cooling....

i have added three external fans to it..refer following diagram..
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i will refer them as "small","LED","NON LED" fan from now on

problem::--

each of the fans run continuously when connected individually---OK

the LED and SMALL one run continuously when connected together..OK
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the NON-LED and SMALL one run continuously when connected together.. OK
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the problem is fans automatically turn off and on repeatedly..if the NON-LED and LED one are connected together
videos are in the attachment...
sorry for the poor quality

i am using a 12V rectifier i made myself...images here
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[pauloynski]

Seems your voltage regulator is geting too hot and shutting down. It needs a heat sink.

 

[nishinavin7399]

well there is an update....

none of them are running continiously in pairs...but they seem to run OK when they are used individually....

and as far as heatsink is concerned te box in which i keep my regulator doesn't seem to be that hot...

can insufficient current from the regulator be a reason???

 

[pauloynski]

I suppose you are using a 1A reg (probably a LM7812). That should be enough. In the photo I didn´t see any heatsink on the regulator. Could you confirm the chip is cool? The temperature inside the box is not a problem. It is the chip´s temperature that is important.

Added after 5 minutes:

Please let us know what type of regulator are you using and what is the voltage at its input.

 

[Audioguru]

Without seeing a schematic that has parts values then we are just guessing.
Maybe the "rectifier" is half-wave instead of full-wave.
Maybe the value of the main filter capacitor is too low.

 

[nishinavin7399]

ok guys just wait a while i am preparing the circuit diagram...

and sorry if i am replying lamely..

actually college server is down and i am on GPRS..and its 0400HRS in night(or say morning)...yawn..

Added after 1 hours 13 minutes:



here is the circuit...

now please tell whats wrong??

Added after 6 minutes:

guys i googled alot and i think absence heat sink is the problem,,,,

Added after 4 minutes:

can someone please give me a link on how to add heat sink to a regulator?

 

[Audioguru]

You show an ordinary transformer but say it has a center tap that is not shown so the label 9-0-9 does not make sense. Is it a 9VAC transformer or is it an 18VAC transformer?

The voltage regulator is missing the extremely important low value input and output capacitors shown on its datasheet that prevent it from oscillating.

C1 is in the wrong position. It will blow up!

If the internal temperature of the regulator reaches 150 degrees C then it will shut down. Its metal tab is made to be bolted to a heatsink with thermal grease between.

 

[smeezekitty]

It looks like there should be a cap across the output.
And WTF is with the cap inside the rectfier?
Also i agree with the above post that the regulator should be heatsinked.

 

[pauloynski]

Here is how to fit a heatsink **broken link removed**