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xxmonkey321xx

12V Fan controller

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I recently made this 12v DC fan controller, and I have a couple of questions..

1) For the capacitors, is 1000uF too much? When I plug it into my computer I think it draws too much power for a second, effectively killing my 12v rail.. I can hear the hard-drive electromagnet deactivating :/

2) Does the LM317T require a heatsink? It doesnt seem to get hot at all after a minute of use..

3) Both Capacitors are electrolytic, is that ok?

4) Would 50uF Capacitors work?

5) Are Axial Lead capacitors teh same as electrolytic capacitors?

Thanks in advance,
Monkey

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I recently made this 12v DC fan controller, and I have a couple of questions..

1) For the capacitors, is 1000uF too much? When I plug it into my computer I think it draws too much power for a second, effectively killing my 12v rail.. I can hear the hard-drive electromagnet deactivating.

Hi Monkey,
Welcome to our forum. ;D
I guess you forgot to look at the datasheet for the LM317.
1) Your power supply already has a filter capacitor so your LM317 desn't need another one. It needs just a small 0.1uF ceramic disc capacitor at its input to keep it from oscillating.
2) The LM317 is a voltage regulator. It doesn't need a huge output capacitor. It needs only 1uF at its output to keep it from oscillating.
3) The LM317 needs an input voltage more than about 2.5V higher than its output or it doesn't regulate. Therefore with a 12V input, its max output voltage is about only 9.5V.

2) Does the LM317T require a heatsink? It doesnt seem to get hot at all after a minute of use.

Power makes heat. Power= volts times amps. Your LM317 doesn't have any volts across it and its load current is low.

5) Are Axial Lead capacitors teh same as electrolytic capacitors?

Axial lead capacitors have the wires at both ends. Radial lead capacitors have both wires at the same end so they mount on a pcb. Any type of capacitor (electrolytic, poly or ceramic) can be either.

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Make a DC to DC converter. LTC1044, MAX1044 and ICL7660 voltage converter chips can do this for you.

...and yes, the 1000 uf capacitors are much too big for a device attached to a PC power supply voltage rail. They are most likely the cause for your 12 volt rail problem.

MP

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It is difficult to stepup voltage. Usually a power supply voltage is selected to be high enough for the application.

Not really. There are several ways to achieve this. Basically, you just need to make a charge pump and proceed with the voltage requirements from there.

If you use one of the voltage multiplier chips, you would use the 5 volt supply and configure it as a voltage tripler. For more current, the MAX660 is available. I don't know how much current your fan requires. I have seen some very low current fans.

Combining the -5 and 12 volt buss is ok, but you cannot connect the common on the fan to the computer common. Other methods besides using a resistor divider or regulator is to use a resistor combined with a zener diode to give you the output voltage you want. LM317 will work well with either the -5 to +12 or the resistive divider, or the resistor and zener. Just remember the LM317 requires a few volts higher input than the maximum output voltage when making calculations for input voltage to the regulator.


but then I would have ~15 volts going into my fan when the potentiometer is all the way on?


No. Not if your are connecting this to the LM317. The output voltage of the regulator will be less than the input. You would just need to calculate the output voltage. For example, if you use 220 ohm for R1 in your LM317 circuit and a 2K pot in series with a 68 ohm resistor for R2 as indicated in the data sheet, this will give you approximately 12.02 volts maximum voltage and approximately 1.6 volts minimum voltage.


MP

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Remember to check the maximum available current for the -5V tab! Also the motherboards current requirements at -5V. Often the current is just -0.5A and this might affect the motherboard even more than other solutions. A fan might use almost as much at startup and this might wipe out the initiation phase of the motherboard causing it to produce errors!

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crap...

Well.. any ideas? I really need an _easy_ way to step up the voltage :/

Or if not I guess I could deal with slower fans, they make less noise :D



Anyone got any ideas? Your gonna have to put them into noob terms, I really have very little knowledge of higher-lever circuitry. Thanks :D

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