Power fan with plug-in transformer

[yyonline]

Hello all,

I'm hoping that someone with a better understanding on electronic theory can double check this for me.

I want to power a 12V computer fan with a plug-in power supply. I'm not sure which fan I am using for the job yet, but I have two contenders. They are low rpm fans, so they're fairly low power.

12VDC 0.05A
12VDC 0.15A

The power supply I was thinking of using is the 200mA version of this:
https://cdn.badcaps-static.com/pdfs/...f665b0c3c6.pdf

Do you think this will work? I'm not sure what excitation voltage is, or if that comes into play with fans.

Also, The 0.05A fan will only be using 1/4 of the 200mA rating, so the voltage may be too high due to the low load. I think I can use a resistor to step the voltage down, but I'm not sure what spec resistor I should be looking at.

Any feedback would be greatly appreciated!

[Th3_uN1Qu3]

Re: Power fan with plug-in transformer

You need a DC power supply. An AC adapter (basically just a transformer) is also going to need a diode bridge and a capacitor.

As for the voltage, don't worry. If anything it will simply run faster. They easily take up to 25 volts.

[yyonline]

Re: Power fan with plug-in transformer

Thanks for your input. I'm venturing into unfamiliar territory here, so bare with me...

I was under the impression that the AC/DC adapter would have a rectifier built in to it. If that's not the case, would running the fan straight off the unconditioned DC output of the adapter cause any issues?

I'm aware that running at a higher voltage won't damage the fan, but the goal here is quiet. I've done a few tests with a 500mA apapter I have. I have a 1000rpm and 1200 rpm fan that both run at about 1350rpm due to the voltage being around 14-15V. I'm assuming this is because the fan isn't loading the adapter enough.

[Th3_uN1Qu3]

Re: Power fan with plug-in transformer

Ah, i read it wrong. It says "AC adapter" but at the bottom it says DC output. That's good.

If the goal is to have the fan quiet then get a 9 volt or 6 volt adapter.

[Evil Lurker]

Re: Power fan with plug-in transformer

Go to your local goodwill store. They usually have for sale some used small switch mode ac adapters (for cell phones, printers, etc) that ppl have donated for $2-3 each. Those are regulated usually via a TL431 or some variant across an optocoupler... so both your amperage and voltage should be in spec no matter what size fan(s) you decide to use.

Crack em open, solder on the proper connection, mount them wherever you want. Its actually cheaper doing that than buying mains AC rated fans. Heck last one I snagged was a 36/16v brick for some HP printer or some crap. I plan on hooking it to an LM317K for a constant voltage adapter.

Of course if you are really brave you can pop off the two SMD resistors going into the '431 and hook up a couple potentiometers and have a mini regulated adjustable power supply! In that case you want as high a voltage as you can get because its easier going down than up... if you go up you have to replace the corresponding filtering 'lytics to the appropriate voltage range.

[Th3_uN1Qu3]

Re: Power fan with plug-in transformer

You only have to replace the bottom resistor on the 431 - the one connected between the 431 and ground. Most times going up in voltage isn't an option anyway unless you live in a 230v area and the charger is meant for universal input.