PC fans wiring?

[Duckmyster]

Hey guys,

New to the forum just been having a wee browse an it looks tip-top. Anyway I am in the process of building a 250 Stealth(ish) box out of MDF and was going to use 2 large pc fans to extract the hot air that has passed though my main fan and carbon filter out of the box.

I was wondering how I go about wiring these fans without a PSU or computer in general at my disposal? I've heard talk of a transistor or something

Thanks in advance

Duckmyster :

 

[flashog]

you just grab any old mobile phone adapter or similar, cut the wires and stick them together.. Check out the voltage.. most pc fans run on 12v, but that doesn't mean that they won't run on less (just not as fast). You can use as many fans per adapter as the total amp of the adapter allows.

 

[Duckmyster]

brillant thanks man i'll try that out

 

[MandraKe]

Hi folks, this is my first post and I'm glad to be able to take part in this community and try to add to the overwhelmingly large info-base here. I havent quite gotten my head around inserting images or links yet, but I've uploaded 2 to my gallery to help explain my post and I guess you can view them there.

Duckmyster, if you're gonna use multiple fans running from a single power source, then one important thing to take note of is the difference between series and parallel circuits:

Gallery image 1 - Series/Parallel

Running in parallel, all your fans will receive the full 12V that a standard PC-fan needs to operate at full speed. But if you wire your fans in series, then the 12V is simply devided across all the fans in the circuit and they'll run slower and pull less air.

The fact that fans run slower at lower voltages can be exploited though, by using a variable-voltage power source. You can pick these up pretty cheap (Argos) and the advantage gained is in control. My advice would be to hack the connectors off (like in the advice given by Flashog above), wire the fans in parallel and run them all at 12V at first, if you find that you're sucking too much humidy out (or if you want to raise humidity for clones/seedlings) then you can just drop the voltage on the adapter itself, and the fans will slow.

Gallery image 2 - AC/DC adapter

Some folk might argue that applying a lower voltage to a motor designed for 12V will burn the motor out, but in my experience, this hasnt happened.

Good luck with your grow!

 

[boroboro]

I found an 18V DC power supply that I used for a few PC fans. Wired two identical fans in series to the power supply, so each would get about 9V, as long as the fans stay identical.

On 9V the fans ran slower but still moved a bit of air around. Next time I'll feed them the full 12 Volts.

Since you can use just about any power supply in the neighborhood of 12V DC, I would just get a 12V power supply at a Goodwill or similar secondhand. The fans use such little power that most any 12V source should do.

On second thought - you already have a fan inside the cab? Do you need another one?

 

[FreezerBoy]

They make AC fans. Just plug them in and you're done. I use a single 120mm 76 CFM axial to cool my 250CMH Freezer.

 

[fatbastard1976]

rather than post a new thread asking my question, i'll jump on this one cuz its the same topic.... sort of.....

i have a plug from an old cordless drill charger. the specs on it say:
Input:120VAC~60Hz 12W (NOM12W)
Output:15.95VDC, 210mA (NOM15,95V_
would this be good to run two say 12volt comp fans? dont have the fans yet, so any suggestions are good.

sorry to jump your thread with my ??

 

[I N Hail]

NO you need it to be 12v, its the mA/Amps you need to be sure will run 2 fans

 

[fatbastard1976]

this is an answer to anouther wiring question.....

MandraKe
Guest

Join Date: Sep 2008
Location: Ireland
Posts: 1
MandraKe is on a distinguished road

Hi folks, this is my first post and I'm glad to be able to take part in this community and try to add to the overwhelmingly large info-base here. I havent quite gotten my head around inserting images or links yet, but I've uploaded 2 to my gallery to help explain my post and I guess you can view them there.

Duckmyster, if you're gonna use multiple fans running from a single power source, then one important thing to take note of is the difference between series and parallel circuits:

Gallery image 1 - Series/Parallel

Running in parallel, all your fans will receive the full 12V that a standard PC-fan needs to operate at full speed. But if you wire your fans in series, then the 12V is simply devided across all the fans in the circuit and they'll run slower and pull less air.

The fact that fans run slower at lower voltages can be exploited though, by using a variable-voltage power source. You can pick these up pretty cheap (Argos) and the advantage gained is in control. My advice would be to hack the connectors off (like in the advice given by Flashog above), wire the fans in parallel and run them all at 12V at first, if you find that you're sucking too much humidy out (or if you want to raise humidity for clones/seedlings) then you can just drop the voltage on the adapter itself, and the fans will slow.

Gallery image 2 - AC/DC adapter

Some folk might argue that applying a lower voltage to a motor designed for 12V will burn the motor out, but in my experience, this hasnt happened.

Good luck with your grow!

so if i run it in series, then the fans would be splitting the 15 volts only getting 7.5 volts each. right? (for some reason, the pics are gone. i didnt cut them out.)

 

[FreezerBoy]

I use a single 120mm 76 CFM axial to cool my 250CMH Freezer.

Whoa. Blast from the past. My first stinky strain (Mandala's 8 Mile High) put an end to the axial. It just couldn't handle a legitimate scrubber. I've moved on to an S&P.

 

[SwitchAvenger]

While you could use that charge to power some computer fans most commercial battery chargers have a response voltage they look for, so if they don't see the voltage they go into fail safe mode (to prevent overcharging batteries, which could explode). If you looking around for something to wire in like that you need to find an AC-DC power supply that is around the voltage and amp range your looking for.

When looking at circuits also keep in mind that there is three things that are always in effect. Voltage, Amps and resistance. V= AxR and Voltage is king! So to increase your voltage has double the effect as Amps in most cases. So yours 15.95 DCV 210 mA power supply on has a 3.35 Watt rating. Where as a 9 DCV running at 1000 mA (or 1A) has a wattage of 9 Watts. To calculate Wattage out put it's Volts X amps = Watts.

Most computer fans tell you how much of an amperage drawl they take. This two can be calculated but when linking more then one fans together resistance plays effect. This is when you can run into three types of circuits. Series, Parallel, and Series-Parallel. For sake of simplicity a wiring your fans into parallel circuits (positive to positive and negative to negative) is usually the best option because your total resistance of your circuit is lower then the lowest load. For an basic example if you have two 4 ohm (or resistance, impedance) wired together in a parallel circuit your total resistance is equal to 2 ohms.

This is a real basic over view and i hope this helps with your question

 

[fatbastard1976]

thanks for the answer switch.
now umm.... huh? i guess my understanding of things i have read is all confused. i didnt realize it was so complicated. i thought i go out buy two 12volt puter fans and find a old cell charger that was 12 volt, i could just wire em up. but the chargers i have are only 5volt so they wont work.
if i bought something at the store, what would i need to look for? someone suggested a adjustable adapter 12v,9v,6v....?

 

[SwitchAvenger]

You can also go to radio shack and buy a power supply that has adjustable voltage out put. But it only cranks out about 300 mA, which isn't bad it can run some computer fans but you have to also check the amp drawl on the fan as well because the fans might not spool as fast as they can. Another option if your feeling adventurous and have an extra computer power supply laying around you could always build one like this.


You could pretty much eliminate all of the other voltage out puts and just have your 0 (ground) and + 12 coming out.

To build one exactly like the one i have it will cost you about 12 dollars if you have a extra power supply. Even less if you don't use all the bananas terminals

And because most computer power supplies handle about 200 watts on the low side, that means at 12V you can handle a 16.6 amp load, so you can chain a bunch of fans together until you reach that 16 amp drawl

 

[Deaner]

Would something like this work for wiring 3 PC fans?
http://www.220converters.com/Universal-Adapter.htm

• Switchable 110V and 220V 50/60 HZ
• Output : 1.5, 3, 4.5, 6, 7.5, 9 and 12V DC
• 500ma max
• Multiple input jacks
• Negative - Positive Polarity settings
• North American wall Plug

 

[ScrubNinja]

Would something like this work for wiring 3 PC fans?

Yes that is what you need but 500mA isn't a lot so it depends on what amperage your fans total before that question can be answered. It will run 3 weaker fans no problem. It won't even power one strong fan safely.

I use one like this, it's 4 amps and I'm running close to 2 amps of fans (needed them all to be synced adjustable voltage). Good luck finding an adjustable voltage wallwart adapter over 1 amp or so. I couldn't.

 

[Deaner]

Thank you ScrubNinja. How much does that thing cost, and what is it called? I couldn't find anything similar under a search for Dick Smith Electronics.

 

[ScrubNinja]

Hi Deaner, Dick Smith is a popular Australian electronics brand/store. Similar to Radio Shack I guess. This is it here:

http://www.dse.com.au/cgi-bin/dse.storefront/en/product/M9941

Costs about $80 AUD, and is regulated and overload protected. PS It's 3 amps, not 4, my bad. I think it was called an international power supply or something like that, on the box.

 

[BL_Zebubba]

I recently picked up one of these.

http://www.coolerguys.com/840556029977.html

They also make a 500mA model as well as a 5000mA model.

 

[Deaner]

I recently picked up one of these.

http://www.coolerguys.com/840556029977.html

They also make a 500mA model as well as a 5000mA model.

Thanks BL Zebubba! So I can power three fans using this device without any problems?

 

[BL_Zebubba]

As long as the current requirements of the fans do not exceed that provided by the power supply, you're good to go. I went with the 2 amp version as I try to follow the Grateful Dead model - always have twice as much power as you really need.