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shadowbearwv
02/05/2009, 04:56 AM
I'm putting together a hood which will include, 2 MH 175W fixtures, 1 T-5 Actinic Fixture w/ 2 bulbs and looking to use 3 computer case fans with LEDs for Moonlighting and Cooling.

My question is what is the best way to power the fans/leds. In my research the typical draw of a computer case fan is 1.5 amps with a max pull at startup of 2.2 amps. This would put the total wattage of the each device at about 18W per fan.

I was thinking of wiring them in parallel. However I can't find a 12v power brick that could handle the draw of 4.5 amps. My next idea was to use an old computer power supply that I have laying around, but I'm worried about water and saltcreap with something so open.

Any suggestions would help.

Thanks

SB

Tiva
02/05/2009, 05:20 AM
Well, obviously you will not want the PSU in the hood, you'll want to mount in down below or behind the tank. For the power draw you're looking at a mini or micro atx style powersupply should be fine. You'll likely want to open it up and snip the extra wires off, as well as jumping the power on leads. I dont remember off hand what color it is, but I think it's green...

The other option you may want to look into is a laptop power adapter. However that wont be as easy to find in 12v, but it is possible.

Whichever route you go, just be safe and please solder and heatshrink all of your connections. Salt water and mist does nasty things to bare metal.

hellssephiroth
02/05/2009, 05:57 AM
yes the jumper is green to a black

jay24k
02/05/2009, 07:12 AM
Just go to radio shack and get a 1000mA power outlet. Just let them know what you want to do. The 1000mA should easily power 3. I power 2 with no issues and have hooked up a 500mA on 2.

mnestroy
02/05/2009, 09:45 AM
If you use a computer power supply does it only use the energy that the fans require?

Most supplies are rated for 250+watts.... be pretty expensive to waste 250w just to power a 12v fan.

swearint
02/05/2009, 09:48 AM
What size fan are you using that is pulling 18W? Here is what I used to cool a hood with two 175W MH and four 96W PC.

http://www.aerocooler.com/shop.cart?action=ITEM&prod_id=FANSOKDE8TBX

http://www.aerocooler.com/shop.cart?action=ITEM&prod_id=MIACDC12V


I used four for around 200 cfm and less than 2A total. Sorry, I don't know anything about powering LEDs.

Todd

stugray
02/05/2009, 10:09 AM
jay24k,

"Just go to radio shack and get a 1000mA power outlet"

Be very careful giving electrical advice.

The OP stated that he needs 4.5 Amps.
That is 4500mA where I come from.



Also I seriously doubt that the computer fans that shadowbearwv are planning on using REALLY draw that kind of current. It is probably more like 0.25 Amps each.

If they really pull that kind of current, they will be WAY too noisy.

I tried 2 fans that pulled ~1.75 Amps each @ 12VDC, and when I fired it up, I thought that the hood was going to blow off my workbench.

Stu

james3370
02/05/2009, 10:53 AM
depending on what size you are looking for (i am using 120mm) use this link to look thru the manufacturers
http://www.newegg.com/Store/SubCategory.aspx?SubCategory=573&name=Case-Fans

i personally like Silenx & Scythe...they have the best airflow to noise ratios & quality built stuff.

as far as powering them, the easiest thing i have found are these power supplies that already have the molex plug end that should plug into the fans. it is the 4-pin molex, so if the fans you buy have the smaller 3-pin molex, you'll need an adapter, but alot of the fan retail packages have the adapter included :)
http://www.jab-tech.com/12v-DC-Power-Supply-with-Single-Molex-Connector-pr-3776.html
they put out 2amps & most of your pc fans draw .25-.5amp per fan, so you should be able to power at least 4 fans off 1 of those

LJA
02/05/2009, 12:25 PM
Radio Shack does not have any AC Adapter that is 4.5 amps. Highest one is 2amps if I remember correctly.

We (Radio Shack) have other types of power supplies though that should do the trick. Stop by your local Radio Shack and talk to an experienced manager, most know quite a bit about electricity.

Good luck.

jay24k
02/05/2009, 12:55 PM
What kind of fan are you using? I'm running two 120 mm fans silverstone brand from newegg on a 1000mA with no issues at all. I didn't see his amperage needs as I assumed it was just for the fans themselves.


Edit: Your power supply from a computer will not use the full wattage listed on it. For example, if you have a 300 watt power supply, it can only use 50 watts if that is what it needs.

I should have other power supplies here if you want one. Just cover shipping and I can have one off to you. Since they are from HP computers that were a couple years old, I would guestimate they are between 200 to 250 watts.

Also, MOST case fans with LED's run around 3 watts per fan. Hope that helps.

jay24k
02/05/2009, 01:06 PM
Also, please correct me if I am wrong, but you divide watts by volts to get amperage.

If a case fan is at the most 6 watts times two fans, then you would have 12 watts which equals 1 amp which is 1000mA.

The worst case scenario is just get two of the small 1000mA plug ins and simplify it instead of having a loud noisier power supply.

Edit: I looked up one of the best fans I believe they have out because this joker pushes out serious amounts. The silverstone fm121 from newegg. I looked the specs on their site and even for this whopping 110 cfm it is only using max amps of .45.

Here is the spec site to show their numbers. Hopefully that helps. Better to be safe and accurate then sorry.

http://www.silverstonetek.com/products/p_spec.php?pno=fm121&area=usa

scrombussquared
02/05/2009, 01:08 PM
I have to agree that the draw from computer fans is around .20- .25 amps. Very low draw. I also power 4 fans from a 1200mA wall wart.

devgru
02/05/2009, 08:15 PM
try looking at low-voltage/cctv/security panel power supplies.
brands like ALTRONIX,MR,or DIGITALSYSTEMS for power supplies.

they range from 1.0amp up to 12 amps.

what size fan are you using?i bought 4 'PC' fans from an electronic supply company here in town and im powering them with a 12vDC 1amp transformer,been running 24/7 for 5+mos

Bamm Bamm
02/05/2009, 09:43 PM
i heard you can use old cellphone chargers also since we all have tons of them laying around

psteeleb
02/06/2009, 12:14 AM
I bought a small transformer at Fry's for $10, powers 3 fans with no issues. And it's the DC voltage out is adjustable, so I can literally speed control the fans at the turn of the dial


pics of my fan set up are on my build log toward the bottom of this page
http://reefcentral.com/forums/showthread.php?s=&threadid=1320654&perpage=25&pagenumber=7

There is a picture of the transformer by it self, a few pages earlier

HTH

shadowbearwv
02/06/2009, 04:19 AM
Just to give a little more information. I was having a hard time when looking at the fans finding what their power draw is/was. I found a document in my searches that stated that power draw for case fans was about 1.5 amps per fan. I was quite surprised cause I really have a hard time believing it was that high, probably an old document.

I had stumbled upon some laptop powersupplies on the web and was thinking that would be the way to go but it sounds like most people can run it with a 1 amp brick.

I'm getting the fans from newegg, probably that Antec with the switch for speed control.

What I probably should do before I even get to the stage of building the hood is just set one up on a case supply and measure the amperage with a multimeter, probably the safest bet.

Thanks for the great information. I'm a ways off on building the hood but I'll try to update with any information I find in my testing.

Thanks again

SB

james3370
02/06/2009, 09:38 AM
my paln is to put 4 of them....2 on each side....& run 1 on each side off a single power supply. that way i can set them on different channels on the reefkeeper & it can cut them on in stages depending on heat issues.

hllywd
02/06/2009, 02:46 PM
I think your decimal point is in the wrong place. I've looked at several fans I have here, all are in the .20A to .30A neighborhood, even the 120V 100 cfm one that I have are .20. I'm using 1 Thermaltake 13mm fan for 2x 250W MH and 2x 96W PCs with no heat issues.
I have 4 LEDs on a Lunar Tracker that came with an 800mA supply, my guess is that it is way overkill.
At the worst you might need two wall warts. IMO a computer PSU would be overkill.

Tim

ecomdesign
02/14/2009, 05:53 PM
is there anyway to have 2 fans running 24/7, and have 2 fans automatically kick on if temps get to say 81 degrees? Kind of a failsafe for warmer days...

jay24k
02/14/2009, 11:01 PM
Yes. Plug the fans into an outlet and they will be on 24/7.

You could get a temp controller that turns on the fans when it hits a certain temp.

ecomdesign
02/15/2009, 07:14 AM
I've looked into temp controllers as you have recommended, but the only controllers I can find ones that are meant to work in conjunction with chillers. I'm just thinking of using something that I can wire in to "psteeleb's" setup above.

His setup has the 12V transformer wired up to his fans, but I'm wondering if you could have a 12v thermostat or swtich in between the transformer and the fans?

jay24k
02/15/2009, 08:41 PM
That I'm not sure. I've never done it. The way I've done it is have the fans automatically come on when my metal halide comes on. This way it can counteract the added heat. If you are worried about an extreme heat, they have devices that will shut off your lights when a temp gets so high.

porterdog
02/15/2009, 10:49 PM
would seriously recomend these. I just got a set and then added 2 extra fans. I have them set at the lowest setting and they dropped my temp over 3 degrees. Really really quiet too. Pluse with the main module easy to add fans in the stand if needed..

http://www.frozencpu.com/products/8475/fan-ac-18/SilenX_AC_120mm_Fan_HTPC_Cabinet_Cooling_System_IXA-CCS.html?tl=g46c301s755