How many AMPS can 1 of my PSU 4pin atachments handle?

[jbslow]

Hi , I have this fan that uses 12v and 5.1a , I had it rigged on a voltage regulator that I got from radio shack. Now I know very very little about V and A and everything so I asked the guy at the counter how can I make my fan run at 7v , "Here you go sir you can use this with it you can adjust the v from 1.5 , 3 , 4.5 , 7 ,9 ,12 all you need to do is splise the fan wires into this and plug it into the wall". Cool thanks guy!

Well it worked great for a day but the regulator only supported 300 mili amps (which I found out when I tried to get a refund) so today after did some mods to the case and went to run this thing and as you can imagine the regulator was fried.

Ok so I sure dont want to fry my PSU so will I be able to run this fan using one of my 4pin contection wires? I have a 300w Sparkle witch I imagine will work.

Also can you tell my how to change the volts to 7 or maybe even 5 , hopefully without needing to buy something else. Of course if its not safe to run this fan without some sort of regulator pleasee tell me couse like I said I know very little about this subject.

Thanks I would really like to get this house fan from the side of my pc and back in the room ;) .

[It_The_Cow]

You should go punch that RadioShack Guy in the face. He should have known better. It's fairly simple modifying your fans to run on a molex connector at different voltages. Most 300 watt PSU draw about 10 amps on a 12 volt line, so you'll be fine there. If you already haven't you can splice or push the wires out of the connectors and put it in a molex connector. Here's how you can get different voltages

[jbslow]

Alright I've found a thread on the voltage mod so I wount nrrd any help there.

Maybe I should buy one of those riostats because I have know idea how many amps my psu can handle at 12v or 7v or 5v.

Maybe someone electically inclined will help me make sensce of this ;

AC INPUT : 115/230V - , 10/5A , 60/50HZ
AC OUTPUT : +3.3V----28.0A(ORG) , +5V----30.0A(RED) , +12V----15.0A(YEL)
+5Vsb----2.0A(PURP) , +5V----0.3A(WHITE) , +12V----0.8A(BLUE)
P.G.SIGNAL(GRAY) GROUND(BLACK)
FUSE RATING : 6.3A 250V (+3V & +5V = 180W Max)
MAX OUTPUT POWER : 300W (+3.3V & +5V & +12V =280W Max)

[jbslow]

Thanks It The Cow you posted while I was typing.

[el]

It cows method is okay but not the best way. I have been investigating fanbuses and it looks like you should build something around a LM317 or LM350(for the big ass fan) just remember that a fan that pulls .4amps at 12volts will pull a bit more at 7volts. depends on the fan but be careful and test circuits before frying power supplies.

[It_The_Cow]

Basic line - You'll be fine whatever you choose to do. At 12 volts, you'll have 15 amps (more than enough), at 5 volts you'll have 30 amps (more than enough), and at 7 volts you'll have 15 amps (more than enough)

Rheostats are cool since you have more control on how much you reduce your fan's power. The RadioShack ones I saw were rated at 3 watts, so you'll have a fairly wide range for adjustments

[It_The_Cow]

Originally posted by el
It cows method is okay but not the best way. I have been investigating fanbuses and it looks like you should build something around a LM317 or LM350(for the big ass fan) just remember that a fan that pulls .4amps at 12volts will pull a bit more at 7volts. depends on the fan but be careful and test circuits before frying power supplies. All those schematics confuse me. Maybe I should stare longer :D

[Patchmaster]

I have this fan that uses 12v and 5.1a 5.1 Amps?! How big is this thing? The Comair/Rotron I got recently only pulls 2.25 Amps and it's the biggest fan I've ever seen used in a PC. (This isn't meant as a challenge for whose got the biggest fan. I'm just saying it's considerably bigger than the biggest fan normally used for PCs.) Most PC fans pull 0.5 Amps or less.

BTW, despite what their commercials used to say, Radio Shack is definitely NOT the place to go with questions about electronics. In hundreds of trips there I've only ONCE had someone wait on me who was clearly knowledgeable and competent. Most of the time you're lucky if they even have a clue what you're asking for and can point you in the general direction.

[jbslow]

Patchmaster its a Pole Blower with 176cfm hence why I must cut the voltage.

here you can see it (http://www.grainger.com/Grainger/searchresults.jsp) , just thank Hoot

update: ah the link no worky , well if your really interested Grainger.com (http://www.grainger.com/Grainger/start.jsp) the part # 2C646.

[Patchmaster]

That is one power-hungry fan! I'm far from an expert at this, but I'd be reluctant to do the 7V thing on something pulling that much power. It seems to me that it's one thing to wire up a .25A fan using the +5V line as ground, but 5.1A? Maybe it would be fine, but I wouldn't want to chance it.

As for a rheostat, you're going to have the same problem I do with the Comair/Rotron fan. If my calculations are correct your fan will use just a bit less than 65W. Most common (and cheap) rheostats will handle only a small fraction of that. The ones that will handle that kind of power are rather expensive. You might try BG Micro (http://www.bgmicro.com). They had a 150W, 7.8 Ohm rheostat for less than $10. The only problem I saw was that it was very big (4" diameter).

Another alternative is to just wire in a resistor. Allied Electronics (http://www.alliedelec.com/default.asp) has some large wattage resistors that aren't terribly expensive. The big problem with this solution is lack of flexibility. Allied also carries the big capacity rheostats if you want to spend the money.

[jbslow]

Your right its exactly 62W , Hoot wrote an artical which he used a LM-388 potentiometer if I can find one and its not terribly expensive I will most likely go that route.

update LM-338K

[Robbie]

well, the power supplies that I have come across have had there power rating on the side. I don' t think the 12v line had as much as 7 amps but I could be wrong. You can wire two 12v lines in parallel, so if it was only 7 amps on one line you would havve 14 amps to work with two lines.

And usually at start up fans draw the MOST current. I don't remember if they rate fans amprage as start up current draw or idle (running) draw. I would imagine start up draw but like I said I can't remember.

Sounds like one H E double hockey sticks of a fan.

Mod on

Rob