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24 Volt DC Power supply

H

holli4pirating

[H]ard|Gawd
Joined
Nov 13, 2005
Messages
1,432
Are there any power supplies that can output around 200 watts of 24 volt DC power? I would prefer the supply to run off a standard United States AC wall outlet. I'm looking because I've found some really good fans, but they only put out good CFM at 24 volts, and I can't figure out how to get that kind of voltage to them.

EDIT: I'd like to power some fan controllers, so a 4 pin molex output would be best.
 
200W @ 24V??? That's 8.3A! How many fans are you powering? 20?
 
The 4112NHH moves the same amount of air as the 4114NHH except it runs on 12V.

If you need molex connectors, wire them up yourself -- it's not hard to do.
 
How about a Meanwell 320W 24V PSU? http://www.power-factor-1st.com/sho...ries/s-320.html
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Any idea what type of connector the output is on that? I can't tell from the picture.

The 4112NHH moves the same amount of air as the 4114NHH except it runs on 12V.
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I looked around for other models, but I can get the 4114NHH for $1.49 each, and normally similar fans go for $25+ each. So it's actually cheaper to get a seperate power supply than similar 12 volt fans.
 
holli4pirating said:
Any idea what type of connector the output is on that?
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The listing says "Connection: 9P / 9.5mm pitch terminal block with cover". Looking at the drawings, I'd expect they're #6 or #8 screws (or maybe a similar size metric screw, like M4), so you can just get a crip-on loop or spaede connector at the car parts store.
 
The listing says "Connection: 9P / 9.5mm pitch terminal block with cover". Looking at the drawings, I'd expect they're #6 or #8 screws (or maybe a similar size metric screw, like M4), so you can just get a crip-on loop or spaede connector at the car parts store.
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I've never done anything like this before, so I'm not really sure how I'd have to wire it up. It also just occured to me that I'm not sure that I've ever seen a fan controller that can run up to 24 volts.
 
holli4pirating said:
I've never done anything like this before, so I'm not really sure how I'd have to wire it up. It also just occured to me that I'm not sure that I've ever seen a fan controller that can run up to 24 volts.
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You haven't, fan controllers run 12/5V and base their output off those. for 24V you'd need to get a rheostat. Finding one that does a few amps is a hard task.
 
If I remember correctly, the +12 and -12 together should work.

Anyone wanna help? I know you use the +12 as a positive and a -12 as a negative, but would it work?
 
Ah, I found a site that has overvolted fans using the +12 and -12 connectors here. I happen to have a spare PSU lying around, so I guess I'll give it a shot when I get my fans. But does anyone know where to find a 24 volt rheostat like madmat suggested?
 
Your -12V capability is only about 1A, so you're only going to have 12W available.
 
Your -12V capability is only about 1A, so you're only going to have 12W available.
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Damn, it sounded like it would either work, or give me a reason to throw out a crappy PSU. Although 12 watts would be enought to run one fan, like on afromods, but it wouldn't help me. So I still need some help on how to wire up a 24 volt power supply and a 24 volt capable rheostat of some kind. Any suggestions?
 
So you want to run 12 fans at 24v, to move about 1800 CFM total. But you don't know anything about electronics, huh?

I have an 8x10 office here at work. With 9-foot ceilings. So the volume of my office is about 720 cubic feet. With that setup, you'd be able to turn over the air in the office, completely, in about 25 seconds.

That's not cooling -- it's windy.

What are the fan controllers for? When would they ever be set at less than, say, 10%?

holli4pirating said:
So I still need some help on how to wire up a 24 volt power supply and a 24 volt capable rheostat of some kind. Any suggestions?
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DigiKey sells rheostats. You don't buy them based on voltage; you choose them based on resistance and power dissipation.

Not to be offensive, but my suggestions are to check your numbers again, and hire an engineer.
 
So you want to run 12 fans at 24v, to move about 1800 CFM total. But you don't know anything about electronics, huh?
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I don't want them all running at full all the time.
What are the fan controllers for? When would they ever be set at less than, say, 10%?
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Some fans will be on radiators, some as intake/exhaust for the case. So some will need to run over 100 CFM, and some won't. For those that won't I'll probably run them on controllers that go up to 12 volts, and they'll run off a normal, 12 volt power supply.
What are the fan controllers for? When would they ever be set at less than, say, 10%?
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The issue isn't that I want them that low, but I would like to be able to get them over half power. So I would need a controller that can handle higher currents.
Not to be offensive, but my suggestions are to check your numbers again, and hire an engineer.
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The only way to learn is by doing...Plus, I'm a college student working a summer research job, so I have a lot of free time.
Perhaps I haven't clearly posted what I need, but this is something I'm still tossing around in my own mind, and I thought thinking out loud on the forums would be helpful.
 
So now I'm thinking that only 3 fans, the three that will be used on a radiator will need to run at high CFM, so a 75 Watt PS should do it.
That means only 3 controllers. There will then be at least 4 more fans as intake/exhaust, with more modded into the case in order to maintain a underpressurized setup. If anyone has suggestions regarding the power supply, since this is a PS forum, please let me know. Also, suggestions on controllers would be good. I'm thinking of modding a 5.25 inch bay cover to house the switches.
 
Let me be clearer: the air flow you're talking about is very massive. I'd like to understand why you need these fans. I'm not sure how you'll mount them in the case, even if three or four are for an external radiator. With six or seven fans even in the largest case I've ever seen, the case will howl and moan with airflow and vibration.

Indeed, the only way to learn is by doing. But maybe you should start with a project that's simpler, since you're new to the field. In engineering, we can learn lots by not doing. Let's try a few more back-of-the-envelope calculations to see what we can learn.

Over at Digikey, they sell rehostats (among other things). The line they carry is pretty broad, you can read the PDF for it here.

IIRC, the datasheet for the fans said the 24 volt models operate from 16 to 30 volts. So we can guess that the stall voltage for the fan motor is 16 volts. They also say the power consumption is 19 watts, which means they're using about 800 mA of current.

800 mA at 24 volts is about 30 ohms. So if we have a 30 ohm rehostat in series with the fan, it should be just about at the stall voltage of 16 volts. It'll actually be a little less.

Of course, no rehostat at DigiKey is exactly 30 ohms.

If you're really going to go ahead with this, you might want to try to empircally find the stall voltage for the fan to make sure you get a usable rehostat. That'll also check my math.

If the fans draw 19 watts, we can put two on one rehostat if we can find a rehostat that can handle 28 watts. But they come in 25-watt models, and 50 watt models. Three fans is 47 watts, but that doesn't seem like a good safety margin; the rehostat itself will get hot.

So let's run two fans on one 50-watt unit. That means you'll need 5 rehostats.

The 50 watt rehostat is Model J on that PDF. It's about 7/8ths of an inch in diameter, so five wide will take 5 inches of panel space if you mount them very tightly together.

Digikey carries a 35-ohm unit at 50 watts (their part number RJS35RE-ND). It costs $27.81 each. Five will cost $139.05, plus shipping and tax.
 
Mikeblas: Thanks for your posts.
Let me clarify the setup I'm thinking of: MountainMods U2-UFO. Three of the fans will run at high CFM to pull air in through a Thermochill HE 120.3 (Front left). At least one other will serve as an additional intake on the front right, relatively low. The three ports on the back will all have exhaust fans running around 12 volts, depending on the noise, because I would like to stay underpressurized for better cooling.
So I'm thinking of starting with three fans on the 24 volt PS and controllers. The other four that I will start with will run on a Vantec Nexus, which I'm pretty sure does 7-12 watts.
Someone else has used the fans and written that the can run under 5 volts, so I'm hoping the can run well at a min of about 7.
 
For the controller, forget running all of that current through an expensive rheostat. Use a transistor in a common emitter configuration to power the fan. Connect a small pot or rheostat to the base side for speed control, and wire the fan in series with the emitter-collector part of the circuit. Much cheaper than a big rheostat, and works great.

For example, controllers I've built use a transistor that handle up to 24V and 2A collector current, 100 gain. I think they were 25 cents apiece from Mouser. The potentiometers are cheap 10K ohm ones from Radio Shack. Solder everything onto perfboard. I would post photos, but I don't have one lying around right now.
 
Bones said:
Much cheaper than a big rheostat, and works great.
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Sure would. But if holli4pirating is struggling to figure out how to physically attach leads to the power supply, I don't think he's going to be able to choose a transistor, not to mention bias it and build a circuit around it.
 
Nevermind, I found some 12 volt fans that can put out over 150 CFM and aren't too expensive, so I'll get those for the rad and undervolt the Papst fans to 12 volts for mounting on the case. But thanks for the suggestions, maybe I can use them as a future reference or the thread might help someone else. The only reason I'd wanted to use the 24 volt fans on a 24 volt PSU was because the fans were so cheap that it was less expensive than buying high CFM 12 volt fans, even if I had to get a 24 volt PSU.
 
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