I've been building a custom acrylic case for my pc and my current power supply isn't cutting it will all the hardware that will be going into it. I've got two 350W PSU's that I want to hookup to my one motherboard. How do I go about doing this?

And please no suggestions on getting a beefier PSU as I have already dremelled out the hole for the second supply

These links may be helpful..........

http://www.pc-mod.com/articles/atx/

http://www.burningissues.net/how_to/power/psu.htm

http://www4.ncsu.edu/~pjgilban/dualps.html

Hey thanks a lot, the last link was the easiest to follow. Got my two PSU's up and running now!

Some pictures would be nice

Wish granted. Sorry for the shakiness, was going fast. Please note I am also not done building the case so this is a work in progress. I started this acrylic case project about 2 weeks ago. It has room fro 8 optical drives and 6 hard drives (after I build the drivecage). I still need to cut the hole in the front add fans and lights etc. And add the other side panel. Then I will be done. I am also moving the yellow case out afterwards. It is just supporting the watercooler right now. The 2nd PSU is hard to see, but it's beneath the motherboard.

I guess this can help those who have two lesser powered or two older power supplies, and avoid buying an expensive new one.

I myself an opting to try it on my b*tch machine!!!

I also think it's a great tip for most people. I've known it for years but haven't ever tried on my PSU myself. I was just not sure where to find the right wire.

There are 300-watt PSU products with prices like US$5 or even lower. I have no idea whether wiring two of them will make it better than US$10 300-watt PSU.

If you hook up the second unit via a 12V relay switch you can have the secondery unit power up when you turn your system on. I can't remember where I got the how-to from but I'll find it if you want to try this.....

Both of mine do turn on when I boot the system, the second one runs my hard drives and water cooler right now.

Which method is that using ?. Did I see a method that *combines* the power of two PSU's ?.
[8]

The third link is what I used, and the both turn on with the booting the pc.

***WARNING*** connecting two power supplies together may cause serious damage to the power supplies and the equipment that they are connected to.

The master/slave setups illustrated in this thread should be okay. But, connecting two power supplies so that their regulated voltages are connected to each other, is BAD.

Background) Most power supplies use one circuit to power one transformer to make all of the various output voltages. Then, one output voltage (usually the +5Vdc) feeds back to tell the input side of the transformer what to do. The other output voltages are controlled by their relationship to the feedback voltage. (They come off the same transformer using different windings) [very over-simplified] So, the input side of the power supply regulates itself to make the regulated voltage come out right; and the other voltages drift according to what is happening to the regulated voltage.

Problem) If the two different power supply regulated voltages are connected to each other, they will make the power supplies unstable.

Lets say PSU 1 regulates it's +5 line to +5.015 volts. Let's say PSU 2 regulates it's +5 line to +5.013 volts. If the two regulated voltages are spliced together, PSU 1 will pull all the load off PSU 2 by pushing the +5V to +5.015 vdc. It's other voltages (+12V, -5 V, -12V and +3.3V) will go high. PSU 2 will reduce it's output to bring the +5V down to +5.013 vdc. PSU 2's other voltages will also go low. The motherboard and other devices will be caught in the middle of the conflict.

Real power supply sharing systems use extra circuits to prevent PSU 1 from affecting PSU 2 and vice versa.

So, link 3 is bad. Don't do it. Your hardware will thank you.

Two power supplies that do not connect to each other (other than to turn on the slave PSU) are okay.

yuknow, I've been thinking about trying this ever since I read the post. I bought a couple of cheep psus from ebay and today have been prepairing to try to splice them together to make a psu for a nice new machine that I'm building. However there was this nagging doubt that it might not be such a good idea so I thought I'd visit here and see how that guy's getting on who did the mod. Luckily for me you got here 'sweetums', with what sounds very much like good advice, and I can see that my worries were right.
You mentioned that this might be possible with the addition of a seporate circut though, do you know how, exactly ?.
Cheers,
n8

I've tried to find out how multiple power supplies are isolated for a long time, but I have not found out how the pro's do it. I work on similar power supplies every day, but my employer's products are not made to be paralleled. I think it is kind of a trade secret thing.

I worked for one manufacturer who made his schematic diagrams hard to read on purpose AND copyrighted the screwy schematics to prevent people from duplicating his products. There are no real secrets in electronics.

If you can take something apart, then you can probably determine enough to duplicate it. But the cost of documenting how it is put together is usually enough to keep people from stealing "your" design.

....when you say that you have not found out how 'the pros' prepair their units so that they can be used in parralel. Who are we talking about here when you say 'pros' ? Also I don't understand what you are trying to say in the last scentance of your post at all, what are you saying ?
Cheers,
Number .o08888|88880o.

Running the two psu's independently of each other like I am, is ok. Trying to combine their power would be dumb. The only splicing is for 1: to allow the 2nd psu to operate without being attached to the motherboard, and 2: to have it boot up when you press the power button. I've been running the two psu's together like this nearly 24/7 since this thread was created. It's perfectly safe.

.....this can be acheived by just grounding the power good and switching this unit on before boot. There isn't any connecting of wires needed.

No its not neccessary, unless you want to flip the power switch manually at boot up.

I think I have got a bit confused because in the third link, that you say you have used, it states;
"What if you could wire two 300's together and make a 600 watt PS? "
and it goes on to explain how to, supposedly, do this.
I got confused by this as the wording seems to suggest that it is a how-to that will enable a person to make a combined watt power unit from two units, rather than a 'how-to' with instruction on how to add a slave power unit to your machine that can be used for farming out to your drives/cooling system/cathode lights.
Hopefully you can see why I might have made this mistake.....
CheerS
8

When I say pro's, I mean the server grade hot-swap power supply manufacturers. ETASIS, 3Y and Delta.

When I was talking about stealing designs, I was explaining why it may be so hard to find info about paralleling "switched mode power supplies", one of the popular generic names for this type of power conversion device.

It is almost impossible to design electronic assemblies that cannot be duplicated and relabeled. If electronics designer-manufacturer "A" designs a hot-swap power supply system that works and becomes popular; then then manufacturer "B" could make it cheaper and sell it for a profit, if he knew how.

Fortunately, for designer-manufacturer "A"; most manufacturers are too cheap, and profit margins are usually so small, to buy something, take it apart and reverse engineer their own product.

There may be reference material on how switched mode power supply paralleling circuits work, but I have not Googled it out yet. The only info that I remember finding is that there is a diode network based passive design and an active design. I have not seen anything beyond that.

End of Parallel SMPS design info search

Master-Slave setups should be fine. There should be no problems as long as "ground" is the only shared output. Problems cannot happen long as both power supplies are NOT directly connected to the same device.

IDE, and SCSI, cable connections between the drives and the motherboard, or controller card, should be okay for standard devices. Neither standard uses a direct power buss connection in the connector cables. (except ground, and I checked SATA too)

BUT, connecting one power supply to the motherboard ATX power connector AND connecting the OTHER power supply to the motherboard's secondary connector is probably a BAD thing. Unless you have a motherboard that was designed (like some server mobo's) to use two power supplies. By secondary I mean the ATX 12V connector or hard drive style connector that some mobo makers add to help people with old fashioned non-ATX12V power supplies.

So long, bye, I have enuff other things to do, I am gone until next time.

I've often wondered if this would be OK to power a video card? The new cards are huge power hogs!!! And now with SLI (two video cards shotgunned toghether), your video cards can draw 150w+!!! That's just too much for a standard PSU to handle, considering you have a CPU that draws 100w, and the drives at 18w-24w each. All this strain is from the 12v rail, the most powerful PSUs have a 30A 360w rail at the most. Some PSU manufacturers have went the route of dual 12v rails. The still only provide about 360w, it's just they split the load over two outputs.

So lets take an average performance PC and add up the load on the 12v rail(s).

P4 3.4ghz prescHOT cpu: 89w for the newer ones 103w for the older ones. Now they have dual core chips!!! Who knows what they're going to draw, but the minimum I've seen is 109w. This is a lot of power, and it takes more to OC it. AMD cpus are a little less for the A64s, I think about 75w.

6800 Ultra/GT or X800/X850 PRO/XT/PE: They all draw within 20w of one another. Lets call it 75w, depending on if you OC it and other things, it will vary. Now we consider that you can put two of the 6800s in a puter, and you double the power.

Drives, cd/dvd drives are 12w-24w, hard drives draw 6w-18w depending on RPM, number of platters, and efficiency of the motor. Lets call it two CD drives @ 18w each, and two hard drives @ 9w each. So you have 54w just in drives, maybe more.

Any lights and fans draw off the 12v rail too! Fans don't draw much, but it adds up! The average 80mm fan draws about 1.5w, high speed fans and 120mm fans draw 6w. Lets call it 4 fans @ 5w each just to be safe, and a light @ 4w.

Cpu = approximately 100w
Video card = approximately 75w
Drives = approximately 54w
Fans and lights = approximately 24w
Total = approximately 253w or 21A This means you need a helluva PSU, and this is without overclocking and one video card. Imagine an overclocked SLI rig!

Dual 12v rails are manditory if you plan on running a dual core chip when they come out here shortly (P4s are allready out). The dual PSU idea is looking better and better. Hopefully you can get away with running the video card(s) and some of the drives on one of them, and plugging the other into the mobo to run the PSU, any fans, and some of the drives. You can move things around to distribute the load.

I just want to know if it's safe to run the video card(s) on a separate PSU from the mobo? That could be handy instaead of spending a fortune on a 700w PSU for such a beast.

If the video card itself needs a molewx connector, then yes, powering from either psu should be fine. As mentioned before, I've been running dual PSU's for quite some time and have had no problems whatsoever.

No, if you have a video card that draws power from the agp slot, then it will have to work
off of the same PSU that the motherboard is hooked up too.

Well, my main concern with such a thing is I don't think the power circuitry is disconnected from the power on the mobo. So I think it would be connecting the 12v rails together through the video card. Even if the video card has a molex connector, the card will still get power from the mobo. It won't run the GPU at full speed, and it will conserve power, but it will still run. This means the card is connected to the power distribution on the mobo. Now lets say the PSU you use for the graphics card is cranking out more voltage than the main PSU for the puter. If that's the case, you're looking at the mobo pulling power through the graphics card if it's connected. This probably is not a good thing! I heard of somebody that tried this and he said it killed his video card. I wasn't sure if he was just a doofis, because from the thread it could have been a lot of things that did his card in, or it actually did kill it. I haven't seen anybody who's tried it since. I'd like to know for sure if the power circuitry is isolated. Also, on the PSUs with dual 12v rails, they would have to be capable of being hooked in paralell if my theory is correct. So if they can have each individual 12v rail connected together, can you take two PSUs that have dual 12v rails, and use them in the same system? For instance, power the video cards off of one 12v rail from one PSU, and the CPU header off of a different PSU. Is it safe to have such a configuration? According to that post by BadSweetums, it could cause serious problems. But if the dual 12v rail PSUs have the capability to have the outputs paralelled, I wonder if it would work with multiple PSUs?

Good point, in that case I would just have the main psu (being the better one) hooked up to the motherboard and just have the mobo, video cards, and other pci cards running on it. Then off your secondary psu, have your hard drives, optical drives, fans, lights, etc.

And come to think of it, isn't the molex connector on the video cards just to power the fans? I'm pretty sure it is.

EDIT: After more thinking I have come to the conclusion that the molex connector on the video card is indeed to power the fan. Any device that is connected to the PCI, AGP, PCI Express will draw its power from the slot on the motherboard. If it drew power from the molex connector for the video card it would short out your agp slot or pci bus. They are separated circuits, so it really doesn't matter which psu is powering the fan on the video card. The video card will always draw power from the psu that is hooked up to the motherboard. The motherboard supplies the power it receives to the video card or any other pci/agp device.

No, the molex on the video cards supplies the GPU! That's why a 6800 Ultra won't let you OC unless you've got two molexes plugged into it! My 6600GT has a molex on it, and if I forget to plug it in (don't ask), it will default to it's 2d frequencies to keep from drawing too much juice from the mobo! The fan still spins regardless of if it's got the molex connector plugged in or not. Plugging all that stuff into just one PSU totally defeats the purpose of having two PSUs, you're not going to releive enough load by putting all the drives on a the second PSU to make it worth while. An agp port is limited to 45w I think, so if your card draws more than that, you have to have a molex connector on it. My 6600GT draws 60+ watts @ stock, who knows what it draws at the speeds I have it clocked to. I dunno, that's why I was curious about the dual 12v rail PSUs. If they can be put in paralell, it would be cool to have 4 12v rails in a dual core SLI rig (which I might build shortly)! I'm sure I'm going to have to have a 600w+ PSU to run the beast, and I don't want to spend the money on a decent one. I'd much rather take two of the 460w or 350w fortron PSUs and have 4x 15a 12v rails to run everything for less than $200. A 600W, decent brand PSU is anywhere between $180 and $350!!! You can get 350W fortron PSUs (they make OCZ PSUs) with 120mm fans, and dual 15a 12v rails for $68!!!!! So for $136, you could have 60A @ 12v, and they're even black with sleeves! You'd have a 700w extra heavy duty PSU for all intents and purposes, with dual 120mm fans! That would be the way to go if they can be hooked in paralell on the 12v rail. I think you can do that with the dual 12v rail models, you'd never have to worry about power!