dual ATX psus in series to power 24v pelt--how?

[Xenogias]

hey kids, its me again. I'm advancing my cooling system...yes, I will be getting that cryobath waterchiller. Anyway today my question is about PSUs.

I know its possible to run 2 atx psus in series to give you 24v, but i was wondering if someone out there has any info on how exactly to go about doing this, a link to an article perhaps? would the 12v lines on the psus need to be rated at the same amperage in order to be effective and not overload either one? Also, as i was thinking about using this as a standalone powersource, i would need info on how to power an atx psu without connecting it to a motherboard...something about grounding one of the pins i remember.

My idea is to have the two atx psus running in series and through a relay, like the kind they have at xtwerkz so they would both be switched on when i power up the pc (which is what i have my current 14.4v 30a pelt powersupply doing)

[bigg]

the psus, independent of the pc's psu's should be of the same model. they can either be turned on by a relay in their 120V power, with their atx connector shorted out, or they can each be run with a 120>120V relay, which plugs into your main comp's molex, and plugs into the extra two pses atx connector

[lechumbl]

Hi Xenogias,

I am at work, but when I get home, I will post a text and picture "how to" for you.
In fact, I will also put it in the FAQ Section on our Home Page.

Take care........

[Player0]

Hi Xeno,

Powersupplies can be connected together like batteries to double the voltage. However, there are some difficulties with this. Normally, you would connect the 12v line from one PSU to the ground line of the second PSU. Then, between the two PSUs you have a 24v potential. Amperage is easy, you only have as many amps as the smallest PSU. So if one PSU has 13a on the 12v line, and the other has 14a. Then the most you can get is 13a at 24v.

The problem is shared-grounds versus isolated grounds. Depending on the design of your powersupply, you might have either one. Dont you have my old BullDog 30a? Or was that someone else? Well that particular PSU has two grounds. One isolated, and one shared. In order to get 24v from two ATX psus, they NEED to be isolated-ground designed. Hooking two shared-ground designed powersupplies together will short one or both of them out and do bad things.

Most ATX psus are shared. But sometimes you can hack them so that the grounds are isolated. To make sure the grounds are isolated, plug both in, connect them both in the case, and use a continuity meter and see if there is any continuity between the ground wires (black) on one PSU and the ground wires of the second PSU. If there ISNT continuity, then you are safe to hook them together for 24v.

If the grounds on both PSUs seem to be connected, then it could be a lot of work modding the PSUs to make them work. You may have to put rubber washers on the PCB of the PSU to isolate the ground wires (black) from the chassis (common-ground).

[lechumbl]

Hi Xenogias,

I am at work, but when I get home, I will post a text and picture "how to" for you.
In fact, I will also put it in the FAQ Section on our Home Page.

Take care........

[Xenogias]

Thanks guys. This looks like some good information here. Let me address everybody who responded.

Bigg: I will definitely take your advice on getting two psus of the same brand. I intend on going cheap so nothing greater than 350w-I'm hoping 20a on the 12v line. I would cut open both of their 120v ac wall-socket cords and feed them into a relay so i could cut down on the number of wall plugs my comp will require. Then I will short out each of their atx connectors by grounding them. Finally I will connect the relay to my main PSU by way of a molex connector so that when I turn on my computer the two extra psu's will start as well. Does this sound about right to you?

Lechumbl: I appreciate any visual aids or guides you could facilitate for me. I'll be checking the FAQs section later tonight or tomorrow. Thanks very much!!

Player0: Yeah, that was me who bought the bulldog from you. so I will have 4 PSUs in one system whenever i get this together. I'm considering blatantly copying you even more and getting a cube case to house all of this madness. My fulltower just doesn't cut it anymore. Now, let me get this straight....When you say "connect them both in the case" You mean physically situate them so metal is touching metal? I plan on having the psu's sitting on top of each other and bolted somehow to the case chassis. So if the psus have common grounding (they will both be the same brand and model as I'm going to buy them new so there's no chance that one will be common ground and the other not) then by physically touching their metal chassis to each other or to my computer case their ground (black wires) will show continuity measured by a continuity tester? If I followed you correctly in that, and I think I did, then I would probably take out the psu internals and give the inside of the psu chassis a double coat of liquid electrical tape. Would that at all effect the functionality of the psu to have it no longer grounded to the metal chassis? Finally, when i connect them in series could i use the 12v lines and ground lines in the molex connectors to link them or should i use the 12v lines and the ground lines from the atx plug?

thanks guys, LN forums has always been the most helpful source of information in all of my computing endeavors. I have a new project in the works, which involves phase-change chilling, pelts, and ridiculous amounts of wattage. hope to have some pics for you guys as this develops in the next months as well as pics from my last pelt/water monstrosity which i never got around to hosting.

[Player0]

Hi Xeno, I'm really curious why you need four powersupplies in your case :) Not entirely sure what your plans are, but I'm interested in hearing them. Anyway, yeah, doubling up ATX powersupplies for 24v is a difficult mod project. I'd give it about a 7 on the old 1-10 scale. A good knowledge of electronics is definitely required so you don't blow yourself up. Having had a 550w PSU blow up in my face before (got wet), I know how much respect and patience you have to have for this stuff.

You sound like you have the understanding down Xeno, and admittedly, my instructions aren't the easiest to follow. You just want to make sure that the powersupplies aren't sharing a common ground, because that is the key here. Like I said, the BullDog has a common-ground, and a negative terminal, and a positive terminal. Common ground is connected to the Earth. It is always at 0v potential. In most ATX powersupplies, the chassis is connected to Earth (to meet federal law). However, many PSU designers also connect the black power leads to common ground as well, since in a computer, you usually want the black wires to be at 0v.

What you are trying to do, is force the black wires on one of the two PSUs to be 12v potential. If those black wires are connected to common ground, it wont work. Cant be 12v and 0v at the same time, or the universe (ie, your powersupply) explodes.

One thing to remember is that you will need a 5v load on those two PSUs if you need them solely as a 24v PSU. You will need a 3-4amp load on each 5v line on each PSU. This should be accomplished with a couple wire-wound resistors (at least 25w each, 50w each the best). Use two resistors per PSU, because they will get HOT! This is a huge energy waster btw, an extra 60w lightbulb/hr on the electric bill just for those 4 resistors youll need. Might want to get heatsinks for those things.

You have a lot of rewiring to do on those PSUs. You can't just connect one of the yellow wires to one of the black wires. 20amps will burn that up FAST. You will want to connect 4-6 yellow wires from one psu to 4-6 black wires on the other PSU. The more the better, and test out how hot they get. If these wires get hot under full load, connect more together. Remember, all 20amps will be going through those wires. If you use 4 wires, each one carries 5amps. If you use 10 wires, each one carries 2amps.

But, first and formost, you have to make sure those black wires aren't connected to common ground (ie, the chassis, or the other PSU). Use a continuity meter. And yes, make sure the metal of both PSUs is touching eachother when you check continuity of both black wires from each PSU. Yes, you may have to take out the PSU internals (and be CAREFUL with this, those large capacitors could kill you. Leave the PSUs off for at least 2 days before attempting to take them apart to do this. I recommend taking a resistor and touching all the power leads together with the resistor before opening the chassis to help bleed any resisdual current). Dont just coat blindly with the liquid tape though. Try to determine by eye and with your continuity meter sources where the black-negative leads may be coming in contact with the chassis/common-ground. This is commonly done at mounting points, where the PCB is bolted down. I have also seen (usually green) wires attatching to the PCB from the chassis, which will need to be removed. Using liquid tape may not be safe enough. I would use nylon spacers in tandem. Or replace the metalic screws with plastic ones, or use nylon washers as standoffs. You dont want the liquid tape ever decomposing or scraping off or causing some capacicitance.

Have you considered getting a second bulldog 30? You can hook those in series for 24v simple as pie because they already have a seperated common-ground and negative terminal. Might be easier than hacking an ATX psu. Or, since you are buying new anyway, why not buy a 24v PSU?

[Player0]

PS - if you want gallery access for your pics, let me know.

[Xenogias]

P0,

A lot to consider here. This is getting to be a lot of trouble for what I'm wanting to do... I think might just look for a 24v psu. I intend to power a 24v 172w pelt that I will install in my mcw-50t and have to possibility to run another 24v pelt from it as well for the northbridge. I might give up on that 2nd pelt option as I found a pretty good 24v 12a linear lab psu for cheap on eBay. My original plans were to utilize a couple of atx psus I picked up really cheap. Then there arose the question of isolated/shared ground and I decided to buy two. But now, when I think about it, thats illogical as it will cost me as much or more than a single used 24v supply.

The tentative plans for the next project I'm working on will be a cryofinger chilled-water setup with a 172w pelt on the radeon, and a separate direct die phase change setup on the processor. I'm thinking prometeia modded to r404 (but this is something to accomplish this summer, with the help of a refrigerator shop in own) In the mean time it will still be cooled by that 226w TEC and the cryofinger-chilled water.

I still need a resevoir. I was thinking of one of those longish upright ones. I also need some good isulation and a cube case (maybe) to house it all as it needs to be somewhat portable. And yes, i would love to host my pics in the gallery. They're all 640x480 as my digicam wont take lower than that.

I'm also still debating which cryo-finger I should get. I'm looking at the CC-100 and the CC-65 from Neslab

here is the 100:
http://www.thermo.com/eThermo/CDA/Products/Product_Detail/1,1075,1000001155170-107-X-107-1000000007818,00.html

here is the 65:
http://www.thermo.com/eThermo/CDA/Products/Product_Detail/1,1075,1000001155165-107-X-107-1000000007818,00.html

I'm leaning toward the 65 as its about $200 less exensive for me and weighs only 37lbs as opposed to 130. Plus I think I can integrate it into my case, even though it wont remove as much heat or chill the water as low, but that shouldnt be an issue once i get some phase-change on my cpu. Then I can get rid of that nasty heat load. Too crazy you think?

[Player0]

Xeno, it sounds like a fun project. I'll whip you up a gallery account later, just email me to remind me if I forget (I usually do lately). Yes, try to find a second hand 24v PSU. If you dig around online, you should be able to find all sorts of weird PSUs floating around. Check HAM sites too. Don't be stuck on 24v either. Sometimes you can find a 20v PSU that may have adjustments that will allow you to go up to 24v or close too it. Just look around before making a decision.

I just so happen to be out of work, have a cube case and a 65a 24v PSU here which I'm not sure what to do with yet, as well as some 172w peltiers, a large heat exchanger and some massive pumps. Its the old dual-loop system which is short some radiators. I thought I would keep the system, but cash is tight right now. If you were interested, I might be able to work something out with you.

I was moving towards a prometia unit myself. Converting one to R404a sounds expensive...does the compressor work with 404a or will you need a new one? Sounds cool for sure. I was (the project is on hold) going to go with an aluminum prometia system (I have the Lian-Li case here already) for the next main gaming rig. It wouldnt be long before I found ways to tweak that one as well. Once I find another job, I will celebrate by getting that thing running :)

If your interested in any of the cube parts I might have, email me at player0@liquidninjas.com. Although I hate to see it go just because things are tight, I know you'll do it the justice it deserves.

Those finger chillers are very neat...but seem to be way underpowered. A 172w pelt running at full power on a GPU is going to dump 325-ish watts of heat in to the water. You need to be removing at least 325w or more of heat in order to keep the water cool. Im just not sure those fingers have enough power to do this. They are meant for smaller applications I beleive, and are expensive because they are more along the lines of scientific equipment. I think a peltier water chiller would work better, as you can stack multiple peltiers. My dual-loop system is a stacked-peltier system right now. 4x172w pelts stacked on top of the 226w pelt on the CPU, so to speak. You really want 2x-3x the heat removal on the water than your putting in if you want sub-zero results.

But, those things look neat, maybe its worth a shot. Experimenting is all part of the game. The wattage numbers just bother me a little. :)

[Xenogias]

yeah, the wattage numbers bother me too, but I'm thinking in the long term, all I will use it for is to cool my vid card and possibly northbridge. I know GPU cores don't put out much heat at all so It may in fact be better to just straight water cool it with chilled coolant since peltiers really lose their effectiveness at low low temperatures. This macine is supposed to hit -60 to -65C at no load. I think the radeon core by itself only puts out 80 or so watts. but if a 172w pelt gives me even lower temps than I would go for that. There is a high wattage alternative, but i've never found one in working condition and its definitely too big to integrate into a case:

http://www.thermo.com/eThermo/CDA/Products/Product_Detail/1,1075,1000001155063-107-X-107-12511,00.html

I'm still kinda up in the air about the whole project. The cooling is going to be expensive and I'm still at school now. I'm also not too sure how well it will work. In truth I'm spending some money I dont have, but will have by the time I have time to work on it (I do have a job--I'm not just some spoiled kid!!, hehe). If you're still holding on to some of those cube M3 parts in a month or two I'll be sure to drop you an email and maybe take a few of them off you hands.

Prometeia can be modded for R404a. The compressor can produce enough psi to condense it. JCViggen over on the xtreme forums has seen it done and I've talked to him about it and I think it would be a worthwhile upgrade as r404a has a much lower boiling point than r134a and I'm really hesitant to build my own direct die phase-change system atm.

[lechumbl]

Hi Xeno,

I have not forgotten about putting the "how to" on the FAQ for you, but my scanner is down till I reload software.
Will do it today, hopefully, and get the pic scanned for you.

Take care........