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Could it be done?

post #1 of 11
Thread Starter 
Hi everyone.....first post. Unfortunately I will not be contributing right away with helpful suggestions but rather with a question. Since I have posted elsewhere the same question I thought of asking two of the best forums on the net for some help.

Thinking about TEC I asked myself the everlasting question of what powersupply to use and rather than spend on a dedicated one, I tried to figure out how I could use those ceap 500/600w atx one can find for less than 70 dollars (45 euros) for a pair of them.

I have found some info on hooking them in series or parallel thus doubling either the volts or the available amps. I have also checked ou the possibilities of connectinf 5v and 12v to get 17v thus powering any TEC close to its efficiency peak (please correct me if I am wrong).

However I have several questions.

Let us assume that I have 2 atx power supplies with the following DC output:

+3.3v @22a // +5v @16A // +12v1 @15A // +12v2 @16A // -12v @0.8A // +5vsb @2.5A

  • first question: given these are allied max 500w models is it safe to assume the 2 12v lines are actually 1 and are simply physicall separated outside the PSU? As far as I know few models actually have independent 12v lines.
  • As a consequence would it be prudent to either join the 12v lines to have a max absorption of 30A @ +12v? and what about hooking up a single +12v with a +5v?
  • Assuming that the answer to both questions is no then would it be possibile to get hold of 4 identical power supplies and achieve the following?
  1. hook them in 2 sets (of twos) each group providing in parallel 32 amps on the +12v line? Then, (with appropriate modifications) connect these "two" "single" powersupplies in series to achieve 32 amps on a +24v line?
  2. Alternatively hook 2 psus to achieve 32amps on the 12v lines and subsequently joining the +5v line (formed by linking the psus in parallel along the 5v lines) from the other psus to achieve a theroretical dc output of 17v @32a?

If point 1 is viable then would it be possibile to gather the dc output and somehow use a powerful potentiometer to modify TEC voltage?
Let us assume this is possible thus using 4 ATX power supplies to provide 768 watts max. The single cables providing current in parallel would be able to sustain the amperage. The cables connecting the "2" sets in series probably would not. More resistant cables would be required, however AFAIK the project could succeed in terms of current distribution safety-wise. Overall absorption @ 24v would be 32 amps (amps are on the low side but I would not be using this voltage anyways with any TEC) consuming 768w out of the 2000w overall possible wattage of 4 500w psus.

Last question: I have devised this ingenious contraption (which in all probability will cause severe injuries to me and/or my family members) assuming that it is better to have a layout envolving: [ joining 12v lines and 5v lines (or 12v lines) in parallel and then hooking the resulting lines in series ] but could it be done the other way around? [ hook 12v and 5v (or 12v) in series to achieve 17v and 16A and then hook the "2" 17v lines in series to parallel to achieve 17v @ 30/32A ]

I hope this will help anyone if the basis is sound that is. I intend to see the project through if viable but I thought of getting some feedback before hand. I must admit I have modest knowledge of PSU. I have learnt a lot in the past months and I am fairly confident of the work envolved in hooking 2 psus in parallel or in series. The combination of both sounds good but I cannot assess its viability on my own.

Thanks in advance

P.s. I ask forgiveness if I may have been unclear in my description. English is not my native language. I may post a bitmap picture if necessary and you all promise not to laugh..

ah what the hell...here ya go:


Very simple diagram which is not correct in terms of symbols or anything. Just couple of details: 2ohm reistance of all 5v lines to achieve correct functioning. Separation of ground wire from case in 2psus. (one for each "group" of parallel psus).

From here, if this is viable I would like to start investigating 5v+12v and such.

If joining the 2 "independent" 12v lines from each psu is possibile (and safe) then I would have a max ouput of 24v@ 64A from 4 psus. over 1500w!!
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post #2 of 11
That's some hardcore :turd:
post #3 of 11
Quote:
Originally Posted by Alexontherocks View Post
I have also checked ou the possibilities of connectinf 5v and 12v to get 17v thus powering any TEC close to its efficiency peak (please correct me if I am wrong).
The most you can reliably get from a computer PSU is 12V (there are -5V and -12V lines but you would be lucky to get more than an amp from either on of them). Connecting the 5V and 12V would be 12-5= 7V.
Quote:
Originally Posted by Alexontherocks View Post
[*]first question: given these are allied max 500w models is it safe to assume the 2 12v lines are actually 1 and are simply physicall separated outside the PSU? As far as I know few models actually have independent 12v lines.
Most likely they are separated by an OCP (over current protection). But since I haven't seen a review on those models, we have no idea of knowing what they are set at. They could be set at just above the rating for the rail (so ~18A or so) or they could be set at like 30A. Since there is no standard and it is up to the manufacturer, we just don't know unless someone tests it and I have yet to see anything. Now you should be able to wire the separate 12V rails back up, essentially bypassing the OCP since they were they same rail to begin with.

So to sum up, 12V is the max you can draw from your PSUs and you should be able to wire up the separate rails to act as one. I have a decent understanding of electricity and circuits but hopefully someone like Duckie can weigh in on this.
Quote:
Originally Posted by Alexontherocks View Post
If point 1 is viable then would it be possibile to gather the dc output and somehow use a powerful potentiometer to modify TEC voltage?
AFAIK potentiometers can only decrease voltage by adding resistance, you would need a transformer to increase voltage. It is really sounding like you need to find a dedicated TEC PSU that is designed for higher voltage and amperages to operate this safely. I also know that only using the 12V rail of the power supply will kill it pretty quickly. So you don't have a serious crossloading issue (not enough load on the other rails), you need to have at least a couple amps on the 3.3V and 5V rails.
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post #4 of 11
Thread Starter 
Connecting two PSU along the 12v lines in series will give you 24v I tried, trust me....And joining two psus in parallel should provide double the current along the chosen lines (12v in parallel for example). This I have not tried but others have.

I was interested in joining two in parallel thus sharing the load across two psus and then joining these two groups in series to provide double the tension (24v)

http://www.procooling.com/index.php?...s&disp=52&pg=1

I followed this article's suggestion and have succesfully hooked two in series.
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post #5 of 11
you do know the max a circuit can put out is like 1500 watts from the wall.
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post #6 of 11
Quote:
Originally Posted by G|F.E.A.D|Killa View Post
you do know the max a circuit can put out is like 1500 watts from the wall.
?? my psu can handle 1200 watts... lets hope i never max it out- have a stereo and a few other things on this circuit as well

this is all interesting to me, especially since I hope to one day go to TEC. sub'd
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post #7 of 11
Quote:
Originally Posted by G|F.E.A.D|Killa View Post
you do know the max a circuit can put out is like 1500 watts from the wall.
And yet they have 2000 Watt PSUs.
post #8 of 11
Thread Starter 
well to begin with I live in Italy and electrical standards maybe somewhat different here but I guess not by much. 2000 psus don't actually consume 2kw of power. I think somebody tried to max out a rig and achieved a peak consumption of 900w but it was an artificail test designed to look into max power consumption. Gues it was enermax, can't recall exactly...

I do not think I have stated anywhere in my posts that I will be feeding all my operating units (pc/screen/modems/lamps etc) from one single socket. I am using 2 actually and for temprary uses I may hook all the psus to a third one.

What I am proposing is redundancy to achieve higher voltage and current output by having the load shared across multiple power supplies. It might be compared to distributed computing using multiple low power cpus.

Anyways I have found a stock of 8 monorail 21amp 12v line psus rated 500w. Any one of them is crap but together they could output almost 85 amps combined @ 24v. Since any device TEC or not TEC will not exceed a max absorption of 35 amps. I get a total of 8,75 amps per every psu. This is of course if we assume that the load will be equally shared and that I run a 24v TEC @ Imax. Most likely i will try to combine +12v and +5v to achieve 17-18 volts. This is close to the efficiency peak of most tecs. At 18v I would have even less load per PSU.

I guess I am trying to build the ultimate distributed power system for TECS. If only I managed to get a "green light" on the electric connections I might be able to build a 10 unit composite unit. GReat improvement would also be a way to vary voltage output from 24v to 0v if this is compatible with ATX psus.
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post #9 of 11
Connecting PSUs in parallel won't give you twice the voltage, just increases the amps. You much connect them in a series, and if you do that, you're very likely to destroy them.

Oh, and if a PSU designed to out put 2Kw, and someone loads it with 2Kw of stuff on the 12v rail, it's pulling 2Kw from the wall socket. The difference is that at 2Kw on a 12v rail, you need 166a, at 120v, you need 16.6a, and that's how much power you're pulling from the outlet.
Edited by RussianGrimmReaper - 6/14/08 at 5:03am
post #10 of 11
Thread Starter 
Quote:
Originally Posted by RussianGrimmReaper View Post
Connecting PSUs in parallel won't give you twice the voltage, just increases the amps. You much connect them in a series, and if you do that, you're very likely to destroy them.

Oh, and if a PSU designed to out put 2Kw, and someone loads it with 2Kw of stuff on the 12v rail, it's pulling 2Kw from the wall socket. The difference is that at 2Kw on a 12v rail, you need 166a, at 120v, you need 16.6a, and that's how much power you're pulling from the outlet.
I believe I have not stated otherwise. Parallel will double the current, series will double the tension. why would any connection in series destroy the psu? I have tried and nothing happened.

Regarding the 2kw psu I just stated that a single rig will unlikely be able to break the 900w effective power use barrier let alone 2kw. If and when it will consume 2kw then of course that will the amount of energy taken from the socket. Nothing can be created or destroyed. I was simply stating that the fact that I want to use 4 atx PSUs (2000w theoretically) does not in any way imply actually usung that amount of power. I will still see the same laws of physics applied so for example a 24v @ 35 imax TEC will need 840w of energy. The only difference is that I want to provide that amount of power through multiple psus and not just a single expensive unit.
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