a cheap power supply?

[Alexontherocks]

Hi everyone. I have already posted in this section to seek some help with an ambitious project envolving a high powere TEC. Unfortunately I have decided to concentrate on the watercooling which is on hold due to exams.

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!!