Why the hassle?
expense I can get a 320w peltier and two copper cold plates for 32 quid.Surely I should give it a try?
please explain?
A PC PSU cannot provide the ampage, and it's very rare that it'd have 320w going spare to devote to the pelt.
Head here:
http://extreme.outervision.com/index.jsp
Stick in your complete rig specs, then subtract the total it comes out with and take that off your Enermax PSUs total wattage. What do you have left...? If there isn't at least 240w left, then you'll need to use a separate external 12>14v PSU... thus the expense. These alone cost £100+ (eg: Meanwell s320-12)
Note, that's only considering the wattage. According to Enermax, their 620w PSU provides 22amps per 12v rail -
http://www.enermaxusa.com/catalog/product_info.php?cPath=21_45&products_id=82_
Yes, it can provide 44amps in total, but you can't combine the 2x 12v rails to use their power. So at most you have 22amps going begging. At the least, you have about 5 amps going begging due to consumption of the rest of your PC.
Now lets look at specs of Pelt. (
http://www.xtremesystems.org/forums/showthread.php?t=67927&page=2)
320w TEC requires 14v and 26 amps for a start to allow it to do 320w worth of work. With a 12v PSU, it'll be shifting 235w and require 22amps free on your 12v rail of your PSU.
So, does your current PSU either provide/have going spare 320 watts, 14v and 26amps, or 235 watts, 12v and 22amps? If not, soon as you hook it up and turn it on, the PSU will likely pop.
Going off specs, your PSU has 22amps on it's 12v rail total. Once you're PC is running, the majority of this 22amps is taken up by the PC... there isn't enough ampage left to run the pelt. Your PC PSU will most definitely emit a loud bang and release the magic smoke within a few minutes of turning it on with the pelt hooked up... so you'll DEFINITELY need a separate PSU.
Now, look at heatload. You have the 320w heatload of the TEC, an average 20w from your pump. That's 340w of heat, without even considering the heatload of your CPU and GPUs. If we use a Core2DUO e6600 oc'd to 3.4Ghz and an NV8800GTX for example, then you need to add roughly another 309w... so that's a total heatload of 629w that you'd need to cool.
Reference the graph below for a ThermoChill PA120.3 radiator...
As this graph shows, to cool 629w of heat will require a liquid flow rate of at least 5lpm, with 3x Panaflo-H 120mm fans at 12v emitting 48dba of noise EACH to maintain equilibrium long term and keep coolant temps within 10 degrees of room temp.
£100 for PSU + £32 for pelts n' coldplates + the value of the rest of your watercooling rig... then add cost of neoprene and dielectric grease. Now compare that total to the price of 2ndhand modded phasechange, which will get you on average at LEAST 50 degrees colder than the 320w TEC setup, with MUCH less noise (usually a max of 38dBA from the fans, x2, + compressor vibrational noise).
Now decide if heading down the TEC route is worth it or not...