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Joining Two Power Supplies to make 17v Peltier PSU

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Ocelaris

Member
Joined
Feb 27, 2002
Location
NYC, Brooklyn
I'm trying to make a little peltier setup, I saw this PSU at newegg for 38$ shipped, has a 22A +12v rail. Could I run two or three 80w Peltiers from this PSU? and a few fans? I want to join the 12v and the 5v to make 17v for some 24v Peltiers. Does this sound feasable? Is there a way to calculate how much draw a pelier is going to take on the PSU? Thanks, Bill
 

ssjwizard

Has slightly less legible writing than Thideras
Joined
Mar 12, 2002
dont quote me on this but i belive that if you hook the ground of the 12V line up to the 5V line on the first psu and then the 12V plus to the posative on the pelt and the negative on the 5V line it will give you 17V inline but im not sure if that will work i know 12v to 12V works that way for 24V though
 

wymjym

Member
Joined
Feb 20, 2002
I read at great length, several months ago, about joining ps to make more power..bottom line is if you do it (it can be done) the odds are that you have shortened the life of all those connected by a great amount.
You would do better (with your time and $) to watch for a deal and get an adequate unit.
wj
 

JFettig

Hey! I showered! Senior
Joined
Jan 5, 2002
Location
MN
ssj thats not how it works.. its a littl diff than that..
 

Since87

Member
Joined
Jul 30, 2002
Location
Indiana
PC power supplies don't have completely independent +5V and +12V rails. They share a connection to ground. None of the negative rails can supply more than 1 Amp so they are useless for powering a pelt.

At 17V the 172 Watt 24V pelt that Danger Den sells will draw about 7.5 Amps. The current draw is low enough that it's reasonably likely you could connect a supply in series with the +12V or +5V output of your system supply to get a +17V to ground voltage.

You can take a 12V supply and a separate 5V supply and connect them in series to get 17V but there are risks involved. The ground of the DC outputs is probably connected to the chassis of the powersupply, which is also connected to the ground lead of the AC cord. You would need to separate the DC ground to chassis connection to avoid shorting out the supplies.

I really don't recommend people do this unless they know what they are doing.

A simpler option might be to get a 24V supply that is rated for 10 Amps minimum (easy to find on Ebay) and hook it up to your pelt with a 1 Ohm 50 Watt resistor in series. The 805F1R0-ND resistor shown here will do the job. The resistor in series with the pelt will drop the voltage to the pelt to about 17V, but the resistor itself will be dissipating 50W and will need to be attached to a heatsink itself.
 

brodo

Member
Joined
Mar 13, 2002
Location
saratoga, ca
226w pelt no connected properly?

Since87 said:


At 17V the 172 Watt 24V pelt that Danger Den sells will draw about 7.5 Amps. The current draw is low enough that it's reasonably likely you could connect a supply in series with the +12V or +5V output of your system supply to get a +17V to ground voltage.

hey since87 - I know you are an EE and this thread is somewhat similiar to my new situation... hope I am not breaking any 'forum policies' that I have not completely read through.

anyway... I just got the 226W pelt from cooltechnia (decent place, fast shipping, etc. - better than swiftnets who still have yet to send out my 75w pelts that I ordered 1 week before cooltechnia)... and I connected it the 12v on a separate cheapy Turbolink 420W PSU - then my HSF (ok just fan) to a separate 250W PSU.

well the results were poor :confused: :eh?: no frost, barely cool. my 20w pelts performed better.

do I need to find a special made PSU like the one they sell at cootechnia or can I do it with a 350W+ PSU. How are the other folks using it here, I know a few have this 226W'er.

here is the link to the peltier in case you are curious and/or want detailed specs.
 

Since87

Member
Joined
Jul 30, 2002
Location
Indiana
Re: 226w pelt no connected properly?

brodo said:
anyway... I just got the 226W pelt from cooltechnia (decent place, fast shipping, etc. - better than swiftnets who still have yet to send out my 75w pelts that I ordered 1 week before cooltechnia)... and I connected it the 12v on a separate cheapy Turbolink 420W PSU - then my HSF (ok just fan) to a separate 250W PSU.

well the results were poor :confused: :eh?: no frost, barely cool. my 20w pelts performed better.

I'm not clear on how you were cooling the hotside. Were you just blowing a fan on it? I hope not, because I'd expect the pelt to self destruct fairly quickly under those circumstances.

Assuming you were cooling the hot side adequately, (At the very least a serious heatsink and fan) I'd guess the power supply was not running correctly. It may need a load on the +5V and/or +3.3V rail to get full 12V output. I suggest you borrow a voltmeter and see what voltage the supply is really providing to the pelt.

I don't really think PC PSU's are a good way to power a pelt. I think a lot of them can't be trusted to meet their specs. I would strongly recommend a dedicated power supply. I don't know anything about the Meanwell supplies. The Astec supply available here is cheaper, and Astec has a good reputation as a vendor of this type of supply.
 

brodo

Member
Joined
Mar 13, 2002
Location
saratoga, ca
Re: Re: 226w pelt no connected properly?

Since87 said:


I'm not clear on how you were cooling the hotside. Were you just blowing a fan on it? I hope not, because I'd expect the pelt to self destruct fairly quickly under those circumstances.

yes I was using a AX-7 with a TT SC-2 fan, I was just being funny saying 'just the fan' because you can not technically connect a heatsink to a powersupply :)

again I have dedicated power supplies. I have a few 350's, a 250 and a couple 400+ watt'ers.

I will try adding load to the 5V, but when I did that previously, the fan appeared as though it was not getting enough juice (made a sound like it was struggling every second) like:

waaaa, vrm,vrm,vrm,vrm waaaa vrm,vrm,vrm

where the 'waaaa' are periods of the fan sounding like it is slowing down and the 'vrm' are regular sounding fan noise :D

This is crazy to spend 3-4x the amount of the peltier on a power supply to push the peltier! but I might get that one you posted, I have been looking at it even before I got the big 226w hog.


I also have a multi-reader so I will check it out and see what's up. actually I think it is an OHM meter (same thing?) dunno if it tells me Amps, but it does tell me volts