Connect 3 psu's in series?

[Makalu]

Well I bought an 80w 16.1vmax peltier to see how effective they are at cooling the air in a case (ala Channel Well IceCube psu or Sytrin Nextherm case) and the answer is erm not very well...at 12ish volts. I don't want to buy a 16vDC power supply for something i may not even use, but i do have 3 working ATX psu's and I was wondering if i can connect the 5v outputs in series for a 15v source? If so, can someone explain in layman terms or diagram how to do this? How would I disconnect/connect the grounds is the part i'm most uncomfortable with. Thanks in advance.

[Shroomie]

Re: Connect 3 psu's in series?

Well, you can get up to 24v from a regular ATX PSU. I don't know how much power the Peltier uses (in amps) though. It's accomplished by wiring the +12v into the -5 (for 17) or -12 (for 24v). I haven't messed with it much, myself, so I'd wait for someone else to explain better.

[jonnyGURU]

Re: Connect 3 psu's in series?

Wire them up in series and you're only going to trip the protection circuit.

Wire up the +12 and -12V and you're only going to be able to move whatever amperage the -12V is rated for (typically 1A or less.)

[Makalu]

Re: Connect 3 psu's in series?

oh yeah the circuit protection wouldn't like that...what about the old AT power supplies? Do they have that? Just curious I guess since I only have one of those and in either case it'd be too cumbersome to keep...43 bucks for a Meanwell 15v 10a unit...decisions decisions

[gonzo0815]

Re: Connect 3 psu's in series?

No, there are no voltage >12v in any AT or ATX psu i know. But those little wallpluggs from laptop`s does have often some 19V /3,5A. Duno if that will rost your peltier or it will trip the OCP circuit.
Probably the cheapest spource for that voltage and power will be some car battery charger. Those are very cheap and mwill deliver something between 13 and 17v. Adding some high capacity (about 4700 to 10000uf) capacitor will increase the voltage.

[gonzo0815]

Re: Connect 3 psu's in series?

Theoretically you can couple those 3 psu`s, as the outputs are galvanically isolated. But i duno if this will do like with linear psu`S.
In any way, it is up to you to try that .
To contect some PSU`S in series, you have to conect the black wire from PSU 1 to the red wire of psu 2 and the black of psu2 to the red wire of psu3.
Between RED on PSu1 and Black on PSU3 you should messure the added voltages e.g between 13,5 and 15,5v. But keep in mind that you need for many psu`S some minimal ballast that they can operate properly. May be you should ensure that with 3 power resistors or some light bulbs for every psu (betwen the 5v o/P and the corosponding black - wire).

IOn any way. as stated abovve, i duno if the regulation of thos smps psu'S can handle that kind of operation or if they are afeckted from it. In theory i think it should work.
EDIT: some crude getto style drawing.

[Makalu]

Re: Connect 3 psu's in series?

yeah i looked at a bunch of laptop bricks and found some that put out about what i need (16v @ 8a) but the price was higher than the Mean Well units. My car battery charger is only 3 amps, but I'm going to check the prices on those because I think you're right about that being the cheapest way to go. Thank you very much for the wiring description and diagram because I'm gonna try that too this weekend and I'll let you know what happens. Been using a couple of old optical drives to bump up the 12v rail but i'm not sure how i'll try and bump the 5v rail on 3 units but guess i'll see if it works first. cheers

[Makalu]

Re: Connect 3 psu's in series?

it works great 15.49v (18amps I assume since that's the lowest output of the three) TYVM!

[jonnyGURU]

Re: Connect 3 psu's in series?

Wow! You got 15V out of it? Did you have to use the resistors? Does all of the 5V leads on the last PSU put out 15V?

I just would've thought the PWM would've freaked out and tripped the PSU.

[gonzo0815]

Re: Connect 3 psu's in series?

The pwm should theoretically work, as every PSU does only see his own voltage, e.g. the own 5v. Of course, the current and the voltage from the other PSU'S are running through the transfomer of each single psu, but as the input current is equall to the outputcurrent, the regulation shouldn`t be affeckted IMHO (the currents eliminate itself)
But for shure, i was sceptical too
Congrats to your succes

Does all of the 5V leads on the last PSU put out 15V?

Well, it depends wich ground you are using. If you conect something only to the molex from any PSU, there is always the voltage from the particular unit, as it would be the ground from this psu, not from the others. At least this is what i expect. The 15 or higher voltage will only be there between the 5v of the first and the ground of the last psu or vice versa.

[gonzo0815]

Re: Connect 3 psu's in series?

Look at the drawing, you will see the 5v marking between each geound and 5v o/p of every psu. The molex, conected only to one psu, is in parralel with that marking.

[Makalu]

Re: Connect 3 psu's in series?

yeah it reads 15+v across any 5v lead on PSU1 in the diagram and any ground on PSU3. I didn't have to add any resistors since they all put out over 5v just powered on alone but PSU2 is an old Astec AT style and it wouldn't power up without a load and attaching an old cd-rom drive worked.

I thought that I'd have to insulate the common ground on like 2 of them but apparently not or maybe I got lucky and they aren't wired that way.

[gonzo0815]

Re: Connect 3 psu's in series?

I thought that I'd have to insulate the common ground on like 2 of them but apparently not or maybe I got lucky and they aren't wired that way.

What you are meaning with "common ground"?
Do you mean the earth ground (e.g insulating the 110/220v ground or neutral?
AFAIk this could be the only ground, wich could be isolated. But for the secondary o/p voltages this ground is not realy something to wich there would be any potential. Due to the galvanic isolation of the transformer, there is no connection.

[Makalu]

Re: Connect 3 psu's in series?

oh sorry DC common ground to earth is what i meant. Thanks for clearing that up