Pelt power supply

I am making a water chiller which uses 2 110 watt pelts. To power these pelts I am going to use 2 300 watt computer power supplies. These things are really crappy, but should be ok for running the pelts. Their ratings are as follows:

3.3V : 15A
5V : 22A
12V : 11A

Do I need to put some load on the 5V or 3.3V lines? I have heard that only running load on the 12V line will kill the power supply after a while. Thanks.

First of all, water chillers are usually a bad idea, but it really depends on the design, but then again they aren't (and never will be) efficient.

If you already have the parts....why not? (I would try it).

To answer your question: I've never heard about that, all I know is that:
1) Everything works fine.
2) Without a load on the 5V line the PSU might not turn on.
3) Without a load on the 5V line the PSU might not put out alot of voltage (10 orso, or less volts).

Hope that helped.

Good luck with your project, and let us know how it goes.

If i were you, here's what I'd do.....


Wire the two 5v outputs in series.

Wire the two 12v outputs in parallel.

This will give you 10v@22a, and 12v at 22a.

Now, one pelt will run a little harder than the other, but the rails will be loaded just fine.

Let me know if you need more help.

Greenman, to go in series, you need to do some possibly dangerous stuff with switching power supplies,

You might need 3 power supplies in parallel to power the peltiers, whats the specs on the peltiers? Vmax Amax etc.


Jon

I've been a little afraid of using serial and parallel on the same PSUs.. so that works?

Finken said:

I've been a little afraid of using serial and parallel on the same PSUs.. so that works?

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no, you can wire two psu in parallel OR serial, but you need 2 or 3 psu and you cant do both it is either serial or parallel!

JFettig said:

Greenman, to go in series, you need to do some possibly dangerous stuff with switching power supplies,

You might need 3 power supplies in parallel to power the peltiers, whats the specs on the peltiers? Vmax Amax etc.


Jon

Click to expand...

I admit I am no switching supply expert, but I would like to know why. It seems as though you can use two rails of a PSU in series, as is the case with 17 volt and 24 volt mods. Why wouldn't you be able to use two in series?

Im not 100% sure why, but I do know that you cannot use 2 rails in one psu in series, I know you can do it with 2 different psus,

I think that part of the reason is that they share a common ground. by putting a 5v line into the ground woudl be just shorting it out. Another reason its not a good idea to go in series is because it increases the voltage overall in the circut and some capacitors can thandle it and would blow up.


Jon

Prandtl said:

no, you can wire two psu in parallel OR serial, but you need 2 or 3 psu and you cant do both it is either serial or parallel!

Click to expand...

Yeah ok, that's what I was thinking, thanks...

Yea, to put 2 powersupplies in series you have to mod one of them so that is basically doesn't have a ground, or has a "floating ground". You then ground the modded power supply to the 12V line from the unmodded supply,making it's "ground" 12V above the computer ground, and there ya go. A power supply that has 2 12V additions in series, giving 24 volts.

Anyway, I don't need to do this. I am basically just making something from crap I have sitting around and a few cheap Parts I will buy.

The Watter chiller will use the 2 crappy power supplis in question, and 2 110 Watt TEK's. I believe that the Vmax on the TEK's is 15 Volts, but running them at 12 is probably a good idea anyway because that is around their maximum efficency (which is still pretty ****ty)

I'm making a Custom water block from some copper bar, and a custom heatsink, sorta like a relly long SLK-800, minus the quality workmanship I'll post a new thread and post some pic's/results when I get it all done.

I found some thing on the net that said I should put a 5 ohm resistor on the 5 volt line to get an amp of current through it, and make the supply work ok. The think I don't like about this too much is that that is just a total waste of power. Anyone have any ideas for things that I could run of the 5V lines to draw about an amp of current?

matttheniceguy said:

The Watter chiller will use the 2 crappy power supplis in question, and 2 110 Watt TEK's. I believe that the Vmax on the TEK's is 15 Volts, but running them at 12 is probably a good idea anyway because that is around their maximum efficency (which is still pretty ****ty)

Click to expand...

Pelt dont really have a point of maximum efficiency, at full voltage the COP (coefficient of performance) is around 0.6, while at 12V (for a 15.2V unit) COP is around 1.0, but if you were to decrease the voltgae even more, then the COP could be well over one (a 15.4V TEC @6V will have a COP of 2.4). The lower the voltage the higher the COP, but the lower the voltage the lower the Qmax and dTmax, so it is all about balancing.
For the record, COP is the ratio of the pumped heat on the power consumption: Q/(V*I)

hmm....that makes sence....I had just head other people saying that they were most efficent at about 85% power and assumed they were right. I guess they were just talking about the best place to run them, from a performance/power point of view.

This is what a power input vs heat pumped curve looks like, but this is only for these conditions. Each set of conditions will change this curve.

I just got a MCW478-UHT and I'm testrunning it right now.

Just a few minutes ago I wanted to try +5 and -5 to get 10V but the PSU shut down... It may have been because of something else, I don't know.
Anyway is there a reason why this shouldn't work?

finken, check the -5v amperage...... Im sure its under 1 amp.

Yes, I know it's 0.something...

But ground has 0 A right? Why can't I use -5 V instead of ground?

umm... ground will take all the amperage you can shove into it befor your case melts....

the -5 only has enough power to provide less than 1 amp, so if you try getting more than that out of it you overdrive the supply, and it shuts down to keep itself from burning.

it only is set up for about .3 amps, that means it can only supply .3 amps. The ground is zero nothin, means it can send or receive stuff, acording to the voltage. The negetive voltage makes it receive when hooked up to the ground, and you still need to have enough power on the neg and the pos to power this thing, they both do the powering.


Jon

ok, so the problem is that the negative voltage acts like positive and tries to supply power...

that's what I wantet to know.
If you measure voltage like +5 and -5 you get +10, but I guess that doesn't apply

thanks, I'll just have to stick to using more then one PSU

Finken said:

ok, so the problem is that the negative voltage acts like positive and tries to supply power...

that's what I wantet to know.
If you measure voltage like +5 and -5 you get +10, but I guess that doesn't apply

thanks, I'll just have to stick to using more then one PSU

Click to expand...

not quite.

Current, or amperage, is a measure of electrons per second. The more electrons that flow per second,the higher the amperage.

Most -5x and -12v lines can only handle less than an amp. That means they can only handle less than an amp's worth of electrons moving through it per second. If you try to move more through, the wires and internals will heat up, and eventually fry.

That is what matters.