24 Volt Power

[Jtw0128]

Ok, I hooked up 2 13.8 volt power supplies I have in series to get an ouput of about 24 volts after lowering the voltage on each a bit. I ordered a drift 0.8 172 watt peltier and hooked it up today, and when I got into the bios, the temps were a little over room temperature, much worse than the 156 watt peltier I was using before. So I got my multimeter and found that when I hooked up the peltier to the power supplies, the voltage dropped from 24 volts to about 10.5 volts. Is there any way to stop this from happening or is there just no way to use these power supplies in series?

[hielko]

Resago: read... a 13,8V PSU a computer PSU?

Jtw0128: I think you just van't run those psu's in series...

[imagex]

that pelt pulls 8 amps ,if your ps's dont add up to atleast 8 amps your volts start to drop. means your ps can't handle the amps. :)

[Cerelac]

It's a very bad idea to run the Drift-0.8 at 24V. ALWAYS RUN YOUR PELTS 80% (OR BELOW) OF Vmax!

[hielko]

Celelac: That's not true, you get the highest DeltaT @ Vmax and Imax.

[Cerelac]

A common mistake newbies make is trying to run pelts at Vmax (ie for 'maximum' performance). Operating at Vmax will make the hot side hotter. So, unless your cooling is perfect, the extra deltaT you got will be negated by the extra heat. In the end, you get virtually the same performance at the same time WASTING ENERGY (more volts mean more power needed).

[hielko]

That's true, but with a good radiator you can propably get the best resultat not 80% but at 95% or something like that.

[Cerelac]

If you want the best out of your pelt, you can always get a GIANT radiator and operate it at Vmax and watch your electric bill go up. Not very practical, isn't it?

In the real world, pelts are operated at lower voltages.

Consult the performance graphs and see it for yourself.

[vodka]

Cmon now. wtf are you talking about?
As long as you can dissipate the heat (that is always assumed) any peltier works best at vmax. That's what vmax is calculated FOR.

[imagex]

hell i go for overkill get it as cold and as fast as i can,if i get a high ele bill,atleast i 'm haveing fun! :)

[Butcher]

80% works better with just about any radiator. I tried it, turning down the voltage got me an extra few degrees even before the water cooled down - the water block heats up less due to the power reduction. The adiator keeps the water cool but if you pump more heat in even with a bigger radiator unless you get a biugger water block your hotside temps increase, and most people can't fit a bigger water block.

[ondaedg]

I am going to sum up what you guys are saying cause you're all right in one way or another. If your cooling system can take the extra heat of running the pelt at 24 volts, then you can run it at VMAX and get the added benefit of 24 volts. If your cooling system can not handle 24 volts as efficiently as 18-20 volts, then you are better off using less voltage. There, now was that hard? =]

[Cerelac]

You people still don't realize that there is no added benefit at 24V!

Analyze this graph carefully:
http://www2.mozcom.com/~ronnieg/driftg.gif

Operating at 21V versus 24V gives you very little Qc in return (the graph is almost horizontal at those points). The pelt's power requirement (and thus its heat output) increases almost linearly and yet the Qc improves very little.

In the end you get nothing.

[Joe]

at 50v I think it just explodes :)

[Butcher]

Why do they even quote 50V, the thing would melt into a puddle on the floor at that sort of voltage :)

[Butcher]

A thought just occured to me. Instead of arguing in here about how much voltage to use, why not just get a variable PSU and try it out. :)

[hielko]

The best voltage is different for every cooling system.

But I don't think the peltier will melt or explode above Vmax, as long it cooled good enough there and the voltage is not extreme high there is not much what can go wrong.

Remember a peltier is a real simple devise created from a few pieces "half geleider" (I hope the english word for it is something similar... :)) which are soldered together.

[Butcher]

"half geleider"... I think the english word is semiconductor, at least that's what peltiers are made of :)
But yes as long as it;s cooled enough... the problem is you're only cooling the ends, not the centre of the semiconductor pellets - could melt a little in the middle.

[[b4k4]]

A thermoelectric ceramic, such as a peltier, isn't actually used to 'cool something off', instead, it's used to actually MOVE heat. Vmax is the point at which the temperature difference between the two sides is greatest, but that's not the point of efficiency. THAT point is approximately 80% of Vmax.

[hielko]

No, that point is at 0.0001V. Look at the performance graphs of a random peltier.

But above approx. 80% VMax the efficiency value drops very rapid. But that doens't mean that it doens't drop from 2 to 3 volt.

[rl.2]

Anyway back to the guys original question, as said in the first few its actually a need for currnet therefore thte voltage drops so the maximum current can be drawn. A good PSU is a toridial transformer. They are around the $70 from stores like dicksmiths, altronics and jayar.

The $70 will do:
12v @ 25 Amps
15v @ 20 Amps
18v @ 16.6 Amps
25v @ 12 Amps
30v @ 10 Amps

Note that each voltage rating is a seperate transformer and the current is derived from the 2 coils being wired in parralell. If u would like anymore info on this type of PSU send me an e-mail and I will send u the page out of the altronics catalogue with the prices on it.

And don't forget U will need to turn the AC outpit to DC. Easy to do if u don't know how just e-mail me and I will send u instrctions.

Me.

[hielko]

And don't forget 12V AC isn't 12V DC

[jastrckl]

I don't remember the guy who brought it up, but car battery chargers are a kick ass source of high current DC power (probably not as clean as some of the other stuff, but probably not attrocious either) Anyway, I found a 12V 50A charger at an auto parts store yesterday for $50... two of these, and you have a 24V 50A supply for $100. Not bad, eh?