Power! I have this idea, see...

[thezfunk]

Alright, basic run-down of my problem:

I have a 172 watt 40mm TEC. 24v at 12amps. In my research I have found that cooling effeciency max on that thing hits at about 18v. BUT, finding a powersupply that does 18volts at 12 amps without spending 400+ dollars is impossible.

Well I work at a casino where we have a bunch of 24v AC powersupplies. I have one for free actually (its 24v at I think 50VA but it might be .250KVA which is 250VA). Using a bridge rectifier I can convert it to DC. With 4 diodes in the rectifier with a voltage drop of .707 volts on each that should give me just alittle above 16v DC. I should only have to find a rectifier that can handle 12 amps or so because there won't be anymore amps flowing through it than the TEC is pulling. Correct?

Comments? Suggestions?

[Groth]

AC voltages expressed as the RMS (root-mean-square) of the sine wave. The peak to peak voltage is sqrt(2) times higher -- 33.9 V in your case. And since only two of the four diodes in a bridge rectifier are active at once, you'll have an output of around 32.5 volts.

[thezfunk]

so is there a solution to get this down to 18v DC?

[ThyKingdomCome]

Meanwell powersupplies in the 24V range can be adjusted for 18V. They only cost $80-$120.

[thezfunk]

awesome...how would you go about adjusting them

[ThyKingdomCome]

They have a variable adjust built in. Get a screwdriver and your in business.

[Butcher]

Originally Posted by Groth

AC voltages expressed as the RMS (root-mean-square) of the sine wave. The peak to peak voltage is sqrt(2) times higher -- 33.9 V in your case. And since only two of the four diodes in a bridge rectifier are active at once, you'll have an output of around 32.5 volts.

No, you'll have around 22V, however it will have a huge amount of ripple. To get 30+V you need to add smoothing capacitors, which will smooth the voltage out at around the peak value. TECs tend to run better on smooth power supplies than rippling power supplies (though a lot of ripple won't damage them, you just get poor performance).

BTW thezfunk, how did you come up with an 8V drop off 4 diodes with 0.707V voltage drop?

[thezfunk]

some misguided info I recieved...it didn't sound quite right to me either so I thought I would fly it by you guys to double check.

[Herr Montag]

Is your Peltier a Kryotherm Drift08? If so, you might be able to get it to hit peak performance closer to 23-24V with a better WB & radiator. I assume by "efficiency" you mean lowest CPU temp.

[JFettig]

What I would do is build a 13.4vdc UNregulated power supply that can supply over your amperage requirement with plenty of capacitance. That will give you about 16-18vdc because of the peak ac voltage is usually what you get out of it. 120vac is actually around 170vac.


Jon