that link didn't work :(

Here is the link, copy-paste in the address bar of your browser:
http://www.allelectronics.com/cgi-bi...790&type=store

And go to page 3. There is a 12.6V 25Amps transformer for $20.

I don't know why my previous link did not work :confused:

Yeah that'd do the job, a 12.6V transformer when hooked up to a rectifier and suitable smoothing capacitors will yield around 16-18V, might want to stick a regulator on that :)

I'm looking at doing this, what rating bridge rectifier do I need, they have them on that site as well..

also how big of a capacitor 10,000uf ??

where can I find one of those??

the bridge rectifier and transformer will only run me $25 so far. Are the large capacitors the most expensive part?

I'm basing my setup off this site http://www.ioport.com/peltiers.html

hmm, just read the article mentioned in previous page, so I just get the biggest rectifier I can (35Amp 800volt) and If I want to power that 220watt pelt with 15v@20A, I need about 90,000 uf capacitance?
correct?

DAMN thats a big capacitor!!!

Is it possible to se several smaller capacitors in paralell, so their combined capacitance equals 90,000 uf?

Yes you can use caps in parallel, check the maximum ripple current, the sum of these should be at least equal to your peak current. As for the bridge, a unit rated to double the voltage and current required is usually fine, it will be BIG - I have a 35A unit with a 1/4" mounting hole! :D

found everything I need, here are the links:

120,000 uf cacpacitors http://www.meci.com/default.asp?mode...s&category=505

50 Amp Bridge rectifiers http://www.mpja.com/listall.asp?dept=111

12.6V 25AMP Transformer http://www.allelectronics.com/cgi-bi...625&type=store

$32 before shipping, woohoo!!!

[ 12-08-2001: Message edited by: resago ]

2 of those places have a $15 and $20 minimum order, so if anyone wants to go in together, let me know.

These capacitors will not handle the voltage.
The transformer will generate 12.6VAC, which after rectification, will give 12.6V * SQRT(2) = 17.8VDC max.
You need a 25V capacitor if you want it to last longer.
At MECI, check this part number: 191-2100

I thought MECI also add bridge rectifiers, but I couldn't find them.

Don't skimp on the voltage for caps, you DO NOT want caps that big exploding on you.

part # 196-0020

10v, 450,000uf , 2 of these in series will yeild

20v, 225,000 uf. $8 total.

of course there's still the minimum order thing.

Didn't think the law of potential dividers works for capacitors...

guess I'll find out, can't be any worse than getting hit with PVC pipe from an exploding potato gun. :D

Actually, you take risks by putting capacitors in series. The voltage will be balanced only by their leakage current, a parameter that varies too much unit to unit to be reliable. In English, that means that one of the capacitor will have more voltage than the other.
You need to balance the voltage with additional resistors, 1 in parallel on each capacitor. 1K should be enough.

In my opinion, it is simpler and safer to spend a few more bucks and get the good capacitors.

true. I've actually got some 55v units from an old HP computer (the kind that used to take up an entire room) but the capacitors are rather large 4" X 9". I was looking for something more compact, but I guess I'll use what I have.

I was thinking, since a peltier is a solid state device, I really wouldn't need THAT much smoothing would I?

I mean, I could probably get away with around 50,000 uf for 25amps@17v, maybe even less.

I'll test and see if it makes a difference, I have several of those large capacitors, I'll just wire up one at a time and see what difference it makes in the temps on the pelt.

[ 12-12-2001: Message edited by: resago ]

I talked to a tec at a pelt company and he told me that while higher ripple won't affect cooling, it will affect lifespan quite badly, especially if used around Vmax but also at lower V.

Edward

ok, so how much capacitance do I need for near zero ripple?

4000 uf/amp was for around %15 ripple.
5000?
10,000?

[ 12-13-2001: Message edited by: resago ]

Woah guys... this topic is GETTING HUGE! Mind if I lock it and start a new continuation thread? LMK...

aw come on, that copper vs. AL thread was like 10 pages long :p

As long as you draw current there will always be some ripple, just a matter of how much. The only way to stop it is to regulate the power, but that's lossy and the power supply will then need cooling.

Edward

You can add an inductor, that will reduce ripple. The problem is to find the inductor that can handle the current. Maybe in an old PSU.
A PI configuration, parallel cap + series inductor + parallel cap will give the best results.

inductor, is that like a choke? where it sets up a magnetic field to take up the slack when current falls?

ie. when current is up, magnetic field is up, when current falls, magnetic field collapses and is convered back to current in the choke to take up the slack.

Exactly.
Inductor stores energy, like a capacitors does. Inductors store current, capacitors store voltage.
Use a toroid choke, they are better and generate less EMI.

Haha okay maybe we'll break some records. I'll let this badboy go.
-Kev

I'm starting to think that I'll have to build this power supply on top of my case. Wish I had a cube case right about now.

This system is going to be a dual athlon XP, quad Peltier water cooled system.

440watt computer PS + 2x425watt peltier PS = 1290 watts!!! Bwah hah hah

Yeah that will be very kind to your electricity bill! :D

Whoa ;']

At this point it looks like you'll need to water cool your room ;']

Edward

yeah, can you say SPACE HEATER?
I'll be nice and toasty in the winter!!

this system is gonna be SO ludicrous.

I've already mounted the capacitor bank on top of the case, need to order the transformers and rectifiers.