a question for our elecrical engeneers

[Richard]

I think a DC to DC converter might be helpful. They're usually very small. Unfortunately they're hard to come by.

If I were you I'd call a large distributor (that sells DC to DC converters) and ask them if they carry the voltage and current you need. Make sure you know how many volts and amps your PS puts out when you ask them.

Jeff Evans (Mar 03, 2001 10:54 p.m.):

klosters64a (Mar 03, 2001 10:49 p.m.):
I am not an EE. If this were my project, I wouldn't dream of involving my PC's PS with one for this Peltier. I don't know it for a fact, but I think your diagram is a recipe for disaster. If you need to run a monster Peltier, shell out the money for a dedicated power supply for the Peltier.

It's not the money that I am worried about. I want to keep my PC as small and portable as it can be. This means stick with a mid-tower, and concealing everything inside of it.

I'm not 100% posotive that it will work either. But I have a few old PSUs kicking around that I can test this on. If it works, great! If it fries an old PSU, it was time and money well spent on an educational expirience.

 

[dimmreaper]

Richard999 (Mar 04, 2001 09:50 p.m.):
I think a DC to DC converter might be helpful. They're usually very small. Unfortunately they're hard to come by.

If I were you I'd call a large distributor (that sells DC to DC converters) and ask them if they carry the voltage and current you need. Make sure you know how many volts and amps your PS puts out when you ask them.

Won't work, as no PC PSU can handle the wattage of the peltier. And on top of that DC to DC converters are rather inefficient, which will require even more wattage.

 

[LimeyGreg]

AT and ATX psu -ve supply rails are usually low current, so, as the total current has to flow through both supplies it will either shut down or get fried.

A DC-DC coverter sounds good but will cost more than a psu, not to mention the fact your psu still hase to deliver all the necessary current - actually it will be more due to the inefficiency of the conversion.

A conventional psu will be quite large (see how big a 12v 10a battery charger is). Also, it needs to be -ve wrt chassis, unless you intend to operate it as a "floating chassis" - but that is a dangerous way to go.

Best solution is a dedicated swithching psu for compactness.

 

[Richard]

Radio Shack, has a book for sale that basically sounds like what you need. I can't remember what it's titled, but it's a HowTo on building Power Supplies.

Also, I did do some searching last night on DC power supplies, and found a pretty compact 24 v / 12 amp. I'll see if I can dig up the specs.

I will also ask for some guidance from the alt.engineering.electical group.

Jeff Evans (Mar 04, 2001 10:32 p.m.):

Richard999 (Mar 04, 2001 09:50 p.m.):
I think a DC to DC converter might be helpful. They're usually very small. Unfortunately they're hard to come by.

If I were you I'd call a large distributor (that sells DC to DC converters) and ask them if they carry the voltage and current you need. Make sure you know how many volts and amps your PS puts out when you ask them.

Won't work, as no PC PSU can handle the wattage of the peltier. And on top of that DC to DC converters are rather inefficient, which will require even more wattage.

 

[dimmreaper]

Richard999 (Mar 04, 2001 11:07 p.m.):
Radio Shack, has a book for sale that basically sounds like what you need. I can't remember what it's titled, but it's a HowTo on building Power Supplies.

Also, I did do some searching last night on DC power supplies, and found a pretty compact 24 v / 12 amp. I'll see if I can dig up the specs.

I will also ask for some guidance from the alt.engineering.electical group.

I already have a book coming from the local book store called "The PowerSupply Cookbook", I have a friend who has it and uses it to build PSUs for his pirate radio projects quite frequently.

 

[Richard]

Jeff, here's a high powered power transformer.

http://209.149.176.131/pdf/acdc201.pdf

Lots of other great stuff there too.

 

[dimmreaper]

Richard999 (Mar 06, 2001 01:49 a.m.):
Jeff, here's a high powered power transformer.

http://209.149.176.131/pdf/acdc201.pdf

Lots of other great stuff there too.

Naw, those are all wussy transformer. I need a transformer thats got high amperage as well as high voltage. I already know were to get good (hammond) center-tap transformers anyway. The transformer needed will cost well in excese of $50 (for just the transformer).

 

[Richard]

25 amps too low?

Did you look on page 2 of that page?

 

[dimmreaper]

Richard999 (Mar 06, 2001 05:24 a.m.):
25 amps too low?

Did you look on page 2 of that page?

I really need a 24V transformer. I decided that it is not worth having to buy a high wattage PC PSU for the peltier. It is much cheaper to just build a 24V PSU and keep my 300W PC PSU for running the computer.

As such I need a 24V 12A transformer. But like I said, I already know were to get them (though they ain't cheap).

 

[Hoot]

A 24V transformer will get you 33VDC after rectification and filtering. That will drop some under load but not back to 24VDC.

Hoot

 

[dimmreaper]

Hoot (Mar 06, 2001 06:29 p.m.):
A 24V transformer will get you 33VDC after rectification and filtering. That will drop some under load but not back to 24VDC.

Hoot

Well I guess it's a good thing that I have not ordered any compnents yet. I decided to get a book first. The book is on the way, and I plan to buy exactly what I need after I know all the ins and outs of home brewed PSUs. So what do you recon I will be needing? An 18V transformer?

 

[Hoot]

That's the ticket, or a 36V center tapped. That way you can run a full wave rectifier (not full wave bridge). It is a lower source impedance and given well to higher current. Either will fit the bill. Don't plan on regulating it as it is not necessary with a peltier. Figure on some stud mount rectifiers and a hefty filter capacitor.

Hoot

 

[Richard]

Damn man, sorry I keep coming up empty handed. It's amazing how hard it is to find prices on this stuff.

I am very interested in what you come up with though. Keep us posted on your progress.

 

[Hoot]

Here you go guys and gals.
From Digikey http://www.digikey.com

1) HM539ND 18VCT 15A Transformer-----$56.77
1) MB2505 50V 25A Bridge Rectifier-------$ 2.36
1) P10017-ND 35V 50k Mfd Capacitor-----$14.82

That's all you need.

Hoot

 

[dimmreaper]

Hoot (Mar 06, 2001 07:53 p.m.):
Here you go guys and gals.
From Digikey http://www.digikey.com

1) HM539ND 18VCT 15A Transformer-----$56.77
1) MB2505 50V 25A Bridge Rectifier-------$ 2.36
1) P10017-ND 35V 50k Mfd Capacitor-----$14.82

That's all you need.

Hoot

Now all I need is for you to show me how I'm supposed to wire it all together, and I can send the book back when it gets here

 

[Richard]

Heck I'll buy it from you when you're done with it.

[img="[URL]http://forums2.overclockers.ws/forums/Public/Images/Default/E28.gif[/URL]"]

 

[Hoot]

This is the best I could whip out on short notice.

Hoot

 

[dimmreaper]

Hoot (Mar 06, 2001 10:42 p.m.):
This is the best I could whip out on short notice.

Hoot

Wow thanks, if only I knew how to read it I got the switch and 5amp fuse and transformer down. But everything on the otherside of the diagram is confusing? (I'm not an engineer, wish I were) So could you please explain it better? Maybe something with color coding?

But if you would rather not, I can wait till my book comes. I should look for that book "Basic Electronics for Dummies". Is there one?

 

[dimmreaper]

wait, I think I get it now, thanks.

Yup, I get it now. Had to call my Dad on the phone to get him to explane how a rectifier works, but I get it.

Thanks Hoot. My Dad also sayed he has the book I ordered, so I'm sending that sucker back when it gets here.

Were would this world be without Dads.

 

[schmidty]

Hey hoot,

I never played with reticfiers when I did all my electronics messing, but how clean is the DC signal that you get from that powersupply? I remember much much larger power supply circuts - but then again it was 7+ years ago.

Just wondering

cheers!