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Building a power supply

B

Berg0

[H]ard|Gawd
Joined
May 16, 2005
Messages
1,038
I'm building a unregulated power supply for use with thermo electric cooling. I've got a couple 80W peltiers laying around and figured I''d cool my GPU and NB a little bit more. I'm jsut building a very simple unit using a 35amp/400V diode bridge, 33 thousand micro farad capacitor, and a transformer. I ran into problems with my transformer though, and i"m hoping someon here could give me a hand, as i"m pretty sure you're all [H]arder than me ;). Instead of trying to describe my situation, here's a pic of the transformer, the model is an ATC-Frost FT2213, and googleing has turned up nothing, i don't know how to identify, without killing the transformer, the primary and secondary leads.

attachment.php
 
Have you figured out if those are separate secondary coils wound on the same core, or taps? If the secondary is tapped, you could take continuity through the wires to find which leads are for the primary. In this case, the two leads that make continuity between themselves and not any other are for the primary.

EDIT: If this is an autotransformer, the continuity idea won't work. You would have to measure resistances instead and infer which are for the primary.
 
99% that the black wires are the primary, and 100% that this is a bad idea. You need a switch-mode power supply, which are not nearly as easy to design.
 
dandragonrage said:
99% that the black wires are the primary, and 100% that this is a bad idea. You need a switch-mode power supply, which are not nearly as easy to design.
Click to expand...

Why do you think a switch mode supply is necessary for this application? The simple linear supply he is building should work fine for the pelts, assuming the transformer can handle the current.

@Berg0: Are you sure you want to use that capacitor? I just did a quick mental calculation, and I think your voltage regulation will be very bad, with heavy ripple on the output. Your diode bridge should be OK, but a lot rides on that capacitor and the ability of the transformer to supply heavy current for a brief time. If I were you, I'd double check my calcs (you did use some math to design this thing, right?)
 
Efficiency. By the way, how heavy is that transformer? If it's not at least 8Lbs or so, it's not enough.
 
Yeah, this thing will run somewhat warm if he gets it working. Borg0, you really need to find the specs for that transformer, and look at the ripple rating of the capacitor. Also, it is a good design principle to use more than one capacitor for this. You will want to fuse this thing, too.

I apologize for the "Power Supply 101" stuff here, you may already know what you're doing. If you don't, though, consider picking up a book on power supplies.
 
yea, I understand what you're saying, and yes, I did the math, it's within spec for what i"m trying to do, I know this wont be particularily clean, but this is a hell of alot easir to do than building a switching power supply. I'll try to pick up another cap to filter a bit better, I might even have a similar or same capacitor around here somewhere and i"ll sjut use them in parallel to possibly do a better job of cleaning this up a bit. The whole point of building this simple unregulated power supply is to save money really, I sjut don't feel like throwing cash down to purchase a meanwell or similar PSU. I'll see what I can do with the equipment I have, a bud of mine has a scope, so i"ll get him to take a look at the voltage ripple before I use it for anyhitng other than testing.
 
so, can someone give me some useful info on this transformer, i actually have a bit of an update, i picked up another unit which is the same i got this transformer from, it's a small cream chiller manufactured for Mcdonalds, it uses two peltiers to chill a bag of cream ot about 4 degrees centigrade, so I know that the transformer should be ablet o handle the load i"ll be throwing at it, I sjut don't know what to do about the 3 leads, the white wire I found out, is grounded, which I thought was a bit odd, and the other three msut be various voltages which all sjut lead to a controller card of some sort
 
Like dandragonrage said, plug it in and use the meter to see what you've got. It is not odd for the white wire to be grounded, that is normal. Take your voltages between the white wire and the other ones. You may also want to look at how you will mount the transformer in it's final enclosure, and the grounding situation... for safety's sake. You probably don't want a floating neutral, and you definitely want to protect against a chassis short.
 
finished my power supply, have enough parts left over for a second too, transformer has 9/12/26 volts on the secondary, kinda neat. I dind't see much improvement in quality using 2 caps as opposed to one, so I think i'm gonna stick with one to conserve space, and my peltier is nice n' frosty :D thnaks for the help
 
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