Wiring a Transformer for Power Supply

[dylar]

I have not wired a transformer before and I'm having some problems.
I am building the ggg isolated power supply for which I've drawn up my own vero layout

I have wired everything up that way I thought it should go, but it doesn't work.  Multimeter reading on the transformer's secondary side output wires is 0.0.  The transformer heats up when I plug it in, but nothing comes out the other side.  My guess is that I have done something wrong in wiring the transformer.  The transformer is soldered onto the board, but the solder points are isolated from the rest of the circuit.

[slacker]

Double check against the schematic, but D3 and D4 are the wrong way round so you're shorting out the secondary.

[dylar]

yes! you were right about the diodes. Thanks.
I switched them around, and now the multimeter reads 3.00v coming right out of the secondary side of the transformer instead of the 12v that it should be putting out.  So it's at least partially working now...
Anyone have any ideas why this is happening?

[dylar]

Also, it seems weird to me that the multimeter reads EXACTLY 3.00 when I touch the leads to the terminals on the secondary side of the transformer.  After the 7809 voltage regulator there's a voltage loss of around 1v.  It will not power an LED, but there is some power getting through.
The transformer is the Radio Shack 273-1385B...which should put out 12.6v, right?:
http://support.radioshack.com/support_supplies/doc40/40996.htm

[dylar]

one more thing--I used 1N4007 diodes instead of 1N4002. Would this cut the voltage?

[petemoore]

  Difference is in current handling capability way above applied current, in this circuit they work alike. 

[davent]

The 4007's are fine. If you've fixed the diode orientation, the banded ends (cathodes) of D1,D4 and the input of the regulator are common- the unbanded ends (anodes) of D2,D3 and the regulator ground are common, then the next thing is the secondary of the transformer is connected wrong going by your pictures. The secondary should have one lead connected to the D1,D2 node and the other secondary lead connected to the D3,D4 node as you show in your vero drawing, not what i'm seeing in the photos.

Also check the datasheet for the regulator, i can't tell from the pictures what's connected where but for the TO220 package pin 1 is input, pin2 ground and pin3 output.

http://www.fairchildsemi.com/ds/LM/LM7805.pdf

Cool little tutorial on silicon diodes. (i can never remember which ends cathode and which ends anode) http://www.wisc-online.com/Objects/ViewObject.aspx?ID=SSE302

Take care
dave

[smallbearelec]

Hi--

I don't mean to be mean...I do hope to spare you from lighting yourself up like a Christmas tree. Wiring a power supply that connects directly to the AC line is fundamentally, inherently dangerous! Emphatically, you should not be attempting to design your own without major, experienced help! I notice that J D Sleep says essentially this in big, red type in the GGG power supply projects section. Please take the warning seriously!

One reasonably safe way to go if you want a quiet supply for effects is to start with a 12-volt DC wall wart and add some filtering and a one-chip regulator. There are numerous DIY builds out there of this kind.

If you do continue the way you are going, please consult with a local experienced builder who can work with you on avoiding the (numerous!) mechanical and electrical land-mines that are part of dealing with house current. If you can't find the right help, please back off, build a pedal for your first project and power it with a battery to start.

Regards, and Happy (Safe!) Construction!
SD

[dylar]

Thanks for your input and concern--this is really a fantastic forum filled with helpful and friendly people.
I am still a noob, but I've built about a dozen effects circuits.  I still have no idea what I'm doing and probably shouldn't be messing with mains wiring...it just looked so easy in the layout.  Also the first time I tried making my own vero, which obv. failed...
Thanks again
D

[JKowalski]

Thanks for your input and concern--this is really a fantastic forum filled with helpful and friendly people.
I am still a noob, but I've built about a dozen effects circuits.  I still have no idea what I'm doing and probably shouldn't be messing with mains wiring...it just looked so easy in the layout.  Also the first time I tried making my own vero, which obv. failed...
Thanks again
D

By the way, it looks like you do not have a fuse on the hot mains line. This is extremely important to have when messing around like this. Without one your transformer could catastrophically fail (say, a short condition that draws kilowatts from the wall and catches the transformer on fire but doesn't manage to trip the breaker)

[dylar]

Ok, I decided to play it safe and not try to wire up my own transformer.  What I did instead was to find a 9v AC adapter at my local Goodwill store.  Multimeter showed it actually put out 12.6v, so there must have been a voltage regulator in whatever device it came from.  I hooked it up to the (fixed) ggg power supply circuit I had built, and viola, it now puts out 9v.  I put it through a distortion effect I built and it seems to work fine.  Below is a picture of the adapter.  It puts out 500mA.  Does anyone foresee any problems with this solution?

[dylar]

P.S. - DO NOT USE THE VERO LAYOUT AT THE TOP OF THIS PAGE - IT IS INCORRECT. (If anyone can remove the image, please go ahead)

[DiscoVlad]

You can edit your post to remove it, the button is in the top right corner of your OP (took me a while to find it too whenever I needed to edit one of mine).

[smallbearelec]

Does anyone foresee any problems with this solution?

Much better! This is more the right idea. A few notes:

--You Don't need the diode bridge. The rectifying (and a little fitering) have already been done inside the wall wart. All you really need is a large electrolytic, say 1000 mf., on the output of the wall wart. Follow with the regulator IC, and a small electrolytic (say 10 mf.) on the output of the IC. If you fish other sites, you will see this arrangement Many times.

--Your idea works fine with one pedal because a 9-volt wall wart invariably puts out much more without a load on it. But the output voltage will drop off a cliff with any substantial load, and there will be some drop across the regulator IC as well. If I were doing this, I would start with a 12-volt DC wall wart. That would leave enough "swing" to power a bunch of pedals. BUT...then you have to learn to properly heat sink the IC.

Further to my earlier post, the "issues" with building your own power supplies are an order of magnitude greater than those with building pedals. It's well-worth learning to do, as long as you do lots of homework before picking up the soldering iron.

SD

[davent]

To edit the vero image out of your first post you have to go back to 'tinypic' the spot you linked the image from,  delete it there. To edit your posts, you only have a limited time before the post is locked and uneditable.

dave