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Old 1st August 2005, 08:44 PM   #1
kepa1 is offline kepa1  France
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Default Basic questions for the power supply

Hi all,

this is time to complete my UCD amp plate project but things get a little complicated

Click the image to open in full size.

I measured the output of both bridge rectifiers and got 0 V DC instead of 30 - is that normal? the bridges are brand new and the transformer output 32 V AC.

Also, I wonder if the unused supply rails should be connected to the ground from the rectifiers or from the capacitors, as shown on the photo (just ignore that black cable hanging around).

And last, the switch I bought has three connectors, how are they supposed to work?

Thank you
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Old 1st August 2005, 10:34 PM   #2
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Hi,

Start by taking a step back and a real deep breath.

Then, look up the data sheets for the parts you have in question, bridge rectifiers for example, that will tell you how to wire them properly if you're in doubt, pinouts etc, they're usually pretty clear though.

Then, once you know how all the parts work, make yourself a wiring diagram on paper, it should work on paper before you ever wire it, then show us that diagram and we can be alot more help. The picture is useless to me at least.

Alternatively, base it off of what you know will work, someone else's wiring diagram. Saaaaay perhaps, from http://www.zero-distortion.com/techn...powersi_05.htm This should really be all you need.

Hope you didn't fry anything costly.

Chris

PS, I wired up a bridge rectifier backwards once (tired) it squeeled like crazy and the xformer got HOT but it all lived. Seems they can take a good beating though. It might be a good idea to place your rectifiers alot closer to your caps though, shorten the wires that is.
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Old 2nd August 2005, 01:53 AM   #3
Stocker is offline Stocker  United States
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Do you have AC out of the transformer secondaries?

The switch you can test with an ohm-meter
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Old 2nd August 2005, 12:51 PM   #4
kepa1 is offline kepa1  France
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Thank you both for the input,

I'll try to explain things better tonight as I am at work now. Fortunately only a fuse blowed and not the transformer
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Old 3rd August 2005, 12:00 PM   #5
kepa1 is offline kepa1  France
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Ok, so the PS is just the same as this one, except it only has one capacitor per rail :

Click the image to open in full size.

I remeasured yesterday evening and the transformer outputs 32VAC but i got this strange result 1. when measuring simultaneously the + / - pins of both bridge rectifiers.

Measuring the + pin and the ground gave 0 V.

Maybe there is another way to test?
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Old 3rd August 2005, 12:23 PM   #6
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The drawing looks OK, that's got to work right?

Triple check your rectifiers yet? Test them on the diode scale just to make sure the parts are good to start with.

At this point take your drawing and trace down every wire one by one, highlight/ mark them off as you go, something in your circuit isn't going to match the drawing. Like for instance, why do you only have three wires going to the upper bridge rectifier in your picture?

Cheers,
Chris
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Old 3rd August 2005, 02:26 PM   #7
soongsc is offline soongsc  Taiwan
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It's hard to tell what's going where in you picture because the transformer is not seen and the wre color coding is not consistent. But if you look at the rectifiers, there is a cut corner, that corner corresponse with where the + side of the rectifier where two arrows point to.
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Old 4th August 2005, 07:58 AM   #8
kepa1 is offline kepa1  France
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Shame on me... the multimeter was calibrated at 20V and couldn't read the voltage coming out the bridges In the end, I read 28V DC out of them.

I have wired both bridges to the capacitors and everything looks good now. the caps deliver a mighty 44V...

... But I still have questions for you guys

These big caps appear to discharge very slowly - half an hour after switch off, they still output 38V after a night I could measure almost 5V.
Should I wear plastic gloves to work on the circuit?

Also, is it OK if the - terminal of cap#1 is connected to the + terminal of cap#2 at the star ground point? or should they be separates to avoid any kind of short circuit or electric shock on the chassis?

Then should the star ground point be isolated from chassis (mine is made out of aluminum and the star ground point is the screw in the middle of the plate)?

Soongsc, the transformer is screwed to the other side of the plate - It's so big I couldn't place it but there.


Cheers
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Old 4th August 2005, 08:26 AM   #9
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Heh heh.... been there! That's when I take a nap. Honestly though, aren't those the best kind of problems?


Gloves? Can't kill yourself at these levels, well you'd have to really try..

No, what you should do is discharge your caps alot faster to keep them happy, yes it loads the supply down a little but...call it insignificant I guess. That depends on how you to do it too I recommend you spend more time at the link I gave you a few posts ago. Click the back arrow on the page a few times to get you to the first and most basic supply and then read how they evolved and you'll get it.

You're putting your caps through a slow death by letting them self discharge slowly like that, they'll tend to want to reform to the lower voltage.

What you want between your caps is a good thick, short wire or bus bar that'll really let the ripple current flow nicely between them. Along this line flows rather turbulent currents, that means it's not a good place for star ground placement as it would pollute all your system grounds.

Connect them together with as short a wire as you can. Then "T"-off that wire and connect to your star ground. This leaves most of the turbulance flowing between the caps and out of your high quality ground point.


As far as floating the HQG off the chassis, that's more of a preventive / band aide cure for ground loops which you should be first trying to avoid.

Good way if you want to mass produce I'm thinking, but it doesn't seem like a hard addition after the fact so I'd try without first, and see what happens?

Cheers
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Old 4th August 2005, 09:46 AM   #10
kepa1 is offline kepa1  France
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All I can say is thank you classd4shure (what you wrote and the above link is a mine of info!) and to the others.

The path is a little tricky but the end is near... I guess!

Cheers

Alain
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