Power supply issue

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Nick
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#31 Re: Power supply issue

Post by Nick »

No.
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#32 Re: Power supply issue

Post by Daniel Quinn »

Thank you .
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shane
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#33 Re: Power supply issue

Post by shane »

No. The positive and negative terminals are the DC outputs of the rectifier. They should not be connected to the transformer.
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#34 Re: Power supply issue

Post by shane »

Nick got there first....
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pre65
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#35 Re: Power supply issue

Post by pre65 »

Daniel Quinn wrote: Sun Jul 31, 2022 2:47 pm I know how to wire a bridge rectifier !
You do now. :wink:
The only thing necessary for the triumph of evil is for good men to do nothing.

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Nick
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#36 Re: Power supply issue

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pre65 wrote: Mon Aug 01, 2022 12:04 pm
Daniel Quinn wrote: Sun Jul 31, 2022 2:47 pm I know how to wire a bridge rectifier !
You do now. :wink:
Ignoring the snark, it may be worth spending 5 minutes looking how a bridge rectifier is constructed fro 4 diodes and if I tell you that a diode will only pass current if the anode is at a higher voltage than its cathode (for conventional current, ignore than DQ, that's to quiet the others down). First think about how and when the sine wave from the transformer in this circuit will pass current into the capacitor, and then do the same for the case of the bridge rectifier, and consider why the first is a half wave rectifier and the second a full wave rectifier.

Image

In this diagram, its important to remember the two ground symbols (the downward pointing triangles) are connected together, you need to know that to see how the current flows back through the bridge.

Image
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#37 Re: Power supply issue

Post by Daniel Quinn »

I thought rectifiers just turned ac into dc . So 18v ac became 18v dc

That as always been the case , but these new ones are driving me mad.

I’m getting 18v ac and 9v dc ( this is without any capacitors) What is going on?

I’ve tried another transformer 35v ac 17v dc it seems to be halving it ?
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#38 Re: Power supply issue

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I thought rectifiers just turned ac into dc . So 18v ac became 18v dc

That as always been the case , but these new ones are driving me mad.
That has never been the case. And I remember telling you that just after you joined this forum.
I’m getting 18v ac and 9v dc ( this is without any capacitors) What is going on?
Well, if you spent the time I suggested you may have had the answer. How are you measuring the DC? Without the cap you will have a rectified sine wave, that will have an average DC level and a peak DC level. No idea what your measuring device is showing you.
I’ve tried another transformer 35v ac 17v dc it seems to be halving it ?
No idea. a rectified and filtered supply (with a cap) will give you 1.414 times the AC voltage as an off load voltage and depending on the load anything from that down to 0v output.
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#39 Re: Power supply issue

Post by Daniel Quinn »

If you have told me I apologise for paying insufficient attention .

Nothing is as simple as it seems and this hobby was supposed to be light relief as I recovered .

So the only law is the dc output after capacitors is 1.4 the ac input ?
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#40 Re: Power supply issue

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No, no law's involved (either sorts), just maths. The peak value of a sine wave is 1.414 (square root of 2) times its RMS (the equivalent power value of a DC voltage) value. With no load, the capacitor after the rectifier will be charged up to the peak of the sine wave, So the peak voltage is 1.414 times the RMS AC voltage. As the load on the charged capacitor increases the average voltage on the capacitor reduces, if the load is 0 ohm, the voltage will be 0v.

https://www.audio-talk.co.uk/phpBB3/vie ... 15#p191815
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#41 Re: Power supply issue

Post by pre65 »

Nick wrote: Mon Aug 01, 2022 2:04 pm
pre65 wrote: Mon Aug 01, 2022 12:04 pm
Daniel Quinn wrote: Sun Jul 31, 2022 2:47 pm I know how to wire a bridge rectifier !
You do now. :wink:
Ignoring the snark,
Not sure what snark is, but I was alluding to the fact that Dennis (DQ) did not seem to understand bridge rectifiers. There is so much to learn.
The only thing necessary for the triumph of evil is for good men to do nothing.

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#42 Re: Power supply issue

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but I was alluding to the fact that Dennis (DQ) did not seem to understand bridge rectifiers
He never said he did, what he said was that he knew how to wire them. Which may or may not have been true. To understand something is a far wider goal that just knowing how to use it, and is a journey that none of us ever probably reach the end of. My suggestion of following the paths the current takes in the two example I gave, and the corresponding voltages generated will IMHO take you along the first part of understanding and help to explain why you use them as you do. And also as it happens will help in understanding the next answer I gave about the value of the DC voltage generated.
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#43 Re: Power supply issue

Post by pre65 »

More power to your elbow Nick, you (and others here) have certainly helped me enough over the years. :D
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
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