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Old 21st September 2012, 09:46 AM   #2891
mikelm is online now mikelm  England
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11.8 x 1.414 = 16.68 - 2 diode drops ( 1.26 ) = 15.42V

As soon as you ask the transformer to do some work the voltage will fall again depending on how much current your circuit will draw - could easily be another 1 - 2V which would give around 13.5 - 14.5V.

Looks like u'll be safe to turn it on to measure actual voltages.

You could try putting the 20R peter suggested in both legs ( apply ground after CRC )

If it were me I'd aim for around 12V before regulators
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Old 22nd September 2012, 01:33 PM   #2892
endia is offline endia  Turkey
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mikelm, thank you.. there are four 20R resistors under the board, do i need additional 20R resistors?

AndrewT, i did your advices with and without smoothing cap and i got this absurd results: 3.65V
also i tried different type of rectifier (kbpc3510) on one output (i have only one on hand) with same result. i'm still reading 11.6V on the output of the transformer and 220V on the input, so my dmm can't be wrong..
what's wrong i'm doing? thanks..
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File Type: jpg P1040142s.jpg (599.4 KB, 363 views)
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Old 22nd September 2012, 01:48 PM   #2893
mikelm is online now mikelm  England
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Quote:
Originally Posted by endia View Post
mikelm, thank you.. there are four 20R resistors under the board, do i need additional 20R resistors?
Can't really comment on that without circuit diagram - it depends how those 20Rs are connected
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Old 22nd September 2012, 01:56 PM   #2894
endia is offline endia  Turkey
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forgot to attach underside of the board photo.. and this is the schematic as far as i know..
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Old 22nd September 2012, 02:03 PM   #2895
mikelm is online now mikelm  England
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looks like you're good to go
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Old 22nd September 2012, 02:23 PM   #2896
endia is offline endia  Turkey
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but i have fantastic 3.6V after rectification
really don't know what's happening.. should i take the risk?
thank you so much..
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Old 22nd September 2012, 04:42 PM   #2897
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by AndrewT View Post
Add a small bridge rectifier and small smoothing capacitor to your transformer secondary.
Measure the "no load" output voltage of the PSU..........
Quote:
Originally Posted by endia View Post
...............AndrewT, i did your advices with and without smoothing cap and i got this absurd results: 3.65V
also i tried different type of rectifier (kbpc3510) on one output (i have only one on hand) with same result. i'm still reading 11.6V on the output of the transformer and 220V on the input, so my dmm can't be wrong..
what's wrong i'm doing? thanks..
without a smoothing capacitor !!!!!
Why?

Do what you have been told, or simply ignore and go away.
Your choice.
__________________
regards Andrew T.
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Old 22nd September 2012, 05:17 PM   #2898
mikelm is online now mikelm  England
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If you don't have a cap after the diodes the whole dynamic of the supply is changed.

If you want to go that route you have to design it that way from scratch but it is radically different and not really necessary for such a low power circuit.

if you don't really understand this stuff best follow the kit as described by Peter before somethings goes horribly wrong !

Good Luck !

mike
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Old 22nd September 2012, 05:25 PM   #2899
endia is offline endia  Turkey
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AndrewT, i didn't want to be annoying you, just was experimenting to write results here.. i learnt lots of things from you here and i always thankful to you..

i find what i'm doing wrong; simly forgotting to switch my dmm after reading transformer's output voltage, ac to dc..

so i wired again with capacitors and read that 14.64V and 14.88V. it should be around 13.4-13.6 after 20R resistors and around 12-12.5 under load.. it looks like safe..
thanks for your helps..
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Old 22nd September 2012, 05:27 PM   #2900
endia is offline endia  Turkey
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mike, thank you so much..
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