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Old 20th November 2014, 01:55 AM   #1
rawbas is offline rawbas  Philippines
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Default Confused!

Hello everyone,

I am a bit confused with the power supply I have, I know there are some factors to consider but not sure what they are.

I have X'former which I made with an output of 2 x (40.5-0-40.5 VAC).

The 40.5 VAC, when rectified (40.5 x1.414) should have 57 Vdc, but I am only getting 53-54 Vdc.

What could be the issue?


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Old 20th November 2014, 03:04 AM   #2
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Quote:
Originally Posted by rawbas View Post
The 40.5 VAC, when rectified (40.5 x1.414) should have 57 Vdc, but I am only getting 53-54 Vdc.
With or without load?
If with load, what load exactly and what VA rating of the Xformer?
Is it a full wave rectifier?
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Old 20th November 2014, 04:24 AM   #3
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Quote:
Originally Posted by rawbas View Post
Hello everyone,

I am a bit confused with the power supply I have, I know there are some factors to consider but not sure what they are.

I have X'former which I made with an output of 2 x (40.5-0-40.5 VAC).

The 40.5 VAC, when rectified (40.5 x1.414) should have 57 Vdc, but I am only getting 53-54 Vdc.

What could be the issue?


Thanks
Don't forget to factor in the voltage drop across the diodes.
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Old 20th November 2014, 04:42 AM   #4
rawbas is offline rawbas  Philippines
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@ ticktock

that's without load
it is rated 620VA and yes full wave rectifier.

@ mcandmar

yes, roughly the vdrop would be 1.4V, right?
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Old 20th November 2014, 10:08 AM   #5
DF96 is offline DF96  England
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Is it rectified and smoothed, or just rectified? If the latter then you are seeing more voltage than you should. If the former then how much does your incoming mains voltage vary from day to day?
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Old 20th November 2014, 10:45 AM   #6
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Connect the smoothing caps as DF96 say's and check again.
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Old 20th November 2014, 10:54 AM   #7
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In Philippines as I read you have 220V.
Maybe the transformer was designed to be use with 230V and using with 220V will exactly make 54V instead of 57V. Or simply the network is not that stable and lower than it should be.
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Old 21st November 2014, 03:32 AM   #8
rawbas is offline rawbas  Philippines
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Quote:
Originally Posted by DF96 View Post
Is it rectified and smoothed, or just rectified? If the latter then you are seeing more voltage than you should. If the former then how much does your incoming mains voltage vary from day to day?

yes it is smoothed, using a 10000uF/63V Capacitor.
well, at daytime it goes to 215V and went to 225V at night, but regardless, I used to measure when the output of the X'former is 40.5Vac
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Old 21st November 2014, 03:35 AM   #9
rawbas is offline rawbas  Philippines
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Quote:
Originally Posted by mrWagner View Post
In Philippines as I read you have 220V.
Maybe the transformer was designed to be use with 230V and using with 220V will exactly make 54V instead of 57V. Or simply the network is not that stable and lower than it should be.

Well I have rewound the output to get a 40.5Vac output, when rectified we should get a close value to 57Vdc, less the vdrop on the bridge rectifier we could get 55Vdc.
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Old 21st November 2014, 03:39 AM   #10
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I really dont think you have a problem being within a few volts of a "theoretical" figure, and as you have noted it will fluctuate with mains voltage and load.
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