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Old 23rd January 2006, 05:19 PM   #1
percy is offline percy  United States
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Default DC offset on household ac line ?

Is there an easy way to find out if there is any (and how much) DC offset is present on my household ac line or not ?
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Old 23rd January 2006, 05:24 PM   #2
poobah is offline poobah  United States
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Not to be snotty but, why would you want to know?

Assymmetry or "offset" in your AC really only matters if you have toroidial input transformer AND the problem is severe.

Do you have a scope?

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Old 23rd January 2006, 05:51 PM   #3
percy is offline percy  United States
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Quote:
Assymmetry or "offset" in your AC really only matters if you have toroidial input transformer
and thus my question.

Unfortunately I dont have a scope yet
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Old 23rd January 2006, 05:53 PM   #4
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What makes you think you have a problem?
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Old 23rd January 2006, 05:56 PM   #5
percy is offline percy  United States
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(I dont want this to start into a toroidal-EI war again so I did not specify earlier but since you asked...)

I dont have a problem as such. I just want to see if toroidal transformers will be a good idea for me or not.
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Old 23rd January 2006, 06:11 PM   #6
poobah is offline poobah  United States
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Well. there are ways to measure it roughly. But it's taboo on this forum...

If your toroids are conservatively sized you should have no problem though. If you don't want to worry about just it; get EI's and get an EI with a shield as one step up.
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Old 23rd January 2006, 06:19 PM   #7
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Default Re: DC offset on household ac line ?

Quote:
Originally posted by percy
Is there an easy way to find out if there is any (and how much) DC offset is present on my household ac line or not ?
I have built an AC Mains servo circuit, to correct for DC-offset.
A simple uA741 OP-Amp will sense any offset via 2 resistors 2 caps network feedback
and activate High Current Relay Switches to correct Mains AC back to zero offset.

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Old 23rd January 2006, 06:32 PM   #8
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Default Re: DC offset on household ac line ?

Quote:
Originally posted by percy
Is there an easy way to find out if there is any (and how much) DC offset is present on my household ac line or not ?
If you plan to use a toroid transformer just go ahead. If it turns out that it on and off hums rather irritating then you have a solution.

To measure the DC is rather hard to do so forget for now.

Here is thread about the topic.
dc filter
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Old 24th January 2006, 09:23 AM   #9
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DC offset should be rare now. The main cause used to be those live chassis TVs from the 1970s that had a horrible half wave SCR regulator. Hopefully these are long gone.

The power companies were not happy about these asymmetric power supplies as the dc load caused problems fot the substation transformers.
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Old 24th January 2006, 09:30 AM   #10
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You have always some DC. The question is if it bothers you.
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