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Old 24th October 2006, 11:56 PM   #1
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Default Does (primary) transformer AC polarity matter...?

In US AC wiring the color codes in house wiring indicate that black is HOT and white is NEUTRAL and green is GROUND.

In most applications the device doesn't care about HOT/NEUTRAL arrangement and ground just ties chassis's together to prevent a human short.

What is the effect of reversing the intended polarity on a transformers primaries?

Regards,
Tom
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Old 25th October 2006, 12:24 AM   #2
novec is offline novec  Norway
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I have an addition to the question - does the primary polarity matter on two transformers sitting next to eachother? I'd imagine they'll create interfering magnetic fields, but I don't know how it'd affect anything.
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Old 25th October 2006, 12:58 PM   #3
kartino is offline kartino  Indonesia
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Hi guys,

Remember when we studied an AC sinusoidal at Junior High?

An AC current polarity is changing time to time, with periodical time. That's why you know there is 60Hz system, mean that the polarity change 60 times per second. Or 50Hz in IEC.

So the polarity it is no matter again. But remember when you paralleling the output of two or more transformer. It will become a fatal damage for the polarity. Wrong polarity similar to two or more series batteries in short circuited.

For magnetic field, the field of transformer are in close core and will not affect to another transformer. Except for sensitive signal such as your pre amplifier, amplifier input, etc.
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Old 25th October 2006, 01:56 PM   #4
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If your components chassis is grounded it certainly can.....
http://www.audioasylum.com/scripts/t...tweaks&m=36908

Alternatively, if you're supplying your mains power to ALL your components via a balanced (technical) power conditioner, its inherent ability to 'cancel' reactive leakage currents to chassis will address such problems -
http://www.equitech.com/articles/widescreen.html

FWIW
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Old 25th October 2006, 02:40 PM   #5
AndrewT is online now AndrewT  Scotland
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Hi,
the transformer isolates the mains from your domestic appliance.

As a result it matters not whether one wire or the other of the transformer is connected to hot or cold, WHEN CONSIDERED IN ISOLATION.

BUT

the transformer is built into equipment and the neutral from the transformer may be connected to other components that are close to chassis or exposed to prying fingers inside the enclosure.

For safety, the hot MUST be connected to the equipment hot connection and the cold/neutral MUST be connected to the neutral connection.

Some equipment (outside the UK) has only single pole switching on the hot line and almost all equipment has the fuse in the hot line. If neutral and hot were inadvertently swapped then the switch or fuse would break the neutral leaving the equipment LIVE and just waiting for an accident.

Finally your statement
Quote:
In most applications the device doesn't care about HOT/NEUTRAL arrangement
is completely erroneous.
There is an important exception:-
double insulated equipment that does not require a safety earth.

Anything else is potentially lethal if the hot and cold are swapped.

I am glad the UK has approving authorities to look after our health. If only the rest of the world had big brother.
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Old 25th October 2006, 03:44 PM   #6
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Andrew,

You raise some good points. Given what I previously posted, I think some caveats are in order.

1. Some older equipment does not follow standard, current build pratices. Specifically, equipment built 35+ yrs ago, that came with non-grounded, polarized 2 prong mains plugs (like some Macs) connected neutral to chassis and/or signal ground. In those cases, without remediation, reversal of ac wiring, if it doesn't blow your equipment, will endanger one's safety.

2. If you admonition against reversal of ac polarity were absolute, balanced (technical) power should be illegal, and at least in the States, it isn't.

3. Current build practices, at least those specified by Stateside ETLs, have the same 'creepage' requirements for both hot and neutral.

Obviously, care should be taken before any reveral of hot/neutral wiring, and if one doen't know what to look for, one shouldn't attempt such.
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Old 25th October 2006, 10:47 PM   #7
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Default Thanks all, but what I was actually after was...

Thanks all, but what I was actually after was whether polarity would affect secondary voltage. I am well aware of the safety issues.

My device is double insulated and chassis grounds both the SMPS and the Hypex 1KVA toroid shielding just to cover the bases.

So, I read an article that stated that AC polarity might affect the secondary voltage on a transformer.

It didn't make sense to me but there was more than one article stating this.

Is this true?

[edit] I suppose I could tear the device apart, meter the xformer both ways and see for myself but I was just curious if anybody could tell me what's up with this before I do that...

Regards,
Tom
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Old 25th October 2006, 11:03 PM   #8
AndrewT is online now AndrewT  Scotland
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Hi,
double insulated should not have a connection to chassis.
What's up Doc?

The secondary voltage will not be affected by swapping the transformer primary connections. Remember what I said
Quote:
As a result it matters not whether one wire or the other of the transformer is connected to hot or cold, WHEN CONSIDERED IN ISOLATION.
I think that answered your question, but my diatribe distracted you from the message contained therein. Sorry but I've done it again. KIS (keep it simple) should become my new motto but I can't stop myself.
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Old 25th October 2006, 11:21 PM   #9
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Default yOUR ANSWER WAS GOOD...

I only grounded the Hypex shielding between windings on the Xfrmr (grn/ylo), carries nothing and is not a "real" ground, (Hypex says to do it for safety in case toroid craps is my guess or just to give stray zap a place to go).

You have to understand my device (in one chassis) carries both a P4 computer AND a set of UcD 400's.

The UCD grounds "float", nothing is grounded to the chassis. Quiet as a mouse. The P4 is only grounded thru it's case screwed to the chassis. Only for basic safety. Otherwise everything else is double-insulated for noise and safety.

The CPU is grounded by virtue of a case ground off the SMPS chassis to keep me from getting cooked if that cheap piece of **** gives up the ghost.

So, my real question is that my UCD400's are "quiet" and I was wondering if my toroid wasn't delivering enuff juice due to an (inadvertant) reversal of "HOT" and "NEUTRAL".

By "quiet" I mean not enuff SPL.

My question has really nothing to do with AC in general and everything to do with amp performance.

I am perfectly happy with my system otherwise.

I measure NO stray voltage anywhere in the chassis.

I appreciate the news that secondary voltage is independent of AC polarity on my Xfrmr.

What the heck else could make my 400's so tame?

Maybe my speaks (which I also built?)

Best Regards,
Tom
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Old 26th October 2006, 07:53 AM   #10
AndrewT is online now AndrewT  Scotland
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Hi,
how many windings have you got on your transformer? list the tappings for us.

Have you measured the voltage coming out of the transformer? and going to the amplifier?

Have you measured the signal going to the power amp and the signal level coming out to the speaker.

Give us some glues, (it's not Cluedo).
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