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How to use 2x 115v transformer on 230v
How to use 2x 115v transformer on 230v
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Old 1st July 2020, 10:28 AM   #1
MrHifiTunes is offline MrHifiTunes
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Default How to use 2x 115v transformer on 230v

Hi, I got a 2x 115 v transfo with 2x9v output.
How can I connect it to 230v?
Secundaire load is not balanced. One will be 15w the other 0.5w.
Will this cause problem as primary current is the same when connecting them serial primary side
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Old 1st July 2020, 10:41 AM   #2
Sangram is offline Sangram  India
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How to use 2x 115v transformer on 230v
You can connect primaries in series with differing loads on multiple secondaries when they share a core. The problem of unbalanced loads and primaries in series applies only to independent transformers. You still need to pay attention to secondary load capability and keep your loading within those limits, but I assume you already know that.
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Old 1st July 2020, 10:58 AM   #3
MrHifiTunes is offline MrHifiTunes
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To make it clear before I blow things.

It's possible with this? See pictures.
I dont know if the drawing that i made is ccorrect on primairy side

secundaire side : One end will feed raspberry pi. Other end DAC board
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Last edited by MrHifiTunes; 1st July 2020 at 11:03 AM.
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Old 1st July 2020, 11:33 AM   #4
FauxFrench is offline FauxFrench  France
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As I understand the marking on the transformer, your diagram is correct.
BUT, just not to harm anything: For a start try the transformer alone with 230Vac at the primary (RED/BLACK) AND A SMALL FUSE (0.2-0.5A) IN SERIES WITH THE PRIMARY! If we misunderstand the marking, the fuse will blow instantly. If the fuse is not blown, check that the secondary voltages are about right (10-15% higher voltage when unloaded).

Last edited by FauxFrench; 1st July 2020 at 11:35 AM.
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Old 1st July 2020, 11:41 AM   #5
duncan2 is online now duncan2  United Kingdom
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Click the image to open in full size.
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Old 1st July 2020, 12:25 PM   #6
FauxFrench is offline FauxFrench  France
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Absolutely agree with Duncan on the principle. The problem for the primaries is that the "dots" are not shown and we have to interpret the text to arrive at the winding polarities.
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Old 1st July 2020, 12:51 PM   #7
JMFahey is offline JMFahey  Argentina
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Primary Red and Brown are labelled "0V" so they can be assumed to be the start/beginning of each winding and "should" match your drawing.

In any case, confirm that by wiring them the way you think , secondaries connected to nothing, and plugging primary into mains, with some safety device added.

A small fuse is fine, as suggested by fauxfrench or use a dim bulb limiter with a 25 or 30W filament ,lamp.
If it blinks, fine, if it stays brightly ON, your wiring is wrong and you mustvreverse *one* primary.

I find it quite stupid they did NOT identify secondaries, using same colour for both ends each. (Brown-Brown and Grey-Grey)

IF you will use them completely separate, no big deal, but if wrong phase, in series you may have 0V end to end and in parallel you will burn the transformer.

Russian roulette with 3 bullets in the revolver.
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Old 1st July 2020, 01:32 PM   #8
MrHifiTunes is offline MrHifiTunes
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Quote:
Originally Posted by duncan2 View Post
Click the image to open in full size.
I asume the labelling is correct.
Your drawing doesnt match my 'planned'setup for the secundairy wiring.
In my idea they stay separately. So 2 X 9V (one for pi and one for DAC board).
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Old 1st July 2020, 01:36 PM   #9
MrHifiTunes is offline MrHifiTunes
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Quote:
Originally Posted by JMFahey View Post
Primary Red and Brown are labelled "0V" so they can be assumed to be the start/beginning of each winding and "should" match your drawing.

In any case, confirm that by wiring them the way you think , secondaries connected to nothing, and plugging primary into mains, with some safety device added.

A small fuse is fine, as suggested by fauxfrench or use a dim bulb limiter with a 25 or 30W filament ,lamp.
If it blinks, fine, if it stays brightly ON, your wiring is wrong and you mustvreverse *one* primary.

I find it quite stupid they did NOT identify secondaries, using same colour for both ends each. (Brown-Brown and Grey-Grey)

IF you will use them completely separate, no big deal, but if wrong phase, in series you may have 0V end to end and in parallel you will burn the transformer.

Russian roulette with 3 bullets in the revolver.
Primary RED and WHITE are indeed indicated as 0V, so I assume it's correct. Secondary will stay separate so 2 x 9V. Is this possible? current in primary will flow through both windings on the front end, but secondary has different load (Pi board = 2-3 A, DAC = 0,1A)
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Old 1st July 2020, 02:58 PM   #10
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by MrHifiTunes View Post
Primary RED and WHITE are indeed indicated as 0V, so I assume it's correct. Secondary will stay separate so 2 x 9V. Is this possible? current in primary will flow through both windings on the front end, but secondary has different load (Pi board = 2-3 A, DAC = 0,1A)
Sorry, you are right, typed from (poor) memory , RED and WHITE are presumed winding start.
Yes, secondaries can have different loads, no problem.
One can even be fully unused.

Yes, both primaries in series will pass any power required by secondaries; any secondaries will provide its rated voltage (in this case 9VAC) , with current up to rated value (1.66A? ... again quoting from memory because while answering picture is not visible )

Secondary current limitation does not come from core saturation (which allows up to 30VA total) but winding wire diameter.

IF some day you want to join them, series or parallel, test them as I mentioned above and then label them for future use, you can paint a white line (printer correction pen) along "0V" wire, add a small tape label or simply tie a knot with the 0V wire.
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