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Transformer voltage output higher than expected

gianlu

Jan 9, 2022
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Jan 9, 2022
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Hi,

I have this transformer: vtx-121-3023-215.
According to datasheet output will be 15VAC with 230VAC input.
With no load my multimeter measure [email protected] on both secondary (pin 6,7 and 9,10).

I test input on primary and is [email protected]

Is transformer damage or am I missing something?

Thanks a lot.
 

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gianlu

Jan 9, 2022
4
Joined
Jan 9, 2022
Messages
4
Yeah, with 1K resistor as load, after a rectifier that increase voltage a little more, voltage drop from 30VDC to 25VDC suitable to power-up voltage regulator. I need 12VDC and 5VDC in my circuit in order to power up 12V relays and 5V microcontroller.
I will test with real load but you got the point and i learned something about transformer. :)

Thanks a lot.
 

davenn

Moderator
Sep 5, 2009
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. I need 12VDC and 5VDC in my circuit in order to power up 12V relays and 5V microcontroller.
20+ VDC is way too much for a 12V or 5V regulator input

You should be using a transformer with a ~10 VAC secondary 12VAC at the shear max


If you are using a 7812 reg., then ~ 15VDC should be the max input
the 5V reg could come off the output of the 12V regulator
 

WHONOES

May 20, 2017
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1,215
Transformer secondary voltages are specified at maximum rated load. As the load decreases so the voltage will increase.
This aspect will be referred to in the Tx spec as its regulation factor as a percentage. For a small transformer regulation can be 20% or more whilst for a large transformer it might only be 2% or so. Thus with no load on a small transformer the secondary voltage might measure 20% (or more) higher than its full load spec'.
Hope that makes sense.
 
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