Help with a Toroidal Transformer voltage readings

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cpietroc

Joined Sep 25, 2017
2
Hi, I'm new to toroidal transformers and I just got one to power a 12v battery charger. (I could not find a EI transformer with a 15-0-15 secondary, even though I don't think this toroidal has this either.) After supplying 110 VAC input, I measured the secondary and then each secondary to ground and got confusing results. I attached the diagram of my test and of the charging circuit I'm trying to power. Will this transformer work? Thanks.
 

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crutschow

Joined Mar 14, 2008
25,645
There should be isolation between the input ground and the output voltage (that's one important function of a main's transformer) so any voltage you read is likely just due to capacitive coupling between the primary and secondary of the transformer which the high impedacne of the meter can read.

Connect a 1kΩ resistor as a load across the meter leads and see what voltages you measure.
It now should be near zero between the output and ground.
 

Thread Starter

cpietroc

Joined Sep 25, 2017
2
Thanks Crutschow, that did the trick, though I don't have a clue what 'capacitive coupling' is. Last question. Since the diagram I am following spec'd a 15-0-15 center tap transformer, will my toroidal work instead. See pic.
 

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BR-549

Joined Sep 22, 2013
4,938
I've never seen that transformer symbol before. I don't like it. Very confusing to understanding transformer action.

Who teaches that? Is that a new symbol?
 

crutschow

Joined Mar 14, 2008
25,645
Thanks Crutschow, that did the trick, though I don't have a clue what 'capacitive coupling' is.
There is a small parasitic capacitance between the primary and secondary windings due to the wires being in close proximity to each other.
The will couple a very small voltage/current between the primary and secondary.
Since the diagram I am following spec'd a 15-0-15 center tap transformer, will my toroidal work instead
Yes.
A toroidal transformer works the same as an E-core transformer, it just has slightly better efficiency and lower stray magnetic fields around it.
 
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