Help with a Toroidal Transformer voltage readings

Thread Starter

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.
 

Attachments

crutschow

Joined Mar 14, 2008
34,280
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.
 

Attachments

BR-549

Joined Sep 22, 2013
4,928
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
34,280
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.
 
Top