Connecting a toroidal transformer

Thread Starter

mike_the_begginer

Joined Dec 7, 2019
6
Hello, I received a toroidal transformer that had the secondary 2x24V / 100VA with median socket. This secondary has been opened in order to be able to connect in parallel the two 24V windings resulting from the opening of the median socket. Unfortunately, the two windings were connected incorrectly and the transformer was powered this way for a few seconds and it heated up (but not very much). Then it was disconnected from the 230V network.
I checked it, it is functional, both secondary have the voltage of 25.5V with no load when 230V at network.
I checked the primary by measuring with the Ohmmeter and comparing it with another transformer that had the primary winding for the same voltage, and the results were very close.
Also, I also checked using the Ohmmeter the secondary and both had the same resistance.
Then I connected in parallel the 2 secondaries (this time correctly) and I powered the transformer and let it powered for 4 hours and it did not heated up.

Are there any other ways I could figure out whether or not there are or will be any problems with this transformer?
 

jpanhalt

Joined Jan 18, 2008
8,303
Welcome to AAC, Mike.

Doesn't sound like you ruined it to me. 60°C feels hot, but is well within operational limits, as is 80°C probably.
 

MaxHeadRoom

Joined Jul 18, 2013
19,393
If you had monitored the secondary voltage during the test period it should have indicated a problem also, if the voltage varied drastically.
Max.
 

Thread Starter

mike_the_begginer

Joined Dec 7, 2019
6
I checked the output voltage with load and without load during a period of about 4-5 hours and it seems to be stable.
The maximum temperature with continuous 3.37A resistive load was about 45 C after 4 hours.
Now my question is: how safe it is to use this transformer into a project which draws about 2A at 24Vac, after the external isolation was opened into a point and then it was rebuild ?
 

Thread Starter

mike_the_begginer

Joined Dec 7, 2019
6
Yes, I do know this, but the fact that I opened the external isolation of the transformer and then closed it back, can lead to unwanted behavior or problems ?
 

Thread Starter

mike_the_begginer

Joined Dec 7, 2019
6
The external isolation is that ”plastic” wrap which is put over the secondary winding (outer insulation). In my case, this outer insulation is made of thin transparent plastic wrap and a black plastic wrap which is under the transparent one.
 

MaxHeadRoom

Joined Jul 18, 2013
19,393
Just removing that should cause no problems, it is done all the time when modifying or adding windings.
One thing to watch for when mounting Toroidal TXFR's is to ensure the center mounting bolt does not include a strap that goes around the outside and touches the mounting frame, essentially creating a shorted turn, I have seen it done a few times!!:(
Max.
 

Thread Starter

mike_the_begginer

Joined Dec 7, 2019
6
One more thing: I used Tesa 53988 electrical tape to glue back the outer insulation and to repair the opened hole in the outer insulation. Can this cause any problems to the transformer ? I used this tape to wrap about 45-50% of the toroid core.
 
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