The secondary wires of a 220 to 12 V transformer got broken. I want to repair it. I can open the laminations but don't know how to fasten them again (They have no bolts). The primary is wound on the secondary.


Can anyone tell me how to mend it?

 

Generally you are better off buying a new transformer. The wires are weakened at this point, and with no stress points you are going to have a fun time. the transformer you describe is a common one, how much amps?

They make liquid insulation (liquid tape is a brand name) that can be used if you to tack wires on the broken stubs. Look for something to attach the new wires on, even if you have to glue it on.

 

Mr. Marsden is 99% right on this one, however.............

You did not specify where, or at what point the secondary is open? Does the secondary have a one shot thermal fuse on board?

Any fault needing the primary unwound to access the secondary, is new tranny time......beentheredonethat, - likely more stubborn than you, and it did not work afterwards anyway. Lacquered or varnished laminations are a sonofabear to reassemble w/ no vibration.
If the leads out are subject to any appreciable movement, ergo broken, you may be able to unwrap the external insulation to mend a break, or install longer leads, and that's about it

rotsa ruck

 

Generally you are better off buying a new transformer. The wires are weakened at this point, and with no stress points you are going to have a fun time. the transformer you describe is a common one, how much amps?

They make liquid insulation (liquid tape is a brand name) that can be used if you to tack wires on the broken stubs. Look for something to attach the new wires on, even if you have to glue it on.

A new one is better coz I can not see anything to attach wires on. It is of 1 A.

 

Mr. Marsden is 99% right on this one, however.............

You did not specify where, or at what point the secondary is open? Does the secondary have a one shot thermal fuse on board?

Any fault needing the primary unwound to access the secondary, is new tranny time......beentheredonethat, - likely more stubborn than you, and it did not work afterwards anyway. Lacquered or varnished laminations are a sonofabear to reassemble w/ no vibration.
If the leads out are subject to any appreciable movement, ergo broken, you may be able to unwrap the external insulation to mend a break, or install longer leads, and that's about it

rotsa ruck

Thanks for an expert help. I want to ask one more thing that if I wound another secondary winding on the primary winding (without opening it), how many turns should be wound?

 

Thanks for an expert help. I want to ask one more thing that if I wound another secondary winding on the primary winding (without opening it), how many turns should be wound?

Sorry, there just isn't enough room on the bobbin to accomodate another coil within the frame laminations. If you were to rewind both coils, [[ as I said, btdt ]] you would have to carefully count turns in each, use identical diameter magnet wire for both, and impregnate the coils w/ varnish to defeat vibration, and then to reassemble the laminations dipped in the same varnish -- this is like trying to get a given product to fit properly back in its original carton -- next to impossible..........

When shopping for a new one, avoid chinese manufacture like a plague.

 

Yes, you are right, it is better to buy a new one than to repair this one. Thank you for saving me from wasting my time on it and blaming myself in the end.

 

I wonder how much current a toroid transformer can safely carry. Hand winding one would be a PITA, but it would be small.

 

I wonder how much current a toroid transformer can safely carry. Hand winding one would be a PITA, but it would be small.

Toroidal current transformers serving as a shunt for old "simpson" analog panel meters to increase the range from 5-50 amps carry at least line current when running a 3-phase motor off our test boards.........

........and yes ! I have wound some small signal transformers on toroids, awa some for current trannys on small reassigned panel meters, and PITA about says it

 

I had to cut a lot of plastic from the transformer before seeing the two broken wires. I pulled the wires a little and then soldered new flexible wires and used paper tape for insulation. Now it works perfect but it has become delicate.