You can not be serious. I take you are meggering the transformer. That is not a short, that is a (now) insufficient isolation value for obvious reasons. A short is measured with a resistance meter or a DMM.
A recycled question: is there a fuse holder and what is the fuse rating? If there was none it had to endure a very high current but below the maximum home installations current (16A?). This adds to a right diagnose. The double nut on a too long bolt is a risk with regards to shorting.
A recycled suggestion: use a fuse holder and connect that unknown transformer with unknown rating with a "just enough" fuse safely to a cable with mains switch. Switch it on from a safe distance, wait one minute. Use nose, eyes and ears. If OK measure secondary voltages safely preferably with previously connected DMM cabling. Draw conclusion and discard the transformer. Find the part that caused the overcurrent.
BTW it is kV.
A recycled question: is there a fuse holder and what is the fuse rating? If there was none it had to endure a very high current but below the maximum home installations current (16A?). This adds to a right diagnose. The double nut on a too long bolt is a risk with regards to shorting.
A recycled suggestion: use a fuse holder and connect that unknown transformer with unknown rating with a "just enough" fuse safely to a cable with mains switch. Switch it on from a safe distance, wait one minute. Use nose, eyes and ears. If OK measure secondary voltages safely preferably with previously connected DMM cabling. Draw conclusion and discard the transformer. Find the part that caused the overcurrent.
BTW it is kV.
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Very small scratch-marks on vindings is the only thing I can find. The damaged transformer still works (w.o. load) and makes nominal output voltage with 230Vac mains.
At this point I'll assume that the transformer was damaged before installation or that some small piece of metal was loose in the cabinet and rubbed on the vindings.
Mains fuse was too big and will be corrected.
The main takeaway is probably that I need to secure transformers better.
Thanks for the input.
At this point I'll assume that the transformer was damaged before installation or that some small piece of metal was loose in the cabinet and rubbed on the vindings.
Mains fuse was too big and will be corrected.
The main takeaway is probably that I need to secure transformers better.
Thanks for the input.
Post 21 : sorry, with a thick secondary wire you can not find the short by simple DMM means.
Isolation failure is a short here.
** Post 21 was heavily edited later, seems to be a habit. **
Isolation failure is a short here.
** Post 21 was heavily edited later, seems to be a habit. **
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Ok. Fair enough. The low breakdown voltage is not a short. It's an indication of an error and I'm assuming the root cause was a short.
Please explain why the double nut is a risk? Maybe I wasn't clear on this, but there is NO METAL over this. The double nut was my best attempt on making it vibration proof, but maybe that's not optimal.
kV it is then. What's your point beside focusing on not important details?
Kind regards
My take is that your secondairy may have shorted to ground, and with too high fusing it could have caused this melt-down. BTW: I did not read the entire thread, just looked at the last few posts. I see no issues with the double nut.
Look at the datasheet for correct fusing. The toroids I use only call for primairy fusing.
Look at the datasheet for correct fusing. The toroids I use only call for primairy fusing.
My point was that this kind of failure could not have happened with correct fusing. The current was way too high but not high enough to trip the (16A?) home breaker. You are not there yet. The damaged transformer still works (w.o. load) and makes nominal output voltage with 230Vac mains. So it was OK and it even still functions (but it's not safe enough to reuse). There likely is a severe error elsewhere. The damaged isolation can also have occurred when taking the thing apart (there is nothing protecting the wires now) and/or the extra heat it had to endure. Let's assume 6A ran through it, you fused it with 10A and the home breaker is 16A. We have to assume as the answers stay open. With 6A it would be 1.4 kVA. A nice heater for 2 minutes.
Also a point to solve YOUR problem: you only rarely reply to suggestions or questions.
Also a point to solve YOUR problem: you only rarely reply to suggestions or questions.
As concluded.
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I can not believe that the transformer is still "working" (post 22).
If you removed the screw it may seem so, opened a short, but it
is not safe.
If you removed the screw it may seem so, opened a short, but it
is not safe.
The question is if it was meggered with or without the metal mounting plate. Also the metal mounting plate does not come even close to the now damaged windings. A short to the metal mounting plate so PE to winding or a too low primary resistance would have been noticed with a DMM too at the primary diagnosing certainly with this grade of damage. I can not imagine this would have gone unnoticed at first sight.
Believing is better done in church. If OP after energizing and measuring says the transformer works OK it works OK.
Diode or cap it is probably.
Believing is better done in church. If OP after energizing and measuring says the transformer works OK it works OK.
Diode or cap it is probably.
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You can not se where the short is.
"If OP says the transformer works OK it works OK." is BS for me.
"If OP says the transformer works OK it works OK." is BS for me.
Post #22 shows damage to the wire windings. Copper is gouged & insulation is missing. Your test without load is not prof that the Tx is OK. Loading causes heat rise, and the thermal rise causes the wire to expand and it may have created a shorted single turn.
It Suprises me that a built in thermal 130-degree fuse is not inside the Tx.
The Tx is not usable, it is a time bomb for LIFE SAFETY.
Duke
It Suprises me that a built in thermal 130-degree fuse is not inside the Tx.
The Tx is not usable, it is a time bomb for LIFE SAFETY.
Duke
Thermal fuses are required for UL approval.
The winding has clearly been mechanically gouged at some time, which has not just stripped the enamel insulation, but even cut into the copper.
The winding has clearly been mechanically gouged at some time, which has not just stripped the enamel insulation, but even cut into the copper.
I think the toroid was dropped, which caused the shorting of the inner primary winding, which seems to be the root cause here.
Or, the transformer was improperly mounted to the bottom metal plate/overtightened.
Shame... all that copper.
Or, the transformer was improperly mounted to the bottom metal plate/overtightened.
Shame... all that copper.
For reference i have small amp PHONIC MAX 500 to drive small compression drivers and last year listen in low level music amp stop working.I opened checking everything was ok except the TRN there is no ac output voltage take out the trn from amp and check on ac outlet .This think just stop working no internal fuse no short no overheat.Open the windings from primary found nothing suspicious until unwound the secondaries and again nothing wrong but i see some bad manufacturing insulation.
Please see post #32 above. I have NO intention of using the transformer again. It is scrap.
If you mean that transformers without thermal fuse is generally dangerous, thats a different thing.
Pretty sure that its common in DK(EU) to have torroids without thermal fuses.
Kind regards TroelsM
That clear tape is usually mylar and taking one example, 3M #56, it's rated to 130C - so it got REALLY hot!
So does anybody know what torque is recommended for the mounting bolt of a toroidal transformer?