Hi.
After 20+ years of tampering with electronics (and getting an EE), I burned my first torroidial transformer!
The issue is that I dont understand why... The setup is 2 identical transformers with primaries in parrallel and secondaries in series.
Its powering a active subwoofer (300-400W classD and in THAM10).
All voltages check out and the setup was working fine for hours with minimal heat.
After the initial test the sub was stored in the basement for a few months and when I took it out for a test one of the transformers started smoking and melted the insulation within 2 minutes. I tuned off power as soon as I detected the fault.
The other transformer appears to be fine. Pretty sure that there is not an overload from the amplifier.
After removing the transformer, it was clear that it had shifted slightly beacuse the mounting pads had also melted somewhat.
I can understand that heavy vibration and melting mounting pads is an recipe for disaster, but Im not sure on the root cause.
One possibility is that I did not thighten the mounting bolt enough. - or maybe too much? - but Im pretty sure both transformers were mounted OK.
Any ideas? how would you secure a torroidial used in a sub? I´ve seen in commercial subs, so I assume its acceptable.
Kind regards TroelsM
After 20+ years of tampering with electronics (and getting an EE), I burned my first torroidial transformer!
The issue is that I dont understand why... The setup is 2 identical transformers with primaries in parrallel and secondaries in series.
Its powering a active subwoofer (300-400W classD and in THAM10).
All voltages check out and the setup was working fine for hours with minimal heat.
After the initial test the sub was stored in the basement for a few months and when I took it out for a test one of the transformers started smoking and melted the insulation within 2 minutes. I tuned off power as soon as I detected the fault.
The other transformer appears to be fine. Pretty sure that there is not an overload from the amplifier.
After removing the transformer, it was clear that it had shifted slightly beacuse the mounting pads had also melted somewhat.
I can understand that heavy vibration and melting mounting pads is an recipe for disaster, but Im not sure on the root cause.
One possibility is that I did not thighten the mounting bolt enough. - or maybe too much? - but Im pretty sure both transformers were mounted OK.
Any ideas? how would you secure a torroidial used in a sub? I´ve seen in commercial subs, so I assume its acceptable.
Kind regards TroelsM
Had you made a metal path surrounding the transformer core as a shorted turn? Putting it in a metal box with a bolt through the centre and top and bottom is enough to do this.
Davidsrsb can you evolve on the subject how a metal boxing can act as a shorted turn? I assume you mean this could be the reason for overheating?
Things like these happen. After having examined a few I saw inadequate diodes (too low voltage rated, often noticed with Schottky rectifiers) that shorted and/or shorted electrolytic caps that were defective because of that or vice versa. Another one with toroids is a dent shorting windings, does not happen much but it happens. A cracked core is rare but it also happens. Overcurrent, a damaged transformer, a shorted diode/electrolytic cap etc. would have lead to severe overcurrent and a sonical indication that something was wrong. Normally toroids then hum loudly in agony.
As usual insufficient info will not lead to a good root cause analysis. For a good RCA one needs to see pictures, know brand/type and ratings of transformer, rectifier diode type and rating and electrolytic cap brand/type and rating. The appearance of parts is the first diagnosis to do. Then to measure the transformer in deenergized and in energized state but in energized state mandatory with light* fusing or a very light breaker out of the casing. At a distance! If only to exclude things. If the transformer now does not overheat and gives correct voltages the PSU it feeds can be connected and measured. If it then goes wrong the PSU must be examined for low impedance, shorts etc. When the PSU works OK with the transformer energized then the device will need examination. Even when it still works correctly the transformer can be considered a loss as it will not meet its required isolation value anymore and using it wil be a ticking time bomb.
* It is worrying that the transformer started melting in just 2 minutes before the fuse supposed to be protecting it did. In fact the fuse did not blow at all. This is very bad and indicates wrong fusing. What is the value of the transformers fuse? And what is the value of the group breaker?
As usual insufficient info will not lead to a good root cause analysis. For a good RCA one needs to see pictures, know brand/type and ratings of transformer, rectifier diode type and rating and electrolytic cap brand/type and rating. The appearance of parts is the first diagnosis to do. Then to measure the transformer in deenergized and in energized state but in energized state mandatory with light* fusing or a very light breaker out of the casing. At a distance! If only to exclude things. If the transformer now does not overheat and gives correct voltages the PSU it feeds can be connected and measured. If it then goes wrong the PSU must be examined for low impedance, shorts etc. When the PSU works OK with the transformer energized then the device will need examination. Even when it still works correctly the transformer can be considered a loss as it will not meet its required isolation value anymore and using it wil be a ticking time bomb.
* It is worrying that the transformer started melting in just 2 minutes before the fuse supposed to be protecting it did. In fact the fuse did not blow at all. This is very bad and indicates wrong fusing. What is the value of the transformers fuse? And what is the value of the group breaker?
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That would be an amateur fault. FWIW OP is an EE.
This happens when the bolt is mounted unisolated to the chassis and the top mounting plate touching a metal cover. Unlikely as even when mounted normally but sticking out and touching a top cover a technical person would not close the cover and gamble things will be OK. The very minimum is 2 mm free space and only so with a plastic sheet against the top cover preventing shorts. Mounting the toroid through and through both bottom and top cover with conductive materials would make his EE instantly invalid 🙂
But let's assume the shorted turn theory is at place here. Then why did the primary fuse not blow? I will keep my assumptions silent 😀
This happens when the bolt is mounted unisolated to the chassis and the top mounting plate touching a metal cover. Unlikely as even when mounted normally but sticking out and touching a top cover a technical person would not close the cover and gamble things will be OK. The very minimum is 2 mm free space and only so with a plastic sheet against the top cover preventing shorts. Mounting the toroid through and through both bottom and top cover with conductive materials would make his EE instantly invalid 🙂
But let's assume the shorted turn theory is at place here. Then why did the primary fuse not blow? I will keep my assumptions silent 😀
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Thank you for all the input so far.
I´m very confident that there was not a shorted turn on torroid.
The construction is a single metal-plate with a 6mm bolt through. There is no metal cover as its mounted inside a wood enclosure (in the horn-path opening, and therefore a little cooling is provided and I could smell the overheating before it escalated.)
The torroid was delivered with some soft pads that are more "foam-like" than the rubber-discs Im used to. Maybe I implemented those wrong.
I agree that its very strange that no fuses acted.
I havnt done a full autopsy yet, but I assume that PSU-diodes and caps are fine.
I´m asking here to learn. As I never had a transformer fail on me before I assume that I did something wrong here.
If time permits I´ll look more into the failed transformer and confirm that all the other parts are still working.
I assume that there could be a valuable lesson in this 🙂
Will return with some more info.
Kind regards TroelsM
I´m very confident that there was not a shorted turn on torroid.
The construction is a single metal-plate with a 6mm bolt through. There is no metal cover as its mounted inside a wood enclosure (in the horn-path opening, and therefore a little cooling is provided and I could smell the overheating before it escalated.)
The torroid was delivered with some soft pads that are more "foam-like" than the rubber-discs Im used to. Maybe I implemented those wrong.
I agree that its very strange that no fuses acted.
I havnt done a full autopsy yet, but I assume that PSU-diodes and caps are fine.
I´m asking here to learn. As I never had a transformer fail on me before I assume that I did something wrong here.
If time permits I´ll look more into the failed transformer and confirm that all the other parts are still working.
I assume that there could be a valuable lesson in this 🙂
Will return with some more info.
Kind regards TroelsM
Don't assume PSU-diodes and caps are fine. There is a reason that stuff burned. Focus on "overcurrent".
- Are you sure there is a fuse holder with correct rated fuse in it at the primary side?
Oh you will learn no doubt. It would be nice to give the readers and people that advise details so they can learn too. The feedback system works here too, advice only improves with the right amount of feedback. Things that go kaput are most interesting. In many cases one gets confronted with ones own inabilities/lazyness/sloppyness only to be forced to self correct and do it better next time. Then have a laugh and go on.
I once had a one week professional training with an African crew. These guys had a lot of fun between very serious germans. The third day they managed to blow up an expensive machine big time with a loud explosion and then all went elsewhere to sit and laugh. The germans were all extremely serious as the damage was expensive and pretty definitive too. They gathered around the (written off as I understood later) machine with grim looking faces and extensive technical explanations. I went to the African guys and asked why they laughed. They answered that they celebrated no one was hurt.
- Are you sure there is a fuse holder with correct rated fuse in it at the primary side?
Oh you will learn no doubt. It would be nice to give the readers and people that advise details so they can learn too. The feedback system works here too, advice only improves with the right amount of feedback. Things that go kaput are most interesting. In many cases one gets confronted with ones own inabilities/lazyness/sloppyness only to be forced to self correct and do it better next time. Then have a laugh and go on.
I once had a one week professional training with an African crew. These guys had a lot of fun between very serious germans. The third day they managed to blow up an expensive machine big time with a loud explosion and then all went elsewhere to sit and laugh. The germans were all extremely serious as the damage was expensive and pretty definitive too. They gathered around the (written off as I understood later) machine with grim looking faces and extensive technical explanations. I went to the African guys and asked why they laughed. They answered that they celebrated no one was hurt.
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Could the combination of movement, and foam pads instead of rubber, have caused wear through the transformer's insulation and thus a short?
I know one would assume the primary fuse would blow, but I'm just thinking of possibilities. It may be intermittent due to vibration.
I know one would assume the primary fuse would blow, but I'm just thinking of possibilities. It may be intermittent due to vibration.
Not sure why somebody insists on a supply short since according to post 1 the other transformer is not affected.
It will be few hours before I maybe get time to investigate more. Feel free to speculate, but until further testing I wont be able to answer anything, - or verify if the other parts are indeed OK.
My own guess so far is that the transformer was not secured correctly and vibration did the rest (like #9 ). I'm hoping that transformer-autopsy will reveal more.
Kind regards TroelsM
My own guess so far is that the transformer was not secured correctly and vibration did the rest (like #9 ). I'm hoping that transformer-autopsy will reveal more.
Kind regards TroelsM
Why autopsy? Is it that far gone? Did you measure it? The "The setup is 2 identical transformers with primaries in parallel and secondaries in series." keeps attracting attention. With a middle point so symmetric I take and possibly with 2 separate rectifiers? You haven't replied if the thingie has a fuse holder at all and what fuse is used. Not the most difficult question. Give & take.
Vibration during months (and even a loose toroid) will not have a toroid damaged fatally. It is not used on a pile driver is it?! Probably it became so hot in the 2 minutes of severe overcurrent that the plastic melted and it slided because of its weight and the now fluid plastics. Normally toroids have pretty sturdy transparent foil wrapped around their windings and you really have to do something mechanically to damage them.
Good luck with the repair.
Vibration during months (and even a loose toroid) will not have a toroid damaged fatally. It is not used on a pile driver is it?! Probably it became so hot in the 2 minutes of severe overcurrent that the plastic melted and it slided because of its weight and the now fluid plastics. Normally toroids have pretty sturdy transparent foil wrapped around their windings and you really have to do something mechanically to damage them.
Good luck with the repair.
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@jean-paul: believe me, its gone. Totally, very, gone. Pics will follow.
It was not months of vibration. A single party of 5 hours, but at full tilt so pretty violent vibration.
If it was overcurrent due to simple overload, I would have expected both transformers to damaged identically, but the other is (visually) in perfect condition and was not hot. (The connected amplifier is a bridge-design and therefore both transformers are loaded identically at all times, - except of cause in the event of strange faults)
TroelsM
It was not months of vibration. A single party of 5 hours, but at full tilt so pretty violent vibration.
If it was overcurrent due to simple overload, I would have expected both transformers to damaged identically, but the other is (visually) in perfect condition and was not hot. (The connected amplifier is a bridge-design and therefore both transformers are loaded identically at all times, - except of cause in the event of strange faults)
TroelsM
Oh I believe you as you have it in front of you. I don't have schematics, pictures or any useful information so I am driving in the dark for enough of my time. This was not a simple overload as it burned because of severe overcurrent that lasted 2 whole minutes without blowing a fuse.
Busy with another issue, ciao!
Busy with another issue, ciao!
Given the extensive experience of the inestimable TG, I doubt handling during any step of the installation caused the fault.
I suspect a manufacturing defect where the enamel had a pinhole and arced across windings.
Without unwinding the Transformer, how can the fault be assessed?
I suspect a manufacturing defect where the enamel had a pinhole and arced across windings.
Without unwinding the Transformer, how can the fault be assessed?
Guess the bad one....
The measure about the same resistance on windings.
The bad one can withstand 2.5Kv from primary to secondary so that's good. BUT from one secondary to the other it fails at about 250v. That indicates a short to me.
The measure about the same resistance on windings.
The bad one can withstand 2.5Kv from primary to secondary so that's good. BUT from one secondary to the other it fails at about 250v. That indicates a short to me.
You should check for a short with ac, but it will tell you no news, the transfomer is destroyed.
Toroidal types can not be manufactured without wires crossing here and there. If you put undue
force on the surface, using thin rubber etc, the short will happen at a wire crossing insulation.
Mains fuse should have prevented this. The transformer can probably be repaired / rewound.
Toroidal types can not be manufactured without wires crossing here and there. If you put undue
force on the surface, using thin rubber etc, the short will happen at a wire crossing insulation.
Mains fuse should have prevented this. The transformer can probably be repaired / rewound.