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Harry

Wed Mar 07 2012, 10:58PM

Registered Member #4081 Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139

I was talking to my physics teacher today about flyback transformers, and he said that if there is no load on it, the corona will eat away at the insulation inside the flyback and kill it. Is this true?
Cheers, Harry.

Thomas W

Wed Mar 07 2012, 11:08PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

i would personaly say, it depends on the voltage, current, type of insulaton and such ^^

Pinky's Brain

Wed Mar 07 2012, 11:23PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

The output voltage of a true flyback transformer (a DC flyback in the local lingo) is dependent on the load. So yeah, if you have poor regulation an open circuit load could in theory ruin the transformer (or the primary switch).

Alex M

Thu Mar 08 2012, 01:12AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

True. I have managed to destroy quite a few of them from corona eating away at the insulation when not drawing arcs (loading it).

Shame really as audio modulation sounded much louder when the thing was covered on corona discharge!

Of-course it also depends on if the voltage being produced is enough to break down the insulation, on lower powers the arcs were quite small with a half-bridge becuase of the primary voltage getting halved.

Harry

Thu Mar 08 2012, 07:56PM

Registered Member #4081 Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139

Alex: Yes I remember the video, interesting to note that it was louder with no load. Would that maybe because there is more corona, hence a larger surface area, acting as a larger 'speaker?'
I am yet to destroy a flyback, at the moment I have a ZVS with a 38V transformer, drops to 20V under 9A load though, need bigger filter caps!
Thanks everyone for the replies.

Xray

Sat Mar 10 2012, 04:26AM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Your Physics teacher is absolutely right. Corona is a real flyback killer. Back in my early days of repairing TV's (I won't say how long ago that was!!) I've replaced many flybacks that were burnt to a crisp because of arcing over the surface to ground or between windings. In almost every case that I remember, the transformers had a layer of dust or dirt on them. Dust and dirt are not very good insulators at high voltages, and over time, corona discharge can break down the dust and dirt, which becomes more conductive. Corona is actually quite hot, and we all know that heat can damage electronic components. If the corona continues for some time, eventually the insulating material becomes so conductive that an arc forms, which is essentially a short circuit. But it only takes a millisecond to destroy a flyback from arcing, which is much too quick to be saved by a fuse or circuit breaker.

Some tips to reduce the chance of your flyback becoming a crispy critter:
1. Do not allow the flyback to operate without an electrical load. Without a load, the high voltage may peak so high that it may result in corona discharges over the surface of the flyback.
2. keep the surface of your flyback clean. Never allow it to become dirty or dusty, and of course if it gets wet from condensation or other reasons, thoroughly dry it off before using it.
3. Do not allow your flyback to get excessively hot. Heat can degrade insulation.
4. When mounting your flyback in your project, leave plenty of room between the flyback and other components, and keep a good distance from the metal enclosure if it's mounted in a box or on a chassis.
5. Remember, a flyback is rather fragile. It will perform wonderfully for you for a very long time if you take care of it and are very careful to not do something that will damage it. Even if you make an unintentional mistake that lasts only a split second, it will die very quickly before you can even think about hitting the power switch!

The flyback is your friend. Treat it well, and it will give you many hours of enjoyment! Just be carefull not to get too close to it while its awake because it will bite you!

Steve Conner

Sat Mar 10 2012, 10:57AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Xray wrote ...

The flyback is your friend. Treat it well, and it will give you many hours of enjoyment! Just be carefull not to get too close to it while its awake because it will bite you!

All very good advice but not really in the 4hv tradition!

That's more like: "The flyback is your victim, overdrive it until it catches fire!"

I had a similar experience when experimenting with the ferrite transformer from an electronic NST. I connected it to a halfbridge driver, and when I hit the resonant frequency of the secondary, the surface of the plastic potted coil turned into a mass of corona. Then as I was admiring the beautiful corona effect, it caught fire.

Re the original post, your physics teacher is right. The flyback was designed for a long and happy life supplying its rated voltage and current to a TV tube. TVs use the resistor chain inside the flyback to sense the EHT voltage, and will shut down if it gets too high.

Xray

Sat Mar 10 2012, 05:51PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Steve Conner wrote ...

All very good advice but not really in the 4hv tradition!

That's more like: "The flyback is your victim, overdrive it until it catches fire!"

Ain't that the truth! Some of us aren't happy unless we make huge lightning bolts, giant balls of fire and loud explosions! What a great hobby we have!

Antonio

Sun Mar 11 2012, 01:05PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Flybacks from CRT monitors have a filter capacitor and a bleeder resistor that are already an adequate load. Of course there is a maximum voltage designed for the device, and something will eventually fail if it is exceeded by a large margin.
Anyway, there is no physical reason for a difference in safety of operation with or without load, if the voltage limit is not exceeded.

Harry

Sun Mar 11 2012, 01:09PM

Registered Member #4081 Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139

Thanks everyone for the help, one more question though, what is the rated voltage for a flyback? I remember one monitor had 28kV, 38uA printed on the circuit board.

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