Author Topic: Flyback secondary burnout  (Read 183 times)

Offline abstruse1

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Flyback secondary burnout
« on: August 02, 2021, 05:47:02 PM »
I've toasted a few old TV flybacks.  I read recently that they shouldn't be run with an open (infinite resistance) secondary because the voltage gets too high for the insulation.  Is this generally true?

One could put a short spark gap or a high voltage resistor across the secondary output.  The resistor might be preferable, except that it would be a drag on the output voltage all the time, not just when a spark gap was sparking.  What does anyone suggest?  If I used a HV resistor, roughly what resistance?  I have several 240k and up from there.

Another idea would be to use a MOT instead of a flyback. Maybe two MOTs could be run in series to get enough voltage?

Than, guys.
Abstruse1
   Been working with electicity for 60 years and still getting
      shocked!

Offline johnnyzoo

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Re: Flyback secondary burnout
« Reply #1 on: August 03, 2021, 06:31:34 PM »
I've toasted a few old TV flybacks.  I read recently that they shouldn't be run with an open (infinite resistance) secondary because the voltage gets too high for the insulation.  Is this generally true?

One could put a short spark gap or a high voltage resistor across the secondary output.  The resistor might be preferable, except that it would be a drag on the output voltage all the time, not just when a spark gap was sparking.  What does anyone suggest?  If I used a HV resistor, roughly what resistance?  I have several 240k and up from there.

Another idea would be to use a MOT instead of a flyback. Maybe two MOTs could be run in series to get enough voltage?

Than, guys.

I'm not sure about TV/CRT transformers specifically, but in general, it is true that transformers operated in a flyback type of converter (1) or in certain resonant converters may be damaged if they are operated without load.

Which is better, spark gap or resistor, depends on your application. A resistor will dissipate some power all the time. A spark gap will only fire when the voltage gets high enough, but then it will appear almost like a short circuit.


Whether using microwave oven transformers is a good solution also depends on your application. Using them in series is not impossible but it requires great care. Note that the other end of the high voltage winding is usually connected to the transformer chassis. The frequency is low compared to flybacks (50 Hz vs some ... tens of kHz) and you will get around 2 kV from one microwave oven transformer. And perhaps most importantly, a microwave oven transformer can produce a deadly amount of current at a very dangerous frequency if you get a shock from it. TV/CRT flyback transformers are safer, although you should always avoid getting a shock. Maintain distance, use insulated stick, stands etc, and keep your work area clean.



1) Storing energy in the magnetic field and releasing it; TV transformers are operated this way in their normal application. Basic mechanical and transistor-based ignition coil circuits also work this way. But not all "flyback drivers" used by hobbyists operate in flyback mode - some of them may operate like ordinary transformers, others may be resonant.
« Last Edit: August 03, 2021, 07:25:30 PM by johnnyzoo »

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Re: Flyback secondary burnout
« Reply #1 on: August 03, 2021, 06:31:34 PM »

 


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