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Broken Flyback

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Franky

Tue Jan 27 2009, 03:02PM

Registered Member #1940 Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34

I have a question about my flyback.
I was doing some test with high frequencies and I noticed that at some point the spark becomes very weak. I didnâ€™t understand it so I let the flyback run at the high frequencies for some time. But now my flyback is broken. It produces a very little spark and it consumes a lot of power. The output is very very weak. The whole flyback wonâ€™t work anymore. What happened inside my flyback? Is there a way to repair it. It is my only flyback

Here is a picture of my flyback
473956477 6 Lp B

KLH

Tue Jan 27 2009, 03:08PM

Registered Member #1819 Joined: Thu Nov 20 2008, 04:05PM
Location:
Posts: 137

You should test your windings with a multimeter to see if they are shorted or open. Also look for melted parts or cracks in the core.

If you overheated the core past its Curie point (anywhere from 100 to 500 deg. C depending on the material) then it is absolutely useless; once a core is heated past its Curie point, it is no longer useful as a permeable material.

Franky

Tue Jan 27 2009, 03:19PM

Registered Member #1940 Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34

Primary windings are OK. Secondary has a resistance of 400 Ohm.
There are no cracks in the core. It never reached high temperatures. When I'm testing, I always check the temperature of everything. The flyback was always cold.

On low frequenties, the flyback still makes noises.

Plasma Lover

Tue Jan 27 2009, 04:40PM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

My advice is - smash it with a hammer until you get the core out then wind your own secondary with (around) 28AWG magnet wire with a layer of insulation between each winding layer. The first layer has to be insulated with something, and I advise a few layers of either mailing or electrical tape. I'd go for around 1000 turns, then wind a new primary (or use the one you've got) then pot it in either oil or wax (was is cleaner) and, if using wax, make sure it stays warm for a long time after the transformer is dropped in, or else you'll have bubbles in the transformer's core.

I'm sure you don't want to take apart your flyback, but it's pretty much useless, now.

You can drive the new core with the same setup as you used before.

Edit - Okay, maybe i got bit excited. Don't smash it with a hammer. That would be reckless. I agree with rp181 that putting it in a pot of boiling water would be safer. But would it be as much fun? Heck no!

At least with rp181's method, you're left with a whole core and not bits and pieces that are useless...

rp181

Tue Jan 27 2009, 04:52PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

don't smash it. Just put it in a pot of boiling water, and pull the core apart.
The outside could be cold, but the inside of the windings burned. Test if the output of the driver s good, and if thats fine, its the core thats the problem. What frequency are you using?
EDIT: What's your power supply? it might not be sourcing enough current.

Dr. Dark Current

Tue Jan 27 2009, 05:53PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Have you tried exchanging the transistor in that 'electric heater' circuit? If it stopped working, it is 90% chance that your transistor let out the magic smoke.

Edit: From the picture it seemed you use the single transistor driver. If you use another one, sorry for calling it electric heater, but the transistor might be dead as well

Antonio

Tue Jan 27 2009, 06:46PM

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

A normal single transistor flyback driver does not get very hot. If this huge heat sink is really necessary, something is wrong with the circuit. The transistor may be operating with insufficient base current (or gate voltage) to really act as a switch, or may be dissipating most of the energy that should go to the output, due to insufficient voltage rating or lack of a proper snubber circuit. Operation at high frequency increases the switching losses too. Verify if the transistor is good.

Franky

Tue Jan 27 2009, 07:06PM

Registered Member #1940 Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34

I'm using the following circuit with some modifications. Iâ€™m using an IRF250 and 35V on the flyback.

The circuit is not broken. Everything works fine.

I have tested the circuit with an ignition coil from a moped. This works fine for some minutes. Then the ignition coil is overheated

edit:
The power supply is not the problem. I have run this circuit with this flyback, without any problems.

Franky

Tue Jan 27 2009, 07:21PM

Registered Member #1940 Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34

I donâ€™t know what frequency Iâ€™m using. The frequency is higher than 20 kHz.
That heat sink is necessary. After 15 minutes it is so hot that I needed a fan. The heat sink also cools my rectifier.

Here is an old video of this circuit. Sounds not to bad.

Franky

Wed Jan 28 2009, 04:45PM

Registered Member #1940 Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34

So, is there something wrong with this circuit?
Because I need such a huge heat sink?
(The flyback is dead. End of that story/question)

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