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Question about a flyback's polarity Answered

Hello,


I am confused with this flyback transformer I have.
I have a pulsed DC input on the primary coil (pulses from 0 to 15V) and that creates high voltage in the secondary coil.

When I connect that input in the opposite direction (wrong polarity) I don't get high voltage any more.
The possible explanation for this is that the primary coil has a diode in series with it.

Now, I'm confused by this because I tested if there actually Was a diode in there (by connecting a DC supply and a DC motor, in series with the coil) and the motor always works!
(also tested with a halogen light)

I put the coil in series with the motor to test if there is a diode inside. If there would be one inside, the motor should not work in one of the two cases, when I switch the pins of the primary coil.

So, as the results of the test tell me: there is no diode in series with the primary coil.

could it be possible that there is a diode in parallel with the primary coil?
If that's not possible, how come the flyback is not working when I connect the polarity incorrectly?


Could someone please help me out with this?

Thanks,

Electorials

8 Replies

user
steveastroukBest Answer (author)2011-11-07

There's often a diode in the SECONDARY
Steve

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user
steveastrouk (author)2011-11-08

I don't live on IRC - if you see Lizzyastro on there, try pinging her.

The "instructable" is a work in progress - no pictures.

Steve

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user
steveastrouk (author)2011-11-08

EXACTLY !

Actually, di/Dt= V/L UNTIL THE CORE SATURATES.

Would you like to see my unfinished notes on FLyback action ?

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user
iceng (author)2011-11-08
user
steveastrouk (author)2011-11-08

No we don't because we switch it off pretty quick, or we WILL saturate the core.

Steve

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user
iceng (author)2011-11-07

Still much fun,
But really the varnish on a small pulsed transformer for residential use must dampen mechanical and magnetostrictive events not just quiet but silent..

The varnish does the job and has a low visible acrid stink if burned.that can
permeate a room..  Avoiding this smelly possibility the fly black transformer
is over designed which explains why they are a favorite among hobbyists .

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user
steveastrouk (author)2011-11-07

DC in a transformer will NOT have no effect - it will cause the core to saturate. You MUST NOT have standing current in the transformer.

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user
iceng (author)steveastrouk2011-11-07

Or acrid smoke will rise up and smite thy lodgings.

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