Transformer Ringback testers

[johnfin]

When I use my flyback tester on a power transformer I can only get a reading on the primary side on all transformers I know that are good. Wonder if thats typical. So, is a good test of a transformer when you put a square wave thru it with a function generator and it comes out on the secondary side?

[Andrew F. Ali]

Re: Transformer Ringback testers

Putting in a square wave may burn the Primary.

[johnfin]

Re: Transformer Ringback testers

I thought SMPS use a high freq. pulse on the primary side. How would it blow the transformer out?

[stj]

Re: Transformer Ringback testers

it wont, the current on a "ringer" is limited to about 30ma usually.
the reason you cant test the secondary is because it does not have enough windings to create an "echo"

is yours based on the dick smith design, or something else??

[johnfin]

Re: Transformer Ringback testers

I was going to build that one but then I realized I could use my function generator and oscilloscope. They basically do the same thing, right?

[stj]

Re: Transformer Ringback testers

creating a pulse and counting the reflections - that;s about it.

[redwire]

Re: Transformer Ringback testers

Mains power transformers are steel-core and flyback transformers are ferrite-core with air-gap. The two core materials have different properties, mainly ringing frequency. Very good detailed article about testing them here:
https://www.repairfaq.org/sam/flytest.htm

The Anatek Blue Flyback Tester applies a narrow pulse (guess 15mA) and then counts rings.

[stj]

Re: Transformer Ringback testers

that's a licensed design, the schems are available to build your own.

[redwire]

Re: Transformer Ringback testers

That kit manual has the schematics, might be worth picking one up.

Few of us are testing TV flyback transformers nowadays.

I remember this thread, that shorted standby transformer could have been found sooner: https://www.badcaps.net/forum/showth...t=59625&page=6

Maybe these transformer testers need to make a comeback?

[eccerr0r]

Re: Transformer Ringback testers

I wonder if the AVR in avrtester is fast and sensitive enough to be a ring tester if you hook up a capacitor in parallel to an inductor before testing...

And I have a Sencore and it ruled out the "flyback" when I was debugging my scope...

[stj]

Re: Transformer Ringback testers

the AVR project doesnt really have enough memory left for more tricks!

[johnfin]

Re: Transformer Ringback testers

The point is, most of us with scopes have a function generator, mine is a $5 home brew, so with those tools is a ringtester a waste of money?

[stj]

Re: Transformer Ringback testers

maybe,
parts cost is about the same as a beer.
it depends if you want a compact device you can throw in the drawer.

[eccerr0r]

Re: Transformer Ringback testers

Can you really use the function generator, I'd think you'd need an open collector/open drain pulse/square generator to do this test because the impedance of the function generator would also damp out the rings...

[johnfin]

Re: Transformer Ringback testers

https://youtu.be/x6mTnWbbmPg

[redwire]

Re: Transformer Ringback testers

Like a guitar string, you pluck it and listen to the note decay.

I don't think you can use a signal generator - they are push-pull output and never unload the coil to let it ring and decay. Unless you add a series diode to the sig gen output.
A narrow pulse from open-collector transistor is what I see used. Same used in that youtube video but he doesn't mention it.

The question of in-circuit testing... for a SMPS, if you excite the core below where the output rectifier diodes turn on, should be able to see the ringing.