Author Topic: Help with primary voltages of unknown transformer  (Read 370 times)

Offline Domo

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Help with primary voltages of unknown transformer
« on: May 13, 2024, 08:43:49 PM »
New to this forum, first post..

I pulled out a flyback transformer from projection TV, and I need help identifying what voltages goes to primary coil. HRDiemen does not have information on this transformer.

Also, pinout would be helpful, but I can settle for voltages if needed.

KFT7AQ051F

(not sure if my attachments will work)
https://drive.google.com/file/d/17r3Sxf2m9pkX77Fn7CH4DWjK7ddPhhpX/view?usp=sharing
https://drive.google.com/file/d/17npglFyROAEjC1xSi3-EkZHn9ViZtKTQ/view?usp=sharing
https://drive.google.com/file/d/17aCCi1XIdt-FW5ezWhzsvoczU1-oWwfK/view?usp=sharing
https://drive.google.com/file/d/17U6lslrG2gnTbk9Tj52BKuQgaI2ZLbtc/view?usp=sharing


« Last Edit: May 13, 2024, 09:05:23 PM by Domo »

Offline alan sailer

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Re: Help with primary voltages of unknown transformer
« Reply #1 on: May 13, 2024, 09:06:59 PM »
A quick Google search shows a dozen or more tutorials on how to identify the primary as well as the secondary
terminals.

https://www.instructables.com/How-to-find-the-primary-and-the-secondary-coils-of/

Harness your google-fu powers and grab that voltmeter...

Cheers.

Offline Domo

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Re: Help with primary voltages of unknown transformer
« Reply #2 on: May 13, 2024, 09:27:58 PM »
Thank you for quick reply.. i can find primary and secondary pins, but I would like to know what B+ voltages are in primary. HRDiemen would specify input voltages on their schematics (90, 170), and I do not want to put too much power into it and fry it.

As for the pinout, i would like to know what others pins do, but its not  important.

Offline alan sailer

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Re: Help with primary voltages of unknown transformer
« Reply #3 on: May 13, 2024, 10:20:19 PM »
I don't  know flybacks to that level of detail. I am assuming you are wanting to make this
into a HV project and not use it in it's original circuit.

If this is true then you drive voltages and waveforms will probably differ from what the
unit was originally driven at. The most important (in my mind) spec on such transformers
 is what voltage they were designed to generate. And without knowing anything about the original
circuit that is pretty impossible to know.

Good luck.

Cheers.

Offline Domo

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Re: Help with primary voltages of unknown transformer
« Reply #4 on: May 13, 2024, 10:28:34 PM »
For example, (and its not on all schematics)
https://www.hrdiemen.com/reparation/flyback/scheme/80121

MAT is HV output in KV.
TYPE is pulsed DC input (not always numerical)
+ is B+ voltage input, aka primary
COL is primary to switch (mosfet, BJT, IBGT, and so on)

I would like to get full potential out of that transformer without frying it. I can start with 90V on primary, but I do not know how much more voltage it can handle.. Heck, I can rectify 120VAC to 170VDC and use that, but I dont want to see smoke..


Offline alan sailer

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Re: Help with primary voltages of unknown transformer
« Reply #5 on: May 13, 2024, 11:44:56 PM »
I do understand what you are asking for.

Good Luck.

Cheers.

Offline klugesmith

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Re: Help with primary voltages of unknown transformer
« Reply #6 on: May 14, 2024, 09:02:28 PM »
At its original design frequency, the flyback voltage is probably limited predictably and softly by core saturation & heating rather than by HV insulation.
   
Is it reasonable to expect that the projection TV "lamps" were operated at NTSC or PAL horizontal scan frequencies?
Then you could start by operating at, say, half that frequency.  That would halve the voltage toleration of core.
See how far you can turn up the primary voltage, while monitoring the magnetizing current.  Onset of saturation is indicated by nonlinear increase, appearing like a hockey stick in a chart of I vs V.
With that same core-magnetization operating point, as you increase frequency you can increase the voltage in direct proportion (while the core heating goes  up in proportion to frequency).
 

Offline Domo

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Re: Help with primary voltages of unknown transformer
« Reply #7 on: May 15, 2024, 05:38:14 AM »
This flyback transformer was taken out of US TV, so I am assuming NTSC frequencies (15.7 kHz).
This was a projection TV, thats why there are 3 outputs, as they were connected to small version of CRT that would project onto a internal screen.
What worries me, is that those small CRT's prolly didn't need 30 kV, so the input wouldn't have to be 170 VDC pulsed.. maybe it was 90VDC.. i do not know, and that's what I would like to know before frying it.
I can start with 90VDC, but I have no way of measuring the output, so I don't know if the output will be 20kV or 30kV..

 

Then you could start by operating at, say, half that frequency.  That would halve the voltage toleration of core.
as you increase frequency you can increase the voltage in direct proportion (while the core heating goes  up in proportion to frequency).
 

If I use lower frequency, won't that cause current to skyrocket? Wont that cause core to saturate quickly?

Offline klugesmith

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Re: Help with primary voltages of unknown transformer
« Reply #8 on: May 15, 2024, 10:58:05 PM »
>> If I use lower frequency, won't that cause current to skyrocket? Wont that cause core to saturate quickly?

The low frequency suggestion was based on having a continuously adjustable input voltage source, and ability to measure input current.
Start at half frequency and much less than half of intended input voltage.

It sounds like your transformer is precious, and you don't want to blow it up.
Without documentation, do you want to depend on trial and error and luck, and knowledge of strangers on the internet?
Is it too much trouble to do progressive experiments like the one suggested, to learn the component's maximum volts-per-hertz without stressing the insulation?

[edit] The approach-to-saturation experiment could also be done with a fixed low-ish input voltage (e.g. 24 V or 48 V) and variable frequency.
Start with NTSC frequency, which ought to be pretty safe.    Then ramp the frequency _down_ and see how far you can go before signs of core saturation.  At that point you have a volts-per-hertz value which is known to be OK for transformer, and would tell you the minimum frequency for working at 90V or 170V.
« Last Edit: May 16, 2024, 12:15:34 AM by klugesmith »

Offline Domo

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Re: Help with primary voltages of unknown transformer
« Reply #9 on: May 16, 2024, 06:58:12 AM »
[edit]
Quote
The approach-to-saturation experiment could also be done with a fixed low-ish input voltage (e.g. 24 V or 48 V) and variable frequency.
Start with NTSC frequency, which ought to be pretty safe.    Then ramp the frequency _down_ and see how far you can go before signs of core saturation.  At that point you have a volts-per-hertz value which is known to be OK for transformer, and would tell you the minimum frequency for working at 90V or 170V.

You have answered what I needed to know.. Excellent idea, and I appreciate your knowledge..
This flyback has triple output, so it is kinda rare for me.. I have some regular TV flybacks, but only 1 triple.
« Last Edit: May 18, 2024, 09:28:49 PM by Domo »

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Re: Help with primary voltages of unknown transformer
« Reply #9 on: May 16, 2024, 06:58:12 AM »

 


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