Greetings everyone.
This is not my first time I wound transformers, but the following I have never seen before.
I have two SE tranys I wound, core is 25 cm sq, measuring with a nice handheld impedance meter at 120Hz and 1000Hz.
One of them is 23H at 120Hz and 20H at 1000Hz, leakage inductance is about 20mH at both frequencies, C primary/secondary 4100 - 3600 pF.
For the other trany, 22H at 120Hz and 10H at 1000Hz, leakage is the same as above, so is C.
Does anyone have an idea on those phenomena?
Thank you,
Andre
This is not my first time I wound transformers, but the following I have never seen before.
I have two SE tranys I wound, core is 25 cm sq, measuring with a nice handheld impedance meter at 120Hz and 1000Hz.
One of them is 23H at 120Hz and 20H at 1000Hz, leakage inductance is about 20mH at both frequencies, C primary/secondary 4100 - 3600 pF.
For the other trany, 22H at 120Hz and 10H at 1000Hz, leakage is the same as above, so is C.
Does anyone have an idea on those phenomena?
Thank you,
Andre
Sometimes impedance meters are not so nice when measuring complex impedance like transformers ... a small difference between the two could trigger a big reading error .
The measurements were done several times, different days, with the same results.
Sorry, the impedance meter is universal, was used for inductance measurments and capacitance, appropriatlely.
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Inductance should drop with rising frequency in a practical iron core inductor:
if it doesn't a primary suspect could be a resonance;
e.g. the inter winding capacitance (not the pri-sec) could form a tank circuit with the inductance;
if you happen to measure impedance close to that resonance frequency, you may be further up or down on the slope of that resonance curve;
20H / 1nF happen to resonate around 1125Hz ...
if it doesn't a primary suspect could be a resonance;
e.g. the inter winding capacitance (not the pri-sec) could form a tank circuit with the inductance;
if you happen to measure impedance close to that resonance frequency, you may be further up or down on the slope of that resonance curve;
20H / 1nF happen to resonate around 1125Hz ...
Tested both transformers (function generator, scope), flat from 10Hz to 40kHz.
Thank you,
Andre
This may be the stupidest idea yet, but can you reasonably easily swap the bobbins from one core to the other and see if the problem stays with the core or the bobbin? (And what is the inductance at 10kHz?)
If you measured frequency response with a low impedance generator connected to the primary, the primary self-capacitance is effectively shunted and will have no significant effect anymore.
To see real frequency response the source impedance should equal the ra of the tube.
Also handheld L-meters measure apparent (not real) inductance.
Apparent inductance heavily varies in the vicinity of the parallel resonance.
Generally L measurements at low frequency are much more reliable.
I assume the transformers have somewhat different primary self-capacitance.
To see real frequency response the source impedance should equal the ra of the tube.
Also handheld L-meters measure apparent (not real) inductance.
Apparent inductance heavily varies in the vicinity of the parallel resonance.
Generally L measurements at low frequency are much more reliable.
I assume the transformers have somewhat different primary self-capacitance.
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That was the first think I did, it follows the bobbin.
I will test the inductance at 10kHz, I also will do the miandre sweep, to see what it looks like.
Thanks Kevin.
" the primary self-capacitance is effectively shunted and will have no significant effect anymore."
I am aware of that, any difference should be visible, or not?
I've done tenths of curious measurements with different 1kHz LCRs. They all measured funny, and differently from one another. Only low-HF core loss, such as nanocrystalline and mu-metal would score close. With HiB, even a slight core between bobbin movement could wreck the value to a funny thing. With a cored transformer, overlooked details such as impedance load, secondary load, core losses, complex HF bandwidth can lead to confusing values of... things.
Rely on low-frequency, high voltage measurement of inductance in order to excite the core until a practical value.
Rely on low-frequency, high voltage measurement of inductance in order to excite the core until a practical value.
L-meters measure and analyse either impedance (in series mode) or admittance (in parallel mode).
They calculate L from the reactive part (using a simple 2-component model) assuming it's all due to inductance.
When there's capacitance as well, reactance is composed of L and C.
The meter interprets the mixture of L and C as (apparent) inductance.
In the vicinity of a resonance apparent inductance strongly varies with capacitance.
At low frequencies (i.e. far below the resonance) the capacitive impedance is large and thus has little influence on apparent inductance.
Above the resonance reactance gets capacitive and apparent inductance is meaningless.
Rikaro, I understand LCR handhelds are not reliable for the real measurements, but for comparing they should be OK, specially when they were done several times between two transformers (wound the same by myself), swapping the irons, with the same results staying with the bobbin.
Look in the first post for the measurements, L at 120Hz, C, Freq response, etc., all the same for both trafos,except L at 1kHz.
Look in the first post for the measurements, L at 120Hz, C, Freq response, etc., all the same for both trafos,except L at 1kHz.
You did something slightly different that is disturbing the meter ... maybe more capacitance in parallel with the primary
As I said these are not made to measure transformers
As I said these are not made to measure transformers
@AndreK :
Seems you're not getting my point.
What I was trying to explain is that your winds propably have somewhat different primary self-capacitance.
Even a capacitance difference of only 10% can have a huge impact on apparent inductance @ 1kHz when the primary resonance is around 1kHz.
Your primary winding capacitance is probably around 1000p.
I'm not speaking of primary to secondary capacitance, which doesn't have much effect.
Measuring inductance at 10kHz makes even less sense.
For comparison you should use your meter only at 100Hz as this gives a reading close to real (but small signal) inductance.
Seems you're not getting my point.
What I was trying to explain is that your winds propably have somewhat different primary self-capacitance.
Even a capacitance difference of only 10% can have a huge impact on apparent inductance @ 1kHz when the primary resonance is around 1kHz.
Your primary winding capacitance is probably around 1000p.
I'm not speaking of primary to secondary capacitance, which doesn't have much effect.
Measuring inductance at 10kHz makes even less sense.
For comparison you should use your meter only at 100Hz as this gives a reading close to real (but small signal) inductance.
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