I have not gotten it out in a while but I still have a General Radio 1652B LCR Bridge that always did a pretty decent job measuring parts. It had a 1khz oscillator built in or you could feed your own external source.
Very interesting. I will need to do some experimenting myself, because I didn't expect the results of shorted turns or the double resonance with open turns. Certainly is food for thought. Thanks!
Thanks for this! Valuable info. Also I find it interesting that except for iron powder rod antennas, pre 1970 radios and equipment used very little, if any of these.
Suppose we have some unknown toroids and we want to test if they would be suitable for an RF amp. What would we need to know and how would we test it? I expect we need to know the frequency response up to the associated RF frequency and it's Q. Please help.
This question is a common one with no simple answer. When something is called a toroid we are referring to the shape and not the underlying material which can be many things resulting in a structure with some permeability value and some amount of dissipative loss when wound with wire and excited with an AC voltage. Most people who ask this question have a bunch of unmarked toroids of unknown origin and want to know what value they might have. I would start by winding some reasonable number of turns occupying about 75 to 85% of the core and measure the inductance vs frequency with a low power device such as a network analyzer. This will yield the inductance vs frequency which will be constant at low frequencies and then rise faster than expected as we start to see the effect of the capacitance between turns and the toroid itself and eventually the impedance will rise and the impedance will become capacitive. Most of the time the most useful frequency range is below 1/2 the frequency where the impedance starts to rise faster than expected. Depending on the accuracy of the VNA you might be able measure the Q of the inductance which will give you an idea of how much power will be dissipated in the core. This will allow you to reject many of the cores you are testing. Cores from many manufacturers have some color coatings which may help but the is not 100% reliable for identification. The final result is pretty simple. The heat in the core is the result of a percentage of the loss in the windings that directly heat the core, the efficiency of the core at the driven flux level, the duty cycle of the RF signal, the frequency, and finally the location of where the toroid is mounted. Saturation of the core due to excessive flux is nearly never a problem except at extremely low duty cycles. Also wrapping tape around a core to increase voltage breakdown will increase the heating. Having the ability to excite a device at the correct frequency, voltage level, with the chosen winding wire size etc. is the best way to determine if the sizing is correct. I use a high power amp than can provide a 100% duty cycle for a time of at least 5 minutes to measure the final core heating. A small thermocouple of an IR spot thermometer on a black paint patch will measure the temperature. Also having a notebook of previous measurements will be invaluable. Happy measuring! Larry, W0QE
What kind of powder core do you recommend for medium frequency 50 Khz for high power SMPS application (instead of Ferrite)? Fe-Si, Sendust, or other. Thanks
There is no way I could recommend what core to use without knowing a lot more about your intended design. 50kHz is a pretty low frequency so the typical cores will have permeability of more than 1000. Larry, W0QE
@@w0qe i want to build a large Pulse Transformer and i am thinking to try high saturation flux density (1.6 Tesla) and low permeability FeSiAl powder core with distributed gap instead of gapped Ferrite with high permeability and low saturation flux density.
Hi Larry, Another EXCELLENT video. Thanks for your time and effort to make these available to us. A question. 1) Do you know of a data source regarding the permeability degradation over time? In particular, I am interested in the slugs we have in our vintage receivers in IF and RF cans. Data on degradation over time for various torriotal cores would also be helpful. I am sure that the more heat a core experiences, as in your 3.5KW amp, the quicker the degradation will occur. 73, Glenn WA4AOS DSM Labs.
Glenn, I think the term you are looking for is disaccommodation or maybe dis-accommodation. Doing a search with this term and ferrite brings up several articles. I'm not sure how well this information might apply to old ferrite material as the ferrite material cocktail is ever evolving and is different between manufacturers. Larry
It's not surprising that the shorting turns does not give the same inductance as removing turns in part because shorting the wires, for example T15 to T16, does not mean there is no current in the 16th turn, but rather, less current in the 16 turn.
Lee, I agree with you and this is expected. Also the Q dropped with the shorted turn which was also expected. When designing a tapped coil there are trade offs such as open, shorted or removed turns which need to be made. Hope you enjoy the videos. Larry, W0QE
@@w0qe I thoroughly enjoy your videos. It's so refreshing to watch someone who knows what he is talking about and clearly explains stuff rather than glosses over it. Look forward to more of your videos.
very interesting info, and i agree "when triodes are glowing electrons are flowing"
That took a LOT of work! Thanks! Great reference info to review many times in the future.
I have not gotten it out in a while but I still have a General Radio 1652B LCR Bridge that always did a pretty decent job measuring parts. It had a 1khz oscillator built in or you could feed your own external source.
Very interesting. I will need to do some experimenting myself, because I didn't expect the results of shorted turns or the double resonance with open turns.
Certainly is food for thought. Thanks!
I love these kind of videos. Thank you very much. I love the experimental nature. Helps me build intuition.
Randy,
Thank you and glad you found the video to be useful.
Larry, W0QE
Thanks for this! Valuable info. Also I find it interesting that except for iron powder rod antennas, pre 1970 radios and equipment used very little, if any of these.
Ryan,
Glad you enjoyed the video. Powdered iron cores began appearing around 1970.
Larry, W0QE
What about the cores in computer power supplies? What are those good for?
Is the difference in data from Wheeler calculaton due to excess /or deficiency in the turn to capacitance created in your experiment ?
Suppose we have some unknown toroids and we want to test if they would be suitable for an RF amp.
What would we need to know and how would we test it?
I expect we need to know the frequency response up to the associated RF frequency and it's Q.
Please help.
This question is a common one with no simple answer. When something is called a toroid we are referring to the shape and not the underlying material which can be many things resulting in a structure with some permeability value and some amount of dissipative loss when wound with wire and excited with an AC voltage. Most people who ask this question have a bunch of unmarked toroids of unknown origin and want to know what value they might have. I would start by winding some reasonable number of turns occupying about 75 to 85% of the core and measure the inductance vs frequency with a low power device such as a network analyzer. This will yield the inductance vs frequency which will be constant at low frequencies and then rise faster than expected as we start to see the effect of the capacitance between turns and the toroid itself and eventually the impedance will rise and the impedance will become capacitive. Most of the time the most useful frequency range is below 1/2 the frequency where the impedance starts to rise faster than expected. Depending on the accuracy of the VNA you might be able measure the Q of the inductance which will give you an idea of how much power will be dissipated in the core. This will allow you to reject many of the cores you are testing. Cores from many manufacturers have some color coatings which may help but the is not 100% reliable for identification.
The final result is pretty simple. The heat in the core is the result of a percentage of the loss in the windings that directly heat the core, the efficiency of the core at the driven flux level, the duty cycle of the RF signal, the frequency, and finally the location of where the toroid is mounted. Saturation of the core due to excessive flux is nearly never a problem except at extremely low duty cycles. Also wrapping tape around a core to increase voltage breakdown will increase the heating.
Having the ability to excite a device at the correct frequency, voltage level, with the chosen winding wire size etc. is the best way to determine if the sizing is correct. I use a high power amp than can provide a 100% duty cycle for a time of at least 5 minutes to measure the final core heating. A small thermocouple of an IR spot thermometer on a black paint patch will measure the temperature. Also having a notebook of previous measurements will be invaluable. Happy measuring!
Larry, W0QE
Good video, Larry, but so much information that I will have to look at it several times.
What kind of powder core do you recommend for medium frequency 50 Khz for high power SMPS application (instead of Ferrite)? Fe-Si, Sendust, or other. Thanks
There is no way I could recommend what core to use without knowing a lot more about your intended design. 50kHz is a pretty low frequency so the typical cores will have permeability of more than 1000.
Larry, W0QE
@@w0qe i want to build a large Pulse Transformer and i am thinking to try high saturation flux density (1.6 Tesla) and low permeability FeSiAl powder core with distributed gap instead of gapped Ferrite with high permeability and low saturation flux density.
@@w0qe available permeabilities for FeSiAl powder cores : 14, 26, 60, 75, 90.
@@szekerespista3758 You may know more about this topic than I do so I don't think I would be of much help. Sorry.
Larry, W0QE
@@w0qe Dear Larrry, thank you for your response!
Shows that mathematical models contains lots of compromize...
Real measurements are required if you really want to understand what happens.
Good Job!!
Modelling and real measurements go hand in hand and even if the results are only close there is still a lot to be learned.
Larry, W0QE
The fact that most cores have distributed air gaps, which makes them CRAP transformers, is causing this?????
Hi Larry, Another EXCELLENT video. Thanks for your time and effort to make these available to us.
A question. 1) Do you know of a data source regarding the permeability degradation over time? In particular, I am interested in the slugs we have in our vintage receivers in IF and RF cans. Data on degradation over time for various torriotal cores would also be helpful. I am sure that the more heat a core experiences, as in your 3.5KW amp, the quicker the degradation will occur. 73, Glenn WA4AOS DSM Labs.
Glenn,
I think the term you are looking for is disaccommodation or maybe dis-accommodation. Doing a search with this term and ferrite brings up several articles. I'm not sure how well this information might apply to old ferrite material as the ferrite material cocktail is ever evolving and is different between manufacturers.
Larry
It's not surprising that the shorting turns does not give the same inductance as removing turns in part because shorting the wires, for example T15 to T16, does not mean there is no current in the 16th turn, but rather, less current in the 16 turn.
Lee,
I agree with you and this is expected. Also the Q dropped with the shorted turn which was also expected. When designing a tapped coil there are trade offs such as open, shorted or removed turns which need to be made. Hope you enjoy the videos.
Larry, W0QE
@@w0qe I thoroughly enjoy your videos. It's so refreshing to watch someone who knows what he is talking about and clearly explains stuff rather than glosses over it. Look forward to more of your videos.
Thank you for making this video Larry! I am of course subscribed with notifications turned on and thumbs up! 73 W3GUY
Muy buena informacion