I stumbled upon your video while looking for something else, and I'm glad I did. I had no idea that the inrush could be so high. I'm just about to start building a +/- 12v PSU and was searching for information about what fuse to use, but it looks as if I might need something to protect the fuse from blowing at initial switch-on. Thanks for an informative video of the problem.
The peak value of magnetizing inrush current really depends upon the load and instantaneous input power factor of the transformer, lower the input power factor higher would be the inrush peak. For transformers under no load, the input power factor is a known value and so special instantaneous switching is done on input voltage to completely eliminate the magnetizing inrush current peak.
From a traditional EE project standpoint, you should really have an AC high voltage safety disclaimer in the video text, or at least state the dangers of electrocution and potential damage to test equipment when using a non-isolated "plug it into the wall" demo. This would also be a good time to discuss the importance of an isolated (power and grounds) AC power supply. I think many engineers working on the bench recognize two basic categories of adjustable isolated AC power supplies. The first category is engineering test and the second field repairs. For doing equipment repair and troubleshooting on US rated mains equipment, the design of the AC isolated adjustable power supply is well understood and many repair technicians and engineers have either modified an existing model or made their own, in that, amongst many other features, is the option of isolating the earth ground from the equipment under test and the supply housing (chassis). This is easily done from a metal chassis by using isolated ground receptacles (usually in the US either Red or Orange in color) and, many times, having the earth ground open, either all the time or with a switchable option. The AC isolated adjustable supply used for engineering test will not have the ground isolated (for obvious safety reasons), but will have many other features for testing (which usually includes power line disturbances) in the context of proper operation and prequalification (PF, brown outs, drop outs, etc.) and it usually can support automated test, which is helpful for batch qualification. Features also include being able to start the AC waveform at any point in the AC cycle when you enable the output, with the start of the waveform usually denoted by 0 degrees representing voltage zero cross for the increasing first half sine (really sine for the mathematicians and cosine for EEs ) wave as referenced to, in the US, Hot (Line, Black) and Neutral (Return, white). This is especially handy in teaching transformer magnetization current in-rush, which if you go through the vector calculus, will, based on idealized component models, have a maximum magnetization current at the voltage zero cross point, but start the voltage waveform at 270 degrees (90 degrees prior) where the flux linkage is at zero, which is the result you see in the video. Essentially, what AC engineering supply provides is a repeatable worse case test (because with a common power switch you are randomly enabling power and might not always get the worse case in rush in a repeatable fashion) to fine tune the soft start circuit, or sizing or the Thermistor as discussed by Eddie in the video. By looking at inrush you can also explore the differences in transformer design, like an E core versus a Toroidal. The Toroidal transformer has a lot of advantages, unfortunately it also has more inrush as compared to an E core. So the Toroidal transformer is a good choice to explore transformer in-rush (magnetization) current.
That is such a great input! That is very true, but I feel that happens sometimes when the magnetics are not designed correctly, or the wrong time delay is grossly misjudged. Thank you for this great comment!!
@@KissAnalog Its because of the disorderliness of the magnetic moments of atoms in the core material of the transformer. During a fresh start, the transformer has to draw some extra current to put those moments in sync. This current can be seen as an exponentially decaying current added to the time shifted sinusoidal current flowing in the transformer...
Ok I’ll do a video on this. This might help. And thank you for your feedback! How thermistor protects your power supply th-cam.com/video/-HDpkn8JT_0/w-d-xo.html
Jerry Moats Thank you, and I’m sorry - I have been delayed. At request, I did start a parallel series that yo can find here. It breaks this subject up a bit different and in small steps. I will release the next in this series Monday/Tuesday. Thanks for the reminder - and 5hank you for the reminder;). th-cam.com/video/zTI7ArPs-FM/w-d-xo.html
THANKS. I DO HAVE ANOTHER QUESTION. I HAVE A TRIPP LITE PR 60 POWER SUPPLY THAT INTERMITTENTLY WILL TRIP MY 20 AMP AC BREAKER IN MY PANEL BOX WHEN I POWER ON THE POWER SUPPLY. I SUSPECT IN-RUSH CURRENT TO BE THE PROBLEM. I AM GOING TO INSTALL AN IN-RUSH CURRENT LIMITER ( THERMISTOR) IN SERIES WITH THE AC SUPPLY COMING INTO THE POWER SUPPLY. MY QUESTION IS IF THIS SOLVES MY PROBLEM THEN WHY DID THE MANUFACTURE NOT INSTALL ONE AT THE FACTORY. THANKS AND GREAT VIDEOS.
WOW!!! Thanks, I feel like a celebrity now!!. Thanks for taking the time to do the video. The device in question at the AC input is the power switch with a neon light in the switch. Yes, you are correct that the power supply has a massive power transformer ( very heavy power supply ). my only other question is does it really matter where I install the thermistor in the ac line ( I would certainly think in series with the hot ac line right after the power switch). Thanks again for taking the time to do the video. Keep them coming. Jerrry
Jerry, I’m not sure that you got my answer regarding the placement of the thermistor... I think as long. It is in series with the primary winding, line or neutral you are ok.
Great video. I see the current is represented as decaying positive pulse train rather than a damped sinusoidal waveform. Is this a limitation of the measurement made?
Hi there, I have a real time problem with an irrigation controller experiencing current surge while a 7 hp pump being shut down. I have a video recorded, could you please help me with that.
VERY INTERESTING
Alice Kichlu thank you!
Finally after more than 30 years I understand why my first power supply blow the fuse, the very first time I turned on.
Thank you
Thank you!
Just finished an undergraduate in EE. Glad to have your videos, explanation with actual components is always better than drawings or photos.
Congrats!! I hope to have more engineering stuff up as time goes by;) What’s your preference; digital, analog, or firmware?
Really good demonstration - thanks for sharing.
You bet! Thanks for your feedback
I stumbled upon your video while looking for something else, and I'm glad I did. I had no idea that the inrush could be so high. I'm just about to start building a +/- 12v PSU and was searching for information about what fuse to use, but it looks as if I might need something to protect the fuse from blowing at initial switch-on.
Thanks for an informative video of the problem.
Thanks so much for your feedback! Let me know if you have any questions...
Hi Eddie, Awesome information. Thank you for this great video.
Thanks - I appreciate you!
Thanks, very useful video!!!
You bet Alvina! Thank you for this! If you have a request for particular information, let me know. I appreciate you!
The peak value of magnetizing inrush current really depends upon the load and instantaneous input power factor of the transformer, lower the input power factor higher would be the inrush peak.
For transformers under no load, the input power factor is a known value and so special instantaneous switching is done on input voltage to completely eliminate the magnetizing inrush current peak.
Semper Fidelis Thanks for sharing your knowledge! I hope to hear more!
Great teacher
Thanks so much!! I appreciate you!
From a traditional EE project standpoint, you should really have an AC high voltage safety disclaimer in the video text, or at least state the dangers of electrocution and potential damage to test equipment when using a non-isolated "plug it into the wall" demo. This would also be a good time to discuss the importance of an isolated (power and grounds) AC power supply.
I think many engineers working on the bench recognize two basic categories of adjustable isolated AC power supplies. The first category is engineering test and the second field repairs. For doing equipment repair and troubleshooting on US rated mains equipment, the design of the AC isolated adjustable power supply is well understood and many repair technicians and engineers have either modified an existing model or made their own, in that, amongst many other features, is the option of isolating the earth ground from the equipment under test and the supply housing (chassis). This is easily done from a metal chassis by using isolated ground receptacles (usually in the US either Red or Orange in color) and, many times, having the earth ground open, either all the time or with a switchable option.
The AC isolated adjustable supply used for engineering test will not have the ground isolated (for obvious safety reasons), but will have many other features for testing (which usually includes power line disturbances) in the context of proper operation and prequalification (PF, brown outs, drop outs, etc.) and it usually can support automated test, which is helpful for batch qualification. Features also include being able to start the AC waveform at any point in the AC cycle when you enable the output, with the start of the waveform usually denoted by 0 degrees representing voltage zero cross for the increasing first half sine (really sine for the mathematicians and cosine for EEs ) wave as referenced to, in the US, Hot (Line, Black) and Neutral (Return, white). This is especially handy in teaching transformer magnetization current in-rush, which if you go through the vector calculus, will, based on idealized component models, have a maximum magnetization current at the voltage zero cross point, but start the voltage waveform at 270 degrees (90 degrees prior) where the flux linkage is at zero, which is the result you see in the video. Essentially, what AC engineering supply provides is a repeatable worse case test (because with a common power switch you are randomly enabling power and might not always get the worse case in rush in a repeatable fashion) to fine tune the soft start circuit, or sizing or the Thermistor as discussed by Eddie in the video.
By looking at inrush you can also explore the differences in transformer design, like an E core versus a Toroidal. The Toroidal transformer has a lot of advantages, unfortunately it also has more inrush as compared to an E core. So the Toroidal transformer is a good choice to explore transformer in-rush (magnetization) current.
In power transformers, the magnetizing inrush current (switching transient) is so high that it sometimes trips the differential overcurrent relay..
That is such a great input! That is very true, but I feel that happens sometimes when the magnetics are not designed correctly, or the wrong time delay is grossly misjudged. Thank you for this great comment!!
@@KissAnalog Its because of the disorderliness of the magnetic moments of atoms in the core material of the transformer. During a fresh start, the transformer has to draw some extra current to put those moments in sync. This current can be seen as an exponentially decaying current added to the time shifted sinusoidal current flowing in the transformer...
pls show how to make slow start,, anti inrush circuit
Ok I’ll do a video on this. This might help. And thank you for your feedback! How thermistor protects your power supply th-cam.com/video/-HDpkn8JT_0/w-d-xo.html
GREAT VIDEO. I CAN'T FIND THE FOLLOW UP VIDEO TO THIS ONE. THANKS
Jerry Moats Thank you, and I’m sorry - I have been delayed. At request, I did start a parallel series that yo can find here. It breaks this subject up a bit different and in small steps. I will release the next in this series Monday/Tuesday. Thanks for the reminder - and 5hank you for the reminder;). th-cam.com/video/zTI7ArPs-FM/w-d-xo.html
THANKS. I DO HAVE ANOTHER QUESTION. I HAVE A TRIPP LITE PR 60 POWER SUPPLY THAT INTERMITTENTLY WILL TRIP MY 20 AMP AC BREAKER IN MY PANEL BOX WHEN I POWER ON THE POWER SUPPLY. I SUSPECT IN-RUSH CURRENT TO BE THE PROBLEM. I AM GOING TO INSTALL AN IN-RUSH CURRENT LIMITER ( THERMISTOR) IN SERIES WITH THE AC SUPPLY COMING INTO THE POWER SUPPLY. MY QUESTION IS IF THIS SOLVES MY PROBLEM THEN WHY DID THE MANUFACTURE NOT INSTALL ONE AT THE FACTORY. THANKS AND GREAT VIDEOS.
Here you go...,
th-cam.com/video/E4-Uss4zUq8/w-d-xo.html
WOW!!! Thanks, I feel like a celebrity now!!. Thanks for taking the time to do the video. The device in question at the AC input is the power switch with a neon light in the switch. Yes, you are correct that the power supply has a massive power transformer ( very heavy power supply ). my only other question is does it really matter where I install the thermistor in the ac line ( I would certainly think in series with the hot ac line right after the power switch). Thanks again for taking the time to do the video. Keep them coming. Jerrry
Jerry, I’m not sure that you got my answer regarding the placement of the thermistor... I think as long. It is in series with the primary winding, line or neutral you are ok.
Great video. I see the current is represented as decaying positive pulse train rather than a damped sinusoidal waveform. Is this a limitation of the measurement made?
I'm going to redo this in my video for the Class A amplifier project ok? Thanks for asking - fantastic question and insight!
like you setup
Thank you!
Hi there, I have a real time problem with an irrigation controller experiencing current surge while a 7 hp pump being shut down. I have a video recorded, could you please help me with that.
Richie SHAO You bet - I’m on the road but will have time now and again.
@@KissAnalog can I email you?
+Richie SHAO You bet!
KissAnalog@gmail.com
Did you email me?
Seeing americans using wago's instead of those stupid wire nuts is always pleasing to the eyes :)
Thank you Wago;)