Dear Sam, your help is very eased my microvibratory equipment design for preventing the fiber stickiness, thank you for your forgiveness. Very simple and effective course.
You've done a lot of great videos but this might be the best. Even really good engineers can learn from your multiple examples that a capacitor charging through a resistor always operates at 50% efficiency, and i have never even seen the relationship between resistor power handling and mass stated in the manner in this video. As with all the best knowledge, once you understand the simple explanation, the result seems obvious, so you can easily remember it over time...
Great video. Would like to mention that inrush current peak and shape strongly depend on the output impedance of input voltage (especially in case 2). Referring to batteries...
Great. I would add that resistors typically start "power derating" at around 70 degree C. Limiting it at 50 degree, as you did, you were ok, but for the last slide, hinting that we could go up to 155 would need to take maximum power dissipation considerations (unless, as for the mosfet, the impulse is very short, a little bit as in the Safe Operating Area that you also show). Again, great video.
Thanks. Power derating may not always relevant power pulse operation. What is important is not to exceed the max temp. Are you involved in resistors manufacturing?
Sam, this video is directly related to two aspects of my designs... One is for power module "hot-swap" capacitor precharging and discharging as well as pulse rating for gate resistors and the like. I have tried to make sure that the pulse ratings of certain resistors are within spec for years now but sometimes it come up to bite me for other applications if not "beefy" enough. For my hot swap, I just use the simpler FET shorting out a precharge resistor and for discharge, a series resistor and FET . Large enough to take the energy but slow enough that it takes its time so not that big of resistors needed. Very good video and another lesson not usually taught in schools ?
For the case where the source charging the capacitor is an AC source connected through a rectifier, it's possible to use an inductor or capacitor in series with the input of the rectifier to provide the impedance to limit the current for precharge, but without (most of) the losses.
@16:16 Why is there a “cooling effect” for thicker gauge wire? For a pulse there’s negligible time for air-convection, right? I’m guessing the thinner wire is more susceptible to thermal runaway (hot spots).
An NTC works better. Initially it is cold, resistance is high and C charges slowly. As the NTC heats up its resistance drops but the voltage across it will decrease as C charges. Properly dimensioned this stabilizes current through and power dissipated in the NTC a bit during the startup time.
@@plemli In a precharge situation, you want the resistance to be low at the beginning of the charge. If you are charging at DC link the precharge time will dictate when the converter will be able to operate. NTC could be used but PTC would be a better choice.
@@mhanssler PTC will yield a high peak precharge current tapering off as it heats up, presenting more current variation than a constant resistance during the precharge time. OTOH an NTC will have less variation. Let's try to convince Sam to evaluate both ;-)
Including the ESR of the inductor (and the ESR of the capacitor), wouldn't the charging method 4 be as lossy as the other methods? Or is there sth am I missing?
Hi Sam, been following your videos for a coupled of weeks. However, is there something else I should have seen before this video? It seems like part 2 of a series of videos but i might be misunderstanding. Keep it up
Hi, I am making a Battery management system in that I am using Precharge circuit using resistance. It work fine . But if at the time of Precharge condition, short circuit occur in that case my Precharge resistance blows. Can u please what , which circuit is preferable in these cases in battery management systems
@@yazhvendan666 if your system is off due to short circuit, then you pre charging nothing. Pre charging works just before turning on your main switch. Then it should be off by any ECU
Dear Sam, your help is very eased my microvibratory equipment design for preventing the fiber stickiness, thank you for your forgiveness. Very simple and effective course.
Thanks
You've done a lot of great videos but this might be the best. Even really good engineers can learn from your multiple examples that a capacitor charging through a resistor always operates at 50% efficiency, and i have never even seen the relationship between resistor power handling and mass stated in the manner in this video. As with all the best knowledge, once you understand the simple explanation, the result seems obvious, so you can easily remember it over time...
Thanks😊
Great video. Would like to mention that inrush current peak and shape strongly depend on the output impedance of input voltage (especially in case 2). Referring to batteries...
Good point
After checking the Key I think I've got a pretty good score. Atleast I believe I got pass marks. Thanks for the great video professor.
👍👏😊
MR SAM thank you very much.I guess I solved motor driver fault of crane.
Very practical design. I really enjoyed it.
Thanks
Thanks always for your great video. Thumbs up!
Thanes
Prof. Sam would you mind if you could make us any chance to learn some knowledge as to varistor and arrestor. Thanks always.
Great. I would add that resistors typically start "power derating" at around 70 degree C. Limiting it at 50 degree, as you did, you were ok, but for the last slide, hinting that we could go up to 155 would need to take maximum power dissipation considerations (unless, as for the mosfet, the impulse is very short, a little bit as in the Safe Operating Area that you also show). Again, great video.
Thanks. Power derating may not always relevant power pulse operation. What is important is not to exceed the max temp. Are you involved in resistors manufacturing?
@@sambenyaakov No, I am not involved in resistors manufacturing.
@@snnwstt👍
thank you, I will be trying this default schematic in my next prototype. seeing 700A peak in rush currently lol.
👍
Sam, this video is directly related to two aspects of my designs... One is for power module "hot-swap" capacitor precharging and discharging as well as pulse rating for gate resistors and the like. I have tried to make sure that the pulse ratings of certain resistors are within spec for years now but sometimes it come up to bite me for other applications if not "beefy" enough.
For my hot swap, I just use the simpler FET shorting out a precharge resistor and for discharge, a series resistor and FET . Large enough to take the energy but slow enough that it takes its time so not that big of resistors needed.
Very good video and another lesson not usually taught in schools ?
Thanks and thanks for sharing
Always the best
🙏😊
Thanks for nice content
Thanks
Helpful video
Thanks
For the case where the source charging the capacitor is an AC source connected through a rectifier, it's possible to use an inductor or capacitor in series with the input of the rectifier to provide the impedance to limit the current for precharge, but without (most of) the losses.
Yes. AS pointed ut in video. An inductor breaks the link between rms current and resistance.
thanks, very interesting as usual
👍
@16:16
Why is there a “cooling effect” for thicker gauge wire? For a pulse there’s negligible time for air-convection, right?
I’m guessing the thinner wire is more susceptible to thermal runaway (hot spots).
Maybe that’s what you meant
Or maybe there’s just less mass in the resistive-wire winding
🙏❤️🙏👍🙏
Thanks😊
It might be interesting to replace the power resistor with PTC and calculate the effects.
An NTC works better. Initially it is cold, resistance is high and C charges slowly. As the NTC heats up its resistance drops but the voltage across it will decrease as C charges. Properly dimensioned this stabilizes current through and power dissipated in the NTC a bit during the startup time.
@@plemli In a precharge situation, you want the resistance to be low at the beginning of the charge. If you are charging at DC link the precharge time will dictate when the converter will be able to operate. NTC could be used but PTC would be a better choice.
@@mhanssler PTC will yield a high peak precharge current tapering off as it heats up, presenting more current variation than a constant resistance during the precharge time. OTOH an NTC will have less variation.
Let's try to convince Sam to evaluate both ;-)
This is indeed correct if there is a long time between pre charges
This is indeed correct if there is a long time between pre charges
Including the ESR of the inductor (and the ESR of the capacitor), wouldn't the charging method 4 be as lossy as the other methods? Or is there sth am I missing?
NO. An inductor breaks the link between rms current and resistance.You can design converters with 90% effiicency and up.
Hi Sam, been following your videos for a coupled of weeks. However, is there something else I should have seen before this video? It seems like part 2 of a series of videos but i might be misunderstanding.
Keep it up
ruclips.net/video/9bZGAflnqNI/видео.html
Hi, I am making a Battery management system in that I am using Precharge circuit using resistance. It work fine . But if at the time of Precharge condition, short circuit occur in that case my Precharge resistance blows. Can u please what , which circuit is preferable in these cases in battery management systems
Hi, you need to make sure that 1. The heat capacity of the resistor is sufficient. 2. That the system if off during precharge.
@@sambenyaakov if I turn off the system, what am I pre charging then?
@@yazhvendan666 if your system is off due to short circuit, then you pre charging nothing. Pre charging works just before turning on your main switch. Then it should be off by any ECU