| Electronics > Beginners |
| Discharge current for capacitors |
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| T3sl4co1l:
Can you post the waveform? While a discussion on capacitor ratings is fruitful, equally valuable is a discussion of numerical stability and running a SPICE engine. It is by no means a set-it-and-forget-it process. Most especially not with the rough compromises that have been made in LTSpice specifically. Tim |
| spec:
--- Quote from: T3sl4co1l on November 20, 2018, 09:03:09 pm ---Can you post the waveform? --- End quote --- If that question is aimed at me, no I do not have a lab at the moment and my wife is fairly unreasonable: she objects when I put my solder station, cutters etc on our nice new oak table. But it is a great idea. I wonder if someone with a high-current rectifier (5A to 10A say) could do the honors. I would very much like to see the actual ripple voltage waveform against the rectifier diode current waveform. |
| spec:
--- Quote from: aheid on November 19, 2018, 07:42:40 pm ---In my simulated case, a mere 250mA load generated 5A RMS current in the capacitor :o --- End quote --- I only just noticed that you wrote 5A. For some reason I read that as 0.5A. 5A just seems way too high. Feel like posting the rectifier circuit so we can check? Simulators are great tools, but you have to be careful of them- I will say no more in fear of triggering a simulator war. :palm: |
| aheid:
--- Quote from: spec on November 21, 2018, 07:12:15 am ---I only just noticed that you wrote 5A. For some reason I read that as 0.5A. 5A just seems way to high. Fell like posting the rectifier circuit so we can check? --- End quote --- As I wrote, I was fooling around (sims are fun!) and while pursuing an idea I didn't notice I effectively had the capacitor shorted to ground via the switching MOSFET (I effectively had + side connected between L1 and M1, and - to GND in the attached circuit). So only thing holding it back was the ESR... :palm: :-DD This goof however is what triggered the question I raised in this thread. Moving the cap back in it's proper place, the RMS ripple current is now down to "just" 1.2A, which is within the limits of beefier caps from what I can gather, see attached image. --- Quote from: spec on November 21, 2018, 07:12:15 am ---Simulators are great tools, but you have to be careful of them- I will say no more in fear of triggering a simulator war. :palm: --- End quote --- Indeed. I'm a relative noob, I feel I have a decent grasp of basic Ohms law and stuff, but I have limited experience with real circuits so far. So when I for example see hundreds of amps in the sim I have no idea if this is a sim artifact due to missing cable losses, parasitic elements or the numerical integrator etc, or if it's a decent reflection of reality. I recently got a decent lab space tho so looking forward to building some of my sim experiments in order to get some intuition of how the real world compares to the sim world. |
| spec:
--- Quote from: spec on November 21, 2018, 07:12:15 am --- --- Quote from: aheid on November 19, 2018, 07:42:40 pm ---In my simulated case, a mere 250mA load generated 5A RMS current in the capacitor :o --- End quote --- I only just noticed that you wrote 5A. For some reason I read that as 0.5A. 5A just seems way too high. Feel like posting the rectifier circuit so we can check? Simulators are great tools, but you have to be careful of them- I will say no more in fear of triggering a simulator war. :palm: --- End quote --- Ah, that clears the mystery :) An interesting exercise, comparing sim with actual- let us know how it goes! |
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