| Electronics > Beginners |
| AC Ripple in DC Line |
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| Blade2021:
Hi All, First post so excuse my ignorance if I miss any rules or regulations. Heres my scenario that i've been fighting with for quite some time. Still haven't gotten really the magical answer. I am working with a Logic Level (5VDC), and industrial level (24VAC) system. I am using a rugged built arduino to control a set of 8 inductive coils to perform various operations on an industrial machine. Works great 85% of the time. However after running for some time, the LCD Display beings to crap out. Aka, starts displaying garbbled text. I have been working on this for over a year now with no fix just yet but I'm very stubborn so it'll give in eventually. I have tried using a MOV, although I do not know the values of it off the top of my head I will get those if requested. I do not know the exact size of the main coil that is causing me issues but we'll get to that. I recently just purchased an oscilloscope to help me troubleshoot the issues i've been having and this is what i've found so far. I do have a 200mV ripple coming out of the DC line. This ripple is not there if I do not run the main conveyor motor. I have unplugged the relays that go to the coils to see if they could be picking up the noise even though they do not connect to the motor directly. This did not change anything. I left the power supply (a typical wall wart) unplugged with the noise still on the DC supply line which leads me to believe it may be an EMI issue, but I don't know if 200mV is within reason for a typical ripple? Another scenario i've been working on is ordering the right MOV for my circuit. Its all 24VAC so if the math from the various websites is correct I should be looking at a varistor with a 36VAC maximum. Correct? Well that was set in stone in my thought, till I looked at the scope and it says my AC wave is typically 40VAC even though its a 24VAC system. Obviously this is probably cause its measuring wave top to wave bottom. So would the 36VAC varistor work or should I be looking at a varistor with a 40VAC rating? Please see attachments for scope images. In the first image I show the ripple coming through my DC power supply. In the second image (pic_12_1), I show the voltage spike when triggering the coil off. Thanks in advance for your time in reading this giant post. - Matt |
| tpowell1830:
First, welcome to the forum Blade2021. This is an interesting problem, however, it will be near impossible to troubleshoot with the given information. If you would post your schematic and the measure points of your scope probe, it would help immensely. Otherwise, we will be here for days speculating the scenario. |
| Blade2021:
My apoligies! I got ahead of myself and forgot to include those. I'll upload the schematics of both my latest design and my sub control which I'll explain below. I placed my probes on two places, which i'll explain here while I try to edit one of the drawings. The first probe I placed on my 5V distribution on the sub control with a link to the ground on the sub control. The voltage spike one shown in my OP, was taken with the ground lead connected to the AC neutral, and the probe connected to the SSR relay, relay #7. Shown on the AASchem. Again I'll do my best to do a quick edit of the drawing to better explain this. Thank you for the welcome, - Matt EDIT: Hello, I just edited the schematic file and included where I put my probes. I also drew boxes around them just to highlight them the best I could. Tinycad doesn't give very many options for that kind of thing sadly. |
| Twoflower:
Depending on the design a garbled text on a LC Display could indicate a problem with your software. That happened to me. After some poking around I found my stupidity: I did not clean up the stack after returning from subroutines (yes it was assembler code). But in your case that might be a memory hole that floods your memory until it reaches the data-structure you want to display. A missing \0 at the end of a string, a for loop that overwrites it. The possibilities for that are manifold and easy to oversee. The 200mV could stray in through inductive coupling as you already assumed. To provide better support a picture or two of the wiring might be useful and probably the location of the 24V transformer. But if this is 'only' the 200mV and the result is all time the same (garbled text on the display) I would spend some time looking into the code. Because power supply inducted problems are usually more random. |
| Blade2021:
--- Quote from: Twoflower on April 13, 2018, 06:31:57 pm ---Depending on the design a garbled text on a LC Display could indicate a problem with your software. That happened to me. After some poking around I found my stupidity: I did not clean up the stack after returning from subroutines (yes it was assembler code). But in your case that might be a memory hole that floods your memory until it reaches the data-structure you want to display. A missing \0 at the end of a string, a for loop that overwrites it. The possibilities for that are manifold and easy to oversee. --- End quote --- You know I didn't think this was the cause in the beginning of trying to debug this but for some reason that does kinda make sense. I will look further into the code to see if I possibly missed something. I update the LCD with alot of information so its defiantly possible. One scenario that does still kinda point the finger at a EMF issue is when I turn the coil on, off, on, off, very repetitively it makes the LCD go completely blank. vs just unreadable text. This is something that is still random but I can reproduce. --- Quote from: Twoflower on April 13, 2018, 06:31:57 pm ---The 200mV could stray in through inductive coupling as you already assumed. To provide better support a picture or two of the wiring might be useful and probably the location of the 24V transformer. But if this is 'only' the 200mV and the result is all time the same (garbled text on the display) I would spend some time looking into the code. Because power supply inducted problems are usually more random. --- End quote --- The 24VAC transformer is located in a separate electrical panel aprox. 3 - 4 feet away from this control box. However getting a picture will be easy enough to produce so i'll grab one. Just don't be to critical on my wiring job ;) I'll edit this post after I get it. |
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