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Forum Index : Microcontroller and PC projects : MM Power supply spikes and resets
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| AndrewB Newbie  Joined: 04/12/2011 Location: AustraliaPosts: 15 |
I have a MM controlling a piece of equipment, giving status reports and responding to control commands via an SMS modem. The equipment has an associated 240volt 1/4 hp induction motor and two 240VAC solenoids. This equipment is on the same AC circuit as the MM. The MM doesn't control the motor etc. directly, the motor is controlled by the equipment the MM controls. The motor etc run for a few seconds every half hour. Once every couple of days, the MM does a reset at the time the motor runs (the system reports all software starts via SMS) so I believe that 240V spikes are causing the reset despite a heavily filtered supply and extra capacitors placed (I believe) in strategic places. Has anyone found a sweet spot to put supply filter caps? I'm going to put more spike suppression closer to the sources tomorrow, hoping that will cure my problem, but since the site is 200km away I'd like to cure this glitch. Any suggestions gratefully received. Cheers. |
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djuqa Guru  Joined: 23/11/2011 Location: AustraliaPosts: 447 |
One possibility is that that reset is NOT PS related but EMI. EMI can be directly affect the Micro-controller and the associated circuitry. Switching can induce large EMI fields. Instead of more filter caps you may need some toroids on the MM power lead and place Faraday (metal Mesh) shielding around the MM circuit board. Also regarding the power supply is it a Linear Supply (i.e. Transformer based) they are more prone to AC pulses. Switch-Mode Power supplies are less prone to AC Noise. VK4MU MicroController Units |
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Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3194 |
Check item 1 in this document: http://geoffg.net/Downloads/Maximite/Top%20Six%20Hardware%20 Issues.pdf I would recommend the ceramic cap solution as that has fixed a couple of situations where noise on the supply caused resets. Geoff Geoff Graham - http://geoffg.net |
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| AndrewB Newbie Joined: 04/12/2011 Location: AustraliaPosts: 15 |
Thanks for the input. I can try improving C5 (thanks Geoff) and putting a ferrite loop on the supply lead (thanks djuqa) to the MM as well as the 'at source' spike suppression. Unfortunately, if it works, I wont know which "fix" made the problem go away, but at least I'll be happy. |
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palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1873 |
Andrew, I had the same problem. I tried running the MM through an extremely good AC filter to no avail. I then replaced C5 wiht the SMD cap. as used in the Mini MM and no more problems. Paul "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| AndrewB Newbie Joined: 04/12/2011 Location: AustraliaPosts: 15 |
Well I went to the site yesterday and put more spark suppression at the source. I didn't have time to find an SMD cap, but did find some tantalums with a higher working voltage as suggested by Geoff. So far so good, but it has only been 30 hours. I'll be sure to report back in a week to let you know if it's fixed. Thanks again guys. |
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| AndrewB Newbie Joined: 04/12/2011 Location: AustraliaPosts: 15 |
Well, it's been more than a week, but not complete success so far. The rate of restarts is lower, but not zero. As it happens, this particular system is pretty tolerant to restarts, and they will only be a problem on two days each year (changes from winter to summer time and back). So, the next step is to buy a ceramic cap before my next visit to site and see if that cures the problem. Question without notice: is there a reason why power supply spikes cause a reset rather than a hang? I've thought maybe I should implement a watchdog timer, but so far it seems unnecessary. |
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darthmite Senior Member  Joined: 20/11/2011 Location: FrancePosts: 240 |
It can be that the 'Brownout' bit is set at compile time. This bit reset the CPU when the voltage drop under a certain level. I used this on PIC18 and it must exist on the PIC32 too. Cheers. Theory is when we know everything but nothing work ... Practice is when everything work but no one know why ;) |
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| plasma Guru Joined: 08/04/2012 Location: GermanyPosts: 437 |
will the maximite run without equipment ? "masseschleife" or "ground loop" maybe why not try a car accumulator for the maximite to cut out powersource spikes?(test) |
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| AndrewB Newbie Joined: 04/12/2011 Location: AustraliaPosts: 15 |
It's been a few months now, but two weeks ago I was able to visit my controller (it's 200km away from home) and replace the cap as recommended with a Y5V dielectric type. This resulted in great improvement; to one restart in two weeks instead of one restart every day on average. So I can definitely support Geoff's recommendation regarding replacing C5 with a ceramic cap with Y5V dielectric. I was able to source a pack of 25 of these caps at a sensible price from RS Components. Thanks to all who have helped. |
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