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Forum Index : Microcontroller and PC projects : Line motor causes MM reboots
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pcaffalldavis Senior Member  Joined: 17/10/2011 Location: United StatesPosts: 187 |
Good morning folks! I’ve got an interesting phenomenon. Still using the original MM’s to run my wood fired boiler. My first one has been running it for two years without few problems. Just the occasional unscheduled reboot. Lately though, and today, I have been getting lots of MM reboots when a line voltage motor is switched on by a 24 volt relay triggered by the MM. This is so strange. There is no electrical connection between the units. The MM is running on 12 volts from a car battery. The 24 volt relay system is run off a line power transformer. The motor runs directly off 110 v line power. Here is what I’ve done so far to trace it down. First, when I disconnect the actual motor load the MM never reboots. I have other line motors running fairly large fans and pumps and they don’t cause the MM to reboot when they start up or run, only this one small motor which opens and closes the Air Intake to the boiler. It is a reversible motor, but either direction may cause the MM to reboot. I put a second original MM on the boiler and it has the same problem, reboots only when this AI motor is started. Hum…. I don't another of these motors or I'd try a different one. So, I put one of the new CGStick1 MM’s on the system and there is no problem with reboots…. BUT with the CGStick1 the four temperature sensors fluctuate wildly within 3 or 4 degrees. I’m using a small wall plug USB power block to power the CGSTICK1 so maybe I need a more robust 5 voltage supply to prevent the temp sensors from fluctuating so much. I’ve got a 12 volt to 5 volt car adapter on order which I think is good for 2 amps so maybe that will be better. BUT, why have the original MM’s started rebooting when a line current motor is engaged? This is really a puzzle to me. We're all here 'cause we're not all there. |
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| robert.rozee Guru  Joined: 31/12/2012 Location: New ZealandPosts: 2350 |
reminds me of events of a quarter of a century ago! an automatic liquid nitrogen filling system that controlled a small compressor via a relay. a partial solution was to place a 0.0047uF (or thereabouts) MAINS RATED capacitor across the relay contacts. this worked kinda ok, but a few of the capacitors blew up. the 100% effective solution was to place a line filter right at the motor. the sort that has a couple of inductors and a few capacitors, all potted into a block of a few cubic inches. the problem was electrical noise from the motor starting being fed back from the motor down the power wires, from which it was radiating into the ether and making its way to the controller. no end of filtering at the controller was tried, and failed. the filtering had to be placed right at the motor. rob :-) |
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| pcaffalldavis Senior Member Joined: 17/10/2011 Location: United StatesPosts: 187 |
I don't have the expertise to make a line filter to place at the motor (or know enough to buy one ready made),but might wrapping an aluminum foil shield all along the mains power line block the rf? Or what specs might I need to find/buy a line filter to place at the motor? Do you think those power line loop magnets might work if I coiled the main power line through them two or three times? I'm talking about the kind you find on so many laptop power supply lines. We're all here 'cause we're not all there. |
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Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3196 |
Hi Peter, I bet that replacing the 10uF capacitor in the Maximite will stop the reboots. The original Maximite used a 10uF Tantalum capacitor which was not the best decision. Replace it with a 10uF ceramic such as this one. It is an SMD part but you can solder it across the original cap's solder pads. I am sure that the CGStick1 used a ceramic and that is why they do not reboot. Geoff Geoff Graham - http://geoffg.net |
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| pcaffalldavis Senior Member Joined: 17/10/2011 Location: United StatesPosts: 187 |
I'm sorry Geoff. I ment MM SM1's. Those were my first MMs. I think they have the ceramic caps. If I was going to replace them though, which ones and with what uf rating? I see caps 1,2,3,4,5, 18 & 20 are all 10uF caps on the SM1. Might it help if I put in different caps? We're all here 'cause we're not all there. |
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BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
Peter The capacitor in question is C10 which is adjacent to the left hand side of the SD card socket. It is quite clearly visible in this image. Here is a circuit schematic of the SM1. The capacitor is shown toward the right hand side and it is connected to pin 56 (aka VCAP / VCORE) of the processor. You should save a copy of the image and the schematic as they may not be there forever and they are different from the original Maximite documentation. I did think of attaching them here as a another source but there may be a copyright issue. How to save them? Just right click each of the links in this post and select Save target as ... and follow the dialog. If you decide to replace the capacitor then it MAY be polarised (have + and -). IF it is then I can't tell you which way that is in the photo. IF this capacitor is polarised then the + side would be the upper side in the schematic. Any replacement on the board should have the same polarity orientation. Anyone else advise Peter on the capacitor specifics? Bob |
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donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
This hardware product was completely open, and won't be repeated as a product, so go for it. As you suggest, the site will not be there forever. It may pay to archive it in a more secure location. Cheers Don... https://www.dontronics.com |
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| pcaffalldavis Senior Member Joined: 17/10/2011 Location: United StatesPosts: 187 |
Thank you very much. I saved copies of each. I did notice they are different. Nice to have the proper schematic and image. Does anyone with engineering know-how have any suggestions for a cap that would be better than a 10 uF ceramic? For starters I put a .0036 uF 1000 v cap across the line voltage going to the motor at the relay. It was as close as I could find. I'll try that for a while first and see if it clears up the problem. It works right now, but this has been an intermittent problem so it may come back at 3 AM. I may also use a different line motor to open and close the Air Intake. One from an old microwave oven that turns the glass platter might work. I think most of those are reversible too. I knew where there was one at the town dump (Hyder Hardware) but by the time I got back there today someone had burned it. Can't get no respect for old hardware these days. Thanks folks! We're all here 'cause we're not all there. |
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| Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3196 |
Looking at the photos it appears that the capacitor is a ceramic so probably that is not the cause of the problem. If you do want to try replacing it, the one that I suggested in the previously post is the best that you can get (it has X5R dielectric). Geoff Geoff Graham - http://geoffg.net |
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| BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
This motor may have carbon brushes running on a commutator or a slip ring and the brushes may be worn. This can lead to arcing and sparking because the brushes won't be making good contact. The clue is an inspection plate in the side of the motor as shown in the commutator link. Isolate the motor from the 110V supply before opening the motor. The Wikipedia article has links to commutator and slip rings. I can't put them in this post because the board software strips out parentheses from URLs. |
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Zonker Guru Joined: 18/08/2012 Location: United StatesPosts: 761 |
Evening Gents..! Another suggestion might be to use an SSR instead of a old-school relay.. Most have a zero-crossing driver in them and will cleanly bring the motor on and off the line, minimizing "mister sparky"... I have used them in the past, always with good results... They are a bit more expensive though...  |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Gday pcaffalldavis, I had a very similar problem many years ago with a sprinkler controller I designed using an AVR basic driven procoessor (I cant remember it now) and I could run it on the bench for weeks on end and no problem, then when I connected the 24V ac for the solenoids the darn thing would lock up within 1min to 1hr later.. I think that if you used the relay to drive a bigger relay (or contactor) you might find it solves your problem... I never tried that myself as my wife cracked the `well lets say she lost patience) and we bought a commercial unit that still works now. But that `problem' has haunted me ever since... Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| crez Senior Member Joined: 24/10/2012 Location: AustraliaPosts: 152 |
I had this sort of problem with a freescale microcontroller driving relays via a uln2003 chip. I fixed it by clamping the output lines from the micro with a zener on each line so that any transient could not exceed the supply voltage of the chip. This cleared up all the problems. The worst culprit was a brush motor in a fan heater but occasionally other relays would cause reboots. This was in a coin operated dog washing system. David |
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| pcaffalldavis Senior Member Joined: 17/10/2011 Location: United StatesPosts: 187 |
All good ideas. I have not had a repeat of the unscheduled reboots since I put the .0036 uF cap across the line voltage. The problem was not repeatable when the line power was disconnected to this particular motor, even though the 24 vac relays were still connected and working. I still have not replaced the line motor. I'm still looking for a used microwave turntable motor. The town dump has not yet proven its benificance. I wonder if a line voltage electric motor soft start unit would act as a filter for line noise too? Or, maybe the soft start would reduce the rf from the carbon brushes? I might give a soft start unit a try if the capacitor across the line voltage doesn't keep the unscheduled reboots at bay which it has the past four days. I have a pile of these electronic motor soft start units someone gave me years ago. I tested them with a kill-a-watt meter and they don't really save much on electrical consumption, but they may extend motor life...or not...I'm not really sure. Maybe I've finally found a use for them as rf line filters! No one knows when they will go Or how long they may stay. Regarding time though this we know We've less than yesterday. Maybe we could remember to act accordingly. On ward and upward. Thanks all! We're all here 'cause we're not all there. |
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| pcaffalldavis Senior Member Joined: 17/10/2011 Location: United StatesPosts: 187 |
David, Can't help but wonder about the coin operated dog washing system. I've never heard of such a thing. Where would one be located and how exactly do they work? Are they like drive through car washes or more like self-serve. The zener seems like a good idea too! We're all here 'cause we're not all there. |
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| crez Senior Member Joined: 24/10/2012 Location: AustraliaPosts: 152 |
It is in a country NSW town co-located with a car wash. It has functions such as shampoo, conditioner, rinse, and blow dry. The original control was an on-line PC. Every time it was used the software developer got a cut of the takings. It was very unreliable so a new control system was made. David |
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