Interference with well pump pressure switch and propeller

I am using the Parallax Propeller to start and stop timers for an auto racing timing system. Out of 250 cars there were timing issues with about 10 or so. It was very random and hard to diagnose. I knew that somehow the input pins were somehow reading high and causing timers to start and stop. I also knew that it was very quick because one chip polling via a loop didn’t show the pin was high and another chip using waitpeq detected it. After creating a pin test program and using a scope I found the problem. When switching on, a well pump pressure switch caused the pin to read high. It wasn’t every time either. (Although the interference was showing up on the scope every time). The pump was cutting on and off about every 5 minutes. About 75% of the time when the relay clicked on it caused the pin to read high. The scope was showing upwards of 2.4 volts. I am not switching the relay via the microcontroller. The relay is in a separate room in the building but still causing interference into my timing system.

I’m very inexperienced but I have a good knowledge of electronics. This high voltage stuff (the pump is powered with 220VAC) is not my thing though. The power supply for the microcontroller is connected in the same electrical panel as the well pump. I have tried using a 12 volt battery instead. No success. I have tried using capacitors on the power supply without success either. When checking the pressure switch I found that the 220 ground wasn’t connected. After connecting the ground it seemed as if it helped, but it still showed reading high about one time in 40 minutes with the well pump switching on and off about every 5. So I think connecting the ground helped but didn’t solve the problem.

Like I said I’m inexperienced, and don’t really know where to start. I have thought about taking a start capacitor off of a 220 air compressor and putting that on the load on the pressure switch. Would this help? Any other ideas on how to fix this problem?

Comments

  • Two possible causes for this come to mind. Pump surge current draw or power line noise from relay contact arcing can cause this type of problem. Using a solid state zero crossing relay should eliminate the problem if it is due to arcing, and may help with the surge current since the relay only turns on when the AC voltage is crossing zero volts.
    In science there is no authority. There is only experiment.
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  • @kwinn

    Thank you for your response. I will try adding a solid state relay at the pressure switch.
  • You can put an RC between the wires and the port pin.Depending on the speed required for your inputs something in the range 100nF/1k would limit the bandwidth to about 1MHz. I don't know how long the wires to the input pins are, but if it is more than 1m I would always do this. Such a wire is an antenna.
    --
    Reinhardt
  • Hi.
    Had sort of the same problem when I started using the Propeller for controlling my micro Hydro powerstation. Airborne noise from a nereby 230v ac contactor, sometimes caused the Propeller to reset. Also got some faulty Readings from the input shift-registers caused by this. Solution: Made a snubber Circuit by 100n cap (250v) in series With a 100R resistor and Connected it in parallell With the contactor coil. (A1-A2) Seems like the coil itself radiated the noise into the air when it charged and discharged. (contactor got turned on and off)
    So, out of my experience, I`m pretty sure that Your noise causing problems is air-borne. Do`nt think it comes over the Power lines and into yout P1.
    Do`nt know if Your well pump has a contactor/relay or if it`s switched directly by the pressure switch?
    Just thaught I would share my experience With a similar problem. Hope it helps, and have fun With Your Propeller.
    :smile:
    :cat: Peter ***Aafjord, Norway***
  • Hi, just some random thoughts -
    often these spikes are picked up from common connections such as how the things are earthed etc - that would explain why using a separate battery supply didn't help. For DC the best way around that would be to isolate the "ground path(s)" using opto-couplers etc
  • A/C relay switching is a big problem for the prop. The solid state relay is the best way to go. Even switching small dc relays with the same power supply as the prop causes issues.
  • Any digital system is sensitive to EMI, not just the Prop. Just think that the very first radio communications was achieved by using spark gaps and then picking this up through the air into a coherer receiver. Even an AM radio will pick up lightning from many miles away.
    If a system is designed well enough it can be fairly immune to EMI but it also helps to reduce the EMI in the first place, so use snubbers or zero-cross switching etc. Most hobby designs are prone to being affected by even the smallest amount of EMI, and the trouble with the Prop is simply that it is used in a lot of hobby designs. But I use the Prop in lots of different industrial designs and have no problem with EMI.

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  • Any digital system is sensitive to EMI, not just the Prop. Just think that the very first radio communications was achieved by using spark gaps and then picking this up through the air into a coherer receiver. Even an AM radio will pick up lightning from many miles away.
    If a system is designed well enough it can be fairly immune to EMI but it also helps to reduce the EMI in the first place, so use snubbers or zero-cross switching etc. Most hobby designs are prone to being affected by even the smallest amount of EMI, and the trouble with the Prop is simply that it is used in a lot of hobby designs. But I use the Prop in lots of different industrial designs and have no problem with EMI.

    Same here. Some of my designs go through tough EMI testing for avionics system without any problems. Immunity was designed in from the beginning. In my designs I never let a naked port pin leave he board. There will always be filters and transient protection. I do this even when it is only an internal (board to board) connection. Of course it is best to avoid to create any emissions, but any device should be designed to withstand EMI. Somebody might later want to use the quick and dirty board for something serious.


    --
    Reinhardt
  • Could this issue occur on 1-wire network with fridge compressor ?
  • yisiguro wrote: »
    Could this issue occur on 1-wire network with fridge compressor ?

    Absolutely! A one-wire network with passive pull-up that utilizes microsecond pulses for communications over long unbalanced lines and possibly unshielded is an antenna begging for EMI. It is hard to filter out noise from such a network because of the nature and speed of 1-wire communications. I read somewhere where this guy's TV would drop out whenever the fridge compressor kicked in. I don't know if that was from a voltage drop (unlikely) or more probably an EM spike.


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  • T ChapT Chap Posts: 3,947
    edited 2019-04-13 - 14:23:48
    yisiguro wrote: »
    Could this issue occur on 1-wire network with fridge compressor ?

    Ideally you would show your design to get the best advice. Is the sensor, cables, and prop board shielded from EMI ie shielded cable and enclosures? Could make a big difference. Any arc like a compressor can disturb signals but sometimes the noise can be managed with shielding and termination.
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