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Robust 24V din rail supply wanted

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  • Robust 24V din rail supply wanted

    I'm having trouble at work with an installation where the switching on and off of a three phase pump motor with a contactor is creating so much crap on my 400V lines that the 24V din rail supplies give +/- 50V spikes on the 24V output. This is not helping my control system which is resetting....
    So, yes the power supplies were not the most expensive, but they were from Phoenix Contact, so I didn't expect them to be too crappy.

    Now, searching for another power supply I'm struggling with how to select one. None of them have clear specifications on surge rejection on the 230V side.
    Does anyone have recommendations for more bulletproof brands?
    My supplier has a reasonable variety of the following brands: Omron, Siemens, TDK, Tracopower. The Siemens are the most expensive so I'm leaning in that direction :-)

    Might not be such a bad idea to install some surge arrestors as well...any recommendations to that effect are welcome as well.

  • #2
    We use "Rhino" brand sold by Motion Industries. So far no problems. Most of our systems are 230/110 single phase.

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    • #3
      Any switching supply should work. But that's probably what you have right now. There is a possibility that the spike is not coming from the power supply but is being induced in the control wiring. What might be the simplest thing is to add a zener diode on the output of the power supply to act as a clamp. Pick a diode a volt or so above the output of the power supply. You could also put a TVS on the input and output of the power supply too.

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      • #4
        24 Volts AC or DC?????????

        What current rating?

        If this is a DC supply, do you have snubber diodes on the contactor? They would help quash the spikes.
        Paul A.
        SE Texas

        And if you look REAL close at an analog signal,
        You will find that it has discrete steps.

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        • #5
          The power supplies are 247 DC 2.5A but I see that even with a lab power supply I still have issues.
          I ordered some surge suppressors for the 400V lines and TVS diodes for the 24th lines , I hope that helps a bit.
          What exactly is a contactor snubber diode? Is that a TVS?

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          • #6
            Eaton PSG series have done well for me in the past.

            http://www.eaton.com/Eaton/ProductsS...sPSG/index.htm
            CNC machines only go through the motions.

            Ideas expressed may be mine, or from anyone else in the universe.
            Not responsible for clerical errors. Or those made by lay people either.
            Number formats and units may be chosen at random depending on what day it is.
            I reserve the right to use a number system with any integer base without prior notice.
            Generalizations are understood to be "often" true, but not true in every case.

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            • #7
              If using the supply for switching contactors and/or relays etc, I really recommend changing to a simple 24v transformer and a bridge rectifier, no cap needed.
              They are way more rugged than a regulated supply and are easy to fix Should they fail, which is not as often as SMPS also easy to put together.
              For snubbers, if AC coils then a R/C type is used, if DC coils, a reverse connected Diode such as 1n4007 etc.
              Systems often use regulated supplies when they are not really required.
              Max.
              Last edited by MaxHeadRoom; 06-28-2016, 07:42 PM.

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              • #8
                You don't mention the size starter or motor you are working with. A large contactor will have some significant flyback voltage when it turns off. In the early days of digital VOMs I fried a couple before I figured out they didn't like big surges from large contactor coils! All contactor coils need snubbers or you will get control system problems.

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                • #9
                  MaxHeadRoom said it. A snubber or suppression diode is a rectifier diode that is connected in reverse polarity across a coil that is operated with DC. When the power is removed, the magnetic field collapses, inducing an EMF in the coil in the reverse direction. That is your spike. The reverse connected diode will conduct for this reverse EMF and, hopefully it will travel no further back down the DC circuitry.

                  A spike in the DC output of a power supply can travel backwards through the power supply's circuitry and get into the primary side. And from there it can go everywhere else in that system and even in the building in general. In general, no power supply is really expected to handle this kind of spike. A 1N4007 or similar rectifier diode will go a long way toward preventing this. Just be sure to connect it backwards so it only conducts for that reverse EMF spike.

                  If the spikes are occurring at other times then you may need some other measures to suppress them. Observe the times they are happening and tell us more about them.
                  Paul A.
                  SE Texas

                  And if you look REAL close at an analog signal,
                  You will find that it has discrete steps.

                  Comment


                  • #10
                    Would using an Uninterruptible Power Supply work? As I understand, many(some?) of them isolate the incoming power and use it only to charge the battery while the inverter uses the battery to supply output voltage.
                    North Central Arkansas

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                    • #11
                      The transformer idea is not bad.

                      However, most of the legitimate type 24V supplies are rated to handle contactors etc. That's what they are for, really And, DC contactor coils are much easier to deal with than AC. We used the Eaton ones for controls and contactors.
                      CNC machines only go through the motions.

                      Ideas expressed may be mine, or from anyone else in the universe.
                      Not responsible for clerical errors. Or those made by lay people either.
                      Number formats and units may be chosen at random depending on what day it is.
                      I reserve the right to use a number system with any integer base without prior notice.
                      Generalizations are understood to be "often" true, but not true in every case.

                      Comment


                      • #12
                        All the systems I install I use a 120/240/24v transformer and a bridge rectifier, using DC for inductive devices prevents burn out in the case of a coil/solenoid that does not pick up completely, this not only tends to burn out the coil but blows the fuse or the SMPS supply, which does not happen with DC.
                        I reserve SMPS supplies for devices that require a regulated supply.
                        Max.
                        .

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