Current Sensing Christmas Present

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  • Condoman44
    Established Member
    • Nov 2013
    • 178
    • CT near Norwich
    • Ryobi BT3000

    Current Sensing Christmas Present

    The other day I decided to make life a little easier when using my miter saw. I was running the shop vacuum with a Dust Deputy through a RF remote. It worked but was a little cumbersome.

    I got the idea to rewire one of the shop outlets to accommodate a current sensing module. After some Google research I settled on the Phenix 9993A (phenixcontrols.com/Current_Sensor/Single_Phase/9993) and ordered it. With a minimum $25 order and for future table saw sensing it came to $58 for two.

    I rewired the outlet with two duplex outlets. One for normal 110VAC the other split for the saw and vacuum. I put a 4 in. square box over the old outlet hole with a 4 in. extension box and a utility cover to hold the outlets. I checked that the vacuum would not exceed the 10A contact rating and did not use a slave relay.

    Finished up the wiring and tested all outlets for correct polarity. Now I can get back to making projects.
  • LCHIEN
    Internet Fact Checker
    • Dec 2002
    • 20914
    • Katy, TX, USA.
    • BT3000 vintage 1999

    #2
    I looked at your switch specs.
    Compared to some switches sold in the woodworking marketplace

    its best point is that it will sense off a completely floating line - e.g. a one turn transformer built into the device. Basically just pass the wire through.
    That allows you to either operate the controlled device on an independent branch circuit (may even be a different voltage) from the sensed device circuit.

    The contacts are limited to 10 A. But you can slave another relay from it like you said to handle larger currents.

    Price is reasonable.

    The downsides I see: Most of the ones sold for woodworking have a few second delay when turned off, this helps clear the lines of dust
    before shutting off the controlled device (the vac). This does not have an off delay.

    10A is a limit - I'm sure many vacs exceed 10A on startup. The inrush of a motor is typically 6 to 10 times the rated current of the Vac. This device uses a mechanical relay so high inrush currents may slowly and eventually damage it every time it is switched on. The spec sheet is specific that motor use (see Motor Load Rating just below Load Rating) the contacts are only rated for 1/3 HP which is about 240 watts or roughly 2 Amps. I think you should use a slave relay that is rated for 10A motor use!

    Would be nice if it had a solid state 20-30 Amp triac instead of a relay... but then you lose the form C contacts (normally ON contacts would be lost.)

    The last thing is for DIYers, having a hole to pass the wire means that the power cord somewhere to the sensed device needs to be broken to pass it through. Not a biggie but inconvenient, but I actually like the feature from the isolation point of view. If you are building an enclosure it means you have to have a separate power connection to pick up the sensed equipment power and an outlet to plug the sensed equipment into. Internally the hot wire has to be routed through the device.
    Last edited by LCHIEN; 12-20-2016, 10:17 AM.
    Loring in Katy, TX USA
    If your only tool is a hammer, you tend to treat all problems as if they were nails.
    BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

    Comment

    • capncarl
      Veteran Member
      • Jan 2007
      • 3564
      • Leesburg Georgia USA
      • SawStop CTS

      #3
      1/3 hp, that's pretty whimpy! I can't remember back when a vac was less than 2 hp, unless it was one of those earlier models that ran on kerosene.

      Comment

      • LCHIEN
        Internet Fact Checker
        • Dec 2002
        • 20914
        • Katy, TX, USA.
        • BT3000 vintage 1999

        #4
        Originally posted by capncarl
        1/3 hp, that's pretty whimpy! I can't remember back when a vac was less than 2 hp, unless it was one of those earlier models that ran on kerosene.
        Shop vacs, particularly Sears, were notoriously bad about inflated HP.

        When they say "developed" HP that's the warning sign that its based upon locked rotor amps which is really not doing any work at all. Its a bogus number.

        The little shopvac I have for cleaning up around the miter saw says 2.25 HP but lists 7.3 A as the rated current. That really puts it about 860 W which is barely over 1 HP.

        The best thing to do is take the rated current and multiply times 120V to get Watts, then divide by 750 to get HP.
        Or going the other way, a 1/3 HP relay is for 1/3 of 750W, or 250 W. At 120 V the limit of current is 2 A which gives a 12-20A current surge using the 6 to 10 times rule of thumb.
        Last edited by LCHIEN; 12-21-2016, 04:23 AM.
        Loring in Katy, TX USA
        If your only tool is a hammer, you tend to treat all problems as if they were nails.
        BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

        Comment

        • Condoman44
          Established Member
          • Nov 2013
          • 178
          • CT near Norwich
          • Ryobi BT3000

          #5
          In my case I was making this part of the outlet cluster so wiring with 12 gauge solid was easy and did not require any cord splitting.

          I know the off delay is desired but I am dealing with the length of the vacuum hose so not concerned much. The on sequence is long enough to clear the hose as the saw & vacuum are powered on before sawdust is produced.

          I think I will make a trip to Grainger for a relay and save those 10A contacts.

          Thanks for the input.

          Comment

          • LCHIEN
            Internet Fact Checker
            • Dec 2002
            • 20914
            • Katy, TX, USA.
            • BT3000 vintage 1999

            #6
            I didn't mean to come off as critical. I guess its in my engineer's nature to look at designs, esp. if I have worked on something similar, and analyze what makes them better or worse. The others are not important but I think the motor rating of the contacts was important.

            Good find on the current triggered relay. I have a couple of the old Sears All-in-one units but they don't make them anymore.
            Last edited by LCHIEN; 12-21-2016, 11:37 AM.
            Loring in Katy, TX USA
            If your only tool is a hammer, you tend to treat all problems as if they were nails.
            BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

            Comment

            • Condoman44
              Established Member
              • Nov 2013
              • 178
              • CT near Norwich
              • Ryobi BT3000

              #7
              I did not consider it critical at all. I just wanted to say I considered some of the items you pointed out. I did measure the draw with a Kill-O-Watt and thought it was close enough to pass.

              I have ordered a SCHNEIDER 92S7A22D-120A to use as a power relay. On that I would like to mention that the Zoro cost was just under $10 while the other purveyors peg it at $19 and up, including Grainger who owns Zoro, go figure.

              Comment

              • LCHIEN
                Internet Fact Checker
                • Dec 2002
                • 20914
                • Katy, TX, USA.
                • BT3000 vintage 1999

                #8
                That's got a stout rating. Should serve you well.
                Loring in Katy, TX USA
                If your only tool is a hammer, you tend to treat all problems as if they were nails.
                BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                Comment

                • Condoman44
                  Established Member
                  • Nov 2013
                  • 178
                  • CT near Norwich
                  • Ryobi BT3000

                  #9
                  Power relay installed. A little snug but it fit in the space OK. Even used both sets of NO contacts since they were available.

                  Comment

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