110VAC power relay w/bounce, chatter & arcing

Discussion in 'The Projects Forum' started by GordoP, Jan 14, 2015.

  1. GordoP

    Thread Starter New Member

    Jan 14, 2015
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    I have a Fuji PXR4 programable micro-controller (time & temp control of a 220V coil-element pottery kiln). A Fuji signal for heat triggers a 120VAC power relay. The Fuji and the relay have been working well for numerous kiln firings.

    But: The relay contacts often bounce or chatter? , & arc during the 11 hour kiln firing with the deterioration of the contacts/eventual relay replacement - $$$. Is there a contact "protection circuit" ......I've heard of a resistor - capacitor network.

    Since I usually prefer an overnight firing, I'd rather not have a "welding of the contacts" event...even if only in my dreams.

    Help would be greatly appreciated.

    GordoP
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    How many Watts is the Kiln?

    How many Amps is the Relay rated for?

    Does the controller switch the 120V cleanly, one snap in, one snap off as the temperature rises and falls, or is there a temperature region where the relay repeatedly goes on/off (chattering)?

    If so, there is normally a "hysteresis" or "deadband" adjustment/setting in the controller that is designed to eliminate the chattering...
    The goal is to have the controller operate just like a house thermostat. The relay will chatter only if the deadband is set too narrow, or if the controller is not set up to drive a relay.

    ps: Page 27 of this manual shows how to set up this controller to drive a relay.
     
    Last edited: Jan 14, 2015
  3. MaxHeadRoom

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    Often chatter or vibration of a AC contactor armature is due to insufficient coil voltage or something has happened to the shading ring.
    Also the armature mating surface should be as smooth as possible, AC contactors are more prone to this than DC, an alternative, apart from a new contactor is to use a DC coil fed by a bridge rectifier.
    Many relay/contactors have replacement coils covering most voltages for DC & AC.
    Max.
     
  4. GordoP

    Thread Starter New Member

    Jan 14, 2015
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    Thanks Mike, & Max,

    Kiln is 2500W Relay is 40A Resistive. The controller & relay make & break cleanly sometimes. 1 snap on/1 snap off, particularly when points were newer. I haven't noticed a temp region with more chatter. The application is: ambient ramp to 300F soak/hold ramp to 700 soak/hold ramp to 1350 soak/hold ramp to 900 soak/hold. Now that the points have burned a bit - not yet pitted, I wipe them with 800 grit paper prior to each session.

    Thanks for the Fuji Manual. I have a copy in-house & in shop. Problem is I just don't understand most of the possible settings; This Fuji PXR4-RAY1 is an amazingly programable controller. I'll check and reset the hystereris and report results when next at my shop. BTW, This model Fuji not able to output DC.

    Thanks very much!
     
  5. tracecom

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    Am I missing something here, or is this a problem?
     
  6. MaxHeadRoom

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    I just assumed it was 120v control circuitry for a 220v heating element?
    Max.
     
  7. MikeML

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    Perhaps Gordo should confirm that the controller is running on 120Vac, and is applying 120Vac to the relay coil, and that the furnace is wired for 240V?

    Is the relay breaking both sides of the 240V line?
     
  8. tracecom

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    The manual seems to indicate that there are three output options, depending on the exact model of the controller: relay contacts, 24DC pulse, or a 4-20mA DC output. Since the OP says there is no DC output, I assume that means the controller is providing a set of dry contacts. I suppose that 120VAC could be routed through those contacts to switch a relay with a 120VAC coil and 240VAC rated contacts, but it seems unlikely.
     
  9. GordoP

    Thread Starter New Member

    Jan 14, 2015
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    My Fuji model PXR4-RAY1 : The "A" stands for Relay Contact Output (100-240V AC), not programable. Fuji Tech suggested buying a "C" instead of the "A" in that position of model number $204. Or sending my Model "A" back and they will reprogram it into "C" output for a 24VDC SSR for $100 & 1 week + shipping.

    Max, Yes to the controller, relay & furnace specs. The Relay is breaking one side of the 240 line - & of course, NO, 40A Res. What does "dry contacts" mean?

    I'm on my way to the shop to check/set the Hystereris function.
     
  10. MikeML

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    The model A relay contact output is just fine. Do not change it.

    Post the model number (or a link to the data sheet) for the 40A relay you are using.
     
  11. tracecom

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    Dry contacts mean that there is no voltage supplied by the controller. It is up to the user to route whatever voltage is to be switched through the dry contacts.

    My earlier comment about it being "unlikely" that a relay might have a 120VAC coil and contacts rated for 220VAC was wrong. They are fairly common, e.g., http://www.automationdirect.com/adc...n-Style,_40A_(AD-PR40_Series)/AD-PR40-2C-120A

    If the relay turns out to be like the one I posted, i.e., double pole, it could indeed be switching both side of the 220VAC. As Mike posted, we need the specifications for the actual relay being used.
     
  12. GordoP

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    Jan 14, 2015
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    Dayton 5Z538 SPST-NO-DM 120VAC 50/60Hz Contacts: 40A Resistive. Just had a session. Not getting bounce/chatter, but a very brief (milisecond) arc almost every time that the contacts open. Would a double pole solve the arcing?
     
  13. MaxHeadRoom

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    Technically if switching N.A. 1ph 240v you should be switching both L1 & L2.
    A contactor known as Special Purpose would be the best, these are built for repeated operations such as HVAC etc.
    But also a R/C snubber across the contacts would suppress the arc in the relay you are using.
    Max.
     
  14. GordoP

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    Jan 14, 2015
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    Thanks to all. I'm ordering a double throw w/magnetic blowout relay. Then will revisit the R/C Snubber network suggestion if necessary.
     
  15. MaxHeadRoom

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    Magnetic blow out, is usually aimed at DC switching contactors?
    Max.
     
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