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Pipestat query

Discussion in 'General Electronics Discussion' started by cygnusv, Dec 5, 2017.

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  1. cygnusv

    cygnusv

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    Oct 7, 2014
    I want to use the pipestat to turn a 12 volt circulating pump on at 30C and keep the pump running until water temp drops below 30C again.
    Whichever way I connect the stat it isn't doing what I want it to. There are 3 electrical connectors in the stat.
    As you may have guessed, I'm not a pro, just a willing amateur looking for advice.
    Am I using the right type of kit?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,801
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    Nov 17, 2011
    We will need more info on the pipestat. Make, model, any schematics available (at least for the terminals)?
    Which pump, which connections did you try?
     
  3. cygnusv

    cygnusv

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    Oct 7, 2014
    Hi Harald, many thanks for the reply.
    Details
    Greenbrook thermostat
    TH90CS-C
    15 amp resistive load
    2 way switching
    UK eBay 1118 0846 3501

    Hope this helps, Stu
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,801
    2,435
    Nov 17, 2011
    The datasheet for the thermostat says on page 2:
    (emphasis by me) which means you may not be able tp use them with a 12 V pump.
     
  5. Alec_t

    Alec_t

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    Jul 7, 2015
    That may not be possible with a simple mechanical thermostat, which will have ~ a degree or two of hysteresis between the turn on and turn off temperatures. The purpose of the accelerating resistor is to help minimise the hysteresis. Hysteresis is generally desirable, to avoid the pump cycling on and off frequently.
     
  6. cygnusv

    cygnusv

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    Oct 7, 2014
    A degree (or 10) differential wouldn't be a problem. The only reason for fitting this is so that the pump will start and stop itself without boiling or running all the time when the water is cold. We don't want to hear the pump any more than necessary.
     
  7. cygnusv

    cygnusv

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    Oct 7, 2014
    Ouch! I hope that's not the case. Can you get a 12 (or 24) volt pipe stat?
     
  8. Alec_t

    Alec_t

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    Jul 7, 2015
    I don't see any DC current rating in the datasheet for your stat? Methinks you could get contact arcing/welding :(.
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    I don't know. Please have a look yourself - I'd have to run a search, too.
     
  10. Alec_t

    Alec_t

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    Jul 7, 2015
    One option would be to use the existing stat to switch the coil of a standard automotive relay or similar. Such a relay has a relatively low coil current well within the stat's rating and its contacts are designed for relatively high DC currents (check the datasheet). Or for a solid-state option the stat could switch a power MOSFET to drive the pump.
     
  11. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    The automotive relay will not tolerate the mains voltage required by the thermostat.

    You could, however, use the thermostat to control mains power to the 12 V DC power supply - provided this is a mains powered power supply. So instead of switching the 12 V output from the power supply you turn on/off the power supply by switching mains.
     
  12. Alec_t

    Alec_t

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    Jul 7, 2015
    True, but as I understand it (if this thread relates to a previous one of his), the TS is not using mains voltage; just a 12V supply on a boat. Perhaps he can enlighten us?
     
  13. cygnusv

    cygnusv

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    Oct 7, 2014
    Yes it is 12 volt, but not actually my boat this time. We're actually 24 volts.
    I've wired the stat thru the common, marked number one, to terminal three ( make on rising temperature). The original problem I had was due to my own fault, a badly made connection. The stat is now working correctly.
    As usual, many thanks for your always welcome help and comments. Stu
     
  14. Alec_t

    Alec_t

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    Jul 7, 2015
    Glad you've got it sorted.
     
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