Dual float switch circuit

Discussion in 'General Electronics Chat' started by GRNDPNDR, Oct 5, 2016.

  1. GRNDPNDR

    Thread Starter Member

    Mar 1, 2012
    435
    7
    Someone on facebook posted this as a dual float switch circuit. The middle block is apparently a DPDT relay.

    at any rate I'm sure this is wired up all wrong but can't really sort it out myself

    At the very least could someone tell me what the diode might be for and if it's actually necessary? 14492588_10154615007652220_3663165223008130999_n.jpg
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    With a DC relay coil, the diode suppresses a voltage spike that happens when you turn off the relay. That spike can damage other electronics in the area, especially the transistor driving the relay coil (if there is one). For an AC relay coil, it might be a part of some cutesy trick to make a normal relay a latching relay, but I'm just guessing there.

    Can't comment on whether the circuit will do what you want, because you haven't told us what you want the circuit to do.

    ak
     
  3. N11778

    Member

    Dec 4, 2015
    39
    7
    the diode is a noise suppressor to protect the float switches and reduce noise in the ckt.
    looks like it turns on the pump with the bottom float switch.
    and turns off the pump with the top float , ????? would be nice if they showed the relay contacts
     
  4. GRNDPNDR

    Thread Starter Member

    Mar 1, 2012
    435
    7

    it's not my circuit, and apparently the bottom float switch will be "upside down" so when it's "on" it will turn the pump off. the upper float switch will turn the pump on.

    He's got it built and working apparently.....so I guess this thread is moot, but thanks for the info on the diode, I couldn't remember it's function.
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Don't think so. Every half-cycle of the 24 Vac it presents a dead short to the driving circuit or power source. With a current-limited source it could be used to allow a DC relay coil to function in an AC environment, but I'd think the contacts would chatter.

    ak
     
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  6. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Without identification of what the terminals are, it's impossible to even guess. Is it using the NO or NC contacts? Is it even wired correctly, as the COM contacts are not identified.

    And +1 to ak's observation.
     
  7. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    AC coils typically don't have the diode. DC coils do. When a DC coil opens, a kickback pulse is thrown back into the electronics. The diode prevents this.

    Depending on the relay, sometimes the contacts are protected. Meaning, an AC rated ZNR is placed across them for AC operation. For DC operation, again transorbs or capacitors. It was recommended for a safety critical system I installed that interfaced to the fire alarm panel.
     
  8. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,005
    745
    Should be DC supply not AC.....
     
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