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  1. #1
    Join Date
    Dec 2009
    Posts
    7

    24 Volt AC latching Saftey Circuit on UPS???

    So we have a circuit that consist of simply 5 botd devices (break on temperature drop) "Freeze Stats". The unique thing about this circuit is that there is a reset in the control panel so the voltage runs through the freeze stats and when on trips.... the relay opens the entire circuit. So we have an uninterpretable power supply and when we lose power the UPS take approx. 30 milliseconds to kick power to all the devices on it. During this time the relay loses power and it acts as if a freeze stat has tripped. The job was speced for this "one button reset".

    Does anyone have an idea how to keep power to the relay for 30-100 milliseconds while power from the ups is kicking in?

    We have already tried a small 63 volt dc non polarized capacitor. This does not work.

    Any ideas would be greatly appreciated!!!

  2. #2
    Join Date
    Sep 2007
    Location
    Under the sea
    Posts
    235
    Lump
    UPS = Uninterruptible Power Supply!
    if the power on the output of your UPS drops for 30ms.... You need a new one!

    What brand UPS is it?
    In case of malfunction-Reconnect brain BEFORE starting mouth.

  3. #3
    Join Date
    Sep 2009
    Posts
    141
    Use an on-line UPS solution for either your UPS or provide a second UPS just for the control circuit. In an on-line UPS there is zero interruption in power but you pay for it with higher cost and generally a shorter battery lifespan.

    D1G

  4. #4
    Join Date
    Mar 2008
    Posts
    82
    Would a time delay relay work in this application? I don't quite understand how you have this wired. If you could explain the detail of the circuit a little better I may be able to help.

  5. #5
    Join Date
    Dec 2009
    Posts
    7
    APC

    We contacted the manufacturer APC and this is standard protocol. We are experiencing this issue on 9 control panels

  6. #6
    Join Date
    Dec 2009
    Posts
    7
    I'm a novice so I recommended a time delay relay do the make on that will stay closed for a period of time we would want it to be a short period like 5 seconds due to the nature of the circuit.

  7. #7
    Join Date
    Sep 2009
    Posts
    141
    You will always have it with a line-interactive or standby UPS, there is a delay between the time you lose power and the processor can switch to the battery.

    An on-line UPS (sometimes called an in-line UPS) the incoming AC is constantly rectified through the battery then inverted back to AC for the output. If AC input is lost or drifts the battery is already supplying power to the inverter, hence no time delay.

  8. #8
    Join Date
    Dec 2009
    Posts
    7
    Quote Originally Posted by D1G View Post
    You will always have it with a line-interactive or standby UPS, there is a delay between the time you lose power and the processor can switch to the battery.

    An on-line UPS (sometimes called an in-line UPS) the incoming AC is constantly rectified through the battery then inverted back to AC for the output. If AC input is lost or drifts the battery is already supplying power to the inverter, hence no time delay.
    We may be forced to try this route I was hoping we could just add something to the circuit, but DIG thanks for the advice

  9. #9
    Join Date
    Sep 2004
    Location
    SoCal
    Posts
    449
    McQuay was famous for using Make-On-Pressure-Rise (MOPR) safety circuits where if the hiigh pressure safety switch closed (set at 400psi) it energized a DPDT relay that opened the compressor safety circuit through the normally open contacts and closed a set of contacts parallel to the high pressure safety circuit - thereby locking out the compressor control and keeping the lockout relay energized until you cycled the control power through a toggle switch. Their issue was POS encapsulated pressure switches that didn't make and the PRV relieved the pressure when the water treatment guy forgot to turn the tower fan back on.

    Hmmmm, I guess this has not much to do with you predicament....unless you can change out all 5 freeze stats..... Are they SPDT? Could you rewire the safety circuit - or is this a factory item?

    Crab, how do you like to handle safeties?
    lb
    A hundred million nodes - it's a LON story.

  10. #10
    Join Date
    Dec 2009
    Posts
    7
    This Forum is great thanks for all the help floks....

    I will try to get a schematic and specs on the relay to better inform you guys of my problem! Won't be able to do it until tomorrow!

  11. #11
    Join Date
    Mar 2008
    Posts
    82
    Try to explain exactly how it is wired and the sequence of operation. Are the freezstats wired in series? are they auto reset? What is the relay and how is it wired? What power is running through it?

  12. #12
    Join Date
    Dec 2009
    Posts
    7
    I can tell you yes all freeze stats are wired in series and yes they auto reset... I need to look at the circuit again to tell more.

  13. #13
    Join Date
    Nov 2008
    Posts
    1,673
    A mechanical dashpot may hold the relay armature in long enough, but make sure it does not cause other problems.

    A capacitor usually won't work with a relay using an AC coil, and changing that relay to one with a DC coil may be more than you want to get into.

    If you do decide to go with the DC coil I can help you design a simple circuit to do this 100 mS delay.

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