Ckt to monitor backup generator

Discussion in 'The Projects Forum' started by kbirecki, Oct 22, 2009.

  1. kbirecki

    Thread Starter New Member

    Oct 22, 2009
    20
    0
    Greetings! I'm putting together a way to monitor our office power, specifically when it switches to a backup generator, and when the backup generator performs it's monthly self-test. I'm going to monitor and log all of this on a computer (and eventually page me if there is a problem).

    Essentially, I'm going to use three power adapters from discarded equipment (each will output 8-12 VDC) and plug them into each power circuit I'm going to monitor - one on the local electric company side, one on the generator side, and one on the load side. Then the output from the adapters will be connected to a serial input on a computer running a VB6 application that polls the serial port. I've worked out how I can monitor three distinct inputs using a single serial port, and the essence of the VB6 app that needs to read inputs from the serial port. My question relates to checking if there is any concern using power adapters providing signals directly to a computer serial port. I am planning to put single-socket surge protectors on each adapter to hopefully protect against reasonable surges. The monitoring computer is going to be about 30 feet away from the outlets it will be monitoring.

    In addition to the surge protectors, should I put some kind of isolation ckt between the outlets and the circuitry providing inputs to the computer? (An OpAmp, maybe?) The output voltages of the power adapters (8-12VDC) are perfectly acceptable and within the range of a serial port. I know in the extreme case of lightning strikes, all bets are off, but are there any recommendations for protecting a computer when taking inputs connected to power outlets?

    Thanks in advance!
    Ken
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    I'm be really suprised your Generator/automatic transfer switch,etc.. doesn't already have functionality built in (like simple relay contact closures) to let you know the status. Thats typically standard features.. Plus there are already products to do what you want.

    Not to mention how electric companies strongly discourage messing with their side of the equipment. You'd better be darn sure that a failure in your rigged up system doesn't cause a hazard on their side..
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    The wall-warts provide Ohmic isolation from AC side to the DC side, right?

    Between the 10V wall-wart and the computer port I would use two series 1K resistors, a shunt capacitor, a shunt zener as shown, and a pull-down resistor. With the Wall-Wart powered, the Port-Pin should be high. With the Wall-Wart unpowered, the 470Ω resistor should pull the Port Pin low. The two series resistors, zener, and capacitor provide a modicum of lightning protection.
     
  4. kbirecki

    Thread Starter New Member

    Oct 22, 2009
    20
    0
    Thanks for the quick feedback. The ATS that we are getting does not have this capability built-in. They are available, but they cost more than we're willing to pay. And I'm not really messing with any provided equipment. I'm just going to have the installer put three outlets next to the circuit box and ATS that are connected to each of the three circuits I want to monitor, then I am going to plug in a power adapter to each. I agree about not messing with the internal circuitry of the ATS. In my original message I mentioned placing three outlets: one on the local electric company side, one on the generator side, and one on the load side. What I really meant when I mentioned "electric company side" was an outlet that only has power when the electric company juice is flowing. And by load side, I meant the load that will be supplied by power from the ATS, so I know it is working. Not the whole building. We're just planning on supplying power to critical areas.

    And I am aware there are products available that do this and much more. All I want are the very basics of "is it on or off" and "is the generator still doing it's self-test as scheduled". My expenditure so far is a whopping $6, and I think my costs for what I am doing may swell as high as $10, plus some of my time. It's just a pet project. I already have the power adapters from old equipment, and I write software for a living. It’s extremely easy to interface with a serial port. However, my electrical training is so old since I don't use it, I just don't know what I don't know. The products out there that do this cost several orders of magnitudes more, and based on my research also require something like a "Power Manager" to interface with the generator, so the costs keep adding up. (It’s the old “Sure, I’ll sell you a monitoring device. That’ll be $X. Now, if you want to be able to use it, you also need this interfacing-what-cha-ma-call-it to actually hook it up that costs an additional $Y.”)

    I can make my own notification service, web interface, and be as fancy or plain as I want, as time permits. I just don't want to blow up my computer. That's the core of my question. I'm not expecting to turn this into a saleable product either. It’s just for internal company use.
    Thanks,
    Ken
     
  5. kbirecki

    Thread Starter New Member

    Oct 22, 2009
    20
    0
    Thank you, MikeML. I appreciate the help. I'll put it together and play my "Back To The Future" DVD and see if the lightning protection works...:)

    I appreciate you and Mcgyvr replying so quickly. I'm not sure how much help I'll be, but I've read a lot of great posts on this site and I'll troll around to see if I can pay the favor forward.
    Have a good day!
     
Loading...