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Measuring AC Voltage and Current with the Basic Stamp — Parallax Forums

Measuring AC Voltage and Current with the Basic Stamp

McCordPDMcCordPD Posts: 4
edited 2006-10-23 13:39 in BASIC Stamp
I need to monitor ac line voltage and current in device I am designing, the voltage will be either ~120v or ~240v depending on configuration, so I would like one solution that would work for both, as for current, I need to have a useable range of up to 50A (I assume that I will be using a Current transformer with a 200:5 ratio) (they are cheap)...

if either to voltage or current is above or below a preset threshold, I want to turn an output pin off (low)

Anyone have any ideas?
-Rich

Comments

  • Sutton MurraySutton Murray Posts: 88
    edited 2006-10-22 10:33
    What does the circuit draw? Will this have one same device connected to it on 120v and 240v, meaning that you will have a fixed current load device used. If so i winding working as a electro magnet, one that can handle both 120v and 240v. This lined up with a hall-effect sensor in turn connected to a A to D Ic. This should give a different voltage reading at the 2 different volts. But some kind of stabled or know drawn on the high current needs to be known. If i under stand you right you want to measure the voltage and the current at the same time. 2 off the 3 values are needed to be know V=I*R. So test must be in two stages first to measure one take the answer (save the answer in the stamp memory) and then measure the next. I don't believe you are going to find a solution testing both at the same time, as meantioned "one solution working both"
  • Tommy BotTommy Bot Posts: 60
    edited 2006-10-22 17:47
    For the Voltage if you are concerned with present/not present then run your control voltage in parallel with an appropriate relay to hold down the coil during normal operation.·Connect Vdd to the hinge side of the contact, and the N/C side to an input.



    Gotta think for the low current issue. There's plenty of options, but not as straight forward as a 10 dollar relay.

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  • McCordPDMcCordPD Posts: 4
    edited 2006-10-22 21:23
    I actually want to measure the ac line voltage with the basic stamp... if it is too high or too low, I wish to turn an externial device off via a relay...
  • Tommy BotTommy Bot Posts: 60
    edited 2006-10-22 21:41
    It would be easier without a Stamp.
    The stamp itself can't handle that kind of voltage so an external device would be needed to monitor line voltage.
    Such a device could be purchaced with settable alarm outputs (dry contacts) to directly control things.

    That's not to say that you "couldn't" route that signal into and back out of the BS2, but it would be wasting 2 I/O points.


    Still not what you need, but I'm just thinking out loud.

    Tommy

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  • McCordPDMcCordPD Posts: 4
    edited 2006-10-23 06:11
    What I want to do:
    I am wanting to use a basic stamp to control a large AC motor, this motor may be powered by either 120v or 240v line (i would love to have a single solution for both) this motor could draw anywhere between 10A-50A depending on size...

    this motor will be in a hostile envirorment, and I want to protect this motor wich only runs 20% of the time...

    if the ac voltage is either 30v above or below 120v or 240v whichever the case may be then I want to turn off the motor...
    if the current draw of the motor is 20% above or below a set threshold I want to turn it off as well...

    I am looking for a way to interface whatever I need to do to make this happen, I understand I will need an a/d chip, any ideas as to which one, and how to do what I want?

    do I need something other then a stamp? perhaps a pic, or arm?
  • Tommy BotTommy Bot Posts: 60
    edited 2006-10-23 13:39
    McCord,



    Check out this link, it will give you·info on what someone else did·to utilize a micro controller for a similar application:

    http://groups.google.com/group/sci.electronics.design/browse_frm/thread/c406881489ff63ea/90317c3c7714b031?tvc=1#90317c3c7714b031



    This one is·general info, not relating to micro control.

    http://www.allaboutcircuits.com/vol_4/chpt_5/4.html



    Hope that helps.



    Tommy



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