ammeter shunt placement

Discussion in 'General Electronics Chat' started by bwanna, Jan 28, 2014.

  1. bwanna

    Thread Starter Member

    Nov 19, 2012
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    That's a good question. The bus is actually only in the neg side. The power source has a single point of generation and then splits out to each of the subsystems. The power source's ground side connects to the Neg bus.

    Because of this, I'd be concerned with simply placing the shunt between the power source Neg and the Bus, for fear of other subsystems bypassing the shunt (by nature of directly being connected to the bus elsewhere.)
     
  2. bwanna

    Thread Starter Member

    Nov 19, 2012
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    I agree with your observations... it seems some of these are designed in a way that doesn't allow sharing V+
     
  3. bwanna

    Thread Starter Member

    Nov 19, 2012
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    I've ordered a dc/dc isolator to power just the meter. Should be here by weekend. I'll post an update.
     
    Last edited: Jan 29, 2014
  4. BillB3857

    AAC Fanatic!

    Feb 28, 2009
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    Sounds like the problem has been solved. Let us know how it turns out.
     
  5. inwo

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    Nov 7, 2013
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    I'm not convinced. As we don't have the details.

    If this is measuring battery current, either high side or low side, and battery is sometimes being charged, it needs to read positive and negative.

    If it is reading current to the load, and charging circuit goes direct to battery, then it should be ok. But then whats the point of the meter?
     
  6. bwanna

    Thread Starter Member

    Nov 19, 2012
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    I agree that placing the shunt in line with the batter (pos or neg) will only read what's happening with the battery. Placing the shunt in line with the generator (pos or neg) will only read what's happening with that.

    Since there are multiple connections for the neg (hence the use of the term 'bus'), my test will be to place the shunt in line with the generator pos using a DC/DC isolator to power the meter. With this approach I recognize that I'll only be measuring what the generator is doing and foregoing what is happening with the battery.

    To know what's happening to the battery, I'm going to design a simple Charge/Discharge Indicator circuit that turns on an led (Green/Red) corresponding to the status, respectively.

    Between these two, I'll be able to know fairly well what the draw is on the two power sources.

    I found this. Seems like it does what I want regarding the Charge/Discharge indicator of the battery:
     
    Last edited: Jan 29, 2014
  7. MrChips

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    Oct 2, 2009
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    Why not just install one of these and be done with it?

    [​IMG]
     
    Last edited: Jan 29, 2014
    inwo likes this.
  8. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Surely you're not implying this "theoretical" exercise is an automotive modification? :rolleyes:
     
    Last edited by a moderator: Jan 29, 2014
  9. MrChips

    Moderator

    Oct 2, 2009
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    The OP wants to know the pros and cons of placing the current sense meter on the +ve side or -ve side of the battery.

    The OP would also wish to know whether the battery is charging or discharging.

    A center-zero ammeter as shown above placed on either side of the battery will provide the OP with the information he seeks.
     
    Last edited: Jan 29, 2014
  10. bwanna

    Thread Starter Member

    Nov 19, 2012
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    Agreed. This would be nice. Do you happened to know where these are available in a digital led read out? I haven't found any. That's what prompted me to ask the original question since I had to choose.

    And this has nothing to do with automobiles! Lol
     
    Last edited: Jan 30, 2014
  11. BillB3857

    AAC Fanatic!

    Feb 28, 2009
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    A lot of the 200mv digital volt meters will read either polarity and indicate negative voltage with a (-) sign ahead of the voltage reading. With a shunt, the polarity of its output will show the direction of current via being positive or negative output from one sense connection to the other.

    edit... here is an example.. http://www.jameco.com/1/1/24297-sp-300-3-1-2-digit-led-voltmeter-module.html
     
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