Digital Ammeter and Voltmeter

Discussion in 'Tools' started by paul_l, May 26, 2020.

  1. paul_l

    paul_l Staff Member Administrator

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    I am in the process of rebuilding my test track / rolling road, and decided to fit a Voltmeter and ammeter to the build.

    Now I already have two Digital Multimeters, but is a faff having to set them up, looking on Ebay I came accross these, for the princely sum of £3.99 for the 10A version Ebay Listing

    upload_2020-5-26_23-15-59.png

    upload_2020-5-26_23-16-44.png

    upload_2020-5-26_23-15-20.png

    They arrived today - a week earlier than advertised, quicker than some stuff sent from the UK :facepalm:

    Of course now I have to cut a rectangular hole for it in 18 mm MDF :scratchchin:

    Paul
     
  2. Mr Porter

    Mr Porter Failure is always an option. Full Member

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    Excuse my ignorance, but how will you wire it up, and what will it tell you. Can you use it on DCC ?

    :headbanger:
    Jim
     
  3. Wolseley

    Wolseley Full Member

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    Simple. just use a rectangular drill.

    Jim
     
    Toto likes this.
  4. paul_l

    paul_l Staff Member Administrator

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    Hi Jim

    Two very good questions, as no wiring instructions are provided :facepalm:.

    First the DCC question, not really, but ...... there is always a but, I will use it to measure the feed to the DCC command station ( in my case an NCE PowerCab), so I can measure the total consumption of the system. For accurate current measurement of DCC you need to use a RRampmeter - approx £85, not going to happen on my work bench, I've lived in Scotland far too long and must have passed through Yorkshire on the way :avatar:.

    The issue is DCC is a high frequency Square wave AC, and Standard Multimeters are designed to measure AC at between 50 & 60 Hz in a sine wave, so the measurements will not be accurate, but will give an indication.

    Now the wiring question.
    I will be using this to measure the DC supply to either the NCE Powercab, or the DC current consumption of the loco, used for running the loco on the rolling road before installing a decoder. The consumption measurement afterrunning in will help determine the decoder, especially with an O gauge loco, if a smaller decoder will work, there is no need to spend twice the cost (and size) if an OO gauge decoder will work.

    Consider the meter as two separate meters

    [​IMG]

    The Ammeter I+ & I-, just connect this in series within the circuit

    + ve ]--------(I+ I-)------(Load - e.g. Loco)-------[ -ve

    The thicker cable supplied will take the full load through it.

    The voltmeter
    Connect GND (balck wire) to the Negative terminal of your DC supply,
    Connect VCC (yellow wire) to the positive terminal of your DC supply - used to power the device
    Connect VIN (red wire) to the place you wish to measure the voltage - for me this will track +ve, and will be connected before the DPDT switch used to set the loco direction

    Hope that helps

    Paul
     
  5. paul_l

    paul_l Staff Member Administrator

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    :avatar:

    Funny you should mention that, I'm sure I have one kept in a safe place for future use - unfortunately my Mum, always said I never looked far enough in to the future, so I'm damned if I can remember where it is :avatar:

    Actually I do have a mortice cutter, but need to replace the bit, but (and another but), I'm leaning towards 3D printing a facia plate as I need to build a controller board as the only DC controller I have is an old H&M Duette.

    Paul
     
  6. Mr Porter

    Mr Porter Failure is always an option. Full Member

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    Thanks Paul
    :headbanger:
    Jim
     
  7. Toto

    Toto I'm best ignored Staff Member Founder Administrator

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    I'm glad Paul answered that and not me.

    I'm using mine for the same purpose. Testing current draw for the purpose of evaluating what type of chip a loco would require.

    It will be attached to a unit on my rolling road and the figures will be assessed when any loco / kit etc is being run in. I would imagine the current draw will decrease slightly over the period of the run in period as the loco motor beds in. Probably negligible but the reading after run in will be the one to use I'd think.

    Cheers

    Toto
     
  8. Keith M

    Keith M Staff Member Moderator

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    Forgive my ignorance (as I use Lenz controllers), but I thought the NCE stuff already had a built-in ammeter in the handset???
    Keith.
     
  9. Graeme

    Graeme Full Member

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  10. Toto

    Toto I'm best ignored Staff Member Founder Administrator

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    Interesting.

    One reason behind getting the independent meter is that when testing and running in a loco build, I usually run them from a DC supply. The intention is to have the meter in line with that between the controller and the rolling road.

    Toto
     
  11. paul_l

    paul_l Staff Member Administrator

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    Yes, but the current draw on a powercab is 1.5A max, with most OO decoders supplying 1.0 to 1.5A max draw for a short while and considerably less for normal running.
    My intension is to run the loco in then establish the stall current by pushing down on the loco until the loco stalls, keeping an eye on the current draw, if the stall current is between 1 and 1.5 A then I can get away with a TCS T1.

    I will need to build myself a simple DC controller, but thats another challenge :avatar:

    Paul
     

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