Getting an amp meter to work

Discussion in 'General Electronics Chat' started by jcubie, Feb 2, 2016.

  1. jcubie

    Thread Starter New Member

    Nov 22, 2015
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    I am a model railroader. The type of power that i use, called DCC- produces an AC wave that cannot be read accurately with a multi-meter. A website recommended using a full bridge rectifier to change teh wave to a DC wave that the meter can read. I have built the rectifier and it measures both peak and average voltage well -- after adjusting for the loss of V by virtue of the inclusion of a CAP in the circuit. The site also advises that you can use a full bridge rectifier to measure amps. My power supply puts out about 13 V and 3.3 A. I first built a rectifier out of 4 1n4001 diodes but it got hot very fast -- since as it turns out the diodes are only rates at a fraction of an amp. However, I did get a reading near 3.3 A. I then bought a Vishnay full bridge rectifier # KBU4D. When I use it the max amps I can measure is 0.3 amps, even with a very heavy load on the circuit. I though that there might be a cap built into this recitifier but I cannot see one in the spec sheet.

    Any advice?
     
  2. SLK001

    Well-Known Member

    Nov 29, 2011
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    228
    The 1N4000 series diodes are rated at 1 amp max.

    Your bridge rectifier is probably bad. Look for some 6 amp diodes and build another bridge. Capacitors are not normally built into bridges.

    You don't use DC PWM for train control? What is DCC? Why can't your multimeter read AC accurately?
     
  3. jcubie

    Thread Starter New Member

    Nov 22, 2015
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    DC is a straight dc flat dc signal. DCC is a square wave signal that both delivers power and allows one to control many function on a model train engine -- sounds, lights, engine characteristics etc. Does it matter what diode I get as long as it is rated 6 amp?
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,791
    945
    Doesn't even need to be 6 amps could be 4 or 5 or 8 etc.
    It MUST be rated for more than the system max output if you want it to last a reasonably long time.

    A single diode followed with a cap of a few hundred micro farad will be enough to get a decent average DC voltage level reading if digital "hash" is causing problems with your meter. (Polarity must be obeyed for meter connections).
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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  6. Bordodynov

    Active Member

    May 20, 2015
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    Use my schema rectifier bridge. Power dissipation is minimal.

    rectifier_bridge.png
     
  7. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Its not a Sinewave he needs to measure, its a fixed value square wave with frequency shifting data.
     
  8. Bordodynov

    Active Member

    May 20, 2015
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    Sinewave is only example.
    My rectifier bridge can also work the other waveform. A more detailed description of your signal.I I do simulation of your process.
     
  9. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Read post #5 then..
     
  10. Bordodynov

    Active Member

    May 20, 2015
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    See:

    rectifier_bridge2.png
     
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