Volt meter on adjustable DC build only shows 15 Volts

Discussion in 'The Projects Forum' started by Seaker, Mar 7, 2013.

  1. Seaker

    Thread Starter Member

    Feb 3, 2013
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    Hello All;
    I have now finished my first project and nothing blew up on me so I consider this project a success.

    The design and drawing are shown at: http://www.sentex.ca/~mec1995/circ/VarReg1/VarReg1.html

    There is however one issue that is not working correctly.

    I purchased an Analog 30-Volt meter as indicated in the instructions and have it connecter as shown to a 10K Burns Trim Pot. The problem is that when I move my 5K Potentiometer to the right to achieve full power to the output lines the meter only shows 15 volts, not the 30 Volts that I thought it would show.
    I checked the output with a meter and it shows approximately 32 volts DC
    coming out of the box so that part of the circuit is fine. I tried to adjust the Bourns Pot and little difference could me achieved.
    I have redone the wiring with heavier wire and checked the connects several times. All appears correct, can any one tell me where I might have gone wrong?

    Thanks you in advance.
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,770
    970
    And have you adjusted P2 to "calibrate" the meter.
     
  3. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
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    The meter in the circuit diagram is a 1 ma current meter. That needs the trimpot/resistor in series to limit the current and make it into a voltmeter.
    The meter you purchased is a voltmeter, so the series trimpot + resistor are not needed.

    I just read the parts list. I understand the confusion. The list calls for "Volt" meter, but the circuit diagram shows a 1 ma current meter.

    And congratulations on completing your first project - and no smoke :)
     
    Last edited: Mar 7, 2013
  4. Seaker

    Thread Starter Member

    Feb 3, 2013
    32
    0
    Hello Tubeguy, thank you for the reply.
    What you are saying is that the author mentions using an Amp meter (1MA) as a volt meter and to do this he used the resister and Bourns Pot.

    As I have finished this project or rather nearly completed this project I need to remove the 27K resister as well as the 10K Bourns Pot then rewire the 30 Volt meter directly into the positive and negative main lines.
    I for the life of me do not understand why the author would confuse the issue by using a Amp meter as a volt meter for a novice project. I have a final question, with
    the configuration that I have at present, is it possible to add easily a digital Amp meter to this project?
    I am not sure what value it might bring as the maximum amperage produced by this project is 1.5 Amps.

    Thank you again for replying.
     
  5. tubeguy

    Well-Known Member

    Nov 3, 2012
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    I bet that was an honest mistake on the authors part.
    But it's tough when you are learning ... been there :)
    That's one reason I think this forum is such an invaluable resource.

    You could easily add an amp meter. You may know this already but an amp meter would be wired in series with the positive output, not between V+ an V- as the voltmeter is.

    Edit: You can make an amp meter with a 0.1 ohm resistor and a 200mv Digital Panel Meter from Velleman.
     
    Last edited: Mar 7, 2013
  6. MrChips

    Moderator

    Oct 2, 2009
    12,440
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    On a side note, most analog meters are just a coil suspended between the poles of a magnet. There are only so many turns of wire on the coil and therefore the coil has low resistance.
    In essence, all meter movements of this nature are ammeters and not voltmeters.
     
    Last edited: Mar 8, 2013
  7. bertus

    Administrator

    Apr 5, 2008
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  8. Seaker

    Thread Starter Member

    Feb 3, 2013
    32
    0
    I will be away for about 5 days and would like to spend a few minutes going over the replies.
    Thank you all for your responses!
     
  9. Seaker

    Thread Starter Member

    Feb 3, 2013
    32
    0
    I have now returned from my trip and I want to thank every one for their replies and valued information. This information has been a eye opener for me and I want to thank you for that.

    There is one last issue/enhancement that I would like your input on and that is whether having an amp-meter on this DC voltmeter would be of much benefit?
    The maximum Amperage on this design is only 1.5 Amps so I wonder if having the Amp-meter would be of much value.
    As I have completed the project I only have room for a digital amp-meter versus a analog meter, which should be fine if it is felt I could benefit from its addition.
    Thoughts please.
     
  10. MrChips

    Moderator

    Oct 2, 2009
    12,440
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    Depends. Having an ammeter is nice but not essential.
    It depends on what you plan to use the supply for most of the times.
    If it is usually to power hobby circuits we do not concern ourselves with the current drawn.
    If you are charging batteries, yes it is nice to know the current.

    There are other considerations and options:

    1) Since you do not have space for two meters, having an analog and a digital meter on your lovely masterpiece would look odd.
    I would not put a second meter on the front panel if you are tight for space.

    2) If you do need to measure current you can always insert an ammeter in series when needed.

    3) Now that you know that almost all meter movements are ammeters and how to convert from ammeter to voltmeter you can install a switch and select the function you need with the single meter.
     
  11. Seaker

    Thread Starter Member

    Feb 3, 2013
    32
    0
    Thank you Mr Chips for the reply!
    The unit is for general use and testing thus an Amp meter will be of little benefit I suppose.
    Thank you again!
     
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