mini volt meter help

Discussion in 'The Projects Forum' started by jessetattoo, Aug 24, 2012.

  1. jessetattoo

    Thread Starter New Member

    Aug 24, 2012
    4
    0
    first off im not that schooled on electronics,

    Now the project im doing is to hook up a small LED digital volt meter to the side of a tattoo machine, now iv ordered some off ebay and im using a 2A-18V ac into dc power supply that would run a tattoo machine. the main issue im having is the meter is only reading half of the volts im pumping into it, and even tho the meter says its rated for dc power from 3.5-17V when i run 10V thru it it only reads about 5.5-6V

    normal well tuned tattoo machines run at around 7-9V however at that low a voltage then meter drops off and will not display anything as it drops below about (3.5v display) it stops working. needs to be 9+ for the lights to even turn on and then its only reading at half or less.

    is there a way to boost whats its reading? or is this an amperage issue, something i know nothing of. please help

    [​IMG]
     
    Last edited: Aug 24, 2012
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,659
    632
    Its hard to diagnose without more detail, but taking a guess at a likely problem, if the voltage to the voltmeter is fluctuating, then the problem most is most likely that.

    Also, not seeing any specifications for the meter, I can speculate that you are running the meter's power supply voltage into the measuring input, and that might not be ok with the voltmeter .

    It seems the key is the specifications for the voltmeter. Do you have it?
     
    Last edited: Aug 24, 2012
  3. jessetattoo

    Thread Starter New Member

    Aug 24, 2012
    4
    0
    Features:

    • Brand new and high quality.
    • Measurement accuracy: 1%.
    • Refresh rate: about 200mS / times.
    • Display: Three 0.36 "digital tube.
    • Measuring range: DC 3.3V-17V (Can Measure Power Supply 3.3-17V Directly).
    • Input range: DC 3.3V-17V.
    • Display Color: Blue.
    • Operating current: Less than 20mA.
    • Operating temperature: -10°c -65°c.
    • Input impedance: About 100K.
    • Reverse polarity protection: None, please connect Red and Black wire correctly.
    • Wiring:.
    • Red: Power Supply +, Measure +.
    • Black: Power Supply -, Measure -.
    • Size:2.3cm x 1.4cm - 0.91inch x 0.55inch.
    one thing that concerns me is at first glance it seems to be rated for 3-17v however it will not even fire up if i use less then about 9volts, and only reads about 4-5v when using 9 ???
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    Is there a potentiometer on the back or something to "calibrate" the display?
    Have you tried just attaching it to a 9V battery or something to see if its working correct?

    Are you sure you aren't feeding it AC?

    Do you have a real multimeter/voltmeter to check it against?
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,148
    3,058
    Is it possible you are connecting your meter in series with your machine, instead of in parallel, across it's terminals?

    When the meter reads 4 and you think it is seeing 9, use another meter to check what is really going on. Your display could simply be faulty.

    The display needs 20mA. Can we assume the tattoo machine uses much more? In other words the display is not overwhelming the power supply, is it?

    Or is the tattoo machine connected when you are seeing the low reading? Maybe it's pulling the voltage down.

    Bottom line, you need a second meter for testing.
     
  6. jessetattoo

    Thread Starter New Member

    Aug 24, 2012
    4
    0
    I do have a normal voltmeter and it reads the 10 for 10v when i hook it up to the powersupply, and no machine is hooked up when i test the mini out, when i hook it up to a 9v bat it reads about 5.5v im starting to think its just the little LED meter is junk, i did order it from china after all. however is there any conceivable way to boost it ?
     
  7. lordofentropy

    Active Member

    Apr 10, 2010
    52
    0
    are you powering the voltmeter from the same source? If so, don't. Make sure to calibrate it as well.
     
  8. wayneh

    Expert

    Sep 9, 2010
    12,148
    3,058
    You may be right. But when it reads 5.5v for the 9v battery, what does your other meter read? An aging 9v could easily read that low under a 20mA load.
     
  9. jessetattoo

    Thread Starter New Member

    Aug 24, 2012
    4
    0
    other (normal) volt meter reads 9 for 9 volts off the batt, as its new. there has to be a way to boost the signal without actually cranking the voltage on the power supply, idealy i would like to run my machines in the 7-9 volts range and have the mini volt meter even just work for aesthetics, but at that range the meter just dont fully light up

    and there is no way to calibrate the meter as it has no parts its just a lil box with 2 wires
     
    Last edited: Aug 24, 2012
  10. wayneh

    Expert

    Sep 9, 2010
    12,148
    3,058
    IMHO, you're out of luck. Short of busting it open, there's not a lot you can do.
     
  11. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    yep..China trash.
     
  12. lordofentropy

    Active Member

    Apr 10, 2010
    52
    0
    Some of these seem good

    http://www.ebay.com/itm/12V-DC-RED-...UGE-VOLTMETER-4-BOAT-/170890103625#vi-content

    http://www.sourcingmap.com/plastic-housing-10a-digital-panel-voltage-meter-voltmeter-p-165530.html

    http://www.sourcingmap.com/dc97a-35...tic-red-led-digital-panel-meter-p-240917.html

    http://www.suntekstore.com/goods.php?id=14001844&utm_source=gbus
    (can't calibrate this guy, it looks like)

    Whatever you get, check to make sure there is a pot on it so you can calibrate it. Set power supply measuring at 0V, and make sure meter reads 0V, now move to some other voltage...say 10V and check measurement. After that, do a slow sweep of voltages to make sure meter is measuring the voltages power supply is sweeping through.
     
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