How to add vintage DC voltmeter and ammeter to 110vac circuit?

Discussion in 'General Electronics Chat' started by Lauri Mueller, Dec 3, 2015.

  1. Lauri Mueller

    Thread Starter New Member

    Dec 3, 2015
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    I have a vintage set of gauges for DC current that I want to make into a steampunk wall display that animates when I turn on the light that's also connected to the circuit. They don't need to read accurately and actually if there is a way to trick the meters to read higher than actual I would love to hear it since they both go 0-75 and all the converters I see only get to about 24v and 10amps. gauges.jpg

    Anyone have any ideas on how to make this work? Is it really just a matter of adding a 110vac to 24vdc converter between the switch and the gauges?
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
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    First step is to determine what those meters want as far as an input. Most likely, they are bare meter movements, the labels on the meters can be meaningless, just an indicator of what the original instrument was measuring.

    Some meters do contain internal current shunts or resistor dividers, you need to sort this out before proceeding- this makes the project far more difficult.

    If they are bare movements, you need to determine what the full-scale current is.
    (typically in the range of 100 -1000 uA - sometimes it's even marked right on the front)

    Then the simplest way to drive them is to get a small AC wall wart power unit with 5 V output and connect a resistor in series with the meter sized to produce the full scale current when the power is on.
     
  3. Lauri Mueller

    Thread Starter New Member

    Dec 3, 2015
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    Thanks for the reply. Isn't the item in the lower right a shunt? I'm not that familiar with shunts but from articles about shunts it looks like one. The ammeter label says to use with an external shunt. These meters came off a military charging device.

    I get your thought about simply using an AC wall wart converter to power the meters but I was hoping to make them animate in conjunction with turning on a steampunk-theme chandelier on a wall dimmer switch. Was going to take apart the old rheostat in the picture and use the dial part on a regular dimmer to give the illusion it was operating the light. So I want to have the meters on the same circuit somehow so they react. I realize that's a whole can of worms I may be opening but thought I would ask before I dismissed the idea. I'm full of awesome ideas I don't know how to execute, lol.
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    Welcome to AAC!

    You could use a photoresistor in a current source to vary current in the meters based on ambient lighting. You could use shunts or skip them and just drive the meters with an appropriate current.
     
  5. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Yeah- the thing on the lower right is a shunt- or 4 terminal resistor. (same thing)

    The dial control idea is cool, but then it gets more complicated and you don't want to mess around with the high voltage mains.

    You could make your own unregulated power supply with a simple step down transformer + diode bridge + capacitor.
    Then the output voltage would vary as you turned the dimmer (expect not-so-linear behavior at the low end) and the meter would move as such.

    The transformer provides safety isolation from the mains.
     
  6. Lauri Mueller

    Thread Starter New Member

    Dec 3, 2015
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    Thanks for the ideas, you've given me something to mull over. I agree that I don't want to attempt anything that will burn down my house. I'm totally good with installing lighting and adding outlets, switches etc. but this is more complicated than anything I've ever attempted. My brother worked in electronics building computer monitors back in the day so he may be able to help. He taught me how to replace capacitors on a board when my Samsung flatscreen went down. Still works years later :) Happy Holidays!
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Sensacell beat me to it.

    ak
     
  8. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    You don't need to make your own supply. A walwart should do. Very safe. If you are a packrat like me you should have a box of them at home. I like dl324's idea. If it is a static display, you might as well glue the needles in place. dl324's idea gives some movement to the needle.

    You could really go crazy and at a proximity sensor. As people walk up to the panel the needles would move! Or a small mic and have a crude vu meter.
     
  9. Lauri Mueller

    Thread Starter New Member

    Dec 3, 2015
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  10. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    You can just create your own crude volt meter. But you need to decide, what voltage want to measure. So what do you want to measure?

    If you purchased a meter you would need to buy a vintage meter as most of the multi meters today are digital. You would need to find one with an analog meter. And most meters were battery operated. I don't recall seeing a n AC operated meter since the days of the VTVM (vacuum tube volt meter ). Perhaps a bench meter would be AC.
     
  11. Lauri Mueller

    Thread Starter New Member

    Dec 3, 2015
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    The meter in that eBay link is analog, AC and has a range of 0-150v. Seems like that would work unless I don't understand something. 110v wouldn't top out the meter and there would be plenty of room on the gauge to show the dimming of the voltage.
     
  12. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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  13. spinnaker

    AAC Fanatic!

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    What eBay link?
     
  14. Lauri Mueller

    Thread Starter New Member

    Dec 3, 2015
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  15. Lauri Mueller

    Thread Starter New Member

    Dec 3, 2015
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  16. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    That is basically the same meter that you have. It is just the movement. The reason they say AC is because of the little sideways S symbol stamped on the meter face. Nothing to do with how it is powered.
     
  17. Lauri Mueller

    Thread Starter New Member

    Dec 3, 2015
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    now I'm totally confused. The second gauge is definitely better in terms of the voltage range it measures. Can't I simply wire from the dimmer to the gauge to the light fixture? The current passes through the gauge, right?
     
  18. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    I like that eBay meter. It is new, no crusty old parts, it is already set up for what you need as far as range.
    All you need is a brass case and some steam vapors pouring out of it.

    I might buy one for myself.
     
  19. Lauri Mueller

    Thread Starter New Member

    Dec 3, 2015
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    LOL, here's a working gauge with a steampunk look already. Wish it didn't have a 300v range because the needle won't travel far but it's good to go:

    http://vintagewireandsupply.com/steamlight-gauge-antique-copper/

    They also sell just the shell if I wanted to attempt to use the eBay one's guts inside:

    http://vintagewireandsupply.com/steampunk-gauge-kit-antique-copper/

    Based on this picture, it's basically what they did. I would make a more vintage face and swap out the dial hand with a fancy watch hand. The face looks too modern:
    SteampunkGauge_Brass_3__15504.1443102125.1280.1280.jpg
     
    Last edited: Dec 4, 2015
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  20. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    FWIW:

    The way your fist pic is SUPPOSED to work, PROVIDING the little black piece is "designed" for the DC ammeter is
    1) the little black piece is called a shunt. It has big and little screws, It's basically a 4-terminal precission resistor. The BIG screw go in series with the DC load.
    2) the DC Voltmeter would go across the DC load to measure the voltage,
    3. The Ammeter is really a voltmeter designed to measure a small voltage, Let's let it be 75 mV for 75 Amps. (This is an example only), so it's little terminals go to the Ammeter masquerading as a voltmeter.

    So, the meters are low current ammeters. When you add an external resistor (usually internal) they become voltmeters. Ammeters with shunt s can't pass the large currents, so the sensitive ammeter is turned into a voltmeter to measure the voltage across the shunt. There's plenty of room to "hide" these components inside or even externally/

    So, what you have is UNKNOWN except for the fact that they are designed for DC.

    The shunt should have some numbers on it. Like 100 mV 50 A or something. If they were a set, your good.

    The voltmeter LIKELY measures voltage like it says.

    You can find the characteristics of your meters with some tricky measurements.
     
    Last edited: Dec 4, 2015
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