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Re: old ammeter

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  • Kerim F
    Message 1 of 51 , Feb 17, 2013
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      ... Will the meter have to measure AC voltage or current? At the input of the variac or its output?

      --- In Electronics_101@yahoogroups.com, Dave C <davec2468@...> wrote:
      >
      > I want to place this meter in a case with a variac to use on my test bench. I would like to switch the variac in or out of the circuit: either vary the mains voltage going to the device under test or provide it directly.
      >
      > There is always the possibility that the device under test might be short-circuited. In this case the breaker on the bench will trip, but in the high-current interval the meter is at risk of being damaged.
      >
      > What are some means to protect the meter from damage under such conditions?
      >
      > Thanks,
      > Dave
      >
      > -=-=-=-
      >
      > > In some applications, the current of the meter has to be controlled, for example to build a voltmeter by adding a series resistor with the meter for example. In the later case, if we look to have a linear scale on the meter of the measured voltage, the resistance of the series resistor (passive... or active as by using a transistor if the input voltage range is relatively low) should be much higher than of the meter coil.
      > >
      > > Kerim
      >
    • Rick Sparber
      In reading the thread, it sounds like you got the help you needed. Rick ... From: Electronics_101@yahoogroups.com [mailto:Electronics_101@yahoogroups.com] On
      Message 51 of 51 , Mar 21, 2013
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        In reading the thread, it sounds like you got the help you needed.

        Rick

        -----Original Message-----
        From: Electronics_101@yahoogroups.com [mailto:Electronics_101@yahoogroups.com] On Behalf Of james nicholson
        Sent: Wednesday, March 20, 2013 1:45 PM
        To: Electronics_101@yahoogroups.com
        Subject: Re: [Electronics_101] Re: old ammeter

        Hi Rick,
        I have another question for you. The control board on our treadmill went out. I have done some tests and the motor is fine. It's a DC 120 volt brush type motor, it has a choke coil in series with the motor. I don't want to spend $120 for a new board unless I have too [ retired & fixed income].I ran the motor with a big ceramic ohmite pot of 68 ohms and then thru a bridge rectifier. The motor ran fine and I could control the speed but the pot got really hot which is understandable because of the iron coil. I found a router speed control on ebay that is good for 120 volt-15 amp--says it is good for any ac or dc motor brush type. What are your thoughts on using this as a speed control. Sent a pic of the motor data plate. Any help would be greatly appreciated Just remember I'm very elementary when it comes to electronics. By the way haven't got to my ammeter shunt yet but will get it.
        Thank you, James
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