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    #1

    Problems measuring mA with multimeter

    I'm brand new to electronics and trying to teach myself using the "make: electronics" book.

    I bought the $45 multimeter Radio Shack along with the components for the first few experiments but I'm having a problem measuring current.

    Supposedly the main raid can measure current, you're just supposed to switch to the other outlet for large currents. I can measure voltage and ohms fine but I can't get the mA to work. I'm using a circuit with 4AA batteries, a resistor and a LED. When i switch to the other outlet it works but it only shows A not mA so I only get one significant digit. I tried switching fuses but I get the same thing.

    Am I doing something incredibly dumb which has cost me two fuses or something incredibly dumb and just not getting it to work?

    Thanks in advance for any help,

    Matt
    Tags: None
    #2
    Re: Problems measuring mA with multimeter

    You have to connect the multimeter inline , not the way you measure voltage and resistance (which is parallel)

    http://www.youtube.com/watch?v=yrpmq2FCnqs

    and you have to pay attention to the maximum mA value supported. If you're not sure how much mA you have, be careful and use the high voltage (low precision) plug first, then move down to the more fine one.

    Comment

      #3
      Re: Problems measuring mA with multimeter

      Originally posted by matt0177 View Post
      I'm brand new to electronics and trying to teach myself using the "make: electronics" book.
      You may want to check eevblog.com if you are learning electronics. Dave Jones has over 200 videos on various electronic topics.

      Am I doing something incredibly dumb which has cost me two fuses or something incredibly dumb and just not getting it to work?
      Generally, the fuses are matched with the dial setting. So for 10A, it will have 10A fuse. For the mA range, it will probably be around 500ma or so. So when replacing fuses, always use the correct rating.

      When measuring unknown amperes, always start with the highest dial setting (10A). If it reads over 1A, then you know it will blow the 500ma fuse if you choose the mA dial.
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        #4
        Re: Problems measuring mA with multimeter

        Thanks to both of you, I'll be checking out those links. I switched to inline and got the led to light up earlier but I still couldn't get it to work when i switched back to the more sensitive outlet. With amps that low, is there anything dumb I could have done to blow the fuse?

        I'm positive I'm doing something dumb, I just want to make sure I don't have a bad meter.

        Comment

          #5
          Re: Problems measuring mA with multimeter

          Originally posted by matt0177 View Post
          With amps that low, is there anything dumb I could have done to blow the fuse?
          You can take both fuses out of the meter and see if it measures less than 1.0 Ohms.

          If you have a manual ranging multimeter, set it to 200 Ohms. If it is reads "1" on the left hand side or "0L", then it is blown.
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            #6
            Re: Problems measuring mA with multimeter

            It's showing 0 so I definitely blew it, I just wished I knew what I did to go through two of them.

            I guess when I go to buy another fuse, I had better get a dozen

            Comment

              #7
              Re: Problems measuring mA with multimeter

              Originally posted by matt0177 View Post
              It's showing 0 so I definitely blew it, I just wished I knew what I did to go through two of them.
              Do you mean "0L" or out of range?

              Or do you mean the number zero for 0.0 Ohms?

              A good fuse should measure LESS than 1.0 Ohms.
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                #8
                Re: Problems measuring mA with multimeter

                It's saying 0.F, which is the same thing it says if I'm not touching anything at all. It's reading resistors correctly.

                Comment

                  #9
                  Re: Problems measuring mA with multimeter

                  Which RadioShack multimeter did you buy? Can you post a link?

                  Most meters say "0L". O.F might indicate that your fuse is open or that it is missing a fuse. The manual well tell you if overload is represent as "0L" or not.
                  Last edited by retiredcaps; 11-26-2011, 07:40 PM.
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                    #10
                    Re: Problems measuring mA with multimeter

                    http://www.radioshack.com/product/in...ductId=2103175

                    I'll go check the manual now. Thanks for all the help!!

                    Comment

                      #11
                      Re: Problems measuring mA with multimeter

                      Originally posted by matt0177 View Post
                      I'll go check the manual now.
                      According to page 2, "0.F" is out of range. Normally, I'm used to seeing "0L". So it looks like your fuse is blown.

                      Also this multimeter only has one fuse (500mA 250V). The more expensive meters have two HRC fuses (one for the 10A and one for the smaller amps).
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                        #12
                        Re: Problems measuring mA with multimeter

                        Thanks. I can't believe that I blew two fuses playing with 4 aa batteries and a led!!

                        Is this a sign of a fault with the meter or is this not that rare?

                        Comment

                          #13
                          Re: Problems measuring mA with multimeter

                          Originally posted by matt0177 View Post
                          Is this a sign of a fault with the meter or is this not that rare?
                          I can't say either way. If you are new to electronics and using a multimeter, technique counts when switching between voltage, resistance, and current. That means, disconnecting your multimeter before switching ranges and functions and double checking everything before applying power.

                          It could also be a faulty meter.
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                            #14
                            Re: Problems measuring mA with multimeter

                            I guess I'll go get two new fuses and play with them, if it happens again, I'll start blaming the meter and get a new one.

                            Thanks again for the help!

                            Comment

                              #15
                              Re: Problems measuring mA with multimeter

                              Part of the problem is also the design of the input jacks on the multimeter.

                              Some multimeters, maybe in order to cut costs, put the V, Ohms, diode, mA, all on the same input jack. So if you are switching ranges and don't pay attention to how the multimeter is hooked up, you can easily blow a fuse.

                              Other multimeters have a separate COM, V/Ohm/diode, mA, 10A input jacks. In other words, the ampere jacks are separated from everything else. Even better multimeters will have a warning or won't let you plug in the probes into the wrong jacks when changing the range switch.

                              The EEVblog.com has a TON of info on multimeters. See

                              http://www.eevblog.com/episodes/

                              Dave Jones has a buying guide, $50 and $100 shootout, teardowns, etc.
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                                #16
                                Re: Problems measuring mA with multimeter

                                I wish I would have come here before I bought mine! Hopefully it's fine and I just did something careless. I definitely be heading to radio shack in the morning for fuses.

                                Comment

                                  #17
                                  Re: Problems measuring mA with multimeter

                                  You may find out that in the future that you need more than one multimeter especially if you have to measure current and voltage at the same time.

                                  I never thought I would end up with 4 multimeters when I first started, but with patience I was able to get some really good deals.

                                  For example, I got an used Meterman 15XP for 99 cents on ebay (I was the only bid). The multimeter was pratically new. So if you have patience, look for used Meterman, Amprobe, Wavetek, Greenlee, UEI, Ideal, BK Precision, Extech.

                                  With luck and patience, you may be able to get a Fluke for a decent price. The used Flukes are very popular on ebay which drives up the bidding process.
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                                    #18
                                    Re: Problems measuring mA with multimeter

                                    I went to buy some fuses from radio shack and they told me to just bring in the multimeter and they would replace it. The new one is measuring current like a champ so I'm guessing it was a bad meter.

                                    Quick question, I'm going through my book and buying the components I need for my projects from radio shack. I'm running into a few projects which require specific items (like relays) which they don't have there. My book mentions mouser.com but are there other sites which are good for small orders without a lot of shipping?

                                    Thanks again,

                                    Matt

                                    Comment

                                      #19
                                      Re: Problems measuring mA with multimeter

                                      Originally posted by matt0177 View Post
                                      I went to buy some fuses from radio shack and they told me to just bring in the multimeter and they would replace it.
                                      How nice of them. Great customer service. I might have to check out their stock.

                                      My book mentions mouser.com but are there other sites which are good for small orders without a lot of shipping?
                                      Digikey has low cost shipping prices for United States Postal Service 1st Class (about $2.75 ish). At least for caps. I don't know for heavier items.

                                      Put it into the digikey shopping cart and there is an "estimate" button with a number of shipping options.
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                                        #20
                                        Re: Problems measuring mA with multimeter

                                        I'll go check them out now, thanks!

                                        Comment

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