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Forum Index : Windmills : Calculating value of shunt resistors
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| maaca Newbie  Joined: 21/11/2006 Location: New ZealandPosts: 22 |
Can any-one help me calculate the value of a shunt resistor required for an amp-meter?. Scale on front is 0-300 dc amps. On the back is 60m. On the front face is fs=50mv. Now from that I assume the internal resistance of the meter is 60 megohms and the voltage drop across the meter is 50 milli volts.I would like the meter to read 30amps full scale and not 300. From here on I am stumped and if you can come up with a figure what do you use for a shunt?. Your help appreciated.Maaca. |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
Hi Maaca fs=50mV means 50mV will give a full scale deflection of the meter needle. So we need a shunt that has 50mV across it when its passing 30 amps. So using ohms law, R=V/I, R= 0.05 / 30, R=0.0016 ohms. A short length of heavy wire would work, it will be a case of adjusting the wire length, using a good multimeter as the reference, untill you get the right reading on you amp meter. Or you could use a length of threaded rod like I did here. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| maaca Newbie Joined: 21/11/2006 Location: New ZealandPosts: 22 |
Hey Thanks Gizmo. I really like the idea of the threaded rod and will give it a go. You have well and truly answered my questions. Many thanks Maaca. |
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