Measuring High Current with a Low Current Ammeter: The Art of Adding a Shunt Resistor (019d)
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- เผยแพร่เมื่อ 25 ม.ค. 2022
- You have a low amperage analog ammeter in your hand and you want to be able to measure higher currents with it.
In this video you will learn how to create a home grown, higher amperage ammeter from that low amperage meter by adding a shunt resistor.
I will step you through the process from the beginning to end using my own 50 microamp meter as the guinea pig. I will create a 250 milliamp meter out of it.
My end product agrees with my DVM within 0.32%!
Here is the link to the formula sheet:
drive.google.com/file/d/1BO4i...
NOTE: A standard Kelvin Connection for measuring resistance places the voltage measurment immediately at the terminals of the resistor in question. The current is usually applied outside these terminals. In this case, I had two terminals. Placing the voltage measurement connection outside the current connection used the leads extending outside of the current connection of the shunt resistor as "extensions" to the voltmeter leads with negligable voltage drop. See my video on "Measuring Low Value Resistors" for more information/explanation.
----------------------------Time Marker Notes
00:05 Introduction
00:50 Preliminaries & What are we doing?
02:18 The Basis of how this works
03:01 Resistor Calculation - the easiest way...
03:23 Calculate the Voltage across the Meter Movement
03:56 Calculate the Current through the SHUNT resistor
04:31 Calculate the Value of the Shunt resistor
05:23 Calculate the Power Dissipation of the Shunt resistor
06:19 Finding an Off-the-Shelf resistor
07:41 Build my own Shunt resistor
10:39 Measuring my Shunt resistor's value
11:03 Setup
13:13 Making the measurements.
14:00 Calculate the value from measured values
15:10 Testing your Design
15:11 Zero your meter
15:23 Install the Shunt resistor
15:32 You could locate the Shunt remotely!
15:54 Measurement setup
16:46 Test Connections
17:24 Making the measurements
18:29 Evaluate the results
19:26 Final comments & toodle-oots
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I wish I had techaers like you in physics and electornics back then. Comprehensive and clear explanation that surely grabs your attention. Thanks!
Wow! Thanks for the great encouragement! 🙂
A great presentation. Comprehensive but clearly explained without dallying for too long in discussion.
Thanks! I am glad it was helpful to you! 🙂
What a great way to begin the day. Notification of a new video from Ralph !
Glad you enjoyed it!
Nice job!
Thanks!
This video was very helpful! New suscriber!
Yay! Thank you and welcome to all the fun!
thank you
You are very welcome! 🙂
So what about going the other way. Using a meter rated for a larger current value and getting it into a requirement for a lower current flow. for example a 1 milliamp meter to replace a 60 microamp meter? Thanks Ben...
I'm afraid you'd have to modify the meter itself to do this. 🙂
Excellent!
Glad you liked it! :-)
good work..thanks
You are welcome!
I found a small ammeter and wanted to use in a classic car. I am assuming I have found it’s beyond use in this application providing I have calculated correctly. The gauge shows 120amps full scale. After characterising I have determined it has internal R = 9.1ohm and 13.5mA full scale. Calculations: 13.54v applied. 992ohm Rs (inline resistor). 0.4ohms offset. 991.6+9.1=1000.7
13.54v/1000.7 = 0.01353 = 13.5mA
If I wanted to use the fullscale of 120A I would need a 0.0010ohm shunt. If I reduced the scale to 15A I would need a 0.008ohm shunt. Possible? Correct? Love the guides. Many thanks
Thank you! And you are very welcome! 🙂
Good question! Yes, if your characterisation of the meter is correct, then you would need a 0.001024Ohm resistor as a shunt for 120 Amps. Be careful! Your shunt needs to have the current carrying capability for the 120 Amps + proper derating. So, in my book this is 120 x 1.5 = 180 Ams at a very minimum. I suggest using some sheet or bar copper as the shunt. Use a Dremmel tool to whittle away the edges to adjust it to your 0.001 Ohms.
Dropping back to a 15 Amp shunt (22.5 Amps for derating purposes), the resistance is now 0.008197 Ohms. Here you could use some #16 copper wire (chassis wiring rated at 22 Amps). This would have to be about 2ft long.
Hope this helps. 🙂
Ralph, another great video. Your thoughts on using nichrome wire for shunt resistor?
Many thanks & 73.
De K4WRF
Thanks! Using nichrome wire is a bad idea ... if you have it. Often the resistor value is quite small, so nichrome wire might be a bit too resistive for this application, depending on the specific resistivity of the wire and the value you are trying to achieve. 🙂
Thanks for the advice Ralph!
All the best.
Wh
@@watthairston1483 You are very welcome! 🙂
Thank you & 73 de YO6OCT!
You are very welcome! 🙂
Very helpful. I’m converting a 50mA analog Simpson meter to indicate 250 mA. Brilliant. Same scale even. My meter will also have a 10 ma scale for reading a grid current in my application. I get to build two shunts!
Woohoo! Sounds cool! I'm glad to hear my video helped you in building your project. 🙂
good video 😊 To deal with electric measurements is like doctor jokes who visited the doctor which visitet dhe doctor of the doctor of your doctor and who was the ethalon first doctor and how and why he is a doctor and like that is also with voltmeters amperemeters and with all meters that exist bcz bro you cant measure infinite you can get close but whe did you refered that you get that precious value if you understand what im meaning
Thanks! 🙂