How do I determine if an ammeter needs a shunt resistor?

Thread Starter

Chris D

Joined Dec 31, 2016
13
Good morning all,

I purchased this 2 amp panel meter on amazon [ https://www.amazon.com/dp/B07JM3CQ74?ref=ppx_yo2ov_dt_b_product_details&th=1 ]. It comes with no information and I couldn't get data off the net.

I believe some ammeters don't need shunts, but some do. How can I determine this? I suspect it is related to the amount of current but beyond that I am without knowledge.

Any help would be greatly appreciated!

Chris
 

Audioguru again

Joined Oct 21, 2019
6,610
Measure its resistance. If its resistance is very low then it has a shunt resistor.
I used an antique mechanical current meter like that 62 years ago. Why not buy a modern inexpensive Digital MultiMeter? Some stores give away a DMM for free.
 
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MisterBill2

Joined Jan 23, 2018
17,814
This is why I do not buy from amazon: NO PRODUCT INFORMATION.
A close examination of the meter might reveal some note, such as FS=2A, or FS=10mA. It might also state FS=10mV, which tells you it must have an external shunt Some meter manufactures put that in the same face as the scale, below, in small characters.
Next, an examination of the back side of the meter to see if there is any obvious shunt visible, either across the two terminals or just inside the case.
If you have a multimeter, either analog or digital, you can measure the resistance while watching to see if the meter pointer moves. If the resistance is less than one ohm, certainly it has an internal shunt, if the resistance is greater than probably not
 

Audioguru again

Joined Oct 21, 2019
6,610
Amazon knows nothing about the junk they sell except they know how much profit they make on each sale.
Why is Amazon still selling an antique moving pointer meter?
 

MaxHeadRoom

Joined Jul 18, 2013
28,513
I purchased this 2 amp panel meter on amazon [ https://www.amazon.com/dp/B07JM3CQ74?ref=ppx_yo2ov_dt_b_product_details&th=1 ]. It comes with no information and I couldn't get data off the net.
I believe some ammeters don't need shunts, but some do. How can I determine this? I suspect it is related to the amount of current but beyond that I am without knowledge.
Place a series load equal to 50ma, if it shows full scale, it requires a shunt, the higher current values do, which are ordered separately.
 

nsaspook

Joined Aug 27, 2009
12,795
Look at the prices for those antique meters!
Being old and good is valuable.

Quality gear is expensive today. I still use them when quick indication of relative unbalance of a set of indicators is needed. A digital fake of an analog indicator is used on some computer screens as process monitors.
1700613139818.png
 

MisterBill2

Joined Jan 23, 2018
17,814
There are applications for both the magnetic analog meters AND the electronic digital meters. and they are not the same place. When there is neither power nor room for the electronics, the analog meter is best. When a very high resolution reading must be made quickly, the digital meter wins. When a trend needs to be spotted quickly, the analog meter wins.
 

Ya’akov

Joined Jan 27, 2019
8,973
Amazon knows nothing about the junk they sell except they know how much profit they make on each sale.
Why is Amazon still selling an antique moving pointer meter?
“Amazon” does know about what they sell—but the majority of items are from 3rd party sellers and they are often just moving products they can get wholesale. While some vendors are good at technical support, most rely one very low impact sales to keep prices down.

I buy a lot of things using Amazon. But I don’t buy components and devices that I need expert help with because I can’t expect that. If I can’t find a data sheet, or a link in the posting to documentation (and there often is, of varying quality), and I don’t already know about what I am buying—or have a reasonable expectation that I can work it out—I just won’t buy it.

My experience is net positive with very few real disappointments. And in the countable-on-one-hand cases, I was able to get a refund very easily, without even returning the product.
 

Janis59

Joined Aug 21, 2017
1,821
Dear Chris - when You shall attend the secondary school class 11, then in the physics will happen the textbook in which chapter of electricity the first theme after electrostatics will happen the shunt resistor and serial resistor calculus for the chosen measuring workheads.
General idea - if measure workhead pass to our wishes, don`t do anything. If it is oversensitive about voltage - add the serial resistor. If it is oversensitive about current - add the shunt resistor. If it is undersensitive - add the amplifier.

Now about things rarely told at school even at those school where at 1/4 staff I am working align my basic work at University, tutoring the physics, thus I know damn well what themes in what week must be explained to young men :) :) ... How to find does the sensitivity is right? Just take one old AAA battery what already lets the lighter work too dark and add to the ammeter for very short time. It must show one Ampere with something, but the same time will not be able to burn down the circuit immediately if shunt is not applied by fault. Less dangerously it may be done via the lab power supply, add to it serially resistor giving no more than 50 microamps - if ammeter shows nil, add the three orders of current and switch on again. And so on until it shows something. Graduating happens the identically - precise voltage, precise resistor and current is defined.
 
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Thread Starter

Chris D

Joined Dec 31, 2016
13
Thank you all for you comments, Here is a bit more information that might narrow down the possibilities.

The 200 mA meter has .4 ohms of resistance.
The 2 Amp meter has .2 ohms of resistance and a larger "thing" on the back of it.

In the photo below, the left one is the 200 mA - right one is 2 amp


200 mA - 2 amp meter .jpg

To answer a question about why analog meter when digital ones are available - simple, I like the look of an analog meter better.

Regarding comment " when You shall attend the secondary school class 11 ", that was about a half a century ago. As for the rest of your questions / statements /comments I could not understand your English but thank you for trying.

Chris
 

ericgibbs

Joined Jan 29, 2010
18,651
Hi Chris,
As I said, the right side meter in your image does not need a shunt..:)

Out of interest, what is your project that uses the meter?
E
 
As one can see from my profile image, I love analog meters.

Another place where analog meters provide a lot of information with a quick and simple glance is VU meters. If anyone has been behind the controls of a mixing console during a live music concert, you know exactly what I mean. The only caveat is that it doesn’t display instantaneous peak levels, but a single LED on each VU meter will allow you to visualize it, also with a quick glance.

EDIT: the image on my name was taken on the engine room of the Iowa- class battleship USS North Carolina. It monitors the power consumed by the ship’s electrical systems. Look at the full scale power!!
 
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