Why Does My Ammeter/Voltmeter Read Incorrectly?

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In summary, the conversation is about a person buying a cheap ammeter/voltmeter from eBay and experiencing confusion with the wire colors and incorrect readings when touching the yellow wire. It is then revealed that the meter is actually a voltmeter and not an amperemeter, and that a shunt is needed for accurate readings. However, a user suggests using a voltage divider instead of a shunt. The conversation ends with the person buying a new meter and expressing dislike for using a shunt.
  • #1
Chrisjohnson
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http://www.ebay.com/itm/291369928250?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

i bought this cheap ammeter/voltmeter off ebay. now, i bought 1 before but it was slightly different. the wires had blue red and black instead of blue yellow and green. this makes it confusing but still i never had the problem I am having now.

so, this one i simply TOUCH the yellow wire and it reads like 10-30 amps. i never had that problem with the other one. what might be causing this?

i can get a volt reading fine, but the amp reading is definitely wrong. if i touch it to anything by itself it read like 30 amps. it doesn't do it with everything but anything like a negative or positive part of a battery or just my finger. it reads and jumps around with amps.

what is causing this? are the wires mixed up? is it a defective one? cause my other one which was almost identical didnt do this.
 
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  • #2
Chrisjohnson said:
so, this one i simply TOUCH the yellow wire and it reads like 10-30 amps. i never had that problem with the other one. what might be causing this?
Which means that you bought a sensitive voltmeter, not an amperemeter.
 
  • #3
my high school electronics teacher taught us boys

"When all else fails
read the instructions..."

Here's instructions i snipped from that Ebay listing :

upload_2016-2-14_6-19-27.png

Hmmmm... they must have lost something in translation.

Svein is right - you have a voltmeter,

are you familiar with use of meters and shunts?
 
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  • #4
deal.rain (ebay seller) said:
more than 10A need shunt

After examining the ebay post I conclude that this means that the 5A and 10A models have an internal shunt. Higher current models will need an external shunt. So like Svein said you have a dual voltmeter calibrated so that a current shunt of the correct value (possibly 1mΩ?) will give you a voltage (100mV??) at 100A to put 100 in the line marked A.

Was the other one 5A or 10A?

BoB
 
  • #5
rbelli1 said:
After examining the ebay post I conclude that this means that the 5A and 10A models have an internal shunt. Higher current models will need an external shunt. So like Svein said you have a dual voltmeter calibrated so that a current shunt of the correct value (possibly 1mΩ?) will give you a voltage (100mV??) at 100A to put 100 in the line marked A.

Was the other one 5A or 10A?

BoB

100A. supposed to be 100v 100a. so i NEED a shunt to make it work right? my other one must have had an internal shunt, the highest amp i measured was under 30A and it worked fine with that. i used my other ammeter as a reference.

so it should read amps with a shunt?
 
  • #6
It should if you find the right shunt. Can you make a voltage divider to put 50mV on the current sense input? That will give you the information you need to source the proper shunt.

BoB
 
  • #7
I ended up buying another one for ~3$ and this one is just like the one I used to have. Wires are red black and blue instead othe the green and yellow plus it reads amps without a shunt.

I still make sure I have it in series with the setup so it doesn't short out (unless I'm using it with my homemade broken solar cell panels, it seems to be unaffected by the short for the "short" term ;) ill deal with the long term damage later.

Thanks for the help everyone, I hate that shunt dang! Pzzz
 
  • #8
So you expected that meter to be able to carry 100 amps with those whimpy wires?
 
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  • #9
Averagesupernova said:
So you expected that meter to be able to carry 100 amps with those whimpy wires?

hahaha indeed

The shunt MUST be external
 
  • #10
My old one did 30 amps. This one does I think 10 but could be more.

So...yeah.
 

Related to Why Does My Ammeter/Voltmeter Read Incorrectly?

1. Why is my ammeter/voltmeter reading incorrect values?

There are several possible reasons for an incorrect reading on an ammeter or voltmeter. It could be due to a faulty or damaged instrument, incorrect connections, or an issue with the electrical circuit being measured.

2. How do I calibrate my ammeter/voltmeter?

Calibrating an ammeter or voltmeter requires a known reference value, such as a standard resistor or voltage source. The instrument's scale can then be adjusted to match the reference value, ensuring accurate readings.

3. Can environmental factors affect the readings on my ammeter/voltmeter?

Yes, extreme temperatures or electromagnetic interference can impact the accuracy of the readings on an ammeter or voltmeter. These factors should be taken into consideration when using the instrument.

4. What is the difference between an analog and digital ammeter/voltmeter?

An analog ammeter or voltmeter uses a moving needle to indicate the measurement, while a digital instrument displays the reading as a numerical value. Digital instruments are typically more accurate and easier to read, but analog instruments can be useful for detecting changes in a circuit.

5. Can using the wrong range on my ammeter/voltmeter affect the readings?

Yes, using the wrong range on an ammeter or voltmeter can result in inaccurate readings. It is important to select the appropriate range for the expected measurement to ensure accurate results.

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