Hello does anyone have experience with digital ammeters from ebay?
I'm thinking about getting one like this:
Digital Ammeter

Will it be appropriate for it to be powered by the same power source that powers the circuit from which this ammeter will be measuring?

If anyone has experience I hope you can throw some tips in on use and calibration and such.

Thanks!

 

What do you plan to use it for? That ammeter is designed for use in a car, which is a modification that would not be allowed here at AAC according to the ToS (which hopefully you have read).

Do you need a module like that, or can you simply get a multimeter? Difficult to answer without knowing your application.

Regards,
Matt

 

This is going to be used for a project. I will be building a solar powered boat and wanted to monitor the current coming from the panels. I want it built in so I can monitor the current without manually connecting a multimeter.

 

I looked at that myself and do not like it for the simple reason, it cant be calibrated - adjusted. I asked them and that is what they said.
There are no pots on the back.

I am interested myself in one of these.
Buy this meter
http://www.ebay.com/itm/191401117588?_trksid=p2060778.m1438.l2649&ssPageName=STRK:MEBIDX:IT

buy the 75mv shunt, 200 amp shunt. Higher amps here is better for the shunt.
http://www.ebay.com/itm/230974566668?_trksid=p2060778.m1438.l2649&ssPageName=STRK:MEBIDX:IT

Buy these both is cheaper.

At least if it is off reading you can fine tune it. I have bought meters from Ebay and one set non adjustable reads .7vdc too low.

 

I think cutting the shunt or adding a parallel resistor (adjustable pot) with the shunt will allow for calibration.

Which meters have you bought from ebay? Thanks for those links.
Also doesn't the amperage reading depend on the shunt? So at 75mV it will read 100A, if you put 200A shunt won't it read 50A since it measures the voltage and has a pre-programed resistance in the software (I don't really know how these ammeters work so I may be wrong here)? Voltage / Resistance = current.

 

I bought two cheap 2 wire LED voltmeters. While it had a nice display and was cheap it was really way off. I dont want to link to it but it was under $2, I got a full refund and they have a lot to sell and have dropped the price. 3 wire volt meters are better, or at least get something that can be adjusted. I mean if you get it and it is off, then your stuck.

Other meters were these here, and it is adjustable. these were also ok with no need to be adjusted.
http://www.ebay.com/itm/201204685005?_trksid=p2059210.m2749.l2649&var=500399379626&ssPageName=STRK:MEBIDX:IT

http://www.ebay.com/itm/291241481557?_trksid=p2059210.m2749.l2649&var=590394305409&ssPageName=STRK:MEBIDX:IT
For this one, I bought blue, it is very bright, but due to white unlit LED segments in sunlight hard to read. So I used a piece of blue translucent plastic and it made it a lot more readable. They are adjustable and I played with the pot and it works.

The shunts, if they 75millivolt, then it will work with all the ebay ammeters. The amp rating is not what determines the readings, the millivolt drop is what allows the readings as ammeters are like voltmeters and read a voltage drop across the shunt.

 

I've used meters similar to the ones sdowney717 mentioned off EBay. Mine came with the shunts for around 15-20 USD free ship.

They self power from the same source as they measure, no sepaate power souce needed.

However, as they are just there to indicate activity (is my unit dead or alive?) I never checked the calibration.

 

Okay thanks for the information.
One of the meters you linked to is used for AC circuits.

With the 200A shunt, is the voltage drop across the shunt 75mV when the current is 200A?
With the 100A shunt, is the voltage drop across the shunt 75mV when the current is 100A?

My question is: when the voltage is 75mV across the "resistor" the ammeter will read 100A or 200A?

Another question: Do you use anything to cover the shunt with insulation? Any ideas?

Gera

 

http://www.ebay.com/gds/A-Guide-To-Current-Shunts-/10000000001675505/g.html
What is a shunt rated meter?

Shunt rated meters take all the work out of reading the current flowing through a shunt. No calculations required as long as the full scale rating of the meter matches the mV rating rating of the shunt. Say a current shunt is rated for 50mV drop. Choose a meter whose full scale rating is 50mV. The marking on the face of the meter should also match the full scale current rating of the shunt. If your shunt is rated for a maximum current of 100 Amps, then choose a meter marked 0 to 100 amps. The marking can be modified if you cannot find a matching meter. The reason this can be done is because the meter isn’t reading 50 amps when 50 amps is flowing through a 100 amp shunt. Its reading 25 mV or ½ the shunt’s maximum rating. Just mark the half way point of the meter’s face for 50 amps, the ¼ point of the meter’s face for 25 amps, and so on.

Just match the meter to the shunt for millivolt, whatever the meter was designed to measure against, ampacity is capacity a higher amp shunt will work if it has the same millivolt reading. If I am wrong, then someone will say so. I have been wrong before, so keep on with the researching.

 

http://www.jamestowndistributors.com/userportal/document.do?docId=126

I googled this up and they are saying match the shunt size to the meter, so a 100 amp shunt works with a 100 amp meter.
That way you know your safe. It is possible using a 200 amp shunt on a 100 amp meter will only show half the amps.

 

Thanks for all the information, I ordered this one:

http://www.ebay.com/itm/Dual-LED-Di...155?pt=LH_DefaultDomain_0&hash=item3a96307c73

 

A 75mV 100A shunt will have been calibrated to read a 75mV drop when 100A is passed through it. It is normal to select a shunt that will be used at 2/3 its stated Amps; exceeding this will overheat the shunt making the calibration inaccurate. The larger the Amp rating the cooler the shunt will work. The mV drop is calculated from the internal resistance of the meter. The shunt will need to be open to the air to dissipate heat, some sort of cage/guard is required.

 

Thanks for the information. I won't be having more than 40amps passing through the shunt for sure. Is the shunt conductive on the outside? Any ideas on how to enclose it?

 

Thanks for all the information, I ordered this one:

http://www.ebay.com/itm/Dual-LED-Di...155?pt=LH_DefaultDomain_0&hash=item3a96307c73

Hi, that looks like a good one, adjustable if needed.
I like the higher rated shunts because smaller ones might not be as accurate at higher amp flow.
And I have also read they should not be used continuously at their rating which kind of limits the usefulness.
On another forum, someone said you can simply use your battery cable (or large wire) with the meter input spread apart the length of the wire. I think it would work, can be used at higher amps, but I dont know how you can calibrate that unless you have a DC clamp on amp meter. If you do, and you have an adjustable meter, maybe you can reasonable readings without needing a specific shunt. I do have an Elenco clamp on DC amp meter. I might some day look at doing that.

 

there are two kinds, one has the parts under the display, the other on the backside. These are often adjustable or you can modify it.

 

there are two kinds, one has the parts under the display, the other on the backside. These are often adjustable or you can modify it.

The ebay picture for his meter, I can see mini pots on the board. There two, my guess is one for the volt meter, one for the ammeter.

 

I think you're right. One for the voltmeter the other for the ammeter.

 

I just love these cheap LED voltmeters and ammeters you can get on eBay.