100V 10A DSN-VC288 DC Voltmeter Ammeter Review – calibration problems

[aidept]

Any idea how can I do myself a 75 mV  small shunt? I do not need to measure more than 5 Amps. I did one using a cooper wire but the reading is far away from a regular multimeter.
Also, with the provided 100 Amps shunt, which is enormous, the readings is not accurated. The potentiometer from behind has no effect. I did the RESET thing, nothin works.
AMAZING thing discovered: when I approach my hand, the amps value is changing! 😁

[xavier60]

Any idea how can I do myself a 75 mV  small shunt? I do not need to measure more than 5 Amps. I did one using a cooper wire but the reading is far away from a regular multimeter.
Also, with the provided 100 Amps shunt, which is enormous, the readings is not accurated. The potentiometer from behind has no effect. I did the RESET thing, nothin works.
AMAZING thing discovered: when I approach my hand, the amps value is changing! 😁

From your first post, I got the impression that you wanted to measure a few milliamps, which would have been possible by paralleling of low ohm resistors. You should start off this way to get an idea of what the display reads for a given input voltage range. and to confirm that the meter is working properly. If too much voltage has been applied to the shunt input, it could have a damaged opamp.
Shunts are usually made from nichrome wire or foil. I have never tried to make one. A lot of ideas can be found with a search, "making a shunt resistor"

[Kiriakos GR]

Any idea how can I do myself a 75 mV  small shunt? I do not need to measure more than 5 Amps.

The math is 75/5 = 0.15 mOhm

If you are 100% determined making your own shunt, then there is a series of steps for you to follow.
1) Get a precision resistor of 0.15 mOhm 1% at 1/4 of Watt.
2) Confirm with that resistor that you do own a multimeter capable to measure that value.
3) Start making your own shunt by experimenting with 3mm in diameter of copper coil wire at two centimeter length, and of 1 centimeter as lead from its side, and then start trimming it as required.

75mV this is also a low value voltage and a challenge for dirt cheap multimeter in the regard of accuracy at measurement.
 
All shunt are made of copper, and copper surface this suffering from oxidation, this will change the shunt value over time.
If you succeed making your shunt by enameled  3mm in diameter of copper coil wire , this will be the best that you can do.
All testing and trimming it should be made with the shunt this soldered on a small PCB.

   

[Kiriakos GR]

Shunts are usually made from nichrome wire or foil.

Hand made Shunts made from hobbyists they will never be as good as high precision factory made ones.
But he may learn allot and gain experiences even with easy to find materials.

My first test project as electrician when I was back in school this was making an electron magnet by the use of a nail (wood working) as core.
Four year later my FINAL exams test and project this was the use of automation, at controlling water tank levels by double set of sensors,  floating type ones among with electrode type ones as second insurance circuit (an 100% fail safe circuit).
   

[aidept]

Got a new one with a small 10 A (onboard shunt).
Did something wrong and now is dead.
I takes the small 10 A shunt and put on the old good board which have an external 100 A big shunt.
Got reading errors like 600 mA instead of 60 mA.
Question: I understand that the smaller shunt is 75mV, the big one is different?
Thank you my friends.

[Kiriakos GR]

I takes the small 10 A shunt and put on the old good board which have an external 100 A big shunt.
Got reading errors like 600 mA instead of 60 mA.
Question: I understand that the smaller shunt is 75mV, the big one is different?
Thank you my friends.

In theory an 100A shunt will deliver 10 times more voltage than a 10A shunt (at full load).
According to specific shunt voltage output, it must be selected and the voltage meter range.

Find the actual specifications of the shunt that you plan to use, and this will guide you of what range of mV meter it is the required one so to use.
 
DEREE Taiwan, has a huge range of shunts, you can collect allot of information's from their website.     

[aidept]

You right.
Any ideas how to modify the circuit to show me 10 time less amperage?
Need to put a resistor in series or in paralel with the shunt?

[Kiriakos GR]

You right.
Any ideas how to modify the circuit to show me 10 time less amperage?
Need to put a resistor in series or in paralel with the shunt?

What you are asking this is too much.
You may simply explore this application example https://www.ittsb.eu/forum/index.php?topic=1488.0   but this is untested as usable solution for a shunt.

[aidept]

Thank you very much I will post the results here.
Please, there is a mobile version of this forum?

[Kiriakos GR]

Thank you very much I will post the results here.
Please, there is a mobile version of this forum?

Due the fact that DSN-VC288 circuit this is a low cost gadget, and neither accurate enough.
It is smart, of not wasting much time with it.

If you own a 100A shunt?  this can become usable by connecting to it an analog panel meter (DC mV voltmeter)
Are you up to measuring, electric bicycle consumption ?   

[aidept]

Yes, use to measure the load from a pedal generator motor or a small solar panel on a 12V battery.

IMPORTANT DISCOVERY TODAY!
Put the 10 A shunt on the 100 A board and look at this! Now I have *10 precision! So happy! 
Edit: of course, there is a ( 54 vs 41 ) = 13 mA difference, but hope at bigger current to be smaller difference.
Edit 2: wrong, 84 vs 60 mA when amperage is bigger...
Edit 3: 100 vs 73 mA...
Edit 4: 570 vs 400 mA
Conclusion: error rising when measured current rising🙁

Note: The Current adjust potentiometer is at the edge of the scale.

[Kiriakos GR]

Conclusion: error rising when measured current rising🙁

Yes this is a fact    when you are using low-end electronics for electrical measurements.
But if you can tolerate emotionally having 3~5% of measuring error?  Then you do not have to buy something better.

More accurate measurement at all scale (for example  0 ~ 10A ) this is described as good linearity. 

You can use the potentiometer so to improve lost linearity at a specific quantity of DC current.
For example.. if you care more about proper review of low current?  the adjust it for proper review of the value of 2A