Hi everyone. I just bought two 500 mA milliameteres, one from e-bay and the other from AliExpress ( https://www.aliexpress.com/item/32981595871.html?spm=2114.12010615.8148356.2.2da1334bMWvsdJ). Although, they seem to be the same milliameters, they don't have the same behaviour when measuring reverse polarity. In specific, while the e-bay milliameter works fine, the AliExpress one does not measure the reverse polarity properly. I have attached some pics in order to show you what i mean. The green is the e-bay one, while the blue is the AliExpress one. Moreover i have attached each one's pcb board in order to have a better look why may this happens. The first three pics refer to the e-bay milliameter, while the other three refer to the AliExrpess one. I hope there is a way to fix the latter.

 

Do you need to show reverse polarity in your application?

 

Do they behave the same with a higher current?
When measuring did you have the two meters in series so there is no doubt that they are each carrying the same current?

If both answers are yes then I suspect it is a software problem and not DIY fixable. Send it back with a fault report.

 

It is obviously faulty. For the price you paid, it is not worth fixing. Save it for an application where you don't need reverse polarity and buy a new one.
Regards,
Keith

 

Quick note: Some are designed to measure current in both directions and some only work with one direction. It is a design choice.

 

Do you need to show reverse polarity in your application?

Yes, i would like the second milliameter to behave exactly as the first one at reverse polarity, i cant understand why this happen as it seems they are exact the same.

 

Those devices are "programmed" to convert a mV shunt voltage to display the current. Looks like the second one is off by a factor of 1000 on the reverse, which suggests they forgot to program in a multiplier for the reverse.

 

Those devices are "programmed" to convert a mV shunt voltage to display the current. Looks like the second one is off by a factor of 1000 on the reverse, which suggests they forgot to program in a multiplier for the reverse.

So, there is nothing i can do to fix it?

 

There are tutorials on setting up an ACS723 spark fun unit which can do + / -
You can check out the datasheet for connections
In addition the video shows a reasonable expectation the precision and unfiltered noise.
youtube copied url at time = 6:50 or you start at the beginning

 

Some digital meters require the meter power to be isolated from the measuring circuit. That is one thing I have not seen discussed so far. That might be an issue in this case.