Current Meter

[Squibcakes]

This sounds like something I could use....

I wouldn't mind replacing the old analog current / volt meter in my 30amp load tester with a digital version, including aHr Capacity.

The current shunt we have produces 50mv max at full load (50amp)

How could this be measured using a pic.. (Use op amp???) of sort?

I would like to know if anyone else has done this before.

On an other topic, has anybody made their own wire wound resistors before?

Cheers

[Charles Linquis]

I have built several current meters using Allegro hall-effect sensors. They offer perfect isolation and have no voltage drop. Depending on the model, they have an output of 20-133 mv/Amp. When measuring DC current, I usually use a rail-to-rail op amp to shift the output to near zero volts (the quiescent output voltage of the sensor is VCC/2) and amplify the output a bit before feeding it into the A/D converter.

Fantastic devices, very accurate and stable. Much neater than using sense resistors.

[MikeTamu]

I have used the Maxim 4172 Current Sense chip and found it to be very easy to impliment and precise.

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1654

[TK5EP]

Hi All,

i also need to measure some current but on a HV supply, with about 500V DC above ground. Current can flow in both direction, negative and positive with a max of 50 mA.

Any idea how i can do this in a safe way ??

Thanks for any feedback.

[Squibcakes]

Wow, those Allegro Hall Sensors look really good. I have order a couple to test them out.

As for measuring the HV supply, I've only ever used a HV probe connected to a DVM. Sorry, no other idea how to do that.

Cheers

[Charles Linquis]

I have used the Allegro Hall-effect sensors extensively. Bi-directional, great isolation. Good accuracy.

[TK5EP]

Hi all,

I looked the datasheet of the ACS704 which is the smallest device by Allegro (+/- 5A) and it shows a 133mV/A sensitivity.
I think it's a bit low for measuring 50 mA max scale....

An application note for the MAX4172 in a amplified high voltage sensor gives 10mV/mA, which seems to be more adequate, but unfortunately it's not bidirectionnal !

Other possibility is to use an amplified Hall effect sensor, but it needs an ground insolated low voltage supply on the sensor side, which is another problem !

Still looking for the right solution....