# 12V DC current sensor

I have a camper trailer with a 110AH 12v battery system. It powers various things as you’d expect.

I have solar panels, a vehicle charging plug, and a 240vAC charging plug, all with regulators (so it pushes ~14v into the batttery to charge it).

I’m building my own status monitor thing for it.

I want to measure battery voltage (that’s easy) and “real time” Current in or out so that I can see if I’m using more than I’m generating while out camping.

I know how to do the voltage sensing, how to output to a display (i’ll probably use a pi for this as I want to do some other stuff over wifi).

I know in general to do current sensing you buy a chip, and put it inline, and it does a proportional voltage you use a lookup table for, but not what chip i should be using.

• It will be in a box and thus might get quite warm
• I’ll be pushing max of ~25 amps in or out for the most part
• The voltage will vary between 8-15v, so I don’t need super high voltage support
• I know how to do a regulator to give it the 5v or 3.3v it will need for powering

Hi Bill,

Welcome to our forums!

Sounds like an awesome project!
For the current sensor, I would definitely opt for something by Pololu, either board should be able to handle the voltage quite easily, but can only handle up to around 30A nominally (also note the gauge of wire you are using as the more current you pass through the thicker the wire must be):

To read the signal from the sensor you will need an analog to digital converter to interpret the signal so that the Pi can read it. Here’s a good one by Adafruit

Rather than a look-up table, you could use a formula to determine the current flowing through the sensor.

The Current sensor should be able to handle the higher temps quite easlily but I’m not too sure about the Pi or ADC board.

PS: In our chat online I did some research and don’t think the regulator idea will work to measure the current. My bad. Though powering the Pi and ADC will require the 5V as you mentioned

Let us know if you have any other questions!

Liam.

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That is why the big holes in the carrier board, to terminate large wires. Also make sure there is plenty of copper in the track between these holes and the chip. If it shows signs of not being thick enough a good trick is to coat the copper track with a heavy layer of solder.
Cheers Bob

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That seems to only do positive biased voltage detection (i’ll be doing pos and negative for when current flows in or out).
If I feed it 5v, it will put out +/-4.54 volts for +/- 30A sensed

My thought is I feed it to BOTH inputs in differential mode, but swapped?
Sensor 1: signal
Sensor 2: ground (aref)
Output 1/2: differential 1 to 2 if signal positive, 0/error if negative

Sensor 3: ground
Sensor 4: signal (aref)
Output 3/4: differential 3 to 4 if signal is negative (remember signal will be negative here), and 0/error if 3 to 4 is positive

Make sense? Any easy better way?

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Hi Bill.
May be wrong here and I haven’t looked up the specs for these things in a while but I thought the scenario was:
Apply +5VDC to the device.
Device output is +2.5VDC or exactly half the applied voltage for 0A.
The output voltage goes up or down @ XmV per Amp depending on direction of current flow. Up for one direction and down for reverse. The output never goes negative.
You then have to do some manipulation with OP amps to get it to read what you want. I am speaking about the bare Hall device here. Possible that the carrier boards do this manipulation for you. Or feed the result into an ADC input in Arduino or similar and do the massaging there.
Cheers Bob

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from the data sheet:

You’re 100% right, thank you Robert!

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