# Off-the-shelf ZERO IDLE CURRENT voltage monitoring module?

Folks

Title says it all. I’m looking to acquire said item for prototype. Currently using the Grove voltage divider, but I believe its always draining the battery via the voltage divider.

I’m looking for something ready to use/prototype.

Thanks

It might be useful to know the maximum voltage of your battery, what interfaces you are willing to use (I2C, SPI, etc), and a bit more about your application.

1 Like

Currently using this …

http://wiki.seeed.cc/Grove-Voltage_Divider/

… with the Electron ADCs to monitor battery voltages up to 20 V.

I am not wed to any particular interface at this point.

@peekay123 this is what the circuit looks like for that board. Can you advise on how much current those resistors are dropping for a VOL = 20?

The current in the left most pair is 66.6uA and the right side is 196uA for a rounded total of 262.7uA at 20V. So around 1/4 of a milliamp–fairly small current.

There will also be some amount of current going to the actual measuring device (ADC, analog input) which could be more or less than the above amount but would add to the total current.

You could just use a INA219 voltage / current sensor and only turn it on when you want to read the battery voltage / current. The INA219 is rated to consume 6uA when sleeping and 0.7 mA when ON.

1 Like

Note that the right side divider will yield a 6.67v output which cannot be connected to any Particle device directly.

@RWB, the only catch with the INA219 is you need a current sensing resistor in the power path, typically on the high side. That resistor needs to be able to handle the current flowing through the load. In the case of the INA219, it is limited to 3.2A at a voltage of up to 32V.

1 Like

@peekay123 Can’t the INA 219 be used to only measure voltage and no current?

Also you can adjust the code settings and resistor size to handle more current if needed. The more current you measure the lower the accuracy per amp. I’m using one to measure 10 amps of current @ 26.5 volts.

@RWB, I stand corrected!

Agree re: current analysis. But some head scratching re: the purpose of the two op amps. Output of U1B is SIG, correct? U1A is only driving the LED? Thanks.

Not shown in the schematic clip is a switch which selects the right or left voltage divider.

Battery voltage measurement is the near term concern. The load will intermittently be as high as 100+ amps (diesel engine starter), way beyond the board’s spec.

For voltage only measurement, I would remove the sense resistor, correct?

Yes, just remove the current shunt and just ignore the current reading, it will still supply the voltage reading.

3 Likes

Thank you

I ended up prototyping with an INA219 breakout from Adafruit. I’m only using the Vin(-) to measure the battery voltage. Seems to be working fine. As I will need at least two battery measurements, I will likely change over to an INA3221 breakout board soon.

I have working code for the INA3221 if you need it.

Thank you.

Yes?

Yep