# INA226 measure current voltage 60V 30A battery

Hello. I want to measure current and voltage of 60V (52V nominal) 30A battery with INA226.
As I understand, I need external shunt 50A 75mV.
Also I need voltage divider with 2 reductors (INA226 only support 36V max).

1. Does reduction ratio influence measurement accuracy?
I can use R1=100k & R2=100K for 1:2 or R1=100K & R2=10K for 1:11. Are 100K reductors accurate enough or better use 10K (10K:10K or 10K:1K relatively)? What would be better approach?

INA226 has an input impedance of about 830K Ω between VBUS pin and it’s ground pin.
According to http://www.ti.com/lit/ug/tidu849/tidu849.pdf

1. I am completely confused with ground circuit. Where end of R2 resistor should be connected? To IN- or Load- or its the same? Also do I need to connect battery ground with Arduino ground like IN- with GND?

Here is my draft schematic. Does it look right?

*Update: after rethinking it I think INA226 should be connected vice versa Load- into IN+ and Battery- into IN-, although, as I understand, it should work both directions.

I think R2 end should go to IN- (top or bottom probably does not matter cause they should be on same lane).
According to youtube videos, as far as I understand, Arduino GND should be connected to IN- as well.

Sorry, I am complete novice in microelectronics. Thanks.

Demion:

1. Does reduction ratio influence measurement accuracy?

I can use R1=100k & R2=100K for 1:2 or R1=100K & R2=10K for 1:11. Are 100K reductors accurate enough or better use 10K (10K:10K or 10K:1K relatively)? What would be better approach?
INA226 has an input impedance of about 830K Ω between VBUS pin and it’s ground pin.
According to http://www.ti.com/lit/ug/tidu849/tidu849.pdf

1. I am completely confused with ground circuit. Where end of R2 resistor should be connected? To IN- or Load- or its the same? Also do I need to connect battery ground with Arduino ground like IN- with GND?

as I understand, it should work both directions.

Sorry, I am complete novice in microelectronics.

No, it reduces resolution (fewer A/D steps per volt).

Yes, you can use 100k+100k (1:1), but note that the datasheet mentions an ~830k input impedance.
That impedance is parallel to R2, and reduces the value of R2.
(100*830)/(100+830)= 89.25K.

R2 should be connected to INA ground.
Battery ground must also connect to INA ground.

Yes, the INA is bi-directional.

Then maybe you shouldn't do this without supervision. 60volt@50Amp is dangerous.
Leo..

Thanks for explanation. I will test with low voltage batteries and low current loads first.

Just to be sure is it safe to connect INA ground (GND) to IN- which lead to shunt “out” and then to battery ground? (as in scheme 2)

Also, as I understand, battery, INA and Arduino will all share ground. Because INA ground and Arduino ground are connected wont 36v (from VBS for voltage measurement) flow through Arduino?

Thanks again.

The INA226 is designed for high-side (in the + line) current sensing.
But in this case that’s not possible because of the high battery voltage.

If you measure low-side then the drawback is that one side of the shunt must be grounded to battery(-), and the other side of the shunt could get negative (when charging or discharging). Negative going range of the INA is only 0.3volt!

A workaround could be to use the shunt in a different place in the battery string.
I would just try it first with battery ground to INA ground.
Leo…