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measure power for battery calculation

Aamir Ali1
Intellectual 375 points
Other Parts Discussed in Thread: INA231

I have a battery operated circuit. 

1. Circuit wake up for 100ms. Do its work & go to sleep for next 1sec.

2. In 100ms, it does many different task. one after another.
So current keeps on varying in that 100ms also.


I have to measure power of circuit so that I can calculate the battery requirement.

1. I tried to put simple ammeter in between but it couldn't measure high frequency spikes.

2. Then I put a 5 ohm resistor in power path, & check the voltage across it with oscilloscope. It shows repetitive readings in the circuit.

At any instant I can get current by dividing the voltage noted from CRO by 5ohm.


By how to consolidate the total power across one cycle.


3. Is there any low cost solution available which can measure the power drawn.

  • 0
    Intellectual 310 points

    Dear Amir,

    "Circuit wake up for 100ms. Do its work & go to sleep for next 1sec." Just for a confirmation if I've understood your statement correctly --> 1) The MCU will normally be in Sleep-Mode, 2) on every second, it will wake up from Sleep-Mode. 3) It has to do some tasks, and those tasks will be completed almost in 100mS.

    So you want to measure the current consumed by the circuit during that 100mS period, right?

    I don't have any idea how much current your circuit consumes during the active period. It would be better if you can include those details.

    I suggest you to use a very low value current-sense resistor instead of 5-Ohm resistor (I guess it's a normal resistor since you have not mentioned anything on it). Connect the resistors terminals to a current shunt monitoring circuit (ICs like INA231 will be a good option, it'll produce a digital output). You can monitor the current periodically based on your requirement.

    The value of resistor shall be based on current consumption of your circuit. If it's in several amperes, you will have to use 0.01Ohm or even less. But everything is just mathematics and you can find those values.

    INA231 is able to measure current/power and produces I2C output, I recommend it. If you need analog output, there's a plenty of options are available from TI.

    Regards,

    Binoy Raphael.

  • 0
    Guru 46710 points

    Aamir Ali1 said:
    3. Is there any low cost solution available which can measure the power drawn.

    Yes. Check EnergyTrace.

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