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Calculate Peukert's law with INA219

The INA219 will measure the voltage and current of a battery at given time spans. I want to know by taking the average of the current and voltage and comparing it to an initial reading, can I use Peukert's law to loosely predict how long the battery may last?

asudem

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Joined: Fri Feb 05, 2016 5:01 pm

Re: Calculate Peukert's law with INA219

Peukert's law applies to lead-Acid batteries. Depending on the battery chemistry you are using, you may need a different model. But the INA219 is capable of making the raw measurements.

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Joined: Sat Feb 07, 2009 10:11 am

Re: Calculate Peukert's law with INA219

So would it be easier of I measure a Duracell AA battery rated at 2850mAh capacity and use the following formula?

Code: Select all | TOGGLE FULL SIZE
`float  c = 0;//combined mA draw readingint t = 0; //number of loopsvoid loop(){float  z = ina219.getCurrent_mA(); //current mA readingc += z;float  y = c/t; //averaged mA draw readingint ratedCapacity = 2850; //rated capacity for the battery in mAhfloat estimatedHours = ratedCapacity  / y * 0.7; //The factor of 0.7 makes allowances for external factors which can affect battery lifet++;}`

asudem

Posts: 55
Joined: Fri Feb 05, 2016 5:01 pm

Re: Calculate Peukert's law with INA219

Alkaline batteries have significant internal resistance, so the effective capacity depends on the rate of current draw. If you check the Duracell site they will have charts that show discharge curves for different discharge rates.

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Joined: Sat Feb 07, 2009 10:11 am

Re: Calculate Peukert's law with INA219

constant-current.jpg (45.65 KiB) Viewed 246 times

Here is, for example, one of those discharge curve charts. However, no precise data is listed. If they listed the formula they used per test, things would be a little easier here, but I can't say for example: If my average current draw is 32.5mA and I've been running the battery for 3 hours that my expected battery life is somewhere between 60 and 100 hours.

Also I am testing only one battery in the circuit when there are multiple batteries used. I can not test 6 AAs because the amperage is too high for the INA219 to test. This also needs to be factored in as well.

asudem

Posts: 55
Joined: Fri Feb 05, 2016 5:01 pm

Re: Calculate Peukert's law with INA219

I don't have any formula for alkaline cells that i can give you.. If you search the net, there are probably some out there.

Posts: 79404
Joined: Sat Feb 07, 2009 10:11 am

Re: Calculate Peukert's law with INA219

adafruit_support_bill wrote:I don't have any formula for alkaline cells that i can give you.. If you search the net, there are probably some out there.

I'll be consulting the net, and probably retake a few physics classes to fully grasp the concept. I'll also see what Amazon kindle has to offer as far as electrical engineering books have to offer, but something like "Electrical Engineering for Dummies" over "AP Physics: The complete MIT course".

I'll keep this thread updated with my findings, as it may be useful for a "Learning" tutorial implementation in the future. :)

EDIT: There is actually a book called "Batteries in a Portable World: A Handbook on Rechargeable Batteries for Non-Engineers", and from the reviews of it, it sounds like just what I need! If they don't touch alkaline, I'm sure switching my device to rechargables wouldn't be the end of the world for the consumers I have in mind.

asudem

Posts: 55
Joined: Fri Feb 05, 2016 5:01 pm