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Calculate Peukert's law with INA219
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Please be positive and constructive with your questions and comments.

Calculate Peukert's law with INA219

by asudem on Wed Mar 02, 2016 4:12 pm

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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Re: Calculate Peukert's law with INA219

by adafruit_support_bill on Wed Mar 02, 2016 4:50 pm

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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Re: Calculate Peukert's law with INA219

by asudem on Wed Mar 02, 2016 5:44 pm

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 reading
int t = 0; //number of loops

void loop()
{
float  z = ina219.getCurrent_mA(); //current mA reading
c += z;
float  y = c/t; //averaged mA draw reading

int ratedCapacity = 2850; //rated capacity for the battery in mAh

float estimatedHours = ratedCapacity  / y * 0.7; //The factor of 0.7 makes allowances for external factors which can affect battery life

t++;
}

asudem
 
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Re: Calculate Peukert's law with INA219

by adafruit_support_bill on Wed Mar 02, 2016 5:59 pm

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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Re: Calculate Peukert's law with INA219

by asudem on Wed Mar 02, 2016 6:19 pm

constant-current.jpg
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

by adafruit_support_bill on Wed Mar 02, 2016 7:56 pm

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.

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Re: Calculate Peukert's law with INA219

by asudem on Wed Mar 02, 2016 8:05 pm

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.

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

Please be positive and constructive with your questions and comments.