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DIY Amp Hour Meter - Arduino
by sspence on May 9, 2012
Table of Contents
DIY Amp Hour Meter - Arduino . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Intro: DIY Amp Hour Meter - Arduino . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Step 1: Voltage Divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Step 2: Current Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Step 3: Math Alert! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Step 4: Serial Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Step 5: LCD Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Step 6: Followup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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http://www.instructables.com/id/DIY-Amp-Hour-Meter-Arduino/
Author:sspence author's website
Professionally, I'm an IT Engineer (Executive Level) and Electronics Tech. Philosophically, I'm a Green Conservative, and probably would have been a hippie
in the 60's if I had been old enough. I live off grid, with Solar (PV), Wind, and veggie oil fueled diesel generator power.
Intro: DIY Amp Hour Meter - Arduino
For my off-grid Ham Radio and Solar projects, I needed a way to measure volts, amps, watts, amp hours and watt hours. There's a couple of commercial products that
can do this, but not with the flexibility I wanted. I designed a Arduino micro-controller based solution that is very extensible. Right now it monitors the above values of
attached gear, and I'm thinking about adding web monitoring and a sd card for data collection. Well, let's get started.
Step 1: Voltage Divider
The Arduino can accept up to 5v on a analog input. Our battery voltage can range as high as 16vdc in certain charge cycles, so we designed a voltage divider that would
provide 5v at 16v battery voltage, and less at various lower voltages. See http://en.wikipedia.org/wiki/Voltage_divider to determine the right values for your application.
The code to read that value is as follows:
batVal = analogRead(batMonPin); // read the voltage on the divider
pinVoltage = batVal * 0.00488; // Calculate the voltage on the A/D pin
// A reading of 1 for the A/D = 0.0048mV
// if we multiply the A/D reading by 0.00488 then
// we get the voltage on the pin.
batteryVoltage = pinVoltage * ratio; // Use the ratio calculated for the voltage divider
// to calculate the battery voltage
More details at http://arduinotronics.blogspot.com/2012/04/voltage-monitor.html
http://www.instructables.com/id/DIY-Amp-Hour-Meter-Arduino/
Step 2: Current Monitoring
The next step is to track the current being consumed by a load, or produced by a source. We are using a ACS715 Hall Effect sensor to track the current being passed.
// read the analog in value:
sensorValue = analogRead(analogInPin);
// convert to milli amps
outputValue = (((long)sensorValue * 5000 / 1024) - 500 ) * 1000 / 133;
amps = (float) outputValue / 1000;
More details at http://arduinotronics.blogspot.com/2012/04/monitoring-power-consumption-with.html
Step 3: Math Alert!
To calculate watt (volts * amps), amp hours (amps * hours), and watt hours (watts * hours) requires tracking the time component, and performing a bit of math:
float watts = amps * batteryVoltage;
sample = sample + 1;
msec = millis();
time = (float) msec / 1000.0;
totalCharge = totalCharge + amps;
averageAmps = totalCharge / sample;
ampSeconds = averageAmps*time;
ampHours = ampSeconds/3600;
wattHours = batteryVoltage * ampHours;
Step 4: Serial Output
We can now output the results of the calculations to the serial port using the following code:
Serial.print("Volts = " );
Serial.print(batteryVoltage);
Serial.print("\t Current (amps) = ");
Serial.print(amps);
Serial.print("\t Power (Watts) = ");
Serial.print(watts);
Serial.print("\t Time (hours) = ");
Serial.print(time/3600);
Serial.print("\t Amp Hours (ah) = ");
Serial.print(ampHours);
Serial.print("\t Watt Hours (wh) = ");
Serial.println(wattHours);
http://www.instructables.com/id/DIY-Amp-Hour-Meter-Arduino/
Step 5: LCD Display
Keeping a computer connected all the time is inconvenient, so I added a lcd display to the project.
lcd.setCursor(0,0);
lcd.print(batteryVoltage);
lcd.print(" V ");
lcd.print(amps);
lcd.print(" A ");
lcd.setCursor(0,1);
lcd.print(watts);
lcd.print(" W ");
lcd.print(time/3600);
lcd.print(" H ");
lcd.setCursor(0,2);
lcd.print(ampHours);
lcd.print(" Ah ");
lcd.print(wattHours);
lcd.print(" Wh ");
Step 6: Followup
All the code, schematics, and photo's along with discussion is available at
http://tech.groups.yahoo.com/group/arduinohome/files/volt%20amp%20watt%20hour%20meter/
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