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at what rate is the battery discharging?


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I ordered bits to make some resistor-based dew strips last night. I put together a little Java program to fine tune my design. The targets for output are just estimates based on what I've read from other dew heater builders.

        double radiusCm = 3.0;
        double stripCm = 2.0 * radiusCm * Math.PI;
        double areaToHeatCm2 = radiusCm * radiusCm * Math.PI;
        boolean resistorsInParallel = true;
        double resistorOhms = 56.0;
        double resistorWatts = 1.0;
        int numberResistors = 8;
        double batteryVolts = 1.2;
        double batteryCapacity = 4.0; //amp hours
        int numberBatteries = 4;
        double batteryEfficiency = 0.7; //http://www.powerstream.com/AA-tests.htm#nimh
        //Do calculations twice for when the battery is fresh or has run down a bit
        //Also voltage is lower when current is high
        String header = "CALCULATION AT FULL VOLTAGE";
        for (double freshness : new double[]{1.0, 0.85}) {
            System.out.println(header);
            header = "CALCULATION AT 85% VOLTAGE";
            //Battery cell
            double volts = numberBatteries * batteryVolts * freshness;
            System.out.println("Battery output is: " + volts + "V.");
            //Circuit resistance
            double resistance;
            if (resistorsInParallel) {
                resistance = resistorOhms / numberResistors;
            } else {
                resistance = resistorOhms * numberResistors;
            }
            System.out.printf("Circuit resistance is %.2f Ohms.\n", resistance);
            //Power
            double watts = volts * volts / resistance;
            System.out.printf("Power delivered is %.2fW.\n", watts);
            //Current
            double current = volts / resistance;
            System.out.printf("Current is %.2fA.\n", current);
            //Watts per resistor
            double loadPerResistor = watts / numberResistors;
            boolean resistorsOverloaded = loadPerResistor > (0.75 * resistorWatts);
            System.out.printf("Load per resistor is %.2fW. %s\n", loadPerResistor, (resistorsOverloaded ? "[FAIL]" : ""));
            //Battery life
            double hours = batteryCapacity / current * batteryEfficiency;
            System.out.printf("Runtime is %.2f hours. %s\n", hours, (hours < 3.0 ? "[FAIL]" : ""));
            //Power per cm
            double wattsPerCm = watts / stripCm;
            double wattsPerCm2 = watts / areaToHeatCm2;
            boolean powerOutOfRange = wattsPerCm2 < 0.07 || wattsPerCm2 > 0.13 || wattsPerCm > 0.3;
            System.out.printf("Output is %.2fW/cm or %.2fW/cm2. %s\n", wattsPerCm, wattsPerCm2, (powerOutOfRange ? "[FAIL]" : ""));
            System.out.println();
        }
It gives this output for my nifty fifty dew heater:
CALCULATION AT FULL VOLTAGE
Battery output is: 4.8V.
Circuit resistance is 7.00 Ohms.
Power delivered is 3.29W.
Current is 0.69A.
Load per resistor is 0.41W. 
Runtime is 4.08 hours. 
Output is 0.17W/cm or 0.12W/cm2. 
CALCULATION AT 85% VOLTAGE
Battery output is: 4.08V.
Circuit resistance is 7.00 Ohms.
Power delivered is 2.38W.
Current is 0.58A.
Load per resistor is 0.30W. 
Runtime is 4.80 hours. 
Output is 0.13W/cm or 0.08W/cm2.  
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