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### Topic: Understanding Fc-51 ir sensor power consumption (Read 1 time)previous topic - next topic

#### tracksuit_arduino

##### May 07, 2019, 03:46 pm
According to data I was able to find, the Fc-51 ir sensor consumes 43mA. What does this mean, in terms of power used over time? I'm trying to understand how to determine how much the sensor drains a battery over time.

#### groundFungus

#1
##### May 07, 2019, 05:04 pmLast Edit: May 07, 2019, 05:05 pm by groundFungus
This page has a schematic of the sensor module.  Note the 100 Ohm resistor in series with the IR LED.  At 5 volts the LED will draw approximately 32 mA.  The other LEDs on the board probably account for most of the other 11 mA.

#### tracksuit_arduino

#2
##### May 07, 2019, 05:18 pm
This page has a schematic of the sensor module.  Note the 100 Ohm resistor in series with the IR LED.  At 5 volts the LED will draw approximately 32 mA.  The other LEDs on the board probably account for most of the other 11 mA.
Does the draw of 43mA mean per hour? It's the unit of time I don't understand. E.g. if my battery has 2400mAh capacity do I simply divide that over 43 to get a rough estimate of battery life? Using consumption rate of 0.7 I get about 40 hours. Is that more our less sounding right?

#### groundFungus

#3
##### May 07, 2019, 05:26 pmLast Edit: May 07, 2019, 05:29 pm by groundFungus
43mA means 43mA, there is no time.  If a circuit draws 43mA for an hour then it is 43mAh.  To get a rough estimate just divide the battery capacity by the current draw.  So 2400mAh / 43mA = 55.8 and change hours.  To get closer, consult the discharge curves on the battery data sheet.  Battery capacity is specified at a certain current draw.  Drawing more current than the spec will result in decreased capacity and less current draw than the spec will yield more capacity.

Quote
Using consumption rate of 0.7
Where does 0.7 come from?

#### tracksuit_arduino

#4
##### May 07, 2019, 05:53 pm
Thanks. 0.7 was just something I read that gives a rough discount of true battery life. This seems to confirm what I'm seeing, having this sensor on kills my battery in about 2.5 days or so.

#### groundFungus

#5
##### May 07, 2019, 06:04 pm
OK I see.  And I agree that the manufacturers stated battery capacity can't be wholly trusted (note the underline under rough).  Their numbers are based on testing under specified laboratory conditions that probably are not duplicated in real use.

#### wvmarle

#6
##### May 08, 2019, 01:40 pm
Using consumption rate of 0.7 I get about 40 hours. Is that more our less sounding right?
Thanks. 0.7 was just something I read that gives a rough discount of true battery life. This seems to confirm what I'm seeing, having this sensor on kills my battery in about 2.5 days or so.
2 1/2 days is 60 hours. So that'd give a correction factor of 1.1 rather than 0.7.

It's also pretty close to 2400/43, much closer than it is to 2400/42*0.7.
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