I am currently working on my first Arduino project and would like to estimate battery life. Many of the datasheets for the sensors I am using have mA given at differing voltages. Is converting the figure given into Watts and then back in the Amps at the specific voltage I am going to use (3.6) the correct way to estimate power?
The best way to estimate battery life is to measure the actual, average current draw of the final circuit. Then, you divide that figure (in milliamperes, mA) into the battery capacity in milliampere hours (mAh) to get a rough idea of the runtime in hours. Some battery capacities are listed in Ah (ampere hours) and 1 Ah = 1000 mAh.
If you are using lithium batteries, be aware that they will be destroyed if any cell is discharged much below about 2.5 V. They are also destroyed by overcharging, so a specialized charge controller is required.
Is converting the figure given into Watts and then back in the Amps at the specific voltage I am going to use (3.6) the correct way to estimate power?
No.
Also assume that the actual battery capacity is somewhere between 30% and 50% of the sticker capacity.
...R
jremington:
The best way to estimate battery life is to measure the actual, average current draw of the final circuit. Then, you divide that figure (in milliamperes, mA) into the battery capacity in milliampere hours (mAh) to get a rough idea of the runtime in hours. Some battery capacities are listed in Ah (ampere hours) and 1 Ah = 1000 mAh.If you are using lithium batteries, be aware that they will be destroyed if any cell is discharged much below about 2.5 V. They are also destroyed by overcharging, so a specialized charge controller is required.
Haven't actually got a circuit just datasheets. The enclosure needs to be tiny so I really need to get an accurate a possible estimate before buying the components. Not going to have much room for a battery.
The approach of designing the enclosure before meeting other critical requirements (like functionality and minimum battery life) is neither wise nor likely to be successful.
Your classic "cart before the horse" scenario...
Perhaps the space has been decided by someone else.
I have had great fun squeezing a battery, an "arduino" with 2.4GHz transceiver and h-bridge, a switch and a rectifier into an N-Gauge model railway locomotive.
...R
cheezburger:
I am currently working on my first Arduino project and would like to estimate battery life. Many of the datasheets for the sensors I am using have mA given at differing voltages. Is converting the figure given into Watts and then back in the Amps at the specific voltage I am going to use (3.6) the correct way to estimate power?
Only if you are using a 100% efficient switch-mode DC-DC converter to power it.
Typically with linear regulators you just add up all the currents, multiply by the supply
voltage to get total power. (Some of that power goes to the regulator).
But of course measuring is more definitive - many devices have fluctuating current
requirements after all, and a multimeter will average those out nicely on a timescale
of a second or so.
Maximum current drain figures in a datasheet are conservative, they cover all
device variation across a large temperature range. Typical current drain figures
are not guaranteed...