My dynamometer is done, and now I want to make it work on batteries, without setting it on fire !
So, I am using:
-A LoadCell that have a maximum excitation voltage of 12VDC and an excitation voltage of 5VDC
-An LCD I²C Screen that works on 5 VDC
-An HX711 that works between 2,6 and 5,5 VDC and 100 µa of digital supply current
-An SD card module that works between 4,5 and 5,5 VDC and 0,2 to 200 mA.
-An Arduino Uno Rev 3
-A push buttton
I want my Arduino to work one hour a week, so, I plan to use a rechargeable battery, with a slot for battery (cylinder type), which voltage and amp should I select for my application ?
Hoe much does the I does the current circuit consume? By measuring the I and knowing the volts you can get a general idea of a Amp/h and an idea of the battery size. I'd add a few Ah to deal with surges that may not be well measured with your amp meter.
The voltage input for the regulator is 7-21volts dc, so if you have a 12 volt supply that will be fine. As for the life you can connect your battery and see how long it lasts as long as it doesn't go outside the voltage range. If I were you I would get a rechargeable 9 volt battery or AAs.
I'd suggest a 5V switching regulator to bring 12V battery source (8-pack of AAs for example) to power the 5V devices.
Bring 12V into an Uno just wastes 7V x current as heat in the 5V regulator, which is hardly efficient. How much current do you need?
Max excitation voltage of 12V suggests a 3-cell LiPo or Li Ion might do the trick for the battery source, with 9 min to 11.1 nominal to 12.6V max voltage when fully charged.
20V is not to be believed.
If you look up the datasheet for the regulator, it may say 20V Absolute Max, and drawing much current with a 15V difference from Input to Output will either damage the part, or if you're lucky just make it go into thermal shutdown.
If the regulator had a 12V to 15V output, 20V input would make sense.
With 5V output, then 12V is about the max you would put in, and 7.5V or 9V makes a lot more sense.
The Uno Rev3 schematic, Rev3E from 6/3/2019, shows NCP1117ST50T3G as the 5V regulator,
The 47uF supply caps on most (clone) UNOs are rated for 16volt.
If... you have an official Uno, and... it has 25volt caps, then thermal limitations of the 5volt regulator will eventually bite you in the bum.
At 12volt on V-in, you might be able to get away with 100mA for sensors,
but at 20volt you can't connect/power anything else from the Uno.
I bought a nice set of batteries with 9v and 650 mAh of charge and its enough for the use that i have of my board. I think that the voltage regulator of the board does the job as it have not burnt yet.
An Ah is an ampere-hour, ie the amount of charge that flows when a current of 1 amp lasts for 1 hour. This is 3600 coulombs of charge in SI units. Battery capacitty is measured typically in Ah or mAh (milliampere-hours).
Roughly speaking a 2Ah battery can produce 200mA for 10 hours, or 100mA for 20 hours, or 2A for an hour (though usually at high discharge rates the yield is less).
Your setup requires regulated 5V so you'll need a voltage regulator to drop the battery voltage down. Say you used a 2S LiPo pack which produces 7.4V, and a 5V regulator, this could work.
You'd use a multimeter with a current setting - read up how to measure current there are many tutorials out there - do not guess how to do it you'll likely damage your battery and blow the meter's fuse if you guess wrong.