Hi,
I finished a tiny project to control some led lights.
It draws 350mA @ +-5v (just measured)from the battery pack.
The batteries are 2000mAh 1.2V ni-mh (GP210AAHCB)
Accordingly to the datasheet it gives 6h of power@400mA.
It should only be on for maybe 5min/day. It auto turns of the led ligh and the arduino itself after 1min.
Should i just use a voltage divider to get the pack voltage? or measure each cell?
What cut-off voltage to use? 1v/cell 4v/pack?
Thanks!
danielb7390:
The batteries are 2000mAh 1.2V ni-mh (GP210AAHCB)
Accordingly to the datasheet it gives 6h of power@400mA.
No it doesn't! 6 hours at 400 mA is 2400 mAh, but you said it is only 2000 mAh.
danielb7390:
It should only be on for maybe 5min/day. It auto turns of the led light and the Arduino itself after 1min.
You are putting it into sleep mode? What sort of Arduino is it? Have you figured out how much current it draws in sleep mode, including the USB chip and the power indicator if these are present?
danielb7390:
Should i just use a voltage divider to get the pack voltage? or measure each cell?
What cut-off voltage to use? 1v/cell 4v/pack?
How do you propose to use the voltage divider? If you are running the Arduino from 5V (be careful - what is the battery voltage when on charge?), then the reference for the ADC is the 5V itself. You can divide the battery voltage and use the more precise internal ADC reference of the Arduino, so you would need a voltage divider for that, but will not the voltage divider be using current from the battery all the time, including during sleep?
What would you do with separate voltage information from each cell? How does that help you as against simply knowing the battery voltage? The only risk with NiMH batteries is a weak cell discharging fully and then being charged in reverse by further discharge. If you limit the discharge to one cell less than full voltage, this cannot occur.
For some reason i didn't get a email notification so i only noticed your reply now! Sorry!
The battery's data-sheet: http://www.gpbatteries.com/INT/images/prod/datasheet/OEM_NiMH/210AAHCB.pdf
Right now i have a normal battery pack connected to a dc-dc converter to give 5v.
When someone presses the momentary switch the dc-dc converter is started and then a relay is activated with the 5v output. Then arduino boots up and starts counting 1min. After that arduino writes a LOW to the relay and the whole circuit is totally off!! No standby power!
After i get this right and solder a pcb for this i think i will be changing the relay with a simple logic level mosfet.
Indeed the voltage divider would draw current but i could place a transistor there to fix that.
I was saying to check each cell just to make sure there's no "weak" cell discharging bellow the others.
Circuit in attachments!
No one can help with the voltage divider calculation? I want to finish this project ASAP but i can't seem to understand how to get the R1 and R2 values...
I want to read 4xAA voltage to a analog input. So its a voltage dividor for lets say 7v(in case i want to use normal battery's) to 5v.
