11.1V 3S arduino monitoring

[scottmurdoch2010]

trying to find a out to monitor a lipo battery with a arduino can anyone help or point me where to look. :D

[Barnaby]

You need to hook up the output of each cell to a voltage devider then to one of the ADC pins. Each ADC pin needs to see 0-5v, so the first cell can be direct, the second cell can use two 10k resistors to halve the voltage and the third cell a 20k and a 10k. Then you can just multiply the reading by these deciders, and subtract the first cell from the second and the first and second from the third.

[Bob Dunlop]

Hi,

On Wed, Sep 04 at 11:14, scottmurdoch2010 wrote:
> trying to find a out to monitor a lipo battery with a arduino can anyone
> help or point me where to look. :D

Some idea of what you are trying to achieve would help.

If it's simple voltage monitoring for discharge and cut off then a simple
resistor voltage divider on the ADC inputs as already proposed may suffice.

Charging would be a different kettle of fish. Constant voltage charging
should limit at 4.2V with damaging over voltage being at 4.23V a
difference of only 30mV. A challenge for the Arduino ADC. Better to use
a dedicated charging circuit.


Several Arduino style boards have LiPoly support built in already.

The Arduino Fio for example https://www.sparkfun.com/products/10116

I use an Olimexino-STM32 Maple clone (ARM based with 12 bit ADC rather than
AVRs 10 bit). https://www.olimex.com/Products/Duino/STM32/OLIMEXINO-STM32/


--
Bob Dunlop

[Stuart Livings]

Just to add to Bob's comments and further re-enforce them. Discharge monitoring (i.e. low voltage cut-out) is fine but don't charge with an Arduino. Charging LiPo/LiIon is a dangerous affair and best left to well-tested circuits. If you're developing your own circuit there are many single and multi-cell charge chips out there which do all the current limiting, voltage monitoring etc for you and limit your exposure to mistakes. I wouldn't hesistate to integrate one of these chips into a PCB I was scratch designing but would not scratch design a charger.

If you're not developing your own circuit just buy one of the balancing chargers that has the same balance/charge connector as your battery pack. Most of these chargers are safe to leave connected 24x7 but do check with the vendor before doing so.

Again, if you're just doing discharge monitoring then the Arduino ADC is fine, just make sure you can cut out in time. I would target a 3.2v per cell cut-off and make sure you can sleep your circuit fully at that level. Then ensure you disconnect the circuit promptly after cut-off so that the sleep currents don't over-discharge the cells. If you can't disconnect the Arduino from the cells promptly after cut-off (e.g. if it's a remote unmonitored system) I'd suggest a relay or other electronic switch that can be used to safely disconnect the battery.

Stuart

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[scott murdoch]

Most of the board I have seen are only 1s..
Yea I understand wot u mean about not using an arduino to charge it. (Seen one go up). The plan is just to monitor it remotely so it/I know when it needs charged.
Maybe something like this hooked up to an arduino http://www.hobbyking.com/hobbyking/store/__22693__frsky_lipo_voltage_sensor_flvs_01.html

[scott murdoch]

Any know or how to find out if it's rs232 or rs485 or something else