Electronic – arduino – Will it be fine to consume 0.0058 mA from a LiPo cell after its lowest discharge voltage of 3V has been reached

arduinobatteriescurrentdischargeover-discharge

I intend to connect a 240mAh 1S 3.7v 25C LiPo Battery with a 5V Step-Up Regulator to the Arduino pro mini v5 VCC pin bypassing the linear voltage regulator.

But the battery datasheet says "Never discharge Li‐Po battery below the Lowest Discharge Voltage 3v per cell"

and the voltage regulator data says "takes an input voltage from 2.7 V to 11.8 V and increases or decreases the voltage to a fixed 5 V output'

Thus the Voltage regulator will discharge the battery to 2.7V causing irreversible damage which will deteriorate the battery performance and cycle life.

If I disable the Arduino on-board power LED and since I am bypassing the Linear regulator in sleep mode the current consumption will be 0.0058 mA, so if I use the SparkFun LiPo Fuel Gaugeprogram and program the Arduino to enter sleep mode at 3V will this be good enough to protect the LiPo battery?

http://www.overlander.co.uk/lipo-batteries-240mah-1s-3-7v-25c-sport-hubsan-x4-mini-quadcopter-type.html

https://www.coolcomponents.co.uk/5v-step-up-step-down-voltage-regulator-s7v8f5.html

Best Answer

Drawing 5.8 uA for a few days would probably be OK especially if you set the cut-off a little higher, but the problem you're likely to have with that regulator is that the quiescent current is about 30uA while shut down so it'll be higher while running, possibly in the order of milliamps (it doesn't seem to be specified that I can see).

It sounds like you may not have considered that while the AVR on the Arduino in sleep mode may only be drawing 5.8 uA the regulator will continue to draw it's usual quiescent current. There's two things I'd recommend:

  • For something robust there are external under-voltage protection circuits you could use. For example I found a Linear Technology application note on a LT1495 based protection circuit that draws 4.5uA.

  • If it's for your own / general hobby use make the setup as described and set the AVR to go to sleep at 3.1 V and make some measurements to see how fast it's dropping towards 3 V. Then you can determine a good cut-off point to use that gives you an acceptable amount of time to remove the battery before it's damaged.

They'll be a bit of compromise between the cut-off voltage and how long it can survive without being recharged, but most lithium batteries rapidly decline below 3.2 V so you probably won't be missing out on a lot of charge.

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