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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

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    \$\begingroup\$ What part of the word "Never" is unclear? \$\endgroup\$ – Nedd Nov 22 '15 at 12:22
  • \$\begingroup\$ Then maybe providing me with a hint or a way around this would help. \$\endgroup\$ – M.Atwya Nov 22 '15 at 12:29
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    \$\begingroup\$ You would probably be better off running your ATmega directly off the cell voltage. If you have a peripheral which runs at 5v you can use the boost converter for that, and have the ATmega enable or disable it based on need and cell voltage. Also, you seem to be making a questionable assumption that the converter will shut itself down at 2.7v - it may not work properly below that, but that doesn't imply a zero-current-draw shutdown unless explicitly stated. \$\endgroup\$ – Chris Stratton Nov 22 '15 at 17:40
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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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OK, here's an idea:
when you do put the system into low current mode (or sleep mode) there is a chance that the battery voltage starts to drift upward. If possible set a wake up timer for a long duration, (several minutes or more), then wake up only briefly and measure the voltage, if it has risen significantly (as if the charger was reconnected) stay fully awake, if not go back to sleep. However if the measured voltage remains close to or hits the minimum value you should have another power off (or disconnect) circuit to do a full shut down. (As in the other answer give yourself a good safety margin.)

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  • \$\begingroup\$ So here are my components: - Arduino Pro mini 5V ( Typical voltage: +5V, Typical current: 25 mA) - Transmitter Module ( Typical voltage: +5V, Typical current: 10 mA - Myoware muscle sensor ( Typical voltage: +5V, Typical current: 14 mA) I intend to power through the VCC pin bypassing the Arduino on-board linear voltage regulator. I am thinking of using a Lithium Ion Polymer Battery - 3.7v 500mAh with a 5V Step-Up Regulator. The battery has its own PCB that will cut-out the battery when at 3V. adafruit.com/products/1578 sparkfun.com/products/10255 How does that sound? \$\endgroup\$ – M.Atwya Nov 22 '15 at 19:28
  • \$\begingroup\$ OK, so that specific battery will protect itself from over drain below 3v. That part of the design is then done. It may also be best to get the recommended charger for that battery (listed on the same page). That will complete yet another part of the design. From there on you can do the sleep mode just to reduce the overall power consumption. Good start, best of luck. \$\endgroup\$ – Nedd Nov 23 '15 at 0:45

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