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Topic: How are people powering battery-driven projects? (Read 1 time) previous topic - next topic

cornwallav8r

It's a quandary...a 4-cell AA battery is too high voltage for the 5v input, but almost too low for the 78M05 regulator input, adn will drop out fairly quickly despite battery capacity left.  A 9v doesn;t have the endurance of multiple batteries. 
I do see however there is a 5v switching arrangement on the Nano at least, to switch, from the USB 5v to the 5v main bus?  Not sure that is an alternative...

So what are people doing in this regard?

Coding Badly

It's a quandary...a 4-cell AA battery is too high voltage for the 5v input,


1.2 * 4 = 4.8 volts.  Why do you believe the voltage is too high?  You are talking about NiCd batteries, right?

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but almost too low for the 78M05 regulator input, adn will drop out fairly quickly despite battery capacity left.


1.5 * 4 = 6 volts.

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The recommended range is 7 to 12 volts.


"Almost too low"?

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So what are people doing in this regard?


Two AA alkaline batteries directly to the processor.

oric_dan

In general, not a good idea to power a microcontroller from a battery directly.

For most of my battery-powered projects, I use a board with 5V LDO v.reg and power
with 6 NiMH AA-cells in series = a bit over 7.2V fully-charged. These cells have 2200-2500
mA-hr of energy, so I can run motors and servos.

7.2V will barely power a regular 7805 with 2V dropout.

Coding Badly

In general, not a good idea to power a microcontroller from a battery directly.


Why?

cornwallav8r

Exactly Oric...(4) AA Alkalines start out at like 6.75 volts, and it is enough at first for the 05 regulator, but will drop out somewhere too soon before the batteries are depleted....If I wire the batteries directly to the 5v bus it exceeds the processor's voltage spec of around 5.5v.   I have a simple project, but the lcd display has a large drain led backlight.   Most cases don't come with capacity for (6) AA or even AAA...so I think it is 9v for me at this time...I need to let a supplier know for prototyping samples.  I suspect a 9v won;t last long.


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