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Anonymous asked in Consumer ElectronicsOther - Electronics · 2 months ago

battery run time?

I want to power a 3 watt / 5 volt amplifier with a power bank that is 30,000mAh / 5 volts at 3 amps. I'm confused how long it will last, 10 hours or 2.5  hours?

2 Answers

  • 2 months ago
    Favorite Answer

    Around thirty three hours, if the power bank capacity is genuine.

    3W at 5V is 0.6A, so the obvious answer is 50 hours (30AH / 0.6A).

    However: Power banks use a single lithium cell (or paralleled cells) as the power storage. The average voltage of that cell or cells is 3.6V, so the voltage has to be "stepped up" by approximately 1.4x

    That means the battery current will be a bit more than 1.4 x the output current; so call it 0.9A average from the battery.

    30000 mAH / 900mA = 33 hours in round figures.

    Another way to do it is convert the power bank capacity to "Watt-Hours", which means multiplying the AH rating by the average battery voltage.

    30AH x 3.6V = 108 Watt-Hours

    108 watt-hours / 3W = 36 Hours. That's not allowing for the power loss in the step-up voltage converter though, so is probably about 10% high, getting it back to around 33 hours.

  • 2 months ago

    It "should" last 10 hours, but battery life is often less than expected

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