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BATTERY help? Answered

i have a rechargeable battery that is 7.2 volts and 3000 mAh Ni-Mh

now is it safe to add a Voltage Regulator to run an led or if not how do i?
what also is scaring me is the 3000 mAh if its good or bad



Best Answer 8 years ago

1) Yes, you can safely regulate a higher voltage down to a lower one. (You could also just use a suitable resistor in series with the LED, if you just want to power the LED, but including regulator should be more efficient and should keep the LED at its fully brightness longer.)

2) mAh is "milliamp-hours" It's an indication of the total energy available from the battery. 3000 mAh means it can provide 100 milliamps for 30 hours while maintaining something close to the rated voltage, or 300 for 10 hours, or 500 for 6 hours. (There limits to how far you can push that trade-off -- if you try to draw too much current at once the battery can destroy itself, possibly catching fire or exploding -- but you get the general idea.)

To know how long this battery will run your LED, you need to know how much power the LED will draw. A more-or-less reasonable number to use for a midrange LED would be 100mA, so this battery should be able to keep it lit for about 30 hours before needing to be recharged; maybe a bit more, though NiMH battery voltage tends to drop off fairly steeply as they run out of oomph.


Answer 8 years ago

ok so its powering a 14.4V drill motor its for a M134 Mini gun im only using 7.2 cause its enough but for the leds they should not draw that much right so it would be safe im also using a relay to turn on the motor circuit or do you think i dont need a relay your very knowledge able


8 years ago

Yes. Pretty much any regulator that will operate off the battery voltage will run just fine.

As Ork noted, the 3AHr rating is the capacity of the battery. It sounds like something to worry about since the number is measured in mAhr instead of Amp hours and 3000 is a big number, but it's not.

For a typical LED, you'll draw somewhere between 10-20mA, providing a considerable amount of "on-time", on the order of 150-300 hours of continuous operation.

The "how" depends on what kind of regulator you'e connecting, but it all comes down to a 2 wire connection, one for the high side and one for the return (or GND/COM).

The regulator circuit is straightforward for the simple 7805 type voltage regulators or LM317 constant current type regulators. If an IC regulator is used, it's a bit different but similar. See the links for example circuits.