# Working out battery life

Discussion in 'The Projects Forum' started by kennedy12, May 29, 2013.

1. ### kennedy12 Thread Starter New Member

May 28, 2013
5
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1-how to calculate and what calculations are needed to know how long batteries will last before replacement batteries.

2-and i was also wonder how transistor stage values were calculated

This what for a bike light circuit based around pic16f684 with a high power led
and a tip122 power transistor (3aa batteries)

was wondering if there was a equation or formula or working it out. any help?

KEN

2. ### #12 Expert

Nov 30, 2010
16,703
7,341
Amp-hours (from the battery capacity) divided by the amps you will be using = hours of battery life.

How to calculate transistor stages requires a small book. You need to ask the question in a better way.

3. ### libra Member

Jul 27, 2012
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Means if we have 3amps battery it run for 3 hours.

4. ### #12 Expert

Nov 30, 2010
16,703
7,341
If you are using 1 amp and the battery is rated for 3 amp-hours, the battery will last for 3 hours.
AA batteries are not rated for 3 amp-hours. More like 1 amp-hour.

May 7, 2013
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6. ### kennedy12 Thread Starter New Member

May 28, 2013
5
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HI, Ive done a circuit for a bike light and i am requireed to work out how long the the batteries will last for.

A TIP22 TRANSISTOR
Pic16f684
3 AA Batteries
10k resistor going through to the high powered resistor

any help on how to calculate the battery life?

7. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
507
Sure.

Any help on what the circuit is, how much current the light draws, what TYPE of batteries are they?

8. ### kennedy12 Thread Starter New Member

May 28, 2013
5
0
thank u very much

350 ohms current

and 3 AAA Batteries (4.5) volts

9. ### #12 Expert

Nov 30, 2010
16,703
7,341
Same as the thread kennedy12 created in Projects, except now the load is provided. A moderator will combine the threads in a short time.

Apr 5, 2008
15,803
2,388
Hello,

As suggested by #12, I have merged the thread.

Bertus

11. ### edwardholmes91 Member

Feb 25, 2013
200
20
Current isn't measured in ohms, it's measured in amps and I'm 100% certain your circuit isn't drawing 350A otherwise it would've fried! With regards to the battery capacity we need to know the mAh (milliamp hour) rating. This will either be printed on the side of the battery or be given in the technical specification for it. As a ballpark figure, Procell AA batteries have a mAh rating of 2700. This means that they can supply 2.7A for one hour. Once we know the average current draw of your circuit and also the mAh rating of the batteries you are using we can help you calculate the life of the batteries.