Is my math correct ?

Im setting up a pic 16f684 with regulator that draws (.115) ma per hour.
I plan on powering a motor for (.5) seconds at 1 amp once per week.
I am going to use aa batteries that have 2800 mah.

At idle for one year the pic wil draw .115 * 24 * 365 = 1007 ma
The motor will draw ( (1000/60)/60))/2 = .13ma per week, or 7.2ma

If my circuit can work as low as .8 volts per cell am i correct in stating
that the batteries will last at least one year?

jkmadsci said:

Im setting up a pic 16f684 with regulator that draws (.115) ma per hour.
I plan on powering a motor for (.5) seconds at 1 amp once per week.
I am going to use aa batteries that have 2800 mah.

At idle for one year the pic wil draw .115 * 24 * 365 = 1007 ma
The motor will draw ( (1000/60)/60))/2 = .13ma per week, or 7.2ma

If my circuit can work as low as .8 volts per cell am i correct in stating
that the batteries will last at least one year?

Click to expand...

That's the basic idea (I can't be bothered to actually check the maths though!). Obviously there are a number of factors that will affect the exact life, but by only drawing a very low current, with very occasional short surges, battery life will probably exceed the rated value - notice how long batteries last in wall clocks!.

You should be aware though, that you can't use NiCd or NiMh batteries to do this, they self discharge in less time than that.

It's also important you have a good sized electrolytic across the supply, so that the motor current surges come from that, NOT from the battery - as the battery gets low it won't have enough power to feed the motor, but will have enough to slowly charge the electrolytic. This is why IR remote controls have electrolytics in :lol: