Re: Power question

Macgyver wrote:

Matt wrote:
Say i have a circuit that runs on 3 v. if the circuit consumes 114 uA.
If the circuit is powered by 2 AA batteries with a 1000 mah rating than
the circuit would have a lifetime of about 1 year. If i replaced the
batteries with a 12 v battery with the same capacity would the lifetime
be extended to 4 years?

The simple answer is no (it will be somewhere between less and much
less, assuming that the circuit has a regulator that can handle the
higher input voltage!).

I am assuming that since you have given 1.5V for the cell voltage you
are currently using Alkaline AA cells. At such a low continuous
current load, converter inefficiency and battery self discharge are
going to become big battery draining factors. Also, you haven't
mentioned what the cutoff voltage for the circuit is. This will
greatly effect how long the circuit is capable of running before the
supply voltage gets too low.

Since it sounds like you have the space (if a 12V battery is an option)
you are better off changing to C or D cells to extend circuit life. If
you want to get a bit more technical, a small solar cell and associated
converter/regulator may be a better long term option (although
regulator and battery choice will effect life).

I concur with the larger cells at 3V idea. But since the device is going
to be running near the cell's shelf life (larger cells will just self
discharge over roughly the same time period), the OP might want to
consider some cells with longer shelf life, like lithium cells.

--
Paul Hovnanian mailto:Paul@xxxxxxxxxxxxx
------------------------------------------------------------------
"A doctor can bury his mistakes but an architect can only
advise his client to plant vines." -- Frank Lloyd Wright
.

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