sizing up power requirements

I'm planning the architecture of my next bot and trying to decide what
sensors/components I want to add with an eye toward how much of a drain they
will place on my system. While I can certainly add more batteries, there
will be a size limit to how much will fit. Is there a rule of thumb for
sizing up a component and determining if the current draw would be too
taxing on the system or will drain the batteries too quickly to be effective
(taking each component independent of on another, then looking at the
overall power needs combined)? Obviously, components draw different amounts
of power during their operation, but I imagine you can estimate a working
condition.
Take for example if I wanted to add the embeddedBlue Series eb500 (bluetooth
appmod module from Parallax)
the specs state:
power:
5-12V DC
current consumption:
9.6kbps data transfer 25mA
idle 8mA
no connect 3mA
Lets say I'm powering the bot with a 9V Alkaline rated at 6AM6
For sake of discussion, other than the basic stamp 2, the bluetooth appmod
is the only other component drawing power off this battery (motors are a
separate supply). I would expect there to be a no connect probably 90% of
the time, idle 8% and transmit 2% (hypothetical). So the avg current
consumption would be around 3.7mA while the bluetooth device is receiving
power. Taking this into account, how could I analyze this to see how
quickly the battery will drain and whether I might need to add more power?
As a followup question. If I add 2 9V in parallel, will that effectively
give me twice as much life (each battery supplies half the current that only
one would supply)?
thanks
Reply to
teranews
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If your battery is rated at, e.g. 3 amp hours (AH), and you draw an average of 100ma, then the batter will last for 3/.1 = 30 hours.
The more current you draw, the faster the battery declines, however, so at an average of 1 amp, the battery will last far less than the 3 hours you might expect from the algebra I did above.
Reply to
Mark Haase

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