> The modems are a few hundred
> dollars (1-off) and only draw about 10mA when idle, which is not too bad
> I guess.

10 mA = 240 mAh/day ~= 1.7 Ah/week.

Present current usage is about 2 AH / week based on your initial
figures, so IF the modems were always on they would come close to
doubling your present energy use. It's annoying how such things add up
:-(.

Polling occasionally with the modem usually in sleep mode could reduce
this substantially. Depends on wakeup time and acceptable latency for
a command response.

Seeing if the motor energy use could be reduced may also pay dividends.

Your carefully vague [tm] description doesn't note whether it's
indoors or out, but the 20 metre range suggests that it MAY be
outdoors. If so, then a modest photovoltaic panel could greatly extend
battery life. Present usage is in the 100 - 200 mW range. Even with
full sun access that would need a 500 mW - 1 Watt panel for full
powering (2 Watt to be safe), but even a smaller one could be useful.
If it's indoors then that level of power would require a very
substantial panel. The very smallest of wind turbines (200 mW mean
output!) would suffice.


      Russell





      Russell
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