Topic: calculating battery run-time

[Brian Skalinder]

CALCULATING RUN-TIME


First, identify the current draw of your gear.  See this thread:

http://www.taperssection.com/index.php?board=14;action=display;threadid=2461

for a list of ballpark current draw for some common taper gear.  Some specs list the current draw, others may require calculating:

Current (amps) = Power (watts) / Voltage (volts)

If you know the capacity of the battery and the current draw of the gear, it's just simple division to figure out the run time:

( Battery Capacity [mAH] / Current Draw [mA] ) * ( .80 )

Note:  A good rule of thumb is to only assume 80% efficiency.  So multiply by .80 since you don't want to run your battery completely down - this will shorten it's life if it's an SLA.  Additionally, most AH ratings are determined using a slower draw than most of our gear, and batteries are not as efficient at faster draws.  So, conservatively assume you'll only use 80% of the battery capacity.  (NiMH batteries will likely get higher than 80% efficiency, but never hurts to estimate a bit conservatively.)

For example, I have a 6v 7.2 AH capcity battery.  My V3 draws roughly 750 mA current.  So, my runtime is calculated as:

( 7200 mAH / 750 mA ) * ( .80 ) = 7.68 hours