minimal voltage and the battery is
Higher currents can damage the
battery similar to voltages outside
the minimum and maximum range.
Figure 3 is a common battery with
these parameters clearly identified.
Using your watt meter, if you
observed a robot consuming an
average of 30 amps and had to run
it for three minutes, you would not
be able to use that 1 Ah 30C battery
because you would run out of
capacity. By matching units, a 1 Ah
battery can provide 60 amp minutes
(1 hour = 60 minutes), but
understand that you cannot provide
more than 30 amps at any time.
So, running a 1 Ah/60 amp
battery at 30 amps yields only two
minutes of run time on the battery.
Most likely, you will not be running a
motor with an average current close
to the C rating, as motors typically
will have a higher starting current
(peak current) that while
momentary, should be used within
the C rating of the battery.
In this way, the watt meter can
provide you start-up and running
currents that will define the needed
battery’s capacity and C rating.
Brownout, and Worst
Much of the testing so far has
focused on running and peak
currents, but remember voltage and
current combine to create power.
Since the battery is a defined finite
power source, large current spikes
create large voltage drops. Between
the batteries and motors reside
controllers, drives, and other
electronics. Most of these electronics
have a minimal operating voltage.
If you momentarily go below
these values, the microcontroller,
Finally, after spending so much
time designing and making our bots,
be prepared to test beyond average
conditions. It may be difficult to abuse
something you have put so much time
into, but it is always better to find
problems when you can correct or
replace them easily. During these
tests, use your watt meter to find the
limits, and know what to expect when
you need it. SV
SERVO 07.2015 25