[NSRCA-discussion] Going Electric - Battery Questions

[Larry Diamond]

Thanks Duane....

The little light went on in my head when Keith's response... My mind was
locked onto voltage control by the ESC, which is evidently not how it
works....

I now understand how the battery voltage directly affects the RPM. And what
your stating makes sense to me. Great explanation by the way...

This helps going forward....

Thank you very much!!!!

Larry Diamond

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Duane Beck
Sent: Friday, December 07, 2012 11:30 PM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] Going Electric - Battery Questions

> The ESC controls the voltage to the Motor, not the battery.

This is not strictly true.  The ESC controls the duty cycle during which the
battery's voltage is applied to the motor.  This has the effect of
controlling the average voltage, but as some fraction of the battery
voltage, not referenced to some absolute voltage.  At 100% duty cycle,
obviously the full battery voltage is applied.  At 50% duty cycle (1/2
throttle, more-or-less depending on the ESC and your throttle curve), about
half the battery's voltage will be applied to the motor.  If the battery's
voltage sags less under this load (because it has a higher C or lower
internal resistance), then the motor will try to spin faster (based on its
KV).  Spinner faster with the same prop (load) means more torque is required
and, with electric motors, current is proportional to torque.  So, for the
same throttle position, you end up with more voltage, more current, and more
power (proportional to the square of the voltage increase).  You can get the
same power output as the lower C  battery by reducing the throttle, but
you're effectively reducing your usable throttle range - and thereby making
it more sensitive.

Duane
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