I’ve been working recently with a friend on his first
large helicopter build. He’s a capable flier, but all his
experience has been with smaller 3-cell helicopters.
One item we discussed at length is why larger helicopters in the 600 class have migrated to 12-cell
power systems. As we discussed the merits of high
voltage (and its associated costs), it occurred to me
that we last covered this topic here in Heli Talk more
than four years ago. Back then, high voltage hadn’t
really caught on, other than for 700-class and larger
machines, while today it’s widely accepted. Let’s take
a look at why that is.
Why is higher voltage usually better?
Text & photos by Jim Ryan
“Watts Is Watts” and Joule’s la W
To start, it’s important to understand that it’s power, measured in watts,
that makes our helicopters fly, and watts are volts times amps. Let’s say
that your helicopter needs 1,000 watts for the desired performance. You
can produce that wattage by running a 10V battery at 100 amps or with a
100V pack at 10 amps. Obviously, that’s an extreme example, but a real-world case could be choosing between pulling 44 amps from a 6S battery
or 22A from a 12S pack. For higher-power applications, the high-voltage
option is the better choice.
The problem for high-amperage power systems is that power losses
increase with the square of the current. This is defined in Joule’s first law,
which is expressed as Q = I² x R x t, meaning that waste heat (Q) equals
the product of current squared, resistance, and time. Because joules per
second equals watts, we can reduce all this to the simpler statement that
High-performance helicopters, like Gaui’s R5
speed machine, are impressively powerful. In
this month’s column, we show why it’s more
efficient to generate that power with higher
volts than to pull massive amps.