Limiting Throttle Will Not Protect Batteries in Systems

[LJENSEN01]

Reprinted with Permission of Castle Creations

Welcome to the first of a series of articles exploring some of the “black science” issues of R/C, where we explain in understandable terms some of the most common technical questions, as well as dispel some of the common myths surrounding R/C electronics.
This time we explore one of the most common misconceptions, and least understood important concepts in electric R/C. Quite often we see posted online, or within conversations with customers, the fact that they have their power systems propped for “over the limits” of their batteries, ESC’s, and motors, but it’s “OK” because they never actually use full throttle. This is 100% incorrect, and the explanation of why, involves a simplified example of how a speed controller works.
We’ll break down an ESC’s operation into blocks of one second for simplicity. We see when the ESC is at full throttle, it is as close to an “open circuit” as possible between the battery and motor, and “on” for the full one-second block of time, and drawing full throttle current. Each of these blocks of time stream together, and for a hypothetical example – you read 15 amps on your whattmeter at full throttle. Also for example, you are using a 1050Mah Apogee lipo pack (11 amps of output capability), and a Phoenix 10 controller. At ¾ throttle you read 10 amps, and the misconception is, that if you just stay below ¾ throttle (or lower the top endpoint on your throttle channel) then everything is OK. What is REALLY happening, is when you are at ¾ throttle, there is ¾ of every second that the ESC is “on”, and the last ¼ of every second it is “off”. The whattmeter averages the current readings it’s getting, and is showing you an average current. Furthermore – if we are at 10% throttle, then the ESC is “on” for 1/10 th of a second, and “off” for the remaining 9/10 ths of a second. Regardless of how long per second it is “off” or “on”, when it is “on”, it is drawing full throttle current from the batteries, through the controller, and into the motor. So, essentially in an everyday application, you are taxing your batteries, ESC, and motor at full throttle amperage the entire time the system is running, regardless of throttle level. With continued use, the above combination will at best most certainly reduce the life span of the lipo pack, the ESC, and the motor as well.
What you’ll find pleasantly surprising is, if you have a set-up as above, and simply prop down to make your full throttle current 11 amps to bring it “within spec” for all the components, you’ll end up with the following: A cooler running (more efficient and longer life) motor, more rpm’s to the prop (due to the increased voltage from a happy pack) with no observable loss in power, a lower temperature ESC (more BEC capacity and longer life), and much longer flight times to boot.
So the next time you put together a power system – make sure to prop the system to be within specs on all components of your power system while at full throttle, and enjoy all the longevity and other benefits that come from today’s modern equipment. The days of having to “push everything beyond the envelope” just to get acceptable performance are over – off the shelf components used within specs are absolutely capable of giving you more power than you’ll ever need.