For those of us that fly electric RC, in the long run we know that batteries tend to be our biggest and most expensive consumable. Motors and ESCs if used properly can last hundreds and hundreds of flights, but Lipo batteries all eventually will expire, just the nature of the beast. As such, I think we all want to extend the life of these batteries for as long as we can as it seems their cost goes up all the time, mostly driven by more strict shipping rules and increased shipping costs.
I just celebrated my four year anniversary of flying electric RC and next month (November 2016) will celebrate my four year anniversary of flying park jets. As you might already know about me, I got into this hobby because of RC Powers and park jets and they are still my biggest passion in RC. I have dabbled in a couple different ARFs over time, but always quickly return to park jets. However, the theory and practice behind brushless outrunners, ESCs and batteries apply whether you fly park jets or large size electric trainers or war birds.
When I first got started, there was a lot of information available, perhaps too much and the amount of conflicting information was quite bewildering, at least to me. There are a lot of different philosophies on the selection, use and care and feeding of Lipo batteries and I suppose me writing a couple articles about my experience might just add to that confusion :/ However, much of what I will write is from my experiences, many of them bad at first, but at about the 1 yr mark of my park jet journey, a "light bulb" went off in my head and I really started to better understand how things work. I now have Lipo batteries I have been using for almost 3 yrs as a result of a change in how I selected and flew with them. It wasn't until I listened to this podcast by the gents at Flitetest that a lot of things really fell into place for me.
Before that, although I was normally charging my batteries correctly, I wasn't paying very close attention to what batteries I purchased nor how I used them. I often used batteries that barely met the requirements of my motor/prop combo or I flew them right to low voltage cutoff on a very regular basis, neither of which is good for the life span of a Lipo battery I came to discover.
So quick and dirty from the podcast. A brushless outrunner motor regardless of the prop size will always try to get to it's theoretical RPM which is determined by multiplying Kv by volts. With no prop on the motor, it draws very little amps, too big a prop or too high a pitch prop and the amp draw required by the motor will continue to climb until it burns itself out. Unfortunately, I have yet to use a motor that cuts off when it hits it max amps, I'm not sure with the inexpensive motors that I like to use, that I ever will :/. If you look at the popular Turnigy D2826/6 2200 Kv motor, it is rated at 34A, but I know from testing it will try to pull more than that, resulting in considerable heat build up and eventually the motor will fail.
So once you have paired the correct prop with the motor, you need an ESC that can handle the amp requirement (more on this in the next article), and then a battery that can handle the amps required as "the buck stops" with the battery and unfortunately most of them have no circuit breaker to control the amp draw, they will continue to try and deliver whatever amps the motor and prop require and pushing the battery to it's limit for too long or too often will result in the battery "puffing" and losing performance rather quickly. Sadly, at my field I have actually seen guys "puff" a brand new battery on their very first flight because they did not pay attention to this. Personally, I have "puffed" batteries in less than 20 flights as I chose the wrong one and pushed them far too hard.
It was around this time (especially after having batteries "prematurely expire" on me), that I started to fully understand how to choose and use the right battery for the right motor/prop combo. I finally started to grasp that I needed to know how much my motor and prop combo were going to need, so I purchased a wattmeter and started doing my own testing as the numbers out there again were at times confusing and incorrect. Using the formula of battery amps multiplied by the C rating, I now understood how to determine the amp delivery capability of my battery. With a 2200 battery with 40C, 2.2 mulitiplied by 40 gives 88A. As I will discuss further in the next article, it also took me awhile to learn that this is also a constantly changing formula as I fly as the 2200 Mah is continually being reduced while flying, but the amp draw of the motor and the C rating do not change. What will change is the battery's ability to give the same amp delivery to meet the motor/prop combos needs.
So after doing a lot of fumbling around for the first year I was in the hobby, I had finally turned a corner in my understanding and setup of my power systems, primarily how to choose the correct battery. The learning curve was still steep and I continue to test and learn all the time as my journey continues, but I am confident I have a pretty good grasp on things now. I now have some batteries that are almost 3 yrs old and although tired, still work for most of the power systems I run now. I have no idea how many flights I have on these batteries, I would guess in the neighborhood of 300+ just based on how much flying I do.
Probably two of the most important tools I picked up around this time were my wattmeter and an inexpensive battery cell checker. My wattmeter is no longer available from Hobby King, but I found this one on Banggood recently which looks like it will do the trick. There are much better pictures of it and more information here. You will note that it does not come with any connectors, so you will need to solder connectors on to allow the wattmeter to be between your motor/ESC and your battery. My wattmeter tells me many more things than I understand or need, the primary two numbers I am interested in are the number of amps drawn as this helps me determine the proper ESC and battery to ensure my power setup runs safely and efficiently. It will also tell you watts produced which doesn't always relate to thrust at the field depending on the prop, but gives you a number to see how much power the motor is producing for a given number of amps drawn.
The beauty of a wattmeter is that it will tell you real time what the motor and prop you selected are doing, regardless of what you might have read or the manufacturer tells you. With many of the inexpensive park jet motors out there, you will get no technical data, so being able to test it yourself, it gives you the knowledge and confidence you need to set up your system correctly.