The Battery Clinic — 2012/11
Electric power is the wave of the future
The following is reprinted with permission from an article written by George Miller and found in the May 2012 issue of Mike Brown’s e-magazine, The Airborne Reader. Please send subscription requests for the newsletter to [email protected]. Past issues can be viewed at www.theclearimage.com.
It's the "wave of the future." Won't be long before you plug your power supply in at the field and the radio transmits the power to the aircraft. Sound is right around the corner. You'll be able to have your aircraft sound like any airplane you want it to. Model trains already have it. No more flight box, needle valves, glow plugs, buying fuel, fuel proofing, and having to clean up that mess all over your aircraft at the end of the day.
It's coming, you wait and see. Electrics have opened some doors for modelers that were always difficult with glow or gas.
- Multiengine has always been difficult. Making sure all the engines were running smoothly, in sync, needles set, idling properly, and it goes on and on. Sure, we did it, but it took a lot of effort and prep. Electric naturally runs smoother and more reliably when set up right — no idle or needle concerns.
- Building a scale airplane that requires a lot of nose weight is easier with electric. With electric, you have a big chunk of necessary weight called the battery, and it can be placed where needed. You can put the ESC in the nose, too.
- Nothing ruins the look of a very nice scale plane like an ugly muffler sticking out the side of the cowl. Electric doesn't have that either.
I converted a model to electric that had been glow a while back. I weighed the motor, muffler, servo, tank with fuel, and discovered they weighed the same as the electric installation.
Now let's talk about arming electric aircraft — making it so it won't attack you. There are many ways to do that, and even some gadgets on the market that will help. But it is very simple if you understand your ESC.
Most know that some ESCs (like E-flite) require you to advance your throttle to the full-speed position, wait for the "beeps," then pull the throttle back to the idle setting to arm the ESC. Fewer know that others (like Castle) require you to have your throttle in the high-speed position when plugging in the battery. Then you bring it down to the idle position and wait for the "beeps" for it to arm. So just figure out how your ESC works, and you will have control of arming your aircraft.
Major handy tools when working with electric aircraft
- The timer in your radio or a separate timer.
- A battery tester that can test LiPo batteries.
- An amp/wattmeter.
With that amp/wattmeter you can sit at home and dial in the settings of your aircraft without any guesswork. Look up the amp and watt ratings of your motor. Plug the amp/wattmeter in between your LiPo and ESC, go to full throttle, and see what you have. Then match a prop to get what you want.
Watts to aircraft weight are what you are really interested in. Watts per pound: 75 for easy flying, 100 for high performance, 150 for "silly" stuff. So you can take it from there. The battery tester is great — you can read your LiPo before flight and make sure it is at 100%.
With a new aircraft setup, I will set my timer at a safe value and fly the entire first flight at full throttle. Land and put the LiPo on the tester and see what percentage of capacity is left. Generally, you can run a LiPo down to about 30% remaining. From this you can figure out how long a flight you can have with this setup. If you account for time off full throttle, you can add that too. No more guessing or making short flights because you don't know.
The size of the battery for your aircraft: when I got back into this hobby I bought a ParkZone T-28 to get the feel of flying again. The hobby shop sold me the recommended LiPo and I was good for about six minutes. I noticed that the battery sat in the aircraft at the CG, and with very little modification I could place a larger battery there. I used a 4000 mAh battery, could fly all day long, and there was no noticeable difference in performance carrying a heavier battery.
Turnigy batteries from HobbyKing have worked very well for me. So look into that before just buying the recommended battery.
I recommend buying an ESC with a larger amp rating than what the motor calls for. If the motor is capable of drawing 50 amps, buy a 75-amp ESC. It will run cooler and, if something goes wrong, it can handle it better.
If your motor has a serious failure — for example, it seizes — it can create a direct short through your ESC so fast that no internal safety can save it from failing completely. If you are using that ESC to power your radio, you are history. I learned this the hard way.
Also, most ESCs have limited BEC output for the radio. I suggest you eliminate the ESC as radio power and use a separate BEC. They are cheap, simple, and provide more reliable power to the radio.
If you have questions about anything I haven't covered here, feel free to contact me. George Miller's contact information is listed in "Sources."
Too Fat to Fly
A 3S 2200 LiPo pack seems to have reached the end of its life. It is only three years old, has gone through 42 charge/discharge cycles, and was never driven below 9 volts. It was always charged with a balancing charger (FMA CellPro 4S). Although bloated, the battery still discharges to about 74% of the rated 2200 mAh.
There are plenty of theories for why this happens, but no manufacturer has provided a substantial explanation for the swelling we occasionally see in LiPos. Some have theorized that it is temperature (either ambient or from too high a discharge rate), being stored when fully charged, or overdischarging.
I would like to hear from a manufacturer about why some LiPo packs swell with minimal use while others remain normal with several years of use.
Time for Battery Hibernation
Don't forget to pull those batteries if you won't be using them during the winter. Take your LiPos down to the storage level of about 3.6 volts per cell. Some say this keeps them from "becoming pregnant." With Ni-Cd and NiMH, the state of charge for storage doesn't matter.
It seems as though there are fewer new things in batteries as the technologies and chargers have matured; therefore, "The Battery Clinic" will be published quarterly rather than bimonthly. The next column will be in the February 2013 issue.
Meanwhile, keep those emails and letters coming. No email connection? Drop me a note at the address listed below. Include a self-addressed stamped envelope if you want a personal answer.
Sources
George Miller [email protected]
The Battery Clinic 12219 NW 9th Ln. Newberry, FL 32669
Reprint permission and subscriptions: [email protected] The Airborne Reader (past issues): www.theclearimage.com
Transcribed from original scans by AI. Minor OCR errors may remain.
