Author: Greg Gimlick
Edition: Model Aviation - 2012/04
Page Numbers: 94,96,98,99,100
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Big Power Made Easy

Greg Gimlick [email protected]

By the time you read this, tradeshow season and the early spring fly-ins will be in full force. I love this time of year! Because I get many questions about building and powering larger electrics, I thought this might be a good time to discuss some easy, off-the-shelf options for doing just that. It's easier than you think.

Anything Is Possible

At the risk of sending my editors over the edge by using this cliché, I'll say it anyway: anything is possible now with electric power. Go to any big event and you'll see things that will amaze you.

Joe Nall is still the king of Giant Scale meets, but it's no longer void of electric-powered models, and some are now prominently displayed during the noon demos. Let's get started on making it easy.

Batteries and Chargers

There is no sense in doing a giant electric model if you can't charge the LiPos with which you're going to power it. My big electrics are 10S and 12S setups, and there will be some 15S setups on the show circuit this year. You'll need to support those packs and it's really quite easy.

I use a combination of 5S and 6S packs wired in series to make my big packs. I can charge them easily on nearly any good charger and can do it at the same time if I use a parallel charging board such as the one from Progressive RC. I went to David Gray at Progressive RC for a solution to high-demand charging and he sold me on what he calls The Solution—an iCharger 3010B and Mean Well SE-1000-24 power supply.

This setup gives me 1000 watts of capability and is bulletproof in my experience so far. I love this reasonably priced setup. Be aware that this power supply outputs 24 volts, so be sure your charger can handle the voltage. Most charger problems I see come from insufficient power supplies. I'll let Red Scholefield (MA's "The Battery Clinic" columnist) go down that road with his column because he's the real expert on batteries and chargers, but I do recommend this setup for your big models and packs.

iCharger 3010B Specifications

  • Maximum charge power capacity: 1000 watts (at input voltage greater than 23 volts; 500 watts at 12 volts)
  • Charge current range: 0.05–30.0 amps
  • Discharge current range: 0.05–30.0 amps
  • Input voltage range: 4.5–38 volts DC
  • Maximum discharge power capacity: 80 watts
  • Maximum regenerative discharge: 1000 watts
  • Maximum external discharge power capacity: 1200 watts at 40 volts / 30 amps
  • Current drain for balancing: less than 500 mA
  • Balance accuracy: less than 10 mV
  • LiPo / Li-Ion / LiFe: 1–10 series (up to 12S LiFe in non-balanced mode)
  • NiCd / NiMH battery cell count: 1–25 series
  • Pb battery cell count: 1–18 series (2–36 volts)
  • Battery setup memories: 10
  • Intelligent temperature control: Yes
  • PC connectivity: USB port
  • Weight: 750 grams
  • Dimensions (L x W x D): 143 x 123 x 46 mm
  • Warranty: 1 year

Mean Well SE-1000-24 Specifications

  • Output power: 41.7 amps continuous, 1000 watts
  • Output voltage: 24 volts DC (adjustable +/- 10% = 22–27.5 volts)
  • Input voltage: 90–132 volts AC, 180–264 volts AC (worldwide use, selected by switch)
  • Protections: short circuit, overload, over-voltage, over-temperature
  • Mean time between failures: 251,600 hours
  • Efficiency: 88%
  • Warranty: 2 years
  • Weight: 2500 grams
  • Dimensions (L x W x D): 278 x 127 x 64 mm

Because big electrics often also draw big current, you need to be sure your LiPo packs are up to the task. This is one area where I don't recommend going cheap. Experiment if you will, but I go with what others have shown me to work and with people I can call or email and get answers.

My 12S and 10S packs are made from packs by Xtreme Power Systems. I'm currently using the company's newest 65C-rated 6800 mAh LiPo packs and they really have some punch to them! They are also competitively priced against no-name brands from companies you can't talk to. 'Nuff said about that.

Sample Project

I thought it might be easy to discuss a recent electric-conversion project I did and how I went about doing it "off-the-shelf." It is literally off-the-shelf because it started in my friend Wayne's shop.

Wayne pulled down an old World Engines Robinhood 99 airplane he had used for aerotowing, which was stored in his rafters for the last 15 years. It had been powered by several different gas engines, most recently a DA-50.

I looked it over and it was in good shape, so the challenge began. I took it home and cleaned it up to see what I would need to do. After removing fuel tanks, old wiring, switches, cobwebs, etc., I could see it was in excellent shape. I weighed the airplane and began to formulate my plan.

There were Futaba servos in the tail that tested just fine, so I finished it off with some new digital Futaba servos for the ailerons and installed my FASST seven-channel receiver and two LiFe Source 2100 mAh 6.6-volt receiver packs in parallel.

Motor Selection

The projected all-up flying weight of the Robinhood was 32 pounds. This airplane had been built for the rigors of gas power and vibrations, and had been reinforced for towing huge aerotow sailplanes. I zeroed in on two choices from Great Planes: the RimFire 50cc and 65cc outrunner motors. These make big power and are reasonably priced.

Modeling both setups in ElectriCalc and MotoCalc showed that either would work and the motor specifications proved it was at the very top of the 50cc capabilities. I called to order the 65cc motor and found they were back ordered. Because mission accomplishment sometimes overrides patience, I ordered the 50cc. This motor's kV rating is slightly higher at 230 vs. 160, but I thought it would be okay and it is.

RimFire 50cc Specifications:

  • Can diameter: 3.14 inches (80 mm)
  • Can length: 2.9 inches (75 mm)
  • Shaft diameter: 0.39 inches (10 mm)
  • Mounting space length: 3.44 inches (87.3 mm)
  • Rpm / voltage (kV rating): 230
  • Input voltage: 33.3–55.5 volts (9–15S LiPo)
  • Connector: 6 mm bullet plugs
  • Maximum constant current: 110 amps (at 12S)
  • Maximum continuous power: 5000 watts
  • Maximum surge current: 135 amps (at 12S)
  • Maximum surge power: 6500 watts
  • Weight: 44.1 ounces (1250 grams)

My surge current is at the limit, but my constant current is well below the motor specifications and it remains cool during the flight.

Controller Choice

When it comes to big ESCs, there are a few choices, but I stay with companies that have a proven track record and those that will support the ESC should I have a problem. Big ESCs are not cheap either, and this is probably one of the biggest expenditures you run into when doing Giant Scale electrics.

I chose a Castle Creations ICE HV-160 for my project. It will easily handle any abnormal spikes in current and offers me real-time in-flight data logging. This is invaluable.

I have much confidence in the HV-160 because once I accidentally set an airplane up for testing and hit 189 amps on a 12S pack. I didn't stay there long and was surprised to see the current go that high, but the ESC stood up to the momentary mistake. Sometimes, although you think you've estimated everything properly, you find you were wrong. That was the case and luckily my gear took it.

Kontronik, Castle, Hacker, and Jeti all make ESCs that will handle a large model's requirements, and each has excellent technical support should you need it. These are not cheap! There are some cheap knockoffs out there, but buyer beware. I don't like taking risks with this sort of power setup. Xtreme Power Systems is going to have a 15S ESC soon, but I don't have a release date.

Propellers

When you get into an airplane this size, the propeller choices narrow and become fairly expensive. RASA, Mejzlik, PT, Engel, Delro, APC, and Vess all make excellent large propellers and some of these companies also make ones for electric power.

I chose a Vess 22a propeller for my application because they have a great reputation and are different from anything else I've seen. I've known Robert Vess since the days when he taught graduate students in the aerospace engineering school at North Carolina State University and he can do some amazing things. He did aerodynamics work for NASCAR and the aerospace industry, so he knows his stuff—and he is an excellent RC pilot.

RimFire motors specifically recommends not using electric propellers and I haven’t been able to get an answer why, but I followed the company’s recommendation and chose a Vess propeller. It is a great-performing propeller and this setup spins it at 8,600 rpm full throttle.

The Results

I could not be happier with the results of the electric conversion. Perhaps the most telling thing is that Wayne flew it and said it performs better than it had previously with his gas engines.

The maximum current spikes on the log were in the 130-amp range, but the average current for the flight was roughly 40 amps. This airplane will fly vertically with no problem and does beautiful, big, lazy aerobatics.

This is a large airplane, at 99 inches and 32 pounds, and is a real joy to fly. The International Miniature Aircraft Association (IMAA) pilots say, "bigger flies better." I’ve always flown a variety of sizes, but this is my biggest electric and it certainly flies well.

Thanks to Great Planes, Xtreme Power Systems, Castle Creations, and Vess Propellers for recommendations and technical support as I did this off-the-shelf challenge! We successfully resurrected a 20-year-old airplane that has been in storage for 15 years.

Taking Off

Now it’s on to Toledo! I hope to see you there, and be sure to check out the equipment I mentioned at the various booths. There truly is no limit except what our wallets can absorb.

SOURCES:

Transcribed from original scans by AI. Minor OCR errors may remain.