A123 batteries for electric free flight

[JohnRiese]

Hi All,

I’m putting together a plane for electric free flight. It’s not a contest plane but rather an old time cabin type. I have never seen an old time SAM type plane as an electric free flight. No, not the “Spirit of SAM” rubber planes or electric Texaco. I’m talking a full sized gas free flight designs that go up fast, I hope.

In order to prove a concept I’m using components from the R/C world, except for the Ztron timer, of course. Here’s what I’ve got. An Ultralfy H12/09, 900kv motor, Turnigy Plush 40 speed control, A123 batteries salvaged out of a DeWalt power pack. All the parts together are maybe $100. No hi tech European stuff like the “serious” flyers use.

I did some bench testing today at work. Holiday, no bosses around. With an HP 1000 watt power supply I was seeing 570 watts on a 12-6 prop with 12.5 volts showing on the Astro Whattmeter at 45 or so amps. This is some serious power. I had the motor fastened to a 1 by 2 clamped in a heavy bench vise and it still walked across the floor. Motor and speed control held this continuously without overheating. I didn’t use a Castle Phoenix speed control, as they won’t handle the voltage, unless one wanted to spend 135 for the high voltage 45amp model. The 34-dollar Chinese one worked fine’ and it’s programmable.

Since I’m not flying to any F1Q rules I can use a heavier battery. The A123 batteries are capable of an enormous amount of power and they withstand abuse. Nominal voltage open circuit is 3.15 volts per cell but at that high current draw the loaded voltage is 12.5 for a 5-cell pack.

How much would a 4 cell LiPo cost that will put out 45 amps and 12.5 volts under load? I’m thinking about 95 dollars. Weight would be maybe 8 ounces. The A123 5 cells weigh 12.5 ounces. They can be fast charged at 10 amps so you don’t need a spare.

I’ve got some TP2100 3s batteries from when we were flying electric controline a couple of years ago. I figured that I could put 2 of them in series and run about 25 amps. The speed control/motor didn’t like the higher voltage, however. More work is needed on this high volts lower amps concept. Right now I’m happy with the power I’m getting without having to spend lots of money.

Comments, please

John, on the dull cutting edge

[Anonymous]

John, are there any manufacturers that supply these batteries to the general modeling population as yet?

[JohnRiese]

Randy,

I don’t know of any off hand. You can go to A123 systems and order their “developer’s kit” to make your own packs, but they are pricey. Ebay has the DC9360 36 volt (10 cell) batteries on sale all the time. There are tutorials on the RC forums that tell you how to dissect the DeWalt battery pack and make your own. Unless you are comfortable around large soldering irons I would suggest finding some ready made. These are high power cells and you must be very careful not to short anything out.

Might be too much weight for free flight, I’ll let you know how my experiment works out.

John in Taxifornia

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