RockyMtnFlyBoy

Electric Motor Folks:

I'm looking for opinions whether the following might work... or whether I'm "looking for trouble" with this set up. Some background...

My nephew is off to college and recently brought me a lot of his old flying stuff. He's discovered triathalon racing (and girls?), and basically out grown RC flying. (Interesting, I'm 59 yrs old and recently starting RC flying, and he's 19... hum...) Anyway...

Part of the stuff he gave me includes an old Thunder Tiger Windstar Sailplane EP. I believe it has a brushed +/- 540 motor in it. (That's the motor specification on the current model Windstar anyway.) It also has a Jeti Jes 25 ESC. The instructions for the Jes 25 ESC indicates it good for 25 amps and from 6 - 10 cells. I assume they're talking about NiCad cells due to the age of the equipment. That being the case, the ESC should handle up to 25 amps at 12 volts = 300 watts.

I have a couple of Koham 1,500 mah 11.1v Lipo batteries. While I don't have the specification on these three cell batteries, I'm told by my mentor out at the flying field that they should be good for 12amps. Wired in parallet that'd be 24 amps.

I'm wondering if this set up might work:

Hook the two Koham batteries in parallel and run them into the Jes 25 ESC.

I can think of the following questions:

... How do I charge the two batteries? Together in parallel? Individually?

... If I charge them individually, won't there be a brief surge of current when I re-connect them in parallel as they equalize in voltage? Would this be a problem?

... How do I adjust the Jeti Jes 25 so it turns the motor off when the Lipos are down to their cut off voltage (that's 3.0 v / cell, right?) I can't find any helpful information on the web about Jeti Jes 25's. My guess is they're too old.

I realize the 580 brushed motor is probably pretty under powered and heavy in today's world of brushless motors. But I took up slope soaring last spring, and figure I will use the Windstar as a sloper-trainer (until I "crunch" it). I'd probably appreciate the slightly heavier "glider" because it'll penetrate better. Then use the motor to power me out of problems and to help me line up for landings.

Also... just in case... what are your recommendations for a brushless motor, and brushless ESC for this thing.

Thank you, in advance, for your thoughts.

Rocky Mtn Flyboy
Boulder, CO

Matt Kirsch

My Feedback: (21)

If you discharge the packs in parallel, you can charge them in parallel. Even if you charge them individually, LiPoly batteries are charged to a fixed voltage, not a "peak" like NiCds. As long as both packs have the same size and number of cells, and they're both fully charged with the same charger, there will be no cross-charging when you connect them together. It is recommended that you charge both packs individually the first time.

I see you're up in the mountains of Colorado. Normally, I would be worried about the 11.1V batteries causing excessive current to be drawn, burning out the motor, blowing the ESC, and damaging the battery. In lower elevations, a 540 brushed motor will draw way more than 25 Amps with an 11.1V LiPoly and a usable propeller. Normally you would run with a 7.4V LiPoly and an 8x4 propeller direct drive, or a 3:1 gearbox and a 12x8 prop. Up in the thinner air of Boulder*, the 11.1V battery might be just about right to compensate with stock configurations.

It would be a good idea to beg/borrow/steal a Wattmeter or similar device to check the Amps once you have it all hooked up, and adjust the propeller size to bring the Amps up/down to somewhere between 20A and 25A.

Just remember that your plane will be a "high altitude special." Take it down out of the mountains, and you'll probably damage the electronics because the thicker air will give the prop too much bite, and draw too much power.

* I wish I could remember the Mork & Mindy opening sequence. It was set in Boulder, IIRC, and they showed a "Welcome to Boulder, Elevation XXX" sign.

RockyMtnFlyBoy

Matt:

Thank you for the detailed reply.

Okay... I'll try this...

1. Charge both batteries on the same charger (Accu-Cycle Elite).
2. Hook 'em up in parallel. Then in the future, charge 'em together. (Same voltage, twice the capacity.)
3. Get a watt meter (can you recommend one?) and tweak the prop to 20A - 25A, max.
4. Fly at altitude.

Boulder's at the western edge of the Great Plains at 5,400'. Home is at 8,300'. I tend to fly in Boulder, but there's one slope I've been eyeing nearer home at about 8,600'. It sounds like the higher the better with respect to not over stressing the motor / ESC / batteries.

One last question... Can I adjust the Jeti Jes 25 for the low voltage for the Lipo's? Or do I just need to keep my run times down and check the battery voltage? Do you know who makes Jeti or distributes them in the USA. Who to contact to ask the same question?

Thank you, again!

RockyMtnFlyBoy
Boulder, CO

Matt Kirsch

My Feedback: (21)

8600' Man, you must have a set of lungs to beat the band.

Hobby Lobby's the Jeti distributor in the USA.

More than likely, though, your ESC is an older pre-LiPoly version. Normally I recommend using a timer whether you have a "LiPoly aware" ESC or not, but in the case of a powered sailplane, you're not depending on the electric motor as your primary source of propulsion, so flying for a fixed amount of time really isn't practical.

There are products called "LiPoly savers" that install between your ESC and receiver. They monitor the battery voltage and will interrupt signal to the ESC when the voltage gets too low.

RockyMtnFlyBoy

Thank you again, Matt.

Please point me towards a "Lipo Saver". What brand? Were to purchase it?

Altitude... I also fly "glow" airplanes out at the local (Boulder) flying field. We also have a very active float fly which I've recently joined. Then just the other day, I took my (somewhat new) Lanier Mariner (OS .46 FX size) up to a friend's lake at 8,400'. Oops! I could barely get it off the water. And in flight it was "snaping" very badly. I guess for 8,400' I was flying it way too slowly. I can't imagine how good the performance of the .46 FX must be at sea level!

RockyMtnFlyBoy
Boulder, CO

RockyMtnFlyBoy

Matt:

Epilogue on the Windstar EP at 5,400':

I couldn't conviently find a Watt Meter with any of the guys at the field, so I flew it anyway. I had two good flights, but then the brushed motor quit. So I was probably over stressing either it or the old Jeti 25 ESC. No damage to the air frame of anything. The plane's "good to go" when I can power it up again.

So... I think I'd like to put a brushless motor in it. It's time that I learn about the "electric" side of things since that seems to be the way the hobby is heading. So... I purchased a copy of MotoCalc today. And after I learn how to use it, will be asking it this same question...

Do you have a recommendation for a brushless motor, ESC, and folding propeller to go with the two 1,500 mah, 11.1v, Lipo's which are now hooked up in parallel in the Windstar EP? (77.3" wing span, 574 sq', about 35 oz "empty")

Thank you, again for all your help!

Greg Hine
RockyMtnFlyboy
Cold & Snowy Boulder, CO