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Old Jul 23, 2002, 06:02 PM
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Are we getting close?

What is the energy density of the average glow fuel?

I understand that glow engines are horribly inefficient. What offsets that is the high energy density of glow fuel.

What I'd like to know is if you compare a highly efficient brushless motor using the new Li-Poly cells, with a glow engine using typical glow fuel, how close are we getting?

Based on info about the new li-poly cells from Fred at FMA Direct, I expect to get nearly an hour of flying time out of my 1/6 scale cub.
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Old Jul 23, 2002, 06:16 PM
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By the way, I'm not trying to stir up the "E vs Glow" argument.
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Old Jul 23, 2002, 09:51 PM
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Wait a minute! What's an e-poly cell? Can they be used with speed 400 or cobalt? Where can I get info on this new technology?
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Old Jul 23, 2002, 10:40 PM
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Lithium Polymer cells. They are the successor to Lithium Ion cells. They provide as much, or more, capacity and are much safe than lithium ion.

Also, Fred will be carrying larger capacity cells in the 3,000 mah range. Early tests show that you can draw anywhere from 5 to 7c from these cells. A 10 volt pack of 3,000 mah cells weighs less than 7oz and can handle 15 - 20 amps draw. Put two packs in parallel and you have a 14oz 6,000 mah pack that can handle 30 amp discharge!!!!

Fred will be selling these larger cells. I don't know how much they are going to cost. I've been buying surplus cells and making my own packs.

Check out this thread for more info.

http://www.rcgroups.com/forums/showt...threadid=49769

Where Fred says, "Just one thing to report tonite as I really have to get to bed. I flew my Flexible Flyer (Falcon 56 size) on Sunday with Derek at McMap. Three of the 3AH cells; Speed 600 motor; geared 2:1; 12X6 APC prop. I flew at almost full throttle for 32 minutes doing toucch and goes and anything else that came to mind and the pack was barely warm. Weight of the pack is 64GX3= 192grams= about six ounces. Attempts with NiMh @ 2350 mah ; 12 cells were very disappointing at < 10 minute and the pack was so hot you dared not touch it. Li Poly is looking great. "
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Old Jul 24, 2002, 01:32 PM
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Fascinating! There I was with Fred and didn't even know it was getting written about. Funny old world.

Interesting asides - to one who isn't that fussed about technoburble. You get current handling capacity as a function of 5 x C, where C is the battery size, so 3AH as Fred's using three of for around 10V's worth allows you to draw 3 x5 = 15A. This is fine for Fred's model, which is a prototype of something I aren't sure I can do more than let you guess about, but if I wanted to escalate matters to replace my dearly beloved 20 x 2400 running 30A, I'd have to start with 6AH cells to allow me to go to 30A.

So my upcoming 1/5th Sig Cub project would need 6 x 6AH cells to get the volts and I'd prop for around 28A to stay under 5 x 6 =30A - fine, as the model weight would drop a fair bit.

If I insisted on leaning on the prop size and pushed the draw over 30A - misery would follow as the cells took a voltage nose-dive (and probably committed hurry-curry over the excessive drain).

Cell cost, as I understand it, is still down the road apiece. Fred is hoping to generate enough volume demand to make them competitive with our dear old faithful nicad and nimh. It's a pretty good deal if he can, as you'll be paying as much per minute in the air, but your model stands to be a fair amount lighter.

Just when I thought I was getting the hang of nicads!
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Old Jul 24, 2002, 10:10 PM
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So where can I learn of these new batteries? By a "Falcon 56" size what do you mean? Weight, wingspan etc...If it's speed 400 size and not out of site cost wise, sign me up!! 32 minutes!!! By the way, what kind of charger do you need for these batteries anyhow?
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Old Jul 24, 2002, 10:17 PM
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Falcon 56
http://usedbits.cohenbrothers.org/co.../falcon_56.htm

56" wing span
4 -4.5 lbs

He was using a speed 600.

There are several ways to charge these types of cells. The smaller cells can be charged with a modified cell phone charger. The larger cells will likely need one of the commercial chargers designed for that purpose.

Many of us are buying surplus cell phone batteries for the smaller planes. They work very well and provide for very long flights. Some of the smaller cells can be wired in parallel to provide enough amps for a speed 400. Fred will be selling the 3,000 mah versions that look like they can handle 15 - 20 amps.

Do a search here for Lithium and you'll find an abundance of information. I hope to get a chance to start a site devoted to the subject.
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Old Jul 24, 2002, 10:21 PM
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I do the search. This appears to be a real breakthrough!
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Old Jul 26, 2002, 12:42 AM
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Quote:
I'd have to start with 6AH cells to allow me to go to 30A.
Actually Dereck, you could run 12-3Ah cells configured by running 6 groups of 2 in parallel, each group attached to the next in series, basicly giving you the 6 cells at 6Ah...


TGP
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Old Jul 26, 2002, 09:31 AM
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Quote:
Originally posted by tphillips


Actually Dereck, you could run 12-3Ah cells configured by running 6 groups of 2 in parallel, each group attached to the next in series, basicly giving you the 6 cells at 6Ah...


TGP
Okay, that makes sense (even if I have a headache thinking about it ). Now - how do I charge them?

I suspect your answer is going to be more complex than "plug the battery into your Supernova and push "auto charge".

Nevertheless, the idea of flying my Sig Cub around in Cub-like fashion for 20 minutes is very appealing...
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Old Jul 26, 2002, 01:50 PM
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I'd like to give these thing a shot on speed 400 or cobalt. I looked on the website and see that the voltage is 3.8 average. So, do I need to wire 3 of them parrallel to get the right volts (around 9.6) that the speed 400 6V normally runs on? Someone helpme here, I'm not an electrical engineer! Thanks in advance!
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Old Jul 26, 2002, 02:55 PM
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You would wire in series to increase voltage. The voltage starts at about 4.2 volts per cell. This quickly drops under load tho. You'll probably see an average of 3.4 - 3.6 depending on the load. So 3 in series would give you about 10.8 volts. That seems a bit high for a 6V speed 400. I normally run 6 or 7 himh cells for the 6V motor. That's 7.2 - 8.4 volts.

Depending on what you are flying you may be able to do with just 2 cells in series for the 6v motor.

You would wire in parallel to increase capacity.

Be sure to post your results.
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Old Jul 26, 2002, 10:31 PM
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As soon as I get some I'll post what happens. www.fmadirect.com will be selling these batteries starting August the 15th. Then there's the charger and maybe a different type of speed control as well. It will be a while, as I'll be on vacation in Iowa (?) from the 2nd to the 6th, then in Tinton, NJ on biz around the 22 to the 26th...
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Old Jul 27, 2002, 03:38 PM
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[QUOTE]Originally posted by Dereck
[B]

Okay, that makes sense (even if I have a headache thinking about it ). Now - how do I charge them?

Try here....
http://thomas-distributing.com/mh-c777plus.htm

Saw this in a post somewhere else, cant remember where but it looks like a great charger for Li-Poly. However im not really sure because i dont really know much about these cells.
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Old Jul 27, 2002, 04:08 PM
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Here is my current setup for charging 2 cell 830s and ultralife 700s.
http://www.rcgroups.com/forums/showt...5&pagenumber=6
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