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Old Sep 07, 2002, 07:07 PM
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20+ min. flight with an E3D!

I thought that might be an attention getter.

The cells aren't available yet (but maybe within the month). For those of you that haven't been following the Kokam Lithium Polymer Batteries thread over in Modeling Science, check it out!

There are 7500 mAh Lithium Polymer batteries that, with 2 - 3 cell packs hooked in parallel, supply the 40-50 amps the E3D needs. That's 15 Ah of energy. The only thing I've envied about glow fliers it soon to be a thing of the past.

I'm so excited about it. It's just around the corner. These cells are being (will soon be) supplied by FMADirect.com

One stoked modeler,
Dan Nash
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Old Sep 08, 2002, 08:47 AM
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Fred at FMADirect.com had a pretty good solution as well and it can be done right now.

How about 2 - 3 cell 3270 mAh packs in parallel. Each cell weighs only 2.29 oz, meaning total pack weight is 13.74 oz. So, take your 56 oz E3D with a 21 oz 10 cell NiCd pack and subtract half a pound for an AUW of 48.74 oz. Current draw needs to be in the 30's for these size cells, but with less weight, less current is needed. If you go full throttle the whole flight, you still get 10 minutes!

Anyone else siked about this?!

A still stoked modeler,
Dan

P.S. Just to repeat some information in the Modeling Science thread, these cells operate at 3.7 V under load and can safely be discharged at 5-6C (so around 16.4-19.6 amps) according to Fred.
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Old Sep 08, 2002, 10:26 PM
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kokam batteries

Are you able to take two batteries and run them in parallel to double the ability of the current draw ?
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Old Sep 09, 2002, 05:57 AM
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How about 4 Kokam 7500s wired in series powering a B50 11S spinning a 12x8 though a 5,2:1 gearbox? Ed's suggestion for the Long Stick...

Numbers from Motocalc...

40 amps static = 5,3C (within the 6C recommended)
570 watts
91 ounces of thrust static
70 mph pitch speed
full throttle duration = 11 minutes (!)
battery pack weight = approx. 16 ounces (!)

Compare to 14x3000 NiMH

full throttle duration = 4 minutes 15 seconds
battery pack weight = approx. 28 ounces

Note: I used the same internal resistnace for both, since I don't know the values for the Kokams.

With throttle management, huge flight times would be possible, esp. since the plane would weigh 12 ounces less!

Time to start saving... don't think the cells will be cheap. Yep Dan, I am also very excited about the idea of flying a plane with these...

Aki
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Old Sep 09, 2002, 06:45 AM
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Exowatt,

Yes, you can hook batteries in parallel and the current draw will be split equally among them. You will also get twice the capacity of the pack since they are now drawing half as much! Of course, you need to have enough in series to have the voltage you want. So, to get an equivalent 8 cell pack, you'd need 3 cells in series, and, if current draw needs to be limited, you'd need 2 packs of 3 cells in series hooked in parallel.

Is it all clear as mud now?

Aki,

Another great power setup. Man, oh, man!

-Dan
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Old Sep 09, 2002, 08:45 AM
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Quote:
Originally posted by AkiP
How about 4 Kokam 7500s wired in series powering a B50 11S spinning a 12x8 though a 5,2:1 gearbox? Ed's suggestion for the Long Stick...

Numbers from Motocalc...

40 amps static = 5,3C (within the 6C recommended)
570 watts
91 ounces of thrust static
70 mph pitch speed
full throttle duration = 11 minutes (!)
battery pack weight = approx. 16 ounces (!)

This is great!

What is the cost for the batteries you propose? If they're going to be a couple of hundred dollars I'll pass.

What chargers support this battery technology and how much are those?

If only FMA is going to sell them I would expect the prices to remain higher than if several companies sold them.

Thanks

Kelvin
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Old Sep 09, 2002, 09:49 AM
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Kelvin,

The cost of the 3 AH Lithium batteries is $27 each. My guess is the price for the 7AH cells will fall in the $30s. So, you are looking at a pack cost of around $120.

Yes, this does stink, but look at all the benefits. Less weight, longer flying time, same power. Plus, the life expectancy of these cells is > 400 charges according to the Kokam website.

Considering that you get 3-4 times the flying time with these packs, it's like you're replacing the equivalent number of NiCd packs. My 10 cell NiCd pack was $52. If I wanted the flying time of one Lithium pack, I'd need 3 or 4 packs for a cost of $150-200ish.

Please, oh, please I hope the 7Ah cells meet Fred's (and our) expectations!

-Dan
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Old Sep 09, 2002, 09:57 AM
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Quote:
Originally posted by Ninjak2k
Kelvin,

The cost of the 3 AH Lithium batteries is $27 each. My guess is the price for the 7AH cells will fall in the $30s. So, you are looking at a pack cost of around $120.

Yes, this does stink, but look at all the benefits. Less weight, longer flying time, same power. Plus, the life expectancy of these cells is > 400 charges according to the Kokam website.

-Dan
$120. I'd go with that as long as they're robust. Is the life expectancy better than Nicads, Nmih the way we abuse them?

Kelvin
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Old Sep 09, 2002, 10:03 AM
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Kelvin,

I don't think anyone really knows because these cells are so new. The only people who might really know is Kokam.

Fred believes that keeping their discharge rates at 5-6C will not damage them or affect their performance. Those are the results of his tests for the 3 Ah cells and below.

To answer your charger question, their are free plans to build Lithium Ion chargers on the web. FMA is also supposed to release a charger for about the same price as the SuperNova. Fred even talked about a simple add-on for owners with SuperNova chargers that would allow you to charge Lithium Ions and Polymers.

-Dan
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Old Sep 09, 2002, 10:26 AM
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Where are these free plan for Li-Ion chargers?

I would be interested in building one

thanks

Paul
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Old Sep 09, 2002, 11:23 AM
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maybe, maybe not

Based on the actual 3270 discharge data presented in the modelling science thread, there are still some questions about the suitability of the Kokam cells for high-power flight systems like that of the E3D. Don't get me wrong, they do look very attractive for many applications, but I don't see any data that convinces me they would provide the anticipated performance improvement in systems that draw 40A+ at full throttle and average 20A+ from Cs packs. Look at the 3270 discharge plots in this thread.

www.rcgroups.com/forums/showthread.php?s=&threadid=56590&pagenumber=3
The 3270 discharge curves presented by ls77 show a runtime of <400 sec. at 12A for 1.3A-h. The capacity increases to 2A-h at 9A. This suggests that substantial energy density gains are only available at discharge rates of <3.5C. The standard setup in many sport planes draws 40A static from Cs cell packs. A good Cs cell will deliver 40A at ~1.0V for 40W from a ~2oz cell. The Kokam 3270 weighs 2.2oz so must deliver 44W for equivalent power density. At 3.5V, this comes to 12.6A. The presented discharge data leaves me wondering if the 3270 will deliver full-throttle power beyond about 1A-h into the discharge. If it does, great! If it doesn't, then the usable energy density becomes approximately equivalent to NiMH 3000 cells. While the Kokam cells may be able to deliver 5-6C current levels, will they do so beyond the initial part of the discharge?

Again, I'm not saying that Kokams won't provide enhancements in sport plane systems, just that there appears to be a few more questions to answer before we all dump our NiCd and NiMH packs in favor of this new, promising product. It would probably work great in 50-80W/lb planes, but may not be a good choice in 100+W/lb planes.

Brad
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Old Sep 09, 2002, 02:59 PM
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Paul,

I'm sorry; the plans I found were for Lithium Metal batteries, not Lithium Ion/Polymer. I'm convinced there has to be something out there though. I'll post here if I find anything.

I agree with Brad that really high discharge rates could be a problem. If discharge approaches those high rates, the best thing is to see if a parallel configuration would work better. Anyhow, we can only speculate so much. I'm looking forward to seeing Fred's (FMA's) results.

-Dan
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Old Sep 09, 2002, 06:19 PM
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Found something that can be used to make your own charger. It's an IC (integrated circuit) made by Maxim for $4.00 that basically is the charger, besides some external resistors and capacitors!

Here is the website http://dbserv.maxim-ic.com/quick_view2.cfm?qv_pk=2217.

The other thing about these packs will be the weight savings. With a lighter aircraft, you can go easier on the Amps.

-Dan
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Old Sep 12, 2002, 06:32 AM
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Got an idea after reading Gary's comments in 'Best Aerobatic/3D plane for a speed 400 size brushless? '.

Running 3 7 Ah Kokam Lithiums with a Magnetic Mayhem at 4.6:1 with a 14x10, you would get 28 min. running only at FULL THROTTLE!

And, the current draw is only 17 amps! Well within 3C discharge for these cells. Amazing... great sport plane setup!

-Dan
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Old Sep 12, 2002, 10:08 AM
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In all of my testing with the cells, it shows the "sweet spot": is the 3.5C-4C area. The cells can be pushed harder but only in short bursts or they will shut down as shown in my tests at the higher current levels. I should note that the Discharger I use holds the current selected no matter what the input voltage is. In actual flight the current will fall as the voltage does so the cells will not shut down as quickly when you push them over the 4C level. I recommend that the 3270's pushed no harder than 10amps or 12-13 in bursts. The 1575's pushed no harder than 6amps or 7-8 in bursts. The 1020's pushed no harder than 4amps or 5 in bursts. The Li-poly tech is not a huge step over the old Li-ion batteries in terms of current handling but when combined with the weight savings & safety factors they do become very attractive. I think that they are still more suitable for the speed 400 & smaller sizes and not so much for the high power ships like the E3D. Mainly due to cost and size. The 7Ah batteries might change this but they are going to be quite large and difficult fitting into a fuse. I was playing around with the idea of making a 24 cell 1575 pack. Its footprint would easily fit in most of the larger planes/helicopters at 2" H x 1.625" W x 9" long. Setup in a 4x6 config, it would net 16.8 volts peak, 14 volts average, 33.6 amps at 3.5C & 48amps at 5C in bursts with 9,450mah on tap. It would be 28 ounces and cost 360 bucks so that kinda kills it but I may build one and let the local E3D/Logo 10 fliers try it out for fun.
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