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Old Sep 25, 2003, 02:23 PM
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Doc Watson's Avatar
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li-poly cells for high power EDF's?

After reading Gordon Whiteheads article in the latest Jet International I'm trying to piece together some info on using li-poly cells for high power EDF applications I have a limited knowledge of these cells but have read the battery forum FAQ and other related threads so hear goes....

First off my current setup is as follows:-

Plettenberg HP220/30/A3 S P4 with Schulze future 18.61 ESC running a Wemotec HW620 fan. Max output is around 40-45A.

Oh yea there are 3 fans in the model................so a total of 48 cells are being used which is 3 packs of 16x1700mAh nicads, each pack is 755g so total cell weight is 2265g.

That equates to about 640W for each fan.

So the info I have for li-polys is....

1 cell provides 3.7V, a 2200mAh cell is 42g (1.5 oz) with a size of 89x56x5mm (3.5 x 2.2 x 0.15 inches) and has a burst (not literally I hope) discharge of 10C.

so using a single cell I can get a max of 22A discharge, obviously not enough so by joining 3 cells in parallel I create a 6600mAh cell capable of up to 66A discharge but still giving 3.7V. If I then connect 5 of these 3 cell packs (designated 5s3p, 5 series 3 parallel) I end up with a cell pack which has a capacity of 6600mAh and a voltage of 18.5V.

The total number of cells for a 5s3p pack will be 5x3 or 15 cells and the weight will be 630g a saving of 125g per pack or 375g total!

thats not all.... the capacity has jumped from 1700mAh to 6600mAh!!!!!!!!! wow

Of course there is a price you pay for this (literally) as currently each cell is about 11.50 each, I need 45 so thats 517.50 (makes a mental note to remortgage the house).

A few questions then...

1) can someone confirm/edit my calculations?

2) can I use my Schultz controller with these cells?

3) anybody know a supplier in the UK for a few 2200mAh li-polys?

4) how do I hide this from the wife?

as a note Gordon stated that Dan the man (schubler) ran his vector for over 15 minutes on li-polys.

Apart from the price it would also require a different cell 'box' in the body of the plane (we could be talking structure #8 but #7 is being used with the nicads and will also test conventional flight), so has anybody here used li-polys in high power EDF's?

Doc
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Old Sep 25, 2003, 02:39 PM
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Hi doc
You should read that thread:
Gordon's edf talon
Gordon (plane crazy) made an impressive job with high power edf- lipo.

Hope to see your work soon in the sky !

Franck
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Old Sep 25, 2003, 02:40 PM
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By the way, hide this from the wife should be the hardest part...
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Old Sep 25, 2003, 03:15 PM
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dallas,tx
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Doc,

don't forget to calculate in that new charger you will need for those cells


ryan d.
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Old Sep 25, 2003, 03:22 PM
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DanSavage's Avatar
Trabuco Canyon, CA
Joined Nov 2000
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Re: li-poly cells for high power EDF's?

Quote:
Originally posted by Doc Watson
Apart from the price it would also require a different cell 'box' in the body of the plane (we could be talking structure #8 but #7 is being used with the nicads and will also test conventional flight), so has anybody here used li-polys in high power EDF's?
Hi Doc,

Your calculations look okay to me. Thunder Power currently only recommends 5C continuous and 8C burst, but Gordon (Plane Crazy) has been drawing 6C continuous on these without any problems. 10C burst sounds a bit optomistic, so you might consider going to an 8.2Ah pack instead of a 6.6Ah one.

Daren and I have been using TP 11.1V 8.2Ah (3S4P) packs in our MiG-29s and so far have really been enjoying them. The higher capacity packs don't have as large of a voltage drop as the nicads they replaced, so we're actually seeing better performance and dramatically longer flight times. The jump in performance going to LIPOs from the 1700mAh packs was about the same as when we went from the 1300s to 1700s.

These use the following setups:

MF480
Hacker B40-10S
Jeti Master 70-3P Opto

We're drawing about 52A at full throttle which is just under 6C. We're getting 11.1V and 575W. Based upon these calcs we could get two 5 minute flights or a single 10 minute flight off a single charge.

We've been practicing throttle management to keep the amp draw around 5C or less. This also helps keep the packs cooler and extends the pack life.

Last week Daren took two 6 minute flights and still had about 2400mAh left in the pack when he recharged them.

The battery weight actually dropped from 17oz. for a 10-cell CP1700SCR pack to 16.2 for the TP 8200 LIPO.

We're both really looking forward to flying the new Flankers on the LIPOs.

Dan
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Old Sep 25, 2003, 03:32 PM
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33102 Paderborn, Germany
Joined Jun 2000
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Hello Doc Watson,

Your calculations are right.

If you want to save more weight and higher capacity is not the point, you will need a cell with a higher discharge rate. The Kokam 340HD will be the right choice.

It is more expensive, but a 5S 9P pack will weigh only 430g incl. cables and soldering material. It will give slightly more voltage than the 2200 cell and has 3.06Ah. The pack can handle 45A easily.

Be careful by using the 6.6Ah solution, you can easily burn your motor after 3Ah. Since I switched over to LIPO`s i always measure motor and controller temperature after flying. 80degrees C on the motor will be o.k.

Daniel
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Old Sep 25, 2003, 03:36 PM
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Wow, sorry gordon missed that one, thanks for the info Dan, and Daniel - do you have info (size and price of the Kokam 340HD's?)

Love that vector, and one day I will have 3 of those fans...one day...

Doc
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Old Sep 25, 2003, 03:44 PM
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33102 Paderborn, Germany
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Kokam 340HD: 9g; 2.8x34x52mm; 15C max. average discharge; price about 6.6 british pounds

Sorry about the fan thing, but we switched over to the new fans last year... maybe one day

The Kokam 1500HD is another good choice, but it will not work at 15C, it is good for 6-7C (10 Amps) and costs 9.45 pounds.
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Old Sep 25, 2003, 03:46 PM
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UK
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Thanks Daniel

so.............

Using Kokam 340HD: 9g; 2.8x34x52mm; 15C max. average discharge; price about 6.6 british pounds

And a 5S 9P pack will give 3060mAh at 19V ish? and 430g

thats 45 cells in one pack at a cost of 300 per pack (ouch)

But a weight saving of 755-430=325g per pack!!!!!!!!!!!

Thats 975g total saving wow!!!!!!!!!!!

Must do the revised duration/amp loading simulation on my 'puter...........

And ring the mortgage lender.....................
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Old Sep 25, 2003, 04:53 PM
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St. Mary, Maryland, United States
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I hesitate to ask

So, have you flown this thing yet?
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Old Sep 25, 2003, 05:06 PM
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Herb's Avatar
Irvine, Calif USA
Joined Feb 1999
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Re: $1000 li-poly cells for high power EDF's?

Quote:
Originally posted by Doc Watson
After reading Gordon Whiteheads [...] and will also test conventional flight [...] Doc
I guess I missed the first flight threads, but for the "unconventional flight" part ie hovering tests, can't you just use a regular $40 deep cycle marine battery from costco - with two thick wires attached ?
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Old Sep 25, 2003, 05:56 PM
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Chris, I'm close.....real close........

You and a few others are first on the video mailing list......

Herb, I've got the cells for the umbilcal thing but need to do it without to 'prove it works'.

Also after realising that it would cost 1000 just for the 3 packs of li-poly cells I think I will buy one pack and use it for the front fan.
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Old Sep 26, 2003, 03:05 AM
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33102 Paderborn, Germany
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Yes, I know, the price is still too high, but I think things will change in the future.

The pack will give you an average 17.5V, not 19V. To get the real voltage of LIPO`s under high current load please check the measurements on my site.

Think about cooling of your motors when you decide for LIPO`s. When I made my first flights with a 9Ah battery I chose a Hacker B50XL (40mm magnet), it worked perfect without damage. A 30mm motor was burned after 5Ah....

Daniel
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Old Sep 26, 2003, 03:31 AM
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I imagine this is why some Hacker C series have a XL rotor option.

Barry
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Old Sep 26, 2003, 05:14 AM
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33102 Paderborn, Germany
Joined Jun 2000
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Hi Barry,

You mean "why some Hacker XL series have a C rotor option" , right?

Daniel
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