|Sep 25, 2003, 03:23 PM|
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?
|Sep 25, 2003, 04:22 PM|
Re: li-poly cells for high power EDF's?
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:
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.
|Sep 25, 2003, 04:32 PM|
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.
|Sep 25, 2003, 04:36 PM|
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...
|Sep 25, 2003, 04:44 PM|
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.
|Sep 25, 2003, 04:46 PM|
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.....................
|Sep 25, 2003, 06:06 PM|
Re: $1000 li-poly cells for high power EDF's?
|Sep 25, 2003, 06:56 PM|
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.
|Sep 26, 2003, 04:05 AM|
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....
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