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Old Apr 08, 2006, 10:17 PM
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How do I know if I am running my Kokam to hard

If I am discharging my Kokam 700mah in less than 5 minuets am I pushing them to hard? I have a balsa products Bm2410-12 running a flying styro 3 blade 9.7 prop in a 12 ounce gws war bird. With a 2 cell pack it is a little sluggish and I have to keep it between above half and full throttle and the pack lasts a little under 5 minuets. Running a 3 cell it is really fast and I can cruse at a third throttle. I think I got just a little over 5 minuets on the 3 cell. With 2 or 3 cell the pack is a little worm after my flight not really hot. Am I going to kill my packs with this setup? Is there an easy way to know when I am pushing my packs to hard? I would think it would draw harder on the 3 cell because the voltage is higher? Or is it harder on the 2 cell because I have to keep on the throttle so much?. Sorry for all the questions but I am totally lost on this stuff. Thanks for any help

Dave
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Old Apr 08, 2006, 10:27 PM
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PS I want to keep the FSK prop.

Dave
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Old Apr 08, 2006, 10:37 PM
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If you are indeed useing up the battery in 5 minutes you are pulling 15C, if your lopo is a 15C or more, you should be fine.

How hot does it get?
the hotter a bettery after discharge the more you are pushing it, if it only get a little warm you are fine.

C Drain = 60minutes / Minutes of flight
So, if you use you battery in 5 minutes from full to empty then.
C = 60/5
C = 15
15C
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Old Apr 08, 2006, 10:39 PM
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I guess the motor is a BP-12
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Old Apr 08, 2006, 10:47 PM
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They are really not that hot, warm to the touch but I could touch them to my face no problem. I do not think they are meant to be used at 15c If I am draining 2 cells and 3 cells to hard I guess my only other option is to change props. It was gutless on the 2 cell so maby I need some other motor?
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Old Apr 08, 2006, 10:50 PM
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C=60/5=12, not 15. Are you running down to near zero capacity?
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Old Apr 08, 2006, 10:54 PM
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I ran them till they started dropping off noticeably.
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Old Apr 09, 2006, 01:54 AM
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hehe, my bad, must be tired.
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Old Apr 09, 2006, 10:23 AM
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So if they only take 40 min to charge at 1c do I use 40/5 insted of 60/5
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Old Apr 09, 2006, 10:34 AM
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Any LiPoly ran close to its max C will be short lived.
If the open (resting / no load) voltage of the battery is below 3.3 volts per cell 10 minutes afer a flight it has been over discharged. A open volts os 3.7 per cell is much better . You should not discharge over 80% of the batterie's cpacity.

LiPoly charge at close to 100% efficeincy so: mAh used *60/ flight time = average in flight load.


0.500 mAh *60 / 3= 10 which would be just over a 15C load on a 700 mAh battery.


700*15=10.5A

http://www.rcgroups.com/forums/showthread.php?t=466758

Charles
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Old Apr 09, 2006, 10:38 AM
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So if my charge time is near 60 minetes I am over discharging my packs?
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Old Apr 09, 2006, 11:08 AM
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So I just charged my 3 cell. It took 44 min to charge so if I had a 5 min flight I would use 44/5 = 8.8c? If this is so I will have to time next flight to see how long over 5 minets I am getting. They are 8c packs so I am close to what I can pull. I guess my other options are to go to a 1500mah pack or prop down? Thanks for all the help!!
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Old Apr 09, 2006, 11:21 AM
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You can not really use the charge time as a indicator. Well you can but it may not be accurate at all. Many chargers have a display which shows the mAh which goes to the battery during charge. If you have a watt meter you can put it in-line beteen the charer and the LiPoly to measure the charge.

If you measure the resting / open / no load voltage afeter a flight it is a fairly accurate full gage of the LiPoly.

An 8C should not be discharged in less than 8 minutes and even then this is max. and battery will most likely last 50 flights or less.

60 minutes in an hour divided by C rate of LiPoly 8C equlas 7.5 minues and that would in theory be with zero remaining capacity.


http://www.rcgroups.com/forums/showp...1&postcount=11

Charles
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Old Apr 09, 2006, 12:41 PM
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Quote:
Originally Posted by Dave K
I guess the motor is a BP-12
Post #1 How do I know if i am running my Kokam too hard?
Answer:1. Buy a watt meter
2. In post #1 you said you are running a 9x7 3 blade on 3 cells.
The mfgs. motor specs. is an 8.43 prop 11.1 volts 10.3 amps
With the 9x7 3 blade I think you are exceeding both the battery
and motor amperage specs. LOL
Bob
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Old Apr 09, 2006, 01:08 PM
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I tried a 8040 HD prop and it still dumped in 6 min. Is there a outrunner style stick mount motor that is going to make this work with a 700mah pack? Do I need to go to a 1500mah pack and a better motor? Thanks

Dave
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