Li-Ion, Experience, Design, and Theory.

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Li-Ion, Experience, Design, and Theory.

Hello Guys! I have taken it upon myself to start a group specifically dedicated to talk about Li-ion use.

There are many who have a considerable amount of Li-Ion experience.

Please use this outlet to teach others, ask questions, post experiences/Ideas, ETC...

Location: DIY DRONES!
Members: 19
Latest Activity: Jan 13, 2016

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Comment by james sowell on January 13, 2016 at 5:54pm
Comment by james sowell on April 11, 2015 at 5:30am
Comment by james sowell on April 15, 2014 at 10:34am
Comment by Holger S on March 11, 2014 at 12:47pm

Hi Justin,

inspired by your post I just browsed some old logs. I found two logs of flights at approximately 1C. All measurements were taken with calibrated SM Unilog current/voltage sensors. Both flights were in Februrary at 14°C, and 16°C respectively. Both packs were quite new, but already done had some break-in cycles.

First flight:

Hobbyking 6600mAh boat pack, 4s2p

  • weight of 1.118 kg incl. approx. 60g of cabling (for paralleling four packs)
  • 11800 mAh during this flight
  • 179.7 Wh during this flight -> 160,7 Wh/kg
  • avg. voltage was 3.807V per cell

Panasonic NCR18650B, 5s3p (on a different copter with slower motors)

  • weight of 0.724kg 
  • used 7680 mAh during this flight
  • used 132.255 Wh during this flight -> 182.67 Wh/kg
  • avg. voltage was 3.444V per cell

So your are not to far from my in-flight measurements. Maybe the things are different in cold or hot weather.

Holger

Comment by Tommy Larsen on February 18, 2014 at 12:44am

Hi

I'm using those cells in a 6s3p x 2 config in my Tarot T810 hexa now and it works good. But after i saw the discharge curve for the LG 18650 D1 3000mah pink cell, i think those would be a better choice for a copter. Panasonic is better for a plane i guess. Use the compare tool here to see the difference. The LG cell have a higher and more flat discharge curve than the panasonic cells.

Comment by Justin Martin on February 17, 2014 at 11:35pm

So, I figure I will start!

First and foremost, I have no flight experience (practical experience) with these batteries. I have only tested single cells with rather cave-man like testing methods. Apply a load, check voltage, record data, move on...

My personal findings are that the higher the load (18650b), the more these cells drop in voltage. Anything above .5c and they seem to drop drastically. I can only assume this is why many people add an extra cell in series in order to "make up" for the loaded voltage. This being said, in MY mind it means that their PRACTICAL density is much lower than the calculated density (250-270 Wh/Kg). 

Taking this into consideration, would it be more beneficial to try the 18650PF cells? They claim to have a max discharge of close to 10c. However, they are only 2900mah. This being said, their calculated energy density is lower. However, In MY mind, it seems that if these cells sag less (voltage) under load, they could potentially have a higher PRACTICAL energy density. Is this so?

Keep in mind, when I say PRACTICAL I mean Real-World.

-Justin

 

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