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Electric Drive System Info

Old 12-28-2009, 09:48 PM
  #26  
1bwana1
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Default RE: Electric Drive System Info

I have been running two sets of Rhinos in my Passport (and other planes) for about a year now.  Well over 100 flights, and they are my best performing batteries.  I also have two sets of a well known brand that have higher "C" ratings.  The high priced ones have dropped off considerably, not the less expensive (cheaper is not the right word) Rhinos.  8 new packs arrived in the mail today, guess which ones I re-ordered. LOL!  At $62 a pack, it's a no brainer.
Old 12-29-2009, 03:04 AM
  #27  
Velco
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Default RE: Electric Drive System Info



To me much more important than loss of capacity after certain number of cycles/time is how packs hold under load, which is influenced by increase in internal resistance. Certain chargers, like Power Peak Infinity from Robbe, do measure it.



I have Kokam H5 3200 30-50C cells in 6S packs and they have 180mOhm internal resistance after being charged from 3,7V/cell at 1C. At the same time Flightmax 6S pack of 3600 30-40C has 80mOhms charged under the same conditions. In practice this reflects as 700rpm more on A5016S with 16x10 prop in favor of Flightmax.



Also, according to Kokam hereyou can see that with 80% discharge rule, capacity loss is just 6% after 2500 cycles! So on a 5000mAh pack the loss would be 300mAh. More importantly is that I have noticed exactly the same loss in capacity on packs that are some 20 months old either sitting on a shelf or being used with 80% rule, some 5%!



But again, loss in capacity is not my worry, if only would packs maintain their internal resistance after 150-200 cycles or 2 yrs time ...

Old 12-29-2009, 11:42 AM
  #28  
DaveL322
 
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Default RE: Electric Drive System Info


ORIGINAL: Velco
Also, according to Kokam here you can see that with 80% discharge rule, capacity loss is just 6% after 2500 cycles!

This is when the discharge rate is 1C....very different from our use of lipos for motors where we are typically averaging 5 - 8C discharge.

Regards,

Dave

Old 12-29-2009, 12:08 PM
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Velco
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Default RE: Electric Drive System Info



Dave,



Thank you, I was hoping someone was going to point this out. The info we get from manufacturers (in this case Kokam) is quite deceiving and nobody is mentioning internal resistance or what effect aging has on LiPo packs. Who cares about discharge at 1C!?  In spring 2008 I had to pay 1000$ for some H5 Kokam packs, and those same packs STILL today cost the same. Not to mention that Rhino 3S 2250 25C (19$) are performing way better than Kokam 3S 3200 30-50C ( 115$) ! All I am asking for is that manufacturers start publishing real life data. OK, that was my rant



As I have already said, I have noticed some 5% loss in capacity BOTH for a pack sitting on a shelf (don't ask why ) and a pack with some 50 cycles, also with the same internal resistance for both.



Velco


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