Discussion List (Batteries)

[Richard Strickland]

Gray, Dean,

While my experience wasn't the greatest--it really wasn't all that bad once we had the bugs worked out.  BTW, it was a Hacker system like Jason's.
One of the issues was to determine how cool the batteries needed to be before putting them back on charge; another was to make sure you were not over or under charging.  Another was to make sure they were balanced.  But for me it came down to weight and longevity.  Contrary to where your information is coming from, my understanding is that modeling IS driving this battery segment along with the military.  I'm reasonably confident there will be significant breakthroughs like that nano-tech unit(Toshiba or some other heavy-hitter like that) posted earlier this year that will impact the market fairly shortly.  The 3200s were under-sized, but 4000s would be also.  The motors would peak out at 67-69 amps on application of full throttle and back down to the 63-65 range.  This system worked well, but we were too close to the edge to lose any capacity and complete an FAI flight.  Temps started with a 40-50 degree rise when we started using them in the upper 70s and 80s and the same and a little more as ambient got warmer.  They got too hot.  We also tend to fly out.

Realistically, if to get decent mileage out of these things and have to stay close to 10C; then you've got to have at least 6000s+ and keep the weight down.  I know zip about batteries, except how to design conveyor systems for them, but they almost need to act like a capacitor--very high charge, discharge rates, and unlimited cycles with no damage.  I can't imagine there aren't MANY folks working on that concept.

Of course there are other alternatives--lighter and/or smaller airframes, different motor, ESC, prop combinations--but if you want unlimited vertical with 11 lbs--then your're going to draw 55-70 amps.

Richard
  ----- Original Message ----- 
  From: Gray E Fowler 
  To: discussion at nsrca.org 
  Sent: Friday, November 18, 2005 10:57 AM
  Subject: Re: Discussion List (Batteries)



  Richard 

  I am not a battery expert, but like everyone else on the list that does not stop me from having an opinion about batteries. 
  First, electric airplanes do not exactly drive the battery market,......even if 50% of the FAI finalists use them. No other applications 
  that I am aware of uses these batteries in the manner that we attempt, which is that massive current draw. What electric planes do 
  to batteries is damaging, as demonstrated by your 25 flights.   
  I would not expect the battery market to develop a battery capable of long life and extreme current draw since no one else uses 
  batteries in such a manner. 

  Invest in bottle of Windex, clean the oil. 



  In fairness to the manufacturers, I don't think they really understood that
  guys potentially would go out and fly 50+ flights per week.  When I finally
  got all my infrastructure charging act together and made time to
  practice--which wasn't all that much, I still was clicking along at a 35
  flight/week pace right up to our first contest in mid June.   As you may
  recall, I was using 20C 3200s on a shared cost beta program.  At 11 lbs.,
  the airplanes were gobbling up 63-68 amps at times and significantly heated
  the batteries and shortened their lives.  The manufacturer came out with
  some 15C 4000s--but there was still the problem of amp draw and heat.  The
  consensus at that point is the batteries aren't very happy at much over 10C.
  The problem I had/have is anything over the smaller batteries was going to
  blow the weight limit--plus, as more information was coming out from some of
  the top guys that they were getting around 50-60 flights on the larger
  packs.  Since I'm not a top dog, I would pretty much have to foot the entire
  bill to switch to the larger units.  As it appeared to me--the batteries
  just aren't quite up to the task for the average guy--so I made an interim
  decision to go back to IC for the rest of the season--hoping the battery
  guys would come up with something more acceptable for '06.

  That didn't pan out very well either, so I was effectively out for the
  season.  (Lots of other contributing factors also)  What I told the battery
  manufacturer was what a guy really needs is five sets of batteries(with the
  then current stuff) and immediate service for turnaround.  Have three sets
  for flying and one or two sets traveling to/from.

  I'm sold on electric--particularly for a guy with limited practice time.  I
  could go on and on....

  Richard 



  Gray Fowler
  Principal Chemical Engineer
  Composites Engineering
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