[NSRCA-discussion] Lipo Stuff...

[Scott Anderson]

Dave,

Outstanding !!!

It just comes down to safety and knowledge !!!

Scott Anderson
Team Tanicpacks.com
----- Original Message ----- 
From: "David Lockhart" <DaveL322 at comcast.net>
To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
Sent: Wednesday, March 22, 2006 7:57 PM
Subject: [NSRCA-discussion] Lipo Stuff...


> In view of the recent discussions on lipos and chargers, I thought I've
> offer a couple thoughts on some basics I have learned in the past 3 years
> with many foamies, about 75 flights on a 40 sized modified MK Mattlas 
> built
> for electric pattern, 28 flights this past winter on an electric Abbra, 
> and
> many hours of reading, discussing, and emailing with people that have
> demonstrated knowledge about electric power systems.  My opinions only -
> your mileage may vary.
>
> For Lipos, ESCs, chargers, balancers, and motors - read the instructions -
> most are available online and most contain the information that if 
> followed
> would prevent 99% of the lipo problems I've read about and personally 
> seen.
> With specific regard to the Astro 109, it uses a different charging
> algorithm than the Schulze, Orbit, Triton, or TP chargers - some special
> "rules" apply to the 109 (instructions available online).  The online 
> forums
> contain a ton of information about darn near every charger (including the
> 109), balancer, and lipo on the market - read carefully and consider the
> source.  There is also some excellent info in the Castle Creations Scribe
> (at the Castle web site).
>
> Get a good wattmeter and a good temp gun and use them, and understand what
> the numbers mean.  It is very important to match the lipo, ESC, motor, and
> prop as a complete system.  The lipo is obviously potentially the most
> dangerous when abused, so size it the most conservatively.  Anytime you 
> make
> a change in the ESC settings, prop, mounting, or cooling, check the setup
> with the wattmeter to see what the changes are, and conservatively fly the
> setup and then check it again (wattmeter and temp) to see if/how much 
> change
> happened in the air.  Do not expect anything with electric power systems 
> to
> be linear - they rarely are - ie, an ambient 10F temp increase does not 
> mean
> the lipos, ESC, and motor will all run 10F warmer - they might actually 
> run
> cooler or substantially warmer.  Different props can be varied degrees of
> stalled on the ground - amps consumed in the air do not always correlate
> with amps on the ground.
>
> Consider the possibility that lipo "C" ratings just might be influenced a
> bit for marketing purposes, and many evaluations/ratings are based on lab
> conditions which may have little or no bearing on conditions the lipo will
> see in flight (which varies substantially in different planes and 
> different
> pilots).  Ambient temperature has huge effect on the voltage under load 
> for
> lipos - and the lipos can deliver substantially more amps and volts in 
> warm
> weather.  I am interested in long life from my lipos, and am going to 
> follow
> a couple basic ideas -
>
> Discharge rate - ignore the burst ratings completely.  "Test" the 
> continuous
> discharge rating for accuracy - start with small props and increase prop
> size until you are down to 3.5volts per cell - do the math and figure out
> the C rate if you really need to know.  If you are not happy with the
> available power, get a bigger battery, a more efficient motor/ESC/prop, or 
> a
> lighter plane.  Keep the discharge to 80% or less - determine this by
> monitoring how much charge goes back into the lipo (ie, you don't want to
> see more than 4000 mah going back into a 5000 mah lipo).  After a brief
> period of rest after a flight, you should see a minimum of 3.7 volts per
> cell, preferably 3.8 volts per cell.  If you are at 3.6 volts per cell or
> less, consider decreasing flight time, amp draw, plane weight, or upping
> lipo size.  You should never let the lipo go below 3.0 volts per cell (a
> good Low voltage cutoff in the ESC won't allow it drop below 3.0 volts per
> cell) under load or resting.  If it does, watch that lipo like a hawk and
> know that the longevity of the pack has been compromised.
>
> Temp - max power will come from the current lipos between 100 - 120F. 
> This
> winter, I have preheated the lipos to 105F on the dashboard defroster and
> picked up substantial power vs 60F.  And the lipos have come down at 95F
> after being preheated.  If the lipos are above 130F after a flight, 
> consider
> more cooling, less throttle, less prop, lighter plane, shorter flights. 
> If
> they are above 140F, seriously consider getting them cooler and 
> acknowledge
> you are likely decreasing the life of the lipo.  If they are above 150F, 
> it
> is very likely damaging the lipos - keep in mind, all cells do not see the
> same cooling, and measuring the case on the outside cells isn't the whole
> picture.  In my experience, heat generated by the lipo increases pretty
> dramatically when discharged deeper than 80%, and the ESCs and motors get
> hotter as well - I attribute most of the heat increase to reduced 
> efficiency
> of the system as the voltage of the lipo drops further into the discharge.
> Maintaining high voltage plays a big part in keeping the lipos, ESC, and
> motor cool.
>
> I suspect good longevity will be the result if temps are kept below 130F,
> discharge is less than 80%, and loaded voltage is 3.5+.  I also strongly
> suspect balancing will not be an issue if the pack is properly constructed
> of quality cells to begin with.  I've had very few balance issues, and 
> none
> when lipos were used within these parameters.  A balancer is not a cure 
> for
> a pack that consistency falls out of balance when charged or discharged - 
> it
> may prolong the life of the pack, but the weak cell is a sign of a pack 
> with
> increased risk and reduced life.
>
> I consider myself a piker who is expanding their knowledge when it comes 
> to
> this electric stuff, but hopefully some of the above info is helpful in a
> practical sense to current and future lipo users.  I'd be happy to 
> entertain
> questions and provide further brainwashing.......with the preface my 
> answer
> might be "I dunno....."  <G>
>
> Regards,
>
> Dave Lockhart
> DaveL322 at comcast.net
> Team JR
> Team Castle Creations
>
>
>
> _______________________________________________
> NSRCA-discussion mailing list
> NSRCA-discussion at lists.nsrca.org
> http://lists.nsrca.org/mailman/listinfo/nsrca-discussion