Charging concerns/questions with NMP Lithium Ion batteries

[Chris Moon]

Ed: I am running a 1450 nimh 5 cell pack at 5oz.  I did some rough 
calculations from my practice flights and figure an average flight with 
10min in the air plus start / taxi times the battery uses 200 mah per 
flight. I am using 2- 8411's  2-9411's and a 331 servo.  So the 1450mah 
is more than plenty and a 1050mah would work too and save a  little weight.
Chris

Ed Deaver wrote:

> OK, Ive had Duralite and subsequently Powerflites for about 5 years 
> now.  Because of the fire hazard, everyone is recommending going back 
> to reg batteries or NMhd(which my charges probably won't support)
>  
> So for 3 digital, 1 4721 and a mini throttle servo, how many mah 
> should I look at buying in old style batteries?  I would only go with 
> 5 cell pack.
>  
> Thanx
>  
> ed
>
> Keith Black <tkeithb at comcast.net> wrote:
>
>     Thanks for your reply Jim.
>      
>     I do like design of the NMP charger and the way it shows how much
>     current is being feed to the battery. This is clearly an excellent
>     design feature.
>      
>     What I gather from your response is it is "possible" for a cell to
>     be charged beyond the safe limit if another cell is either out of
>     balance or defective. Also, I understand your point that one may
>     be able to spot a bad cell after becoming familiar with the charger.
>      
>     As it relates to the cells being unbalanced, will lithium
>     batteries equalized each other via a "trickle" as is the case with
>     NiCad batteries?
>      
>     Jim, I really appreciate your always candid responses and
>     willingness to assist others on the list.
>      
>     Thanks,
>     Keith
>
>         ----- Original Message -----
>         From: JOddino <mailto:JOddino at socal.rr.com>
>         To: discussion at nsrca.org <mailto:discussion at nsrca.org>
>         Sent: Friday, May 07, 2004 10:30 AM
>         Subject: Re: Charging concerns/questions with NMP Lithium Ion
>         batteries
>
>         Hi Kieth,
>         I believe the NMP solves most of the problems we have all read
>         about.  1) it is the right type of charger for Li-Ions and is
>         dedicated to that chemistry by limiting the current and the
>         voltage. 2) it is set for two-cell packs and that cannot be
>         changed by the operator or on its own. 3) it limits the
>         current to less than the 1C rate (for 2000 mAh packs).
>         Probably its best feature vs. the other chargers is the meter
>         that tells the operator what is going on.  After you use it a
>         few times you will be able to predict the current at the
>         beginning and during the charge cycle depending on how many
>         flights you had.  If something is wrong, like a cell way out
>         of wack, it will give you an indication.  Of course it tells
>         you when the pack is charged and if for some reason it was
>         taking too long you would figure it out.  In other words you
>         will learn what is normal proper charge current vs. time and
>         could spot an unbalanced pack.  It cannot assure you a cell
>         will not be overcharged if the cells are not matched but I
>         believe you would spot it.
>         I've been using it for over a year and always charge the packs
>         in the plane.  The total charge time is relatively short so
>         you can monitor it, but I have left them plugged in over night. 
>         I have only seen one pack (a Duralite which was in a plane I
>         bought) with a slight unbalance.  It was a 2S2P configuration
>         and I don't have much experience with that configuration.  I
>         have never seen a simple 2 cells in series pack unbalanced.
>         Where you really need to worry about this is in long strings
>         like those used in electric flight.  I talked to Fred Marks
>         (FMA) about bringing out each node so each cell could be
>         checked and charged individually if required.  He said they
>         plan to do that in the future.
>         In the mean time, I believe one could stick a pin through the
>         heat shrink to check the cell balance.  I'll try that today
>         and get back to the list.
>         Regards, Jim
>
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