Charging concerns/questions with NMP Lithium Ion batteries

[Dean Pappas]

Hi Dave,
Maybe I shouldn't have stayed silent so long ... I don't have to go back to MiCads, as I never left! I still run my SR NiCads, using a Sirius charger to top-up a 5-cell 500mAH pack after each flight. It takes just about 20 minutes, and the whole thing weighs under 3.5 ounces. Since the Sirius doesn't peak, I don't even use a regulator. My Futaba digitals haven't protested yet! Of course, the old engine test-bed Ariel uses nickel and cadmium as noseweight, so that ship has a 1000mAH pack.

Oh yeah ... I don't get anything for free from Larry Sribnik, and I like the man 'cause he sells me good stuff that hasn't let me down. Back in the early Stone, Age NiCads had problems ... now they are close to bullet-proof. According to Larry, someday other technologies will get that robust, but for now it hasn't happened. By the way, he is actively working on both nickel metal-hydride and litium battery technologies that he would be willing to sell, and I am waiting ... patiently.

You know ... there are just too few of us to ever be mad at each other. I do think that the sponsorship culture has run amok, though.   

Regards to all
Dean P. 





-----Original Message-----
From: David Harmon [mailto:K6XYZ at comcast.net]
Sent: Friday, May 07, 2004 9:55 PM
To: discussion at nsrca.org
Subject: FW: Charging concerns/questions with NMP Lithium Ion batteries


I don't hear anyone recommending going back to nicads....
Just use the proper charger properly and set it correctly and Chicken
Little will stop crowing.
I have been using the SR 1000 5 cell packs and they are great. They are
1000mah and I get 
5 flights with a similar setup as you describe.
This pack weighs 5 oz and I use the Jaccio regulator too.
That is 2.5oz more than someone else said the NMP weighs but so what?
I use both types of batteries and am going to change completely to NMP
Ni-Ion as soon as the 
rest of the Nicads go bad.....and I am gonna BUY them from Central Hobby
as I am not sponsored by
them....if anything WE sponsor CH and the other fine businesses as well....I
can think of several.
It buggsss me because somebody took a swipe at Troy because he is
sponsored....he SHOULD be sponsored!

Regards

Dave Harmon
NSRCA 586
K6XYZ[at]comcast[dot]net
Torrance, Ca. 
-----Original Message-----
From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]
On Behalf Of Ed Deaver
Sent: Friday, May 07, 2004 6:34 PM
To: discussion at nsrca.org
Subject: Re: Charging concerns/questions with NMP Lithium Ion batteries

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 
To: 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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