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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.<br>
Chris<br>
<br>
Ed Deaver wrote:<br>
<blockquote type="cite"
cite="mid20040508013404.4550.qmail@web11801.mail.yahoo.com">
<div>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)</div>
<div> </div>
<div>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.</div>
<div> </div>
<div>Thanx</div>
<div> </div>
<div>ed<br>
<br>
<b><i>Keith Black <a class="moz-txt-link-rfc2396E" href="mailto:tkeithb@comcast.net"><tkeithb@comcast.net></a></i></b> wrote:</div>
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<div><font face="Arial" size="2">Thanks for your reply Jim. </font></div>
<div> </div>
<div><font face="Arial" size="2">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. </font></div>
<div> </div>
<div><font face="Arial" size="2">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. </font></div>
<div> </div>
<div><font face="Arial" size="2">As it relates to the cells being
unbalanced, will lithium batteries equalized each other via a "trickle"
as is the case with NiCad batteries?</font></div>
<div> </div>
<div><font face="Arial" size="2">Jim, I really appreciate your
always candid responses and willingness to assist others on the list.</font></div>
<div> </div>
<div><font face="Arial" size="2">Thanks,</font></div>
<div><font face="Arial" size="2">Keith</font></div>
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<div
style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-stretch: normal; font-size-adjust: none;">-----
Original Message ----- </div>
<div
style="background: rgb(228, 228, 228) none repeat scroll 0%; -moz-background-clip: initial; -moz-background-inline-policy: initial; -moz-background-origin: initial; font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-stretch: normal; font-size-adjust: none;"><b>From:</b>
<a href="mailto:JOddino@socal.rr.com" title="JOddino@socal.rr.com">JOddino</a>
</div>
<div
style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-stretch: normal; font-size-adjust: none;"><b>To:</b>
<a href="mailto:discussion@nsrca.org" title="discussion@nsrca.org">discussion@nsrca.org</a>
</div>
<div
style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-stretch: normal; font-size-adjust: none;"><b>Sent:</b>
Friday, May 07, 2004 10:30 AM</div>
<div
style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-stretch: normal; font-size-adjust: none;"><b>Subject:</b>
Re: Charging concerns/questions with NMP Lithium Ion batteries</div>
<div><br>
</div>
<div><font face="Arial" size="2">Hi Kieth,</font></div>
<div><font face="Arial" size="2">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).</font></div>
<div><font face="Arial" size="2">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.</font></div>
<div><font face="Arial" size="2">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. </font></div>
<div><font face="Arial" size="2">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.</font></div>
<div><font face="Arial" size="2">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.</font></div>
<div><font face="Arial" size="2">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.</font></div>
<div><font face="Arial" size="2">Regards, Jim</font></div>
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