<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content=text/html;charset=iso-8859-1>
<STYLE></STYLE>
<META content="MSHTML 6.00.2900.2802" name=GENERATOR></HEAD>
<BODY id=MailContainerBody
style="PADDING-LEFT: 10px; FONT-WEIGHT: normal; FONT-SIZE: 12pt; COLOR: #000000; BORDER-TOP-STYLE: none; PADDING-TOP: 15px; FONT-STYLE: normal; FONT-FAMILY: Lucida Sans; BORDER-RIGHT-STYLE: none; BORDER-LEFT-STYLE: none; TEXT-DECORATION: none; BORDER-BOTTOM-STYLE: none"
leftMargin=0 topMargin=0 acc_role="text" CanvasTabStop="true"
name="Compose message area"><!--[gte IE 5]><?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->
<DIV>
<DIV>Jim</DIV>
<DIV> </DIV>
<DIV>I like your idea of using telemetry to see what's happening. I'm sure
everyone would welcome the info, I for one...</DIV>
<DIV>When I prepared to start flying my Impact, I started thinking about the
motor cut off. Now, I realize that with no cut off, we stand to damage a
battery due to over draw. Then I got to thinking... One of
these batteries could go south at any given time, for any given reason.
You can take as much care as posible with charging and monitoring voltages and
the like, but the battery could lose a couple cells at any moment. I
stand to lose a battery with no cut off if I fly too long and over draw the
battery, but on the other hand, if the battery starts to fail during a flight
and power starts to go away, I don't really want the speed controller
to shut the motor off and keep me from making it back to the field.
If that happens, I've not only lost the battery, but the plane as well. I
plan to leave the cut off turned off. I will fly only a given time and no
longer. I've flown enough now to know how much I'm using out of my
batteries during a 8 minute and 10 minute flight. The most I've used in a
10 minute flight, in a pretty good wind is 3690 mAh. When I changed props
from the 22X12 to the 21X13, the results went down to around 3400. I'm
using the TP 5300 packs. The only thing I can do is keep up the
diligence of monitoring the charge results and keep records to see how the
batteries are doing... </DIV>
<DIV> </DIV>
<DIV>Rex Lesher</DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV style="FONT: 10pt arial"><B>From:</B> <A
title=mailto:joddino@socal.rr.com
href="mailto:joddino@socal.rr.com">J.Oddino</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=mailto:chad@f3acanada.org
href="mailto:chad@f3acanada.org">chad@f3acanada.org</A> ; <A
title=mailto:nsrca-discussion@lists.nsrca.org
href="mailto:nsrca-discussion@lists.nsrca.org">NSRCA Mailing List</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, March 27, 2006 11:16
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [NSRCA-discussion] Reducing
the odds...</DIV>
<DIV><BR></DIV>Hi Chad,<BR><BR>I'm about to launch my first electric pattern
plane and I'd like to get your<BR>opinion on my logic for setting the cutoff
voltage. First of all I'd prefer<BR>that I'd never let any cell get
below 3.3 volts per cell. However, I'd also<BR>prefer that the motor
never stopped. My plan is to get to know the battery<BR>voltage vs.
flight profile to accomplish both. I will set the cutoff<BR>voltage very
low so it will never cut the motor. I will telemeter the<BR>voltage and
current and keep track of the mAh consumed. If I see the<BR>voltage
getting too low (<33V)under max load or use more than 80% of
the<BR>capacity I will land. If I can't get through the pattern I'll
probably need<BR>to go to a smaller prop. Once I am confident that the
profile is consistent<BR>I can remove the TM system. What do you
think?<BR><BR>Jim O<BR><BR>----- Original Message ----- <BR>From: "Chad
Northeast" <<A title=mailto:chad@f3acanada.org
href="mailto:chad@f3acanada.org">chad@f3acanada.org</A>><BR>To: "NSRCA
Mailing List" <<A title=mailto:nsrca-discussion@lists.nsrca.org
href="mailto:nsrca-discussion@lists.nsrca.org">nsrca-discussion@lists.nsrca.org</A>><BR>Sent:
Sunday, March 26, 2006 10:45 AM<BR>Subject: Re: [NSRCA-discussion] Reducing
the odds...<BR><BR><BR>> Hi Eric,<BR>><BR>> Regardless of cutoff, its
the resting voltage that is of paramount<BR>> importance for good pack
life. A 1C discharge with a 3V/cell cutoff<BR>> will leave you with a
very low resting voltage, as compared to a 15C<BR>> discharge with the same
cutoff. Recently there has been a number of<BR>> discussions about
increasing safe cutoff values as the C rates go up<BR>> since most of the
current packs hold voltage so well up until then end<BR>> when they simply
dump everything they have....so 3 v/cell now equals to<BR>> a much deeper
discharge than in the past.<BR>><BR>> Then there is the problem that the
ESC is only seeing average pack<BR>> voltage and not cell voltage...so its
entirely possible while under<BR>> discharge to have a pair of cells at
3.2v (6.4 total) and the third at<BR>> 9-6.4....or 2.6V, and now your ESC
will cut properly...but that one cell<BR>> is being
damaged.<BR>><BR>> If you run a bit higher cutoff (3.1-3.2) and fly so
that your open<BR>> circuit resting voltage is 3.75-3.8 you will have very
happy batteries.<BR>><BR>> I agree...there is not enough of this
information available without a<BR>> lot of online reading. There is
a lot of this on RC Groups...although<BR>> it can take a significant amount
of time to wade through the BS and<BR>> gather what is
useful.<BR>><BR>> Chad<BR>><BR>> Grow Pattern
wrote:<BR>><BR>> >Chad,<BR>>
> The speed
controller cuts out at 9V. It actually drops to about<BR>> >8.3V under
load and then settles back to 9.0V after the motor cuts.<BR>> ><BR>>
>You know it's not so much that I am reporting what I personally do
as<BR>much<BR>> >more like I am stating what the system does.<BR>>
><BR>> >The voltage cut-off end-user value options on the speed
controller are<BR>> >selectable but still have fixed values. A
three-cell pack has to use the<BR>> >9.0V option. I used my in-line
meter to monitor and measure these<BR>results.<BR>> ><BR>> >Once
again we are back to the instructions verses acquired knowledge!<BR>>
><BR>> >Regards,<BR>> ><BR>> >Eric.<BR>> ><BR>>
><BR>> >----- Original Message ----- <BR>> >From: "Chad
Northeast" <<A title=mailto:chad@f3acanada.org
href="mailto:chad@f3acanada.org">chad@f3acanada.org</A>><BR>> >To:
"NSRCA Mailing List" <<A title=mailto:nsrca-discussion@lists.nsrca.org
href="mailto:nsrca-discussion@lists.nsrca.org">nsrca-discussion@lists.nsrca.org</A>><BR>>
>Sent: Sunday, March 26, 2006 10:30 AM<BR>> >Subject: Re:
[NSRCA-discussion] Reducing the odds...<BR>> ><BR>> ><BR>>
><BR>> ><BR>> >>>I now believe that I had a bad cell on
the one that blew-up.<BR>> >>><BR>> >>><BR>>
>>If you were discharging to 3 v/cell as I read it from your data then
its<BR>> >>not surprising that you would have bad cells....a 3v/cell
resting would<BR>> >>indicate that you are discharging much below
that under load.<BR>> >><BR>> >>shoot for 3.7-3.8 v/cell
resting (5-10 minutes) after the flight and<BR>> >>your batteries
will be much happier, and stay in balance all by<BR>> >>themselves
for the most part.<BR>> >><BR>> >>Chad<BR>>
>><BR>> >><BR>> >>Grow Pattern wrote:<BR>>
>><BR>> >><BR>> >><BR>> >>>First of all
thanks for all of the suggestions and advice from the list<BR>>
>>>surrounding the charging of my Lipo's.<BR>>
>>><BR>> >>><BR>> >>><BR>> >>>I
have been messing with the big Lipo's since before Jason flew
his<BR>most<BR>> >>>notable entry at the world's four years ago.
This was my first<BR>> >>>catastrophic<BR>> >>>failure
of a battery pack. I have spent around $7000 on electrics in<BR>that<BR>>
>>>period of time and have closely monitored their technical
development.<BR>> >>><BR>> >>><BR>>
>>><BR>> >>>Right now I am working on sport type or sport
level electrics. Not the<BR>> >>>foamy<BR>> >>>type or
super light type of models, but the alternatives to 40 sized<BR>glow<BR>>
>>>motor powered models.<BR>> >>><BR>>
>>><BR>> >>><BR>> >>>I particularly like the
HIMAX offerings where they sell a motor, a<BR>motor<BR>> >>>mount,
a matching speed controller and a prop all in one box. This<BR>saves a<BR>>
>>>lot of guessing and previous trial and error on the part of the
buyer.<BR>You<BR>> >>>are left with the choice of what battery
pack and what plane to put it<BR>in.<BR>> >>><BR>>
>>><BR>> >>><BR>> >>>Which brings us back to
the exploding Thunderpower 4400 pack. I had<BR>been<BR>> >>>using
my Astroflight 109 chargers with great success. I have 4 of them.<BR>>
>>>This<BR>> >>>was before the little add-on balancers
were available. They charged a<BR>> >>>bunch<BR>>
>>>of different packs up to and including the big 4S3P packs with
no<BR>problems<BR>> >>>etc. I am familiar with their warning etc.
In particular, it states<BR>that<BR>> >>>it<BR>> >>>is
not recommenced to charge a fully charged pack, (note:
not<BR>forbidden).<BR>> >>>It<BR>> >>>further states
that the charger will shut down the charge after about 4<BR>>
>>>minutes if you actually try and do this.<BR>>
>>><BR>> >>><BR>> >>><BR>> >>>Now
we get to the 3S pack in question. I was not satisfied with the<BR>>
>>>knowledge of what happened and the comfort of how to prevent
it<BR>happening<BR>> >>>again. I did not have another pack, or at
least I was not going to risk<BR>an<BR>> >>>old friend's second
and last pack. I did a couple of things.<BR>> >>><BR>>
>>><BR>> >>><BR>> >>>I measured the each cell
of my 3600 mAh Tanic's using the voltage taps<BR>> >>>that<BR>>
>>>are part of the assembled pack.<BR>> >>><BR>>
>>><BR>> >>><BR>> >>>CELL
UP
CELL DOWN<BR>> >>><BR>>
>>>I
4.18
3.01<BR>> >>><BR>>
>>>II
4.18
3.00<BR>> >>><BR>>
>>>III
4.19
3.01<BR>> >>><BR>> >>><BR>> >>><BR>>
>>>Charging the pack when at 9.2V gave-<BR>> >>><BR>>
>>><BR>> >>><BR>> >>>CELL
UP<BR>> >>><BR>>
>>>I
4.18<BR>> >>><BR>>
>>>II
4.19<BR>> >>><BR>>
>>>III 4.18<BR>>
>>><BR>> >>><BR>> >>><BR>>
>>>Charging the pack when fully charged caused the charged to read it
as 3<BR>> >>>cells. It went through the 3 minute determination
pause. Charged for<BR>> >>>about<BR>> >>>a
minute and said "I'm done!" did this with two different 3600
mAh<BR>packs.<BR>> >>>The charger did what it said it would
do.<BR>> >>><BR>> >>><BR>> >>><BR>>
>>>Then just as an FYI, I flew the model with both packs wired
in<BR>parallel.<BR>> >>>One<BR>> >>>pack was giving me
5 minutes of flight at full throttle. I needed more<BR>>
>>>air-time on the sport plane. (World models Sky Raider). I now had
10<BR>> >>>minutes<BR>> >>>plus and the flight did not
run out of steam.<BR>> >>><BR>> >>><BR>>
>>><BR>> >>>The two packs were fully charged and the
plane flown for about seven<BR>> >>>minutes.<BR>>
>>><BR>> >>><BR>> >>><BR>>
>>>This created a 3S2P pack. The readings were very
encouraging.<BR>> >>><BR>> >>><BR>>
>>><BR>> >>>PACK-A<BR>> >>><BR>>
>>>CELL
UP
CELL PARTIALLY DOWN<BR>> >>><BR>>
>>>I
4.18
3.68<BR>> >>><BR>>
>>>II
4.18
3.68<BR>> >>><BR>>
>>>III
4.17
3.67<BR>> >>><BR>> >>><BR>> >>><BR>>
>>>PACK-B<BR>> >>><BR>> >>>CELL
UP
CELL PARTIALLY DOWN<BR>> >>><BR>>
>>>I
4.18
3.68<BR>> >>><BR>>
>>>II
4.19
3.68<BR>> >>><BR>>
>>>III
4.18
3.67<BR>> >>><BR>> >>><BR>> >>><BR>>
>>>The cells were discharging and charging nice and equally.<BR>>
>>><BR>> >>><BR>> >>><BR>> >>>My
charging practices have been upgraded to.<BR>> >>><BR>>
>>>1. Test voltage of each cell before each charge.<BR>>
>>><BR>> >>>2. Monitor the charge initiation.<BR>>
>>><BR>> >>>3. Place pack on 1/2" metal plate on table
outside of van. (Deep Cycle<BR>> >>>marine 12V is in back of
van).<BR>> >>><BR>> >>>4. Check reading
periodically.<BR>> >>><BR>> >>>5. Test voltage of each
cell after each charge.<BR>> >>><BR>> >>><BR>>
>>><BR>> >>>I now believe that I had a bad cell on the
one that blew-up. I also<BR>would<BR>> >>>not charge the TP pack
without the after-market device. In fact I now<BR>do<BR>>
>>>anything to reduce the odds of another accident.<BR>>
>>><BR>> >>><BR>> >>><BR>>
>>>Just looking at the display on the 109 charger tells you a lot.
The<BR>number<BR>> >>>cells, the voltage during initialization and
during charge, must be<BR>> >>>correct,<BR>> >>>or at
least in range. Putting the pack in a fire safe place is<BR>paramount.<BR>>
>>><BR>> >>><BR>> >>><BR>>
>>>Regards,<BR>> >>><BR>> >>><BR>>
>>><BR>> >>>Eric.<BR>> >>><BR>>
>>><BR>> >>><BR>> >>><BR>>
>>><BR>> >>><BR>> >>><BR>>
>>><BR>> >>><BR>>
>>>_______________________________________________<BR>>
>>>NSRCA-discussion mailing list<BR>>
>>>NSRCA-discussion@lists.nsrca.org<BR>>
>>>http://lists.nsrca.org/mailman/listinfo/nsrca-discussion<BR>>
>>><BR>> >>><BR>> >>><BR>>
>>><BR>> >>><BR>>
>>_______________________________________________<BR>>
>>NSRCA-discussion mailing list<BR>>
>>NSRCA-discussion@lists.nsrca.org<BR>>
>>http://lists.nsrca.org/mailman/listinfo/nsrca-discussion<BR>>
>><BR>> >><BR>> >><BR>> ><BR>>
>_______________________________________________<BR>>
>NSRCA-discussion mailing list<BR>>
>NSRCA-discussion@lists.nsrca.org<BR>>
>http://lists.nsrca.org/mailman/listinfo/nsrca-discussion<BR>>
><BR>> ><BR>> ><BR>>
_______________________________________________<BR>> NSRCA-discussion
mailing list<BR>> <A title=mailto:NSRCA-discussion@lists.nsrca.org
href="mailto:NSRCA-discussion@lists.nsrca.org">NSRCA-discussion@lists.nsrca.org</A><BR>>
<A title=http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
href="http://lists.nsrca.org/mailman/listinfo/nsrca-discussion">http://lists.nsrca.org/mailman/listinfo/nsrca-discussion</A><BR>><BR>><BR>>
-- <BR>> No virus found in this incoming message.<BR>> Checked by AVG
Free Edition.<BR>> Version: 7.1.385 / Virus Database: 268.3.2/293 - Release
Date:
3/26/2006<BR>><BR><BR>_______________________________________________<BR>NSRCA-discussion
mailing list<BR><A title=mailto:NSRCA-discussion@lists.nsrca.org
href="mailto:NSRCA-discussion@lists.nsrca.org">NSRCA-discussion@lists.nsrca.org</A><BR><A
title=http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
href="http://lists.nsrca.org/mailman/listinfo/nsrca-discussion">http://lists.nsrca.org/mailman/listinfo/nsrca-discussion</A><BR></BLOCKQUOTE></DIV></BODY></HTML>