<div dir="ltr"><div>Hi Mike,</div><div><br></div><div>Yes you can monitor IR under discharge conditions. First I'll tell you how, then I'll offer an opinion on why it's probably not worth the effort. You calculate IR of a cell as cell voltage divided by current. So put a cell meter on the battery that displays voltage of each cell and do a ground run up with your watt meter. Record the cell voltages and the current and calculate the IR's. IR's under 20 or 30C discharge will likely be quite different than under 1C charge (what your charger tells you) and the IR's will change as the battery heats up and discharges. So I'm not sure what all this will tell you other than which cells are bad, and you don't need IR to tell you that. Bad cell(s) will sag in voltage (which will make them look like low IR even though this is not a good thing). </div><div><br></div><div>The only use for this that I can think of is if you plan on trying to replace bad cells in the pack. That's doable but generally not worth the trouble. I've done that once, on a new pack where I screwed up and discharged 2 cells in a 5 cell pack (left a cell meter plugged in for 2 weeks). I wouldn't go to the trouble for a used pack since most likely the next weakest cell will soon need replacing and you'll just end up chasing your tail replacing cells. Better to just get a new pack.</div><div><br></div><div>Ed</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Nov 10, 2014 at 7:08 PM, Michael Cohen via NSRCA-discussion <span dir="ltr"><<a href="mailto:nsrca-discussion@lists.nsrca.org" target="_blank">nsrca-discussion@lists.nsrca.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><div dir="ltr">Ooops, I actual meant to send this e-mail to the group!<div><br></div><div>Mike C<br><br><div><hr>From: <a href="mailto:precisionaero@hotmail.com" target="_blank">precisionaero@hotmail.com</a><br>To: <a href="mailto:vincebrc@gmail.com" target="_blank">vincebrc@gmail.com</a><br>Subject: RE: [NSRCA-discussion] Resistance and retirement<br>Date: Mon, 10 Nov 2014 18:07:30 -0700<br><br>
<div dir="ltr">The issue I am having is with some packs I use for an EDF. Under the "load" of takeoff, two of the three packs I use noticeably sag. I took off after the sag the first time and was able to make it around for a landing, but I don't think I took a breath the whole time. I topped off the packs and ran them on the ground and could hear the sag then too. I did not hook up my watt meter in line because the watt meter has Deans connectors and the EDF has 5.5mm bullets. I did cycle both packs on the chargers and they had about 3 to 4 mOhm resistance on 5 of the 6 cells with one pack having a 6 mOhm resistance and the other 12.5 mOhm resistance on an individual cell. I guess I am surprised the higher resistance on one particular cell could cause a problem, but I know the EDF systems hit the batteries really hard. Any thoughts on why I am seeing an issue? Is it related to the higher resistance? Is there some device out there that tests individual cells under a discharge load?<div><br></div><div>Mike C <br><br><div><hr>Date: Mon, 10 Nov 2014 11:02:18 -0600<br>To: <a href="mailto:chuenkan@comcast.net" target="_blank">chuenkan@comcast.net</a>; <a href="mailto:nsrca-discussion@lists.nsrca.org" target="_blank">nsrca-discussion@lists.nsrca.org</a><span class=""><br>Subject: Re: [NSRCA-discussion] Resistance and retirement<br></span>From: <a href="mailto:nsrca-discussion@lists.nsrca.org" target="_blank">nsrca-discussion@lists.nsrca.org</a><div><div class="h5"><br><br><div dir="ltr">I use TP. The IR is usually around 2-3 when new. I usually use them for practice and contest until around IR gets around 5. Over 5 I start to feel the power loss and I don't use those anymore. I don't like to take the smoke risk. In general, I get around 80-100 cycles. <br></div><div><br clear="all"><div><div>Vicente "Vince" Bortone</div></div>
<br><div>On Mon, Nov 10, 2014 at 9:18 AM, Phil S. via NSRCA-discussion <span dir="ltr"><<a href="mailto:nsrca-discussion@lists.nsrca.org" target="_blank">nsrca-discussion@lists.nsrca.org</a>></span> wrote:<br><blockquote style="border-left:1px #ccc solid;padding-left:1ex"><u></u>
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<font face="Arial">Yes, Dan, these things work on the Smooke Principle
-- if you let the white smoke out, they quit working...</font><br>
<pre>Phil Spelt, KCRC Emeritus, Secretary
AMA 1294 Scientific Leader Member
SPA L-18, Board Member
(865)435-1476v, (865)604-0541c</pre><div><div>
<br>
On 11/9/2014 5:47 PM, Dan Curtis via NSRCA-discussion wrote:
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<div style="color:rgb(0,0,0);background-color:rgb(255,255,255);font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px">
<div><span>Ah, flag, that is where I was making my mistake. I
thought it was white smoke.</span></div>
<div style="color:rgb(0,0,0);font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px;font-style:normal;background-color:transparent"><span><br>
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<div style="color:rgb(0,0,0);font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px;font-style:normal;background-color:transparent"><span>Dan</span></div>
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<div dir="ltr"> <font face="Arial"> On Sunday, November 9,
2014 4:42 PM, Ed White via NSRCA-discussion
<a href="mailto:nsrca-discussion@lists.nsrca.org" target="_blank"><nsrca-discussion@lists.nsrca.org></a> wrote:<br>
</font> </div>
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<div dir="ltr">I don't go by IR differences. I eventually reach a
point that in a practice flight I pull up for the last maneuver in the
sequence and the battery puts up a little white flag and says, "not
gonna happen". Then I retire the pack.<br clear="none">
<br clear="none">
Ed<br clear="none">
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<div>On Sat, Nov 8, 2014 at 1:56 PM,
Michael Cohen via NSRCA-discussion <span dir="ltr"><<a href="mailto:nsrca-discussion@lists.nsrca.org" rel="nofollow" shape="rect" target="_blank">nsrca-discussion@lists.nsrca.org</a>></span>
wrote:<br clear="none">
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<div dir="ltr">Is there any rule of thumb for how much difference
between individual cell resistances is OK before a back should be
retired?
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<div>Regards,</div>
<div>Mike C</div>
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