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Old Oct 26, 2010, 03:46 PM
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United States, AL
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Got mine today. It's a very nice looking device. Some well used a123 cells give about 13mOhm and a TP Pro Lite V2 2600 pack is about 18mOhm per cell. Both packs were at 18c. Simply putting a pack in your pocket for a few minutes is enough to make a noticeable change in IR. Ensuring the pack is at a uniform temperature and including the temperature in your measurements is obviously very important.
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Old Oct 26, 2010, 04:01 PM
Joined Jan 2004
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Recieved mine today, thank you.
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Old Oct 26, 2010, 11:16 PM
Reduce the drama...
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USA, OR, Damascus
Joined Apr 2004
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Wayne and Phil Thank you!
Received today, A great tool for my toolbox.
First pack IR read
37.24
37.20
37.16
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Last edited by rick.benjamin; Oct 26, 2010 at 11:23 PM.
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Old Oct 27, 2010, 12:37 PM
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United States, AL
Joined Apr 2007
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So when you measure the IR of a pack the resistance of the wiring from the meter and male dean's plug is included in that measurement...

Those same a123 cells drop to 10mOhm at 24c. Seems like a big change for such a small temperature difference, I guess make double sure you keep track of temperatures too!

Those a123 cells are in 4s packs connected with the dewalt spot-welded tabs and they have maybe 10cm of 12g deans wire and a deans connector. The individual cells add up to about 41mOhm and the whole pack is about 49mOhm. I would have expected more resistance for the wiring and spot-welded tabs.

One suggestion I'd make is to use a shorter switch - it sticks out from the case much farther than the button. I'm just going to dremel mine shorter. Not a big deal and it's still well worth the money.
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Old Oct 28, 2010, 03:55 AM
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Rugby, UK
Joined Feb 2007
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Quote:
Originally Posted by rick.benjamin View Post
Wayne and Phil Thank you!
Received today, A great tool for my toolbox.
First pack IR read
37.24
37.20
37.16
Rick,

That must be a small pack (< 1000mah?), but at least it is very well matched.
Try looking at your dodgy packs (you must have some, everybody has) as an ageing pack often shows mismatch.
A flying mate had a problem with a fast jet last week (surging) and thought it was a radio problem. Checking with the meter showed two cells were about 5 milliohms and one over 35milliohms; mystery solved; an ex-lipo!

Wayne
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Old Oct 28, 2010, 10:55 AM
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Rugby, UK
Joined Feb 2007
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Quote:
Originally Posted by rick.benjamin View Post
Wayne and Phil Thank you!
Received today, A great tool for my toolbox.
First pack IR read
37.24
37.20
37.16
Rick,

Second thoughts on this; don't know why, my brain probably wasn't engaged in first reply! These are obviously cell readings, but they look very high and too close for reality. The "Cell" range is only specified for 0 - 30 milliohms, although the meter will read up to nearly 40milliohms. If you do not plug the search wire into the balance connector (so that it is monitoring one cell), then the meter will read it as over-range, in which case it will read the highest it can, which could be any value between 35 and 40 milliohms.
This suggests that the search wire was not connected or the balance leads on the pack are open circuit. Does the meter read 'Cell' Voltage before you press the 'Operate' button??
What size pack is it in mAh??

Wayne
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Old Oct 28, 2010, 11:17 AM
TJin(Guy + Tech)
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United States, NM, Socorro
Joined Jun 2008
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You say a 16A load is applies during measurement. Won't that effect different capacity packs differently and cause error?
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Old Oct 28, 2010, 11:25 AM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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FWIW (not much) I checked an old 2006 Hyperion Velocity Lite 3S 1320 12C on one of my POWERLAB 8 s. At 90F cells 37.6 / 25.9 / 25.9 and drifting.

At 80F (my normal IR check point) cells 39.8 / 27.3 / 26.2
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Last edited by everydayflyer; Oct 28, 2010 at 11:47 AM.
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Old Oct 28, 2010, 11:46 AM
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Rugby, UK
Joined Feb 2007
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Quote:
Originally Posted by tjinguy View Post
You say a 16A load is applies during measurement. Won't that effect different capacity packs differently and cause error?
No, as you are just measuring resistance. We chose 16A because it is not too high for the small 500mAh packs (32C but only for a short pulse) and yet it is getting towards a real flying current for medium size cells and not too small for even large cells. I suppose ideally it could be higher for really large cells, but IR is largely independant of current, although not completely.
The other limitation is that the poor little powerfet has to withstand over 400Watts during the pulse on a 6 cell pack!

Wayne
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Old Oct 28, 2010, 01:26 PM
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United States, AL
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I put the a123 pack in the fridge and it shot up to just over 80mOhm for the pack.
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Old Oct 28, 2010, 02:20 PM
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Rugby, UK
Joined Feb 2007
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Morgan,
Quote:
So when you measure the IR of a pack the resistance of the wiring from the meter and male dean's plug is included in that measurement...

That's correct.. It is a practical measurement as that is what the load sees in practice.


Quote:
Those same a123 cells drop to 10mOhm at 24c. Seems like a big change for such a small temperature difference, I guess make double sure you keep track of temperatures too!
10 milliohms/cell at 25deg. is about right for A123s; both Charles and I measure them at that. Your latest post (>80milliohms in fridge) demonstrates the difference in winter conditions.
Difference of 40 milliohms at, say 40A, equates to an extra 1.6V drop in a 4S pack which is about 12% drop. This will translate into about 25% fall in power.

Quote:
Those a123 cells are in 4s packs connected with the dewalt spot-welded tabs and they have maybe 10cm of 12g deans wire and a deans connector. The individual cells add up to about 41mOhm and the whole pack is about 49mOhm. I would have expected more resistance for the wiring and spot-welded tabs.
Generally you will find that the leads and a Deans type connector will add about 6 - 7 milliohms to the cell total. As you say this includes all the intercell connections.

Not sure about chopping the switch. I think it is like a std TX switch, ie it looks like a solid lever but it is probably tubular - be careful as it would be a real problem to change the switch as it is soldered into the PCB and is a press fit.

Wayne
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Old Oct 28, 2010, 02:42 PM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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4S A123 Systems LiFePO4 2300 from E Bay DeWalt 36V pack 2007 with 174 flights on it. 78F 9.5 / 8.4 / 8.9 / 7.9


Cells at 90F 8.4 / 6.8 / 7.7 / 6.6

Reading obtained with POWERLAB 8

Wayne's cold temp. performance drop sounds about right. When I was flying A123s in the winter they were stored inside in the 70s and I warmed them on the dash (defrosters) on the way to the field. They were warm after a flight and charged at 20 amps. they stayed warm and I flew only a couple of packs so they never had time to cool down.

Charles
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Last edited by everydayflyer; Oct 28, 2010 at 03:12 PM.
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Old Oct 28, 2010, 03:07 PM
Xtreme Power Systems
Lake Havasu, AZ
Joined Jun 2005
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Got our tester today. Shows our A123 cells here (we are a U.S. distributor for A123) are right at 8.3 at 75 degrees.

It also shows us that our 5000mAh 65C cells are 1.9-2.0 (new, not broken in) at 75 degrees... but, our 2200mAh 65C cells are showing as 4.9-5.1 (new, not broken in). We are going to test a few here to see how much these come down. We checked dozens of packs today and found none that were way off like what Charles receivd.
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Old Oct 28, 2010, 03:20 PM
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So. Cal.
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Looks like you got some decent numbers Jim. My personal internal resistance 'number' for high performance cells is 12000 / cell capacity, when measured after stabilization at room temp (~72F) for 1 hour minimum.. Anything around or below this number I consider to be outstanding performance.

Mark
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Old Oct 28, 2010, 09:56 PM
Xtreme Power Systems
Lake Havasu, AZ
Joined Jun 2005
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We keep our cell inventory climate controlled at 75 degrees and <10% humidity, 24hrs a day, year round. So, it will be easy to compare various cells.
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