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Old Jan 12, 2015, 09:30 PM
Wild Weasel... YGBSM
UH_60_UAS's Avatar
United States, IN, Indianapolis
Joined Mar 2013
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Temps were in warmer Ca. Why would cells vary this much
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Old Jan 13, 2015, 01:06 AM
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CelloGuy's Avatar
Australia, NSW, Sydney
Joined Apr 2013
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John, thanks again for the info. Interesting stuff.

Chuck, do you use a lipo warmer to heat them? Just wondering if they're worth buying.
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Old Jan 13, 2015, 12:08 PM
chuck
santa barbara, CA
Joined May 2009
4,422 Posts
yes i do warm them , started out just in the pocket , then the car heater on the way to fly . but after doing a bit more research of my own and in this thread i am a bit more scientific now. i have looked at the lipo warmers but they scare me a bit ........... 1 haywire chinese thermostat and it could get ugly! as of now a large bottle of hot water in a small cooler is my failsafe way. works well and cant get to hot and lasts for hrs at the field

but my comments here w/ re to uh 60's post was aimed at testing ir at a controlled temp . the posted #'s looked a bit high but w/ out knowing the temp at test it does not mean much. as far as the variance in ir goes i have seen better and worse . at this time i am in a bit of a struggle w/ buddy rc over some new batteries i bought that have some cells more than twice the ir of others. it does seem common to have up to 25% difference in some brands and it makes sense that IF the highest ir cell is still in the acceptable range the pack may be fine. i would rather have a low average ir than matched high ir.


chuck.
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Old Feb 18, 2015, 10:39 AM
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Ventura, CA
Joined Jul 2010
30 Posts
Bad Battery Test

I purchased an ESR meter several years ago and have been tracking my batteries for some time. I had hoped that the meter would tell me that a battery was going bad before it caused a crash.
I have read all 52 pages of this forum looking for some clue to tell me how to spot the warnings but didn't find anything. Post #431 was asking the same question and the responses were just questioning his test techniques. His problem is similar to mine where the pack IR readings are OK, but the battery will not support any load. I have 3 batteries that look good but won't hold charge under a 6 amp load for more than 10 seconds.
The first picture shows the IR readings for 3 batteries that won't hold a charge.
The second picture is just data from all my HP 2200 mAh batteries over time. Some of these have died but I didn't take final IR readings. The first one doesn't have a balance connector.
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Old Feb 18, 2015, 02:57 PM
chuck
santa barbara, CA
Joined May 2009
4,422 Posts
do u have data from the batteries in question when they were ok? although your #'s dont seem real bad , the change in ir from the start might tell more . i have 2200's that are good and below 5 / cell . if they jumped to your #'s they would be suspect at that point.


chuck.
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Old Feb 18, 2015, 04:40 PM
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Ventura, CA
Joined Jul 2010
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Here is the historical data I have for my NT 2200 batteries.
All readings were taken in my "man cave" (a room inside my house). Temperature variations are within 10 degrees F.
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Old Feb 18, 2015, 08:21 PM
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Ventura, CA
Joined Jul 2010
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I just noticed that the Max-Amp was computed using the minimum IR, not the max IR in my spreadsheets.
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Old Feb 18, 2015, 10:39 PM
ancora imparo
jj604's Avatar
Melbourne, Australia
Joined Jul 2005
7,313 Posts
Bill, Mark may want to chime in - he isn't far away from you!

In the meantime here are some thoughts on why you might get the results you are seeing.

1. The particular cells that are in your packs are very slow to respond and the relatively short pulse is not allowing voltage to reach the bottom of the curve. I have seen this typically on a very old pack I had which gave reasonably low IR values but very poor performance. Wayne designed the IR meter after extensive testing with various packs to have a long enough pulse to allow the voltage drop to stabilise but not overstress the internal components. This was found to work well for a wide range of packs in "good condition". When the pack is in poor condition, it may take much longer than 25mS for the voltage drop to a stable value. Then the meter is seeing only a small voltage drop by the end of the load pulse because it has seen only the first part of the decay curve and calculates a low IR accordingly. The longer pulse of an iCharger might corroborate this.

2. Measurement conditions (perhaps warm home) and usage environment (very cold outdoors) are vastly different. Not likely to be the case here.

3. The packs have lost a good amount of capacity and are simply being completely discharged sooner than labeled capacity. This could be verified by noting voltage after flight.

4. Drawing more current than recommended because the motor / prop combo are inadequate for the model. Perhaps LVC is improperly set on the ESC.

5. The main connectors are poor/corroded and there are significant losses between pack and model. Clearly, this will not show up in an ESR meter measurement as it employs Kelvin technique and is thus ignoring all power lead/connection losses.

Just some ideas. Not possible to say if any actually apply here without testing for them.

John
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Old Feb 18, 2015, 11:03 PM
chuck
santa barbara, CA
Joined May 2009
4,422 Posts
something seems amiss as the ir generally is dropping as the batteries age. at any rate the voltage under load test tells the story for these . were the batteries used w/ success after the 7-13 test? as far as predicting a failure If it had been 1 1/2 years since the last known good date , and they were mine , i would do both a ir test and a voltage under load test. fwiw.

chuck.
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Old Feb 19, 2015, 04:02 AM
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Hampshire, U.K.
Joined Jun 2008
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I would get one of those cheap battery checkers that plugs into the balance lead and cycles through the individual cell voltages. Plug it in, tether the model and run the motor up.

I had a similar problem some years ago and, after running okay for a couple of minutes, one of the cell voltages just collapsed over the space of a second or two. This was in the days before I got into measuring EIR so I can't comment on what the readings would have been leading up to this failure.

In my case, two batteries failed this way in the same model in consecutive flights. As you can imagine, I went on an extensive wild goose chase for other causes before this simple test pinned it down.
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Old Feb 19, 2015, 09:34 AM
Frankenstein recycled packs
rampman's Avatar
USA, AZ, Gilbert
Joined Jan 2006
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What Trevorh explained is good but make it easier on yourselves by using a cell checker with the low voltage buzzers. Set it to your LV and you only need to hear it, not see it.
I use this setup when discharging packs. I just work in my shop and when I hear the buzz, very LOUD buzz, I remove the load.

As for Bill.'s problem, I never use IR only when testing packs. When I have suspect packs/cells I perform IR tests and then a capacity test.

Another time I had some cells that had very good IR but would get warm when charging. These were salvaged cells from close to 100 5800mah 3S packs. I even posted my findings on here; at the time IR was determined by my PL8.
I parked these with the V written on each single cell and set them in the fridge ~40F for around 6 months. When I pulled them out each cell was way lower than 3 volts, most at/near zero volts.

Nothing is perfect in this world and sometimes we are thrown a curve ball. When I have a suspect cell I throw all testes I know at it and if still in doubt I discharge and toss.

Rick
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