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View Poll Results: Which pack is better?
Pack A 2 20.00%
Pack B 6 60.00%
I don't know 2 20.00%
Voters: 10. You may not vote on this poll

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Old Sep 07, 2014, 07:42 PM
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Which of these lipolys is better?

Which lipo is better? Pack A or Pack B? Pack A is the black line and Pack B is the red line. Both packs charged at the same charge rate on the same charger to the same voltage. Discharge for both packs performed at 10 amps.

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Old Sep 07, 2014, 07:59 PM
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Assuming the pack temps/C rating are the same I vote for Pack B

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Old Sep 07, 2014, 07:59 PM
Battery Puffer
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Why do I feel like this is a trick question

Mark
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Old Sep 07, 2014, 08:02 PM
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Originally Posted by MarkF View Post
Why do I feel like this is a trick question

Mark
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Old Sep 07, 2014, 08:12 PM
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neither they are both the same.
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Old Sep 08, 2014, 03:28 AM
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I generally prefer a graph with more area under it so I'll go for Pack B .

Steve
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Old Sep 08, 2014, 04:42 AM
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Pack A's voltage initially drops rapidly as it is discharged, and stays below "B". To me this indicates that "B" is the better battery. Another indication would be the amount of current needed to bring the cell voltages down to 3.2-3.3 V. For comparison in this type of test, I'd likely use say an initial at rest cell voltage less than fully charged. Perhaps 4.0v for simplicity.

Another rule of thumb to size a lipo for flight power.
5 minutes =~ 29A (80% of capacity ) (2200mah lipo)
Either A or B might be capable of providing the needed power.
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Old Sep 08, 2014, 11:03 AM
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Are they the same battery discharged at different temperatures?

Mark
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Old Sep 08, 2014, 12:33 PM
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I was thinking the same thing. Same pack, just discharged at a different temperature.
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Old Sep 09, 2014, 06:17 AM
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Bigger is better
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Old Sep 10, 2014, 07:37 PM
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Ok gents, time to let the cat out of the bag...

Those who answered "I don't know" got it right, as did several commenters.

'Pack A' and 'Pack B' are indeed successive discharges of the same pack. The pack was charged, allowed to rest in my test room for 1 hour, and was then discharged at 10A. This discharge is represented by the black line (Pack A). The same pack was then allowed to rest for another hour, charged again to the same termination voltage, and this time was immediately discharged without being allowed to return to room temperature. This discharge is represented by the red line (Pack B).

My purpose for this exercise is to show what many of us already know - lipolys perform better when they're warmer. This is also a clear demonstration of why it's extremely important to control starting voltage and temperature when performing any kind of comparative testing. If starting voltage and temperature are not known and stringently controlled prior to initiation of the test, the results will most assuredly vary and are not to be trusted.

Cheers,
Mark
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Old Sep 10, 2014, 08:03 PM
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The red pack costs 2X as much to buy ?










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Old Sep 11, 2014, 06:40 AM
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Quote:
Originally Posted by mrforsyth View Post
Ok gents, time to let the cat out of the bag...

Those who answered "I don't know" got it right, as did several commenters.

'Pack A' and 'Pack B' are indeed successive discharges of the same pack. The pack was charged, allowed to rest in my test room for 1 hour, and was then discharged at 10A. This discharge is represented by the black line (Pack A). The same pack was then allowed to rest for another hour, charged again to the same termination voltage, and this time was immediately discharged without being allowed to return to room temperature. This discharge is represented by the red line (Pack B).

My purpose for this exercise is to show what many of us already know - lipolys perform better when they're warmer. This is also a clear demonstration of why it's extremely important to control starting voltage and temperature when performing any kind of comparative testing. If starting voltage and temperature are not known and stringently controlled prior to initiation of the test, the results will most assuredly vary and are not to be trusted.

Cheers,
Mark
Awesome info Mark.

Reminds me of the old days to charge the NiMH KAN 1100mAh packs, just ahead of flying. That moment they had best performance.

Lipo and temperature.......
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Old Sep 14, 2014, 04:35 PM
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Thanks for posting. I usually use 1 pack per model on a given day. Charging at 2-3C immediately after landing then flying once charged.

I only charge to 95%. Typically 4.15v. Does this help pack life?
The packs I use:
http://www.rcgroups.com/forums/showp...7&postcount=88
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Old Sep 14, 2014, 07:11 PM
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Originally Posted by like2fly! View Post
I only charge to 95%. Typically 4.15v. Does this help pack life?
There's a good amount of data that lower voltage stress = greater useful cycles. Some states that .1V/cell lower termination voltage = 2X useful cycles.

I also charge to ~4.15 volts / cell prior to flying and most of my batteries are quite happy. I have some that are 5 years old this month with well over 300 cycles and have nearly identical measurable performance as when new.
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