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Why such a big variation in watts on my Integral?

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Why such a big variation in watts on my Integral?

Old 11-19-2009, 05:02 PM
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2Sunny
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Default Why such a big variation in watts on my Integral?

So being the geeky guy that I am, I log all my practice flights. Today I noticed an enormous difference in power usage between runs. The plane is an Integral with a 13XL, 20.5x14 APCe, and Jeti 99 esc. The first graph is 8 minutes on a set of Rhino 4900s. The second graph is 8 minutes on a set of True RC 15C 5000s. What's intriguing me is the variation in average watts. On the one hand I'm running 800 watts on average and then less than 600 watts average for the last flight. I flew the sessions identically. 5 minutes 30 seconds of Intermediate Sequence followed by 2 mins 30 secs of outside loop practice.


Could the variation be due to battery differences, or do I simply need to learn to be more consistent on the throttle, or is there another factor I've not yet thought about?

Anyways, nothing too Earth shattering . . . just curious as usual
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Old 11-19-2009, 05:21 PM
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Default RE: Why such a big variation in watts on my Integral?

Next session, repeat the experiment with the batteries used in reverse order (True first, Rhinos second). That will tell us if you are inconsistent or the batteries are different.
Old 11-19-2009, 05:22 PM
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Default RE: Why such a big variation in watts on my Integral?

My guess is the TrueRC 15C batteries are not holding voltage as well as the Rhinos. This will really show up in mah used if you are approaching full throttle often during the flight. The Rhinos will probably hold the voltage better and when you throttle up, you will generate more watts for the same throttle setting.

Woodie
Old 11-19-2009, 05:34 PM
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Default RE: Why such a big variation in watts on my Integral?

I agree with Woodie. The graphs show the Rhinos with higher average voltage throughout the flight - that coincides with the higher average watts also. The Rhinos have a more consistent top peak of 2200 watts and a higher voltage during the peaks.

As an aside, I also bet the packs were cool or cold when you flew them as the Rhino's voltage should not fall that far under load unless the packs were cold. (Cold = 80 +F or below).
Old 11-19-2009, 07:19 PM
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Default RE: Why such a big variation in watts on my Integral?

Ha HAH!! What a master you are! You got my lie even before I knew I was lying [sm=omg_smile.gif]


The first graph is a TP Pro Lite V2 5300 pack. Here's the Rhino graph and they DO hold their voltage much better . . .

Ahh master, I can only hope to gain one tenth your wisdom someday




Question: Is the prop spinning slower on average with the True RC packs? Can I check the RPM without having to buy one of those silly photometric or magnet gizmos?



And, I agree it will be more interesting (atleast for me ) after I get a second and third set of data on the same setup and sequence.



Ultimately I'm just trying to make myself more consistent and maximize my practice times by being efficient. Obviously if I can fly the sequence with a little less power on the good batteries then maybe I can squeeze out an extra minute of time.



JP
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Old 11-19-2009, 08:17 PM
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Default RE: Why such a big variation in watts on my Integral?

Also, if the last graph is the Rhino 4900 and you actually used 4200 mah (your charger will tell you for sure), then don't expect the batteries to last too long. You are up in the 85-86% mah used zone. As a general rule, try not to use more than 80% of your available capacity. I am pretty religious about this and have had pretty good battery life from TP and Hyperion batteries. I just got a set of Rhino 4900s so don't know what to expect from them yet.

Woodie
Old 11-20-2009, 11:24 AM
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Default RE: Why such a big variation in watts on my Integral?

Joe,

You can use an optical tach on the ground.....with 10S 2M pattern applications, the RPM in the air does not change very much - at most 200 RPM for a typical pattern flight. You might see a bigger change if you went full throttle in an extended dive (not recommended).

Regards,

Dave
Old 12-13-2009, 02:29 PM
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Default RE: Why such a big variation in watts on my Integral?



I have nowhere found any official data about aging of LiPo packs. My experience so far is 5% loss in capacity even for a pack that has been sitting on a shelf for 12 months.



The 80% rule is something we should really stick to, for many different reasons, but the most important one is coz we avoid discharging a cell below 2,7V in flight. Cell logger is a mighty tool, I suggest everyone should have one. Thats the only way of saving our LiPos from discharging too much in flight.



Also if you stick to 80% rule, capacity loss is below 5% after 3000 cycles! 



One more thing I have discovered is about the nomenclature of LiPo capacity. Well, Kokam gives you nominal capacity for a discharge of 0,5C which actually is 90% of the nominal capacity under discharge of 30C.What I have fund is that for Rhino and Flightmax nominal capacity is for the C rating of the battery. So you should get 4900mA from a 20C Rhino pack if you discharge it with 20C! I have never owned Polyquest, TP, FP or any other packs but I am very pleased with my Rhinos and will never again buy Kokam!!!

Old 12-14-2009, 04:04 PM
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Default RE: Why such a big variation in watts on my Integral?



What E logger is not telling you is the individual Voltage/cell.



First time I plugged a Cell logger into my plane I was shocked how differently each cell behaves under load. As pack is discharging the differences become more obvious.






What you see here is Flightmax 2650 4S 30C. The max load was 53A, so 20C. It seems that anything below 3V/cell is very unhealthy for LiPo. Here one of the cells was at 3.15V and the other at 3.42V under load. 30 more seconds of flying and the cell would have been permanently damaged.



Very, very useful tool!




Old 12-15-2009, 04:11 AM
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Default RE: Why such a big variation in watts on my Integral?

Velco,

Interesting fixture, and highly relevant info that will contribute to understand the individual cell condition.

This Cell-logger is only connected to the balanceport , right ?

I would like to try this logger on my 10s setup ( 2x5s).
Is it an idea to have two logger`s for each 5s ? ( getting complete data from the same flight ).

Thanks in advance,
Kjell Olav

Old 12-15-2009, 04:30 PM
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Default RE: Why such a big variation in watts on my Integral?



Yes it only connects to a balancer port. Also the software in the logger can be updated via USB which is very good. Internal memory capacity is good enough for 17 hours of logging if a log is taken each second. The logging interval can also be selected from 0,5s to 2s.



Ideally for 10S setup you would need 2 of them.



From my point of view an indispensable tool for monitoring health and performance of LiPo packs.

Old 12-16-2009, 06:33 AM
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Default RE: Why such a big variation in watts on my Integral?

Great,

2 more item`s will be added to my E- item arsenal

Thanks,
Kjell Olav

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