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Old Feb 15, 2006, 02:37 AM
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Quote:
Originally Posted by Mister UHU
But why the hell are your graphs marked in FAHRENHEIT ??

Why aren't you using S.I. units ?????

This is the 21st century you know.
I know, but most of RCG still use the Imperial Units.

(all the data is in Celsius; if you find it easier drop me a PM)

Rod
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Old Feb 15, 2006, 05:02 AM
Giz
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Another view of the whole cost/weight/power/temperature thing

Rod,

The graph of the Kokam 2000 at the higher rate to match the 2100s allows an interesting comparison because generally, what I want is a pack to deliver a certain power level and hence current draw with good voltage stability. I don't want a pack that will run at xC because different sizes will deliver different powers even if they meet their claimed ratings.

Anyway, it can be seen that the Kokam 2000 and ProLite V2 packs give about 430 watts +/- for the duration (PQ2100 is similar for two cells). The Kokam gives about 1750 mah and reaches a temperature of about 128 deg F. The ProLite V2s give about 2100 mah and reach perhaps 143 deg F. But at the 1750 mah point, the temperature of the ProLite V2s is very similar to the Kokams at 130 deg F.

So, if you used these two packs in a certain aeroplane, propped for a certain power to match the chosen profile and flew for a set amount of time (which I do so that I don't rely on the LVC), the packs would perform about the same and reach about the same temperature. I would probably choose between them based on weight, cost and longevity (if that were known).

Previous threads making comparisons of similar packs have possibly exaggerated the perceived performance differences between them. Maybe, for real applications, the differences are far smaller than we think?

Of course, testing the packs at their claimed rating extremes is a very valuable service to the community so that we can all avoid using our packs in ways that will damage them. But this technique of testing the performance of packs for a profile at a particular power level gives a good indication of what might happen when they are used in a practical situation. It helps us to get a good feel for choices such as "do I use a 20C 1800mah or 16C 2100mah pack in my aeroplane".
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Old Feb 15, 2006, 05:45 AM
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Quote:
Originally Posted by Giz
Of course, testing the packs at their claimed rating extremes is a very valuable service to the community so that we can all avoid using our packs in ways that will damage them. But this technique of testing the performance of packs for a profile at a particular power level gives a good indication of what might happen when they are used in a practical situation. It helps us to get a good feel for choices such as "do I use a 20C 1800mah or 16C 2100mah pack in my aeroplane".
Giz,
It is becoming clear (to me) that there are three additional critical pieces of information that we need in order to make informed selections for our applications, as a single number does mean very little:
  • Static discharge curves up to rated spec.
  • Discharge performance curves under 'realistic' profiles
  • Cycle life at both rated and 'realistic' discharge levels
At present very few vendors supply this data, and none seem to apply the same criteria / test conditions. I hope that discussing what these profiles mean here, and trying other profiles, may lead to some forms of acceptable profiles that others can use - who knows some of the vendors might find it useful themselves and start to implement.

The profile I have applied so far is one I synthesised from in-flight logs from one of my models, I'm working with Ashley at TrexTuning to do a similar one for the Trex based on in-flight logs, but what about EDF, park-fliers, pylon and F3A? I'm making an open call here to suggest some profiles (from logs) that I am willing, and able, to implement for some of these packs.

When I look at the profiled discharges I find that there is a heck of a lot of information that can be gleaned from them:
  • How 'constant' is the power delivery? (controllability)
  • Do the cells maintain balance? (life issues)
  • How warm is the pack likely to get? (life issues)
  • Is it possible to push the 'burst' harder than shown? (limits)

I'm very interested to see where this leads us.

Regards,

Rod
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Old Feb 15, 2006, 07:35 AM
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Hi Giz,
Thanks for sharing your interpretation.
This is exactly what I have been trying to explain for the last few months.
The V2 tested here is the same as ProLite Rod tested in his thread "let the testing begin"(you can verify with the supplier of the cell)

Regards,
Charlie

Quote:
Originally Posted by Giz
Rod,

The graph of the Kokam 2000 at the higher rate to match the 2100s allows an interesting comparison because generally, what I want is a pack to deliver a certain power level and hence current draw with good voltage stability. I don't want a pack that will run at xC because different sizes will deliver different powers even if they meet their claimed ratings.

Anyway, it can be seen that the Kokam 2000 and ProLite V2 packs give about 430 watts +/- for the duration (PQ2100 is similar for two cells). The Kokam gives about 1750 mah and reaches a temperature of about 128 deg F. The ProLite V2s give about 2100 mah and reach perhaps 143 deg F. But at the 1750 mah point, the temperature of the ProLite V2s is very similar to the Kokams at 130 deg F.

So, if you used these two packs in a certain aeroplane, propped for a certain power to match the chosen profile and flew for a set amount of time (which I do so that I don't rely on the LVC), the packs would perform about the same and reach about the same temperature. I would probably choose between them based on weight, cost and longevity (if that were known).

Previous threads making comparisons of similar packs have possibly exaggerated the perceived performance differences between them. Maybe, for real applications, the differences are far smaller than we think?

Of course, testing the packs at their claimed rating extremes is a very valuable service to the community so that we can all avoid using our packs in ways that will damage them. But this technique of testing the performance of packs for a profile at a particular power level gives a good indication of what might happen when they are used in a practical situation. It helps us to get a good feel for choices such as "do I use a 20C 1800mah or 16C 2100mah pack in my aeroplane".
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Old Feb 15, 2006, 07:50 AM
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Quote:
Originally Posted by Charlie Wang
The V2 tested here is the same as ProLite rod tested in his thread "let the test begin"(you can verify with the supplier of the cell)
The supplier states:
Quote:
With over 200 life cycles, this one is 4 times longevity thanthe old PROLITE version which only has 50 life cycles
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Old Feb 15, 2006, 07:58 AM
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Rod,
People lie just to promote sales, please check with the manufacturer.
They should remove from their website any false information.

Regards,
Charlie

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Old Feb 15, 2006, 08:28 AM
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Originally Posted by RC-Tester
OK,

A couple of you are aware that I have been implementing 'variable profile' discharge testing of my own. Well now it is ready, and the calibration complete. I now have the capability to replay DPR-50 in-flight log files as a discharge profile 'on the bench', as well as setting arbitrary profiles.

For my initial two studies I selected a 2S PQ2100XP and a 2S 'Impulse Power' (Saehan ProLite V2) 950 pack. The discharge profile I chose to put on them was one that I had seen for one of my electric aerobats: 8 seconds low C discharge (~6C) followed by 2 seconds of high discharge at ~20C - all on a repeat.

The graphs of delivered power, voltage and temperature is shown for these two packs, and I invite some interesting discussion.

Rod
Hi Rod,
What was cut-off condition during pulse discharge ?
Is PQ pack PCB soldered ?
Polyflex
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Old Feb 15, 2006, 08:41 AM
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Quote:
Originally Posted by Charlie Wang
People lie just to promote sales, please check with the manufacturer.
They should remove from their website any false information.
Thankyou CW - as you have pointed out - if that information is not correct then only you and Saehan can get it corrected: please do so as it is in your power.

... Can we get back to the topic in hand and examinine profiled discharges, what it means and the relevance? Maybe you could outline your thoughts on 'burst' profile discharges?

Rod
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Old Feb 15, 2006, 08:58 AM
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Quote:
Originally Posted by polyflex
What was cut-off condition during pulse discharge ?
Is PQ pack PCB soldered ?
Polyflex
First off (to everyone here) these packs are not 'virgin' packs. They have all been subjected to static discharge studies previously, in one case (the FMA/Kokam) it had also previously been subjected to 'abuse' that I thought would kill the pack. That is why I stated at the start of this thread that I was interested in studying 'burst' profiles as very few have a definition of what they are and how they relate. I hope that we will be able to try various profiles based on real-flight logs in order that we can approach a standard test that we can use in future.

I should also make sure that people are aware that there will be some single cell 'profile' tests carried out later on some 'later generation' XP cells that Enerland have supplied to myself and RD. This will not happen though until we have tied down the required test methodology.

In order to answer the specific questions raised:
1. Cut-off condition is 3.0V per cell - 6V for a 2S pack.
2. The pack does appear to have PCB attached at (both?) ends. below is an image of the pack so you could probably confirm about your product. For reference this pack was purchased in October so that I could test before buying a 5S 3200 XP for one of my models.

HTH

Rod
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Old Feb 15, 2006, 09:30 AM
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I think a 8 to 10 sec low C discharge with 3 sec high C discharge is very good profile test.
Below is my thoughts:
For 15C cell:Low C discharge at 6C for 10 sec, burst at 21C for 3sec.
For 20C cell:Low C discharge at 8C for 10 sec, burst at 28C for 3 sec
If you think this may be too hard for some cell, try this

For 15C cell:Low C discharge at 6C for 10 sec, burst at 18C for 3sec.
For 20C cell:Low C discharge at 8C for 10 sec, burst at 24C for 3 sec

I think this is very good discussion here.

Regards,
Charlie


Quote:
Originally Posted by RC-Tester
... Can we get back to the topic in hand and examinine profiled discharges, what it means and the relevance? Maybe you could outline your thoughts on 'burst' profile discharges?

Rod
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Old Feb 15, 2006, 09:42 AM
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Rod,
Burst profiles will be as varied as airframe types and flying styles. It will be very difficult to get a concensus on a generally accepted burst profile test standard.

I, personally, have no burst applications such as yours that results in 6 minutes or less of available flight time. That being the case, I would vote for a profile that has a lower duty cycle and lower baseline current, with the same burst amplitude. This would reduce the cell temperatures, and the effect the elevated cell temperature has on the cell's ability to maintain voltage during the bursts. Also, within my style of flying, burst durations tend to be more in the 5 sec range, although this varies greatly.

Another application I'm interested in is that of the hotliner. This is one of the least complex and may be one of the most severe. Something like 20C bursts for 10 sec (mine aren't that long, but some might be) repeating every minute with no load between bursts might be appropriate. Cell temps should stay relatively cool, so the bursts later in the discharge could become challenging.

Brad
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Old Feb 15, 2006, 09:59 AM
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Quote:
Originally Posted by Brad S
Burst profiles will be as varied as airframe types and flying styles. It will be very difficult to get a concensus on a generally accepted burst profile test standard.
I agree Brad, that is why I am trying to entice anyone to drop an image, or the file, from their in-flight log into here. Hopefully then we can have a look at how flying styles, type and power train system alter key characteristics of the discharge. If I'm lucky we might four or five broad discharge profiles that meet the majority of the types, that I am also prepared to run on the bench.

Quote:
Originally Posted by Brad S
Also, within my style of flying, burst durations tend to be more in the 5 sec range, although this varies greatly.
OK - duly noted. this means similar to CW's second set of proposed but slightly longer time periods for both phases?

Quote:
Originally Posted by Brad S
Another application I'm interested in is that of the hotliner. This is one of the least complex and may be one of the most severe. Something like 20C bursts for 10 sec (mine aren't that long, but some might be) repeating every minute with no load between bursts might be appropriate. Cell temps should stay relatively cool, so the bursts later in the discharge could become challenging.
You don't have any in-flight logging for the hotliner do you? This looks an interesting one.

What about EDF? 4-5 minute flights at an average of 13-14C, bursts to 20C, base level of 12C in an 80%/20% split?

Rod
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Old Feb 15, 2006, 10:32 AM
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Rod,
You obviously put more stock in data from inflight recorders than I do. In my view, the first such plots I saw were interesting and, in some cases, enlightening, but all subsequent ones I've seen within a common airframe with similar flying style really didn't tell me anything new. The ones I've seen for airframes and flying styles similar to my own did nothing more than confirm my profile expectations, based on known typical average and maximum current values. In light of this, my hobby dollars migrated toward buying another airplane rather than an inflight logger.

Did you really generate an inflight log consisting of a uniform 8 sec at 6C / 2 sec at 20C? If so, you're a much more structured flyer than I am - my load levels tend to move all over the place, except in the hotliner application.

Brad
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Old Feb 15, 2006, 10:41 AM
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Quote:
Originally Posted by Brad S
Did you really generate an inflight log consisting of a uniform 8 sec at 6C / 2 sec at 20C? If so, you're a much more structured flyer than I am - my load levels tend to move all over the place, except in the hotliner application.
Nope - that was a more regular synthesis of the flight log; frequency filtered and mean pulse behaviour extracted. I can do the same for another log file by running it through similar FFT processing. That is why I'm asking!

Regards,

Rod
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Old Feb 15, 2006, 10:45 AM
Southern Pride
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Quote:
Originally Posted by Brad S
Rod,
You obviously put more stock in data from inflight recorders than I do. In my view, the first such plots I saw were interesting and, in some cases, enlightening, but all subsequent ones I've seen within a common airframe with similar flying style really didn't tell me anything new. The ones I've seen for airframes and flying styles similar to my own did nothing more than confirm my profile expectations, based on known typical average and maximum current values. In light of this, my hobby dollars migrated toward buying another airplane rather than an inflight logger.

Did you really generate an inflight log consisting of a uniform 8 sec at 6C / 2 sec at 20C? If so, you're a much more structured flyer than I am - my load levels tend to move all over the place, except in the hotliner application.

Brad
Interesting observations Brad and I agree. The creater of this device

http://www.bnbproducts.com/

made the comment many months ago in so many words that in his opinion it would confirm what experience flyers already knew.

Charles
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