SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Aug 02, 2005, 10:16 PM
Space Coast USA
hoppy's Avatar
Space Coast
Joined Oct 2000
21,107 Posts
Cycle Life - What affects it? Motorola Report

Found this googling - A motorola report on cell phone battery cycle life and what affects it.

This is one interesting excerpt: (DOD = Depth of Discharge)
"The relationship between DOD and cycle life is logarithmic. In other words, the number of cycles yielded by a battery goes up exponentially the lower the DOD. Research studies have shown that the typical cellular phone user depletes their battery about 25 to 30 percent before recharging. Testing has shown that at this low level of DOD a lithium-ion battery can expect between 5 and 6 times the cycle numbers of a battery discharged to the one hundred percent DOD level continuously."

Might supports higher LVC values in exchange for cycles.

http://www.motorola.com/testservices/article1.htm
hoppy is offline Find More Posts by hoppy
Reply With Quote
Sign up now
to remove ads between posts
Old Aug 02, 2005, 10:30 PM
Southern Pride
everydayflyer's Avatar
Haralson County GA. USA
Joined Oct 2004
34,833 Posts
Thanks Hoppy, very good read and once again shows the futility of trying to pack that last 5% into a LiPoly or using the last 20% unless of course ones really enjoys purchasing replacement LiPolys.
While flying glow for many years I tanked for 10 minutes and flew for 8 to help avoid lean runs and dead sticks. It is so much faster to swap out a LiPoly than to refuel and restart a glow that I have no problem doing the same with LiPoys.

Charles
everydayflyer is online now Find More Posts by everydayflyer
Reply With Quote
Old Aug 02, 2005, 10:41 PM
I don't want to "Switch Now"
pmackenzie's Avatar
Toronto (Don Mills), Canada
Joined Dec 2002
16,953 Posts
The exact numbers and test methods need to be known before drawing conclusions.
Taking what was written, 5 times the number of cycles, but this is at 25% to 30% DOD per cycle.
Total flying time over the life of the pack is therefore only improved by from 25% to 50%.
Pat MacKenzie
pmackenzie is offline Find More Posts by pmackenzie
Reply With Quote
Old Aug 02, 2005, 10:42 PM
Cogito ergo fly!
TubaTom99's Avatar
Kansas City, MO
Joined Jul 2004
266 Posts
Interesting, Hoppy. So tell me if I got this right, instead of discharging a 2000 mAh at 15 amps for 23 minutes (fairly deeply depleted - FDD) it may be best then to get a 3000 mAh, run it at 15 amps (an even more gentle discharge than with the 2000) and run it for 15 minutes? This may give me significantly more cycles? If I get 5+ times the cycles then it is well worth the extra cost of the larger pack and for me the couple ounces would not ruin the way I fly.

Interesting.

Tom

PS. I don't know if you are still keeping track of LiPo mishaps, but a person in one of my clubs burnt at least some of his basement when he put a new LiPo pack to charge and left the house.
TubaTom99 is offline Find More Posts by TubaTom99
Reply With Quote
Old Aug 02, 2005, 10:42 PM
Space Coast USA
hoppy's Avatar
Space Coast
Joined Oct 2000
21,107 Posts
only 25-50%
hoppy is offline Find More Posts by hoppy
Reply With Quote
Old Aug 02, 2005, 10:51 PM
Space Coast USA
hoppy's Avatar
Space Coast
Joined Oct 2000
21,107 Posts
Quote:
Originally Posted by TubaTom99
Interesting, Hoppy. So tell me if I got this right, instead of discharging a 2000 mAh at 15 amps for 23 minutes (fairly deeply depleted - FDD) it may be best then to get a 3000 mAh, run it at 15 amps (an even more gentle discharge than with the 2000) and run it for 15 minutes? This may give me significantly more cycles? If I get 5+ times the cycles then it is well worth the extra cost of the larger pack and for me the couple ounces would not ruin the way I fly.

Interesting.

Tom

PS. I don't know if you are still keeping track of LiPo mishaps, but a person in one of my clubs burnt at least some of his basement when he put a new LiPo pack to charge and left the house.
TT,
That's what they seem to think - different cells then we use but a 'thinking point'. I think it pertains to everything in life, "less strain, longer life". No surprise there....they just put some numbers on it that I haven't seen before.
It kinda fits my flying...70% of the C rating and 70% of the capacity.

I'm still adding to the failure list - see if you can get some more details.
hoppy is offline Find More Posts by hoppy
Reply With Quote
Old Aug 02, 2005, 10:57 PM
I don't want to "Switch Now"
pmackenzie's Avatar
Toronto (Don Mills), Canada
Joined Dec 2002
16,953 Posts
Quote:
Originally Posted by hoppy
only 25-50%
I will try to explain:
Lets say a full discharge gave you 12 minutes.
What they are saying is that if you expect say 100 12 minutes flights, you could instead get 500 3 minute flights.

Using the full capacity with three packs you could fly for 36 minutes in one session.
To get the same time the other way you would need 12 packs.
I will stick with the 3 packs. It is cheaper.

What they don't say is how an 80% DOD will effect cell life.
They do use the term "exponential" which would imply that there would be even lower gains than 25% for the 80% DOD case.

IMO there is not enough information in that link to reach any real conclusions about cycle life versus DOD.
Even the stated gains at very low DOD are not very impressive.
Pat MacKenzie
pmackenzie is offline Find More Posts by pmackenzie
Reply With Quote
Old Aug 02, 2005, 11:03 PM
Space Coast USA
hoppy's Avatar
Space Coast
Joined Oct 2000
21,107 Posts
True, I understand where you are coming from, it's just a thinking point to muse on.
hoppy is offline Find More Posts by hoppy
Reply With Quote
Old Aug 02, 2005, 11:04 PM
Cogito ergo fly!
TubaTom99's Avatar
Kansas City, MO
Joined Jul 2004
266 Posts
Quote:
Originally Posted by hoppy
TT,
That's what they seem to think - different cells then we use but a 'thinking point'. I think it pertains to everything in life, "less strain, longer life". No surprise there....they just put some numbers on it that I haven't seen before.
It kinda fits my flying...70% of the C rating and 70% of the capacity.

I'm still adding to the failure list - see if you can get some more details.
Thanks, Hoppy. I was thinking hard about going to larger capacity cells as my planes can push the 2000 mAh's (20amp max discharge, 15 constant) a bit hard, and this info pushes me even more in that direction. In fact, even with the newer higher C rated batts, I still think the larger mAh 10C packs will work more for me better than the larger rating. I mean, more mAh per pound and therefore a more gentle use. I wish my life could be as easily regulated!!

Details? As in charger, battery, charger rate, etc? I'll see what I can do.

Tom
TubaTom99 is offline Find More Posts by TubaTom99
Reply With Quote
Old Aug 02, 2005, 11:15 PM
Southern Pride
everydayflyer's Avatar
Haralson County GA. USA
Joined Oct 2004
34,833 Posts
Pat I agree that the imformation is very general and they are not testing the same class of cells or at the same discharge rates which we subject our to however I have seen a major improvement in all of my LiPolys which I do not abuse so severly. In the past I did well to get 100 cycles before losing 20% or more capacity and seeing a noticeable decrease in performance.While it is true that I only have one packs with over 300 cycles on it and most others of mine are still well below 100 cycles I can still tell they are doing better than in the past.My problem is with so many LiPolys it is difficult to fly them enough to get them past 100 cycles. I would say that a great deal of the increased life is due to improvements in the cells themself however I know somone who is still flying Gen 1 Thunder Powers with well over 200 flights on them. He never charges past 4.15 per cell and always leaves 20% capacity.

Charles
everydayflyer is online now Find More Posts by everydayflyer
Reply With Quote
Old Aug 03, 2005, 12:26 AM
Registered User
IA-Flyer's Avatar
United States
Joined Nov 2003
1,569 Posts
Great article hoppy, thanks for sharing it.
I thought this quote was interesting also.

"Generally lithium-ion cells will deliver the most cycles when charged to 4.1 volts. Cell manufacturers usually suggest charging to 4.2 volts to get the maximum capacity from the cell and still insuring 500+ cycles. Testing has shown that overcharging by 0.1 V or 0.25 volts will not result in safety issues but can reduce cycle life by up to 80 percent."

I've read before that charging to 4.10v (90% capacity) instead of 4.20v increases the number of cycles by about 10%. Seems like an even trade, and it may not matter much unless you plan on getting more than 500 cycles from a pack? I'd sure like to see a cycle graph, the benefit must be more than 10% of 500 cycles, or they wouldn’t talk about it.

As far as discharging is concerned, I keep my packs above 3.70v per cell after a flight.
I think a great deal of confusion comes from the fact that lipo’s are rated to a very low voltage, selling every last drop. And people’s lack of understanding on how little power is available below 3.70v resting.
This complicated graph is going in my graph thread later, but it seems fitting here too. Resistance does appear to increase slightly at the top of the charge.

Jim
IA-Flyer is offline Find More Posts by IA-Flyer
Reply With Quote
Old Aug 03, 2005, 12:42 AM
Registered User
Gaithersburg, MD, USA
Joined Jun 2000
1,070 Posts
Cycle life

Quote:
Originally Posted by hoppy
Found this googling - A motorola report on cell phone battery cycle life and what affects it.

This is one interesting excerpt: (DOD = Depth of Discharge)
"The relationship between DOD and cycle life is logarithmic. In other words, the number of cycles yielded by a battery goes up exponentially the lower the DOD. Research studies have shown that the typical cellular phone user depletes their battery about 25 to 30 percent before recharging. Testing has shown that at this low level of DOD a lithium-ion battery can expect between 5 and 6 times the cycle numbers of a battery discharged to the one hundred percent DOD level continuously."

Might supports higher LVC values in exchange for cycles.

http://www.motorola.com/testservices/article1.htm

Hoppy,

The Motorola report correlates with what Kokam chemists have told us and we have passed along several times. Under the low discharge conditions for notebook computers, etc that is a Motorola concern, if we keep charge to a maximum of 90 % and DOD to < 80 %, life cycle can be as much as 1000 cycles.

In our work at FMA we have validated those findings but feel that all need to be aware of one other cell killer: over temperature. Overtemperature is generaly occurring because cells are being run at high discharge rates without adequate cooling. Just one run at a temperatuire over 140 Deg F drops capacity considerably. The new Skyvolt sysyems can keep the cell withing the 90% charge to 80% DOD readily, but the user has to be sure to have cooling air on the pack. More about this later.
electroman is offline Find More Posts by electroman
Reply With Quote
Old Aug 03, 2005, 07:52 AM
Registered User
Joined Jan 2002
6,587 Posts
Quote:
Originally Posted by electroman
... Just one run at a temperatuire over 140 Deg F drops capacity considerably...
Here is a graph of a cell discharged four times to temperatures over 140F., the last time to 175:

http://www.rcgroups.com/forums/attac...hmentid=448963

Capacity loss was negligible:

http://www.rcgroups.com/forums/attac...hmentid=449287

There are other LiPos in the battery graph vault which also have sustained temperatures over 140 without substantial capacity loss.

- RD
RD Blakeslee is offline Find More Posts by RD Blakeslee
Last edited by RD Blakeslee; Aug 03, 2005 at 04:15 PM. Reason: accuracy
Reply With Quote
Old Aug 03, 2005, 10:21 AM
Southern Pride
everydayflyer's Avatar
Haralson County GA. USA
Joined Oct 2004
34,833 Posts
The amount of increased flight time one can achive by pushing a pack in real numbers.
One of my ESPA3D models powered with a LensRC CBX 2.5 15Turn. GWS RS 1260 , TP ProLite 3S 1320. AUW 12.9 oiz. max. static amps. 9.5 ,in flight average 4.75-5Amps Normal flight 13-14 min. recharge 1.1Ah -1.15 Ah. open volts 11.1 plus---- Flew to 9 volts LVC ,flight time 16 min. 48 seconds. Open volts 9.65 - charge started at .1Ah and after 0.115Ah(115 mAh) open volts back up to 11.15. I fell to see how that extra 3 minutes flight time is worth the potencial damage done to the battery.

Charles
everydayflyer is online now Find More Posts by everydayflyer
Reply With Quote
Old Aug 03, 2005, 11:28 AM
Cogito ergo fly!
TubaTom99's Avatar
Kansas City, MO
Joined Jul 2004
266 Posts
Well, even if this info is not earth shattering, it does go another step towards what Charles, Hoppy and the rest of the LiPo Guru Gang have been saying, that the more gently you treat the packs the returns seem exponential. If it just as simple as choosing a slightly higher capacity pack, discharging it easier, not draining it to death, and not over stuffing it, then I am all for it. I would love to get 300+ cycles out of my packs. I have less than 100 (70ish) on each of mine and so far they are all working really well.

OK, so about the temp. Is it similar to the DOD issue where the lower the temp the gains are exponential, or is there something devastating that happens right at 140 Deg?

Tom
TubaTom99 is offline Find More Posts by TubaTom99
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion What do we know about cycle life under bursts? Neil Walker Batteries and Chargers 10 Aug 31, 2006 09:37 PM
What constitute to Cell with long cycle life:heavy,light,hot... Charlie Wang Batteries and Chargers 1 Oct 01, 2005 04:49 PM
Partial lipoly discharge and cycle life KatManDEW Batteries and Chargers 2 May 06, 2003 12:48 AM
need info on cell size vs amps vs cycle life ? epkoncept Batteries and Chargers 0 Dec 22, 2002 12:49 AM