How many cycles?

[F1 Rocket]

I know this is a question usually asked in the battery forum but I'm looking for info from folks who are actually flying the same types of aircraft I'm flying. What I'd like to know is how many cycles you are getting out of your packs before they start to drop off in performance.

What I'm seeing is 50-70 cycles. I fly once a week and typicaly put 1-2 cycles per pack per flying day. This is about a years worth of flying at my rate. I use good chargers, balance as I charge and have never puffed a good quality pack in 2 years of flying electrics. I'm fairly carefull not to discharge more than 80% or run things over 140F and typicaly check temps on everything after each flight. I'm not complaining here. I'm having a blast. I just want to know what I should expect.

I've asked a few guys who rep the major pack manufactures and have been told by some that they've gotten 300+ (one said 380) cycles out of their stuff. That would be several years flying for me.



Danny

[blucor basher]

The 140 number catches my interest. The most knowlegable people I've talked to indicate that for maximum lifespan, we'd like to stay below 125F.

My 20C packs, taken proper care of (3.5V/Cell resting after flight, 125F or below, 1C charge, 20C max peak discharge) have been lasting 100-200 flights without serious performance loss.

I also have some 20C packs that I've abused the crap out of during development of the 55" aircraft, specifically by balance charging at 2C and 3C day after day. After 75 cycles, they're getting weak.

A more interesting case is the new 25C TPX. I've got about a dozen of these in various sizes. Although there is no clear pattern, I think (and a couple of other people I trust agree) that the major performance advantage these have over the 20C packs goes away after 20-30 cycles if they are used moderate to hard. So far (knocking on wood) I have not had a single failure with a TPX discharging them at 20C max, but the power rush doesn't last indefinitely. They do, however, seem to settle down to approximately the same power level at all my 20C packs. Since they're not significantly more expensive and appear to be durable, I'm OK w/ that.

[F1 Rocket]

The number I've been told to stay under by the pack reps is 140. In the summer my packs come down at 130-135. Keeping them below 125 is a challenge but if that's the path to longer life I'll try and stay below that. What I have noticed is that the temp will rise dramatically if the packs are discharged too much so I really try and limit this. For the 3700 packs I typicaly put back 2600-2800 mah after a 7-8 min flight.


Danny

[blucor basher]

I have heard the 140 number before, too, but I thought it was in the context of "unless you want instant pack death".

I had a really interesting battery tech call the other day. A university had purchased a bunch of pro-lites from us for use in a UAV project. The batteries only lasted through one flying session. A month after the flight, the team tried to fly again and there was no power. It took a while on the phone to figure it out, but here's what happened:

The batts are permanently mounted in the airframe, and a master control unit monitors all aircraft funtions. It gets plugged into a DC umblilical when on the ground, and the master control unit handles charging duties when needed. I checked their ranges (3.5-4.2V per cell) and it all looked good, until they mentioned "and the system is always cycling". Aha. Turned out, even when on the umblicial, the power for the plane came from the batts, and so they were discharging constantly at a fraction of an amp, and then being re-charged, constantly. Turns out, the batteries actually had thousands of cycles on them.

[hermperez]

that is why many of us are flying with A123 packs.. the low cost, 15 minute recharges the moment you land, no fire hazzard and no hatches in the planes help too. There really is no weigh penalty considering you can discharge them 100% if you want, repeatedly.

[F1 Rocket]

that is why many of us are flying with A123 packs.. the low cost, 15 minute recharges the moment you land, no fire hazzard and no hatches in the planes help too. There really is no weigh penalty considering you can discharge them 100% if you want, repeatedly.


I've looked at the A123's but larger stuff like our Sundowner would require a 14s2p pack. These would be alot heavier than the LiPo packs I currently have.

Danny

[F1 Rocket]

I was hoping I'd get more input from you guys. Is there anyone else willing to share their pack life experiences? :D


Danny

[rclark]

Under 100 ... The packs are still usable but definitely not like when new :) . My 15C packs normally run way below 15C. Bursts are usually around 14C. I have a timer, so never run my packs down to LVC. Packs come out just 'warm'. So I don't 'abuse' them. I normally buy new batteries at start of every year. They are typically disposed of in 2 years (Seems I remember shelf life is only 3 years anyway) . Anyway that's my experience so far.... Note I've just bought an TP Extreme pack.... See how that lasts ....

If the A123 Technology came in 'nice' small package like LiPo, I'd be buying them . Problem is you can't beat the performance of LiPo for the weight! A123 just won't work well in 20-30 oz airplanes..... Unless you like flying bricks.

[Dora Nine]

I had a gen 1 TP 2100 3 cell last over 300 cycles... I've had some other TP's last to a similar numbers.. It personally saddens me to think that some of the extreme high dicharge batteries are only lasting 75 cycles. Pretty sad for what they cost.

Or as I once heard..."they're just batteries man."

[Carlyle Harper]

I have one 20c 5000mah 5 cell lipo from electrifly. It typically sees a 30-35 amp discharge about once a week and it only gets to a maximum temp of 100F. I have about 20 or so cycles on it, two of those cycles went to lvc at 3v/cell. As of now I can't tell a difference from when it was new.

I also have a couple of A123 setups.

One is two 5 cell A123 packs that get run in parallel in the same plane with an average amp draw of 15 for each pack (30 total). I recharge at 7 amps per pack (14 amps total). I have determined this amount of recharge time is ideal for me to rest and watch others fly their planes. These packs probably have close to 20 cycles on them with no perceivable loss of capacity and they barely get warm after each flight or recharge.

The other A123 setup is two 12 cell packs for my P51 mustang. Currently the mustang is, well, back in the shop. These packs see a total 70 amp draw and get very warm after each discharge. I may have 7 or so cycles on them and so far they are holding but I'm a little worried about how warm/hot they get. I guess I will just keep running them until they give out.

[desert_flyer]

My understanding is that higher C-rating = lower the internal resistance = less cycle life.

The batteries with extreme ratings are also heavy in comparison to prolites and evolites. If you fly with the prolites and/or evolite batteries you can carry more mAh into the air for the same weight. This provides longer flight times and lower average C-draw. For example, if your average draw is 40A, then a 3700mAH extreme battery setup will be operating at an average of 11C, whereas a 5000mAH lightweight setup will be operating at 8C.

I have seen several larger setups where the owners boast of having batteries that can deliver 5000W. All of them have motor/prop combinations that draw less than half of that power, so I'm not sure what the advantage is. They could easily get by with less aggressive batteries and enjoy the benefits of lighter weight/longer flight times/cooler packs and increased cycle life.

Of course the battery manufacturers are riding high on this craving for excess power because they know you'll be coming back for more packs in the near future :D

[F1 Rocket]

My understanding is that higher C-rating = lower the internal resistance = less cycle life.
:D


My experience is the lower the internal resistance the lower the operating temp IF the current draw is equal. This usualy means going to a little bit smaller prop when using the higher C pack in place of the lower C pack.


Danny

[Gary Hoorn]

I had a gen 1 TP 2100 3 cell last over 300 cycles
I have 3 of these "old soldiers" who refuse to die! Been used and abused in TRex Helis and have lots and lots of cycles on them. I have Extremes and Prolites that are never going to last as long. I balance charge, monitor temperatures and avoid over discharging. The old Gen Lipos had no balance taps. I charge them at .8C. I like the new technology but don't expect them to last as long.
Gary