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rcpilot
11-15-2005, 02:46 PM
I am new to LiPo's and have been flying a Rimfire brushless + BL-08 controller on a Kokam 1500 mah 2 cell pack's for the last two months or so. Basically a relaxed weekend flyer

I never abuse the batteries - max amp draw well below 10 C - and rarely recharge the pack at the field

Just wondering how long will the battries last - I mean how many rechagres?

Also what kind of life does one get from LiPO packs when used on hot 3D aircraft ?

Any source where I can get info regarding life of LiPO's

Unbalanced prop
11-15-2005, 03:09 PM
Tough question rcpilot.........I have packs that didn't make fifty cycles, but I also have a few in the 100 to 200 range. I would beware of the cheap "China made" packs as they don't seem to last. Right now TP Prolites and Tanic packs are performing the best for me. I am also using a Dualsky (1050) pack that is holding up well also. I don't push my packs hard and I think that helps with pack life.

You'll probably get a lot of different opinions on brands and I don't want to bash any product. I have used Apogee, Kokams, Polyquest, Maxamps, Etecs, TP, Tanics and Dualsky cells. There are a lot of brands I have no personal experience with that probably perform fine and it seems each new "generation" of cells is better then the previous. Like I said.....tough question! Your mileage may vary.

Doug

hoppy
11-15-2005, 03:45 PM
Speaking in broad generalities, perhaps ~50 cycles under maximum draw use and up to 500 cycles at 1C draw.
The lower the current draw the longer the pack will last.
Charging to less than 4.2V/cell increases cycle life.
Discharging only to voltages well above the LVC increases cycle life. (Stop flying before LVC kicks in)
Cooling battery increases cycle life.

Short life techniques-
Run battery at maximum continuous discharge level.
Discharge battery to less than 3V/cell
Run battery in an insulated space.
Charge to 4.2V/cell or higher.

Like I said, generalities...... I'm sure some will argue:)

Some reading on the subject-
http://www.motorola.com/testservices/article1.htm

timocharis
11-15-2005, 05:43 PM
I'm right there with hoppy. The only thing I'd add is, it's hard to be sure what's going on in the real world. I have batteries running that I bought almost two years ago, and others that died in a couple of months.

I generally charge at .8C, never get to cutoff (or rarely) and never run a battery at full rated capacity (other than occasional burst).

But some die early. Why? I think crashes are the thing that makes it hard to know what's going on. Even a small crash can have give a LiPo a tough time, and as a 3D foamy type there will be some impacts.

So if you fly sedately and have good landings every time, I wouldn't be surprised to see the batteries last well over a year with daily use. If you have a boo-boo, all bets are off.


Dave North

tkilwein
11-16-2005, 04:30 AM
I have several lipos I have been using for over a year with 1 to 3 charges a weekend and still going strong.
I have lost one to leaving plugged in and discharging to 2v on a 11.1v
Boy did it swell up to past drum tight.
Lost on to the outer limits of air, very sudden stop, pack heated up to 160f
and became a puffer.

I discharge a 10c at 2-10c and up to 15c for 5 to 15 seconds.
Charge them back up at 0.6c rating. I have 1-1350, 5 - 2100, 2 -4000 and 1-8000 mah batteries, all 3 cells and 1 2100mah 14.4v



Tony

Jimmy Hoffa
11-16-2005, 05:17 PM
Another factor that could shorten a battery's life would be improper break-in. Im seeing more info about that all the time.
Phillip

Matt Kirsch
11-17-2005, 12:07 AM
What break-in process would that be? I'm not aware of a break-in process for LiPolys.

Unbalanced prop
11-17-2005, 12:40 AM
What break-in process would that be? I'm not aware of a break-in process for LiPolys.

Apogee suggests a break-in. Not sure if anyone else has anything specific or not. Can't prove one way or the other if it is a good thing.:confused:

http://www.pfmdistribution.com/files/Apogee_Battery_Guidelines_Oct_12.pdf

Doug

Jimmy Hoffa
11-17-2005, 01:16 AM
What break-in process would that be? I'm not aware of a break-in process for LiPolys.
The first battery's cycle is the most important. If it is discharged at it's maximum rated capacity, overly discharged and/or overheated, it will never be OK.

I think Thunder Power reccomends going easy for least 5 cycles, Apoogee quite a few more. If a battery is broken in properly, it can be "leaned on" with minimum damage. Also, do not let the discharged resting (measured 1 hr after discharge) voltage go below 3.7 volts per cell.
Phillip

Fred Marks
11-17-2005, 02:33 AM
I am new to LiPo's and have been flying a Rimfire brushless + BL-08 controller on a Kokam 1500 mah 2 cell pack's for the last two months or so. Basically a relaxed weekend flyer

I never abuse the batteries - max amp draw well below 10 C - and rarely recharge the pack at the field

Just wondering how long will the battries last - I mean how many rechagres?

Also what kind of life does one get from LiPO packs when used on hot 3D aircraft ?

Any source where I can get info regarding life of LiPO's
Jimmy,

The data attached is the first realistic test daat for life cycle seen in any of fht forums. Nathan Gwozdecki ran life cycle teats on the popular FMA Direct Kok 2000 HDR pack in 3S configuration.


Salient observations:

1. All done under carefully controlled lab conditions using precision test equipment.
2. The data is very conservative with the cells not cooled during charge or discharge but cooled by fan after discharge and before charge as one should do in the field. Any cooling in the airplane would extend life.
3. All runs were at a constant 17.5 amps discharge reflecting the average current drain for may applications in helicopters and with the many new brushless motors thta draw some 15 to 25 amps and are replacxements for Speed 400 brushed motors. . Discharge was cut off at 3V/cell based on individual cell voltage. cell voltage charactristically rebounds to the neighborhood of 3.65 to 3.8 V when load is removed and the cell cools a bit. This amounts to about a 5% rebound of capacity.
4. All charges were done at 3C to 94% (1785 mAh) to expedite time. Even so, the tests took almost 14 solid days.
5. The test pack is a 3S CellPro pack with tap and connector so that cell voltage could be recorded ala CellPro.
6. Handling and plugging/unplugging of the pack was minimized.
7. Cycle life as defined by international standard 80% of base capacity was 450 cycles. The pack was run to complete death just to see what would happen. Results are interesting: Capacity declined slowly and steadily to 475 cycles, then plummeted. Dissassembly of cells confirms the rapid formation of salts (dendrites) as the cell dies.
8. The peak temperature rise for eacy cycle is recorded and averaged 65 Deg F over the life of the pack. It is interesting that, as cell capacity falls gradually and run time shortens very sligtly, rise temperature falls very slightly as well. Since discharge current was always a constant 17.5 amps, this implies that internal resistance was not degraded and, if anything, increased only slightly. The data recorded by Rod shows that the TP 2100 runs 161.5 Deg F at the 17.5 amp discharge , so it will be history very shortly as test runs begin.
9. The need for and achievement of cell balnce is also graphed. Cell voltage was brought to wihthin plus and minus 5 millivolts even after 450 runs. This is a powerful statement of the desirability of cell balancing as done by FMA BalancePro systems.
10. The discharge profile matches the flight profile for a typical trex heli or any of the new generation of brushless motor propulsion systems that demand an average 200 watts.
11. Life cycle cost for a stock KOK 2000 3S pack is $83.50/450= $0.18/flight compared to $1.41 per flight per the 60 cycles for a TP 2100 that RC Tester and trex report. Nathan will validate that figure very soon as it won't take long to run 60 cycles.

Jimmy Hoffa
11-17-2005, 02:39 AM
Fred,
That's a lot of data, I'm not sure what it all means though.
Phillip

Fred Marks
11-17-2005, 02:45 AM
Fred,
That's a lot of data, I'm not sure what it all means though.
Phillip

Phillip,

Break in provides hardly enough gain to take the trouble. It is much more important to maintain proper balance over pack life.

The blue cycle life curve shows the decrease in cell capacity as the pack is "used up" The red temperature curve shows why the life cycle is so long: the FMA pack never exceeded 133 Deg F even with the 17.5 amp load. Competing cells of may brands reach over 160 Deg F at that load and heat shortens life.

There are two important facts here: The pack was charged on every cycle at 3C and the BalancePro 6S charger brought each cell to within 5 millivolts of 4.2V on every charge, even the 452 nd charge. These are the things that help bring long life. It is doubtful that many people would ever fly a pack 450 flights as new generation packs arrive and most will replace them before end of life. That simply does not happen with non-balance charging and unbalance can end pack life very early.

qban_flyer
11-17-2005, 04:00 AM
11. Life cycle cost for a stock KOK 2000 3S pack is $83.50/450= $0.18/flight.
To me this speaks volumes about the KOKAM packs. I would have been satisfied with a life span of 400 cycles. As it stand now, and based on the test conditions specified, I have a tendency to believe they will last to well over 500 cycles, especially if charged at no more than 70% of 1C.

Thanks for the info Fred. Very useful.