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Old Dec 01, 2002, 10:40 AM
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London, England
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Some advice on using my lovely new Kokam 1020 cells

Hi,
I just got some of these wonderfull Kokam cells to use in my Hornet (hacker 20-26 with schulze 20he and lots of lovely upgrades from Andy N, John K and electric rotors).

So the thing is i want to make sure that i treat the Kokams correctly from the beggining. All the cells are reading 3.84v (as measured on my battery test meter) does this mean that they are all in the same charge condition, and are therefore safe to make up into a 3 cell pack imediately. Or should i discharge them down to a particular condition and then charge them back up to max and then solder them together and if so what is the recomended discharge statethat i should take them to. Should i then solder them together and then charge them up as a whole pack.

I have a Schulze isl 6-636 charger which has a charging program for up to 3 LiIon cells can anyone comment on how well this program works wiyh the Kokams. Presumably it is still a good idea to watch the charger anyhow. Am i correct that they should terminate at 4.2v per cell.

Finally -- when i am using them in the hornet will it be self evident when they have discharged to the safe/correct level for good long term usage. I believe they shouldnt go below 3v per cell but since 9v is probably more than sufficient to drive the hacker with i am concerned about going to far -- or is there an obvious power drop as they approach the 3v point. Indeed should they be taken down to 3v per cell regularly or should i aim to stop at some slightly higher point say 3.3v to avoid danger of damage.

I look forward to your knowledgeable answers.

Cheers Nigel
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Old Dec 01, 2002, 11:05 AM
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Rochester, NY, USA
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Hi Nigel,

You should be fine to go ahead and make up your 3-cell pack. The 4.2v per cell can be measured from the pack when it is removed from the charger. A fully charged 3-cell pack is 12.6 volts.

When charging LiPoly cells, try to use a manually selected cell count instead of an auto-detect mode. This is a safer approach.

I'm not sure about the Hornet, but, all of my airplane applications have proven that you can no longer fly long before you reach the LiPoly cell minimum voltage.

Good luck!
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Last edited by Greg Covey; Dec 01, 2002 at 11:08 AM.
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Old Dec 01, 2002, 12:22 PM
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London, England
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Greg,

thanks for the advice.

OK pack nicely soldered up.

Now would it be best to charge the pack fully or fly it to empty or discharge it on the bench and then give it a full charge.

cheers nigel
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Old Dec 01, 2002, 01:11 PM
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Rimrock AZ. USA
Joined Mar 2000
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You are aware that 4 amps is all you want to draw out of the 1020 cells?? You might get away with pushing it to 5 amps for short burst. Check the cell temp., if it is a little warm you are pushing it as far as you want to go.
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Old Dec 01, 2002, 01:34 PM
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London, England
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Greg,

thanks for the advice.

OK pack nicely soldered up.

Now would it be best to charge the pack fully or fly it to empty or discharge it on the bench and then give it a full charge.

cheers nigel
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Old Dec 01, 2002, 01:35 PM
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It is possible to fly the LiPo batteries to the LVC of the ESC with the right aircraft. I fly my Dusk Stick with a 2 cell LiPo pack and have been up very high when at 45 minutes into the flight, the LVC of the ESC was hit. First time this happened I thought something had gone wrong with the plane till I got it on the ground and then realized I could rearm the ESC and start the motor again, although briefly. I now usually end the any flight at 40 minutes as the first time it the cutoff happened I was very high and far away. Didn't think I was going to get the plane back but it managed to glide to with 5 feet of the runway, which still amazes me.
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Old Dec 01, 2002, 06:13 PM
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Nigel,

There is no need to cater to the "ecentricities" of LiPoly cells. Simply, fly or charge -- whichever you wish. No need to cycle or discharge them.

GBR2,

The LVC disconnect feature of the ESC was not what we were discussing eariler but rather the lowest safety voltage of the LiPoly cell itself. The ESC's LVC cutoff voltage can vary with the manufacturer. Some ESCs have a programmable cutoff voltage.

Regards.
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Old Dec 01, 2002, 07:00 PM
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I understand but the LVC for this ESC is a non changeable 5v, which works out to 2.5v a cell. So it is possible to hit the lowest level you should with a LiPo cell and still be flying.

That being said, it is important to know what the LVC of any ESC that you use and set it accordingly, if programmable, to be with in the safe limits of these new cells.
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Old Dec 01, 2002, 09:44 PM
BEC
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Just charge - no need to discharge first. And once they are charged, they'll stay full for days, maybe weeks.

I haven't tried charging 3 cells on my schulzes, but it works fine with two (thought it stops a bit before they're completely full). Do you have a 13.8V power supply for your isl-6? Otherwise it may not be able to get the 3 cell pack full as their full voltage is 12.6V or so - more than a 12V battery can put out, never mind any overhead from the charger.
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