While on the second flight of the day with the 1/2a Pathfinder the motor quit just as I was finishing the overhead eight.  Some fast backpeddling saved the plane but left me a little unnerved.  When I checked the battery on the tester everything looks good, all the cells are nominal and the total pack voltage was over 11v and the remaining capacity was in the mid thirties.  I know the KR timer monitors pack voltage via the motor feedback path, and when it drops below a set level it will shut down the motor.  I am guessing one of the cells in the pack was dropping down under load.  I flew the plane twice more on different packs an no problem.  Needless to say I will be discarding the suspect pack.  The only warning I got was the plane did seem a little light on the lines in the overhead and the hourglass before it, but I didn't give it much thought.  I sure will next time.  

Keith if you are out there what is the threshold voltage for a three cell battery at which your timer shuts down the motor?
Andy

Not intending to hijack the thread but,

When you have one cell going bad in a pack does the ESC attempt to draw more current from the remaining cells due to your programing, possibly causing a meltdown? I realize voltage would drop.

Not intending to hijack the thread but,

When you have one cell going bad in a pack does the ESC attempt to draw more current from the remaining cells due to your programing, possibly causing a meltdown? I realize voltage would drop.

Hi Douglas, what happens when these batteries get old and bad is that the internal resistance goes up and then the voltage drops as the current goes up like when you load it harder. A few years ago I bought some Flight Power Lite lipos (the green colored ones) and they were not light in weight, but in C-rating. They did not work for many flights with the CL pattern that hammers batteries like 3-D helicopters. I found them very useful though for testing the trigger point on my shut-down program.

Keith R

Andrew,
   There is ton of info on RCGroups.com on lipo battery care Read up on the research by a guy called EVERYDAYFLYER he is all over RCGroups and is considered the top expert on lipos.To give you a summery of his work and what has been working for me. Lipos should never ever be stored fully charged even 1 day can hurt them. Most chargers have a storage mode that takes the batteries to the proper level.. 50-60% is considered fine. If the lipo isn't going to be used for a few weeks or you cant fly in the winter then it good to put it in the refrigerator. I put mine in a doubled freezer bag squeezing as much air out as possible. NEVER FREEZE THEM!!!. Some people will argue that its OK to store them in the fridge fully charged for a few days. I kind of disagree with that as they still need a 24 hour warm up period before you use them. If they are in storage mode and in the fridge they also need 24 hour warm up period before you charge them. I have been using this program since last year and haven't lost one battery yet. I have budget batteries with over 50 cycles on them and they still are as strong as new. Of course your milage may vary. All the batteries that I did not have on this program have failed.
  On another note, I know that the next thing that will be asked is."How come it takes so long for my charger to discharge the batteries?". Well most budget chargers do not have a very high discharge rate. I did the whole budget charger thing so I know. I highly recommend a good charger like the I-charger 306B or the powerlab 6 or 8. YES they are expensive!! but you will make it up in saved batteries many times over. If you want to use a lower priced charger then get yourself a charger that is a minimum of 200 watts output. Most of those have a decent discharge rate even if a bit slow.
William

Andrew,
If you are using a Castle controller for your discharge setup remember that you can custom set the cutoff voltage and use a hard cutoff. If not you should watch it carefully as to not to take it down more than necessary. This will allow you to bring them up quickly. If your speed controllers allow you should set them for the lowest possible cutoff voltage and a SOFT CUTOFF for flying. This is supposed to keep the motor from completely shutting down suddenly if you should have a failing battery.I'm not 100% sure how well this will work for you as your timer only gives you 1000 rpm drop before shutoff. We do use different setups, but some of the basics should remain the same. There is NO reason whatsoever to use a hard cutoff for control line flying regardless of what setup you are using!!!!! That is strictly an RC setting and can cause a CL plane to crash because I can guarantee you that if a hard cutoff it kicks in it will be at the wrong time and you will stand a good chance losing your plane. With a soft cutoff you will see and feel the voltage sag and have time to level your plane off.