Uh oh, did I ruin my SMC Lipo's?
 

Uh oh, I think I screwed up. I just took my Savage Flux out today and I might have pushed the Lipo's a little to long. I"m running SportMax 6000mAh 28C 2S Lipos in my Savage FLux and I've been running the stock 20/44 gearing and i've had punch control at 30% with 15% brake drag, 40% reverse throttle with 3.0v Auto lipo cutoff set on my Castle link. I got around 31 minutes of run time of mostly spinning around in the dirt and high speed runs when I started running the truck in circles in the grass when the LVC started to kick in but I wasn't sure cause the grass was bouncy so I think I kinda went overboard. When I got home, the batteries felt warm but not hot and I dunno wether it was just me but it seem like they "puffed" slightly on the outside casing.

I did notice that my motor and my ESC were pretty warm as well but I never heard the fan kick on the ESC.

Did I just make at $190 mistake? I immediatly threw one of the batteries into my Triton2 EQ charger and initial voltage reading was 7.02v before it started to charge. I've balanced these Lipos from day one. Right now its charging at 6.0A and its behaving fine, and both cells are showing very close voltages to eachother, but im really worried I mighta bit the weeny on this one. Any incite?

7V resting on a 2s is fine. A "little" puffing is not bad and should receed eventually. I've had a small amount of puffing on my new Neu 3300 packs but after 5 cycles they're still running perfectly. If it were puffed to the point of rocking back-and-forth on the table like a (insert appropriate metaphor here) then there would be a problem.

Watch them carefully, but they seem fine from your description.

They cooled down and seem fine. I honestly can't remember now if the case was slightly puffed before or not on one of them. ARRRGGH now im gonna be paranoid forever about this! So far, once is taking its charge good with no issues. I'll post the final charge specs when their done.

I went ahead and increased my LVC on my Castle link to 3.1v. Is it the LVC that causes the truck to run and then all of a sudden stop when I try to run it?

The short answer is- Yes. The LVC should really be set to 3.2vC. That will prevent any damage from being done to the pack.

I'm noticing that im not getting a total of 6000mAh of charge anymore like I did when I first got them. Now its dropping and the batterys don't even have 20 runs in them. Now im really freaking out. :oh:


http://i100.photobucket.com/albums/m.../emptybats.jpg

5982mah returned isn't bad at all. Looks like you have yourself a very healthy lipo there.

But if you're freaking out and it's being hard on your nerves, you can send them to me. :lol: No More Worries. LOL

That was when I charged them for the first time, now its barely over 5520mah

A MT running 4s can pull some juice... I have a feeling you are pushing the SMC packs a bit more than they like. If you are hitting the lvc and not getting the rated mah back into the pack (within 100mah or so) you have a higher amp draw than the lipo cells like. Temps are not really as good of an indication as Mah used... I guess keep using them and see what happens. Keep a log of runtimes, pack temps (not really useful as you have hardcase lipos), other component temps, mah used and balance condition. That will give you some info to go by if you plan to question SMC about their product.

If you want to keep your batteries lasting as long as possible, then raise the LVC even higher. Typically mine is set at 3.3v, even with ~5000mah 20C batteries. You'll have less usable capacity with a higher LVC but which would you rather have: a battery which has a longer life and 1min. less runtime (if that) or a battery with a shorter overall life and that extra bit of runtime?

I cannot remember off hand, but I think most of the airplane guys who pull their packs hard figure out how long the flights will be to remove no more than 80% capacity from the lipo. That seems to make them last longer...

I generally run 3.2v per cell cutoffs, unless I have a super low draw (HV...) setup.

Yes, 80% is a critical point in lithium polymer/Li Ion cells, the cycle life is drastically reduced after that point. In fact, the less DOD (depth of discharge) you go, the longer they will last. Exponentially.

Well thats just fucking great......:grrrrrr:

Thanks, ZPB! I had the DOD term on the tip of my brain, just could not think of it! I do remember reading this somewhere, and the guy had posted graphs and all kinds of other info too.

Look at it this way, if you buy a zippy lipo for 80 bucks and get 100 cycles out of it, cost is 80 cents to run it for 30-40 mins. So that is 1/2 cent a minute. Not sure what the charging will do to you electric bill, but it cannot be much?

Take nitro costing 30 bucks a gallon, and the average tanks size is 5oz and yields about 8mins runtime. So that would be 25 tanks per gallon, 1.2 dollars a tank, so about 15 cents a minute.

At 14 cents a minute difference a 200 dollar charger is covered in 1400 minutes, about half of what I posted a zippy should last. So you could buy a new charger every 50 cycles and still not have spent as much as you would have on nitro fuel for the equivalent runtime.

Not sure if that is right, seems very good for lipo... Maybe I got something wrong, although the math is pretty simple.

Big difference, huh... And if you get past 100 cycles the difference is even more.

Yeah I try to keep to the 80% rule. Using the entire packs seems to shorten its life a lot, compared to using ~60% at a time.
For most of my use there is only a few minutes difference between 80% and 100%, so for me it's usually not worth running right to the end.