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.

Here is something else to remember.....
If you increase your LVC from 3.0/cell to 3.2/cell it will decrease your runtime (which inturn will reduce the mAh you put back into the cell).
I don't know if a loss of 5-10 minutes runtime is the appropriate runtime loss, but some runtime loss should be expected. Keep running at 3.2 for a several charges and see if it hold steady (runtime as well as mAh replaced). If it hold about steady you should be fine...


But then again my opinions seem to be a bit off lately, so I might be way off base.

I would say that is a fair trial there. If it's consistent at 3.2v cutoff for 8-10 charges I would say everything is okay. But if you loose 100mah or more across the 8-10 charge cycles keeping the lvc the same at 3.2v then you are over stressing your packs.

Linc, I know lipo's are not like A123's for cycle life, but you get more than 100 cycles out of them don't you?

Another example... say if you DID get 100 cycles from 80% DOD, then you can expect somewhere around 150 cycles at 60% DOD. And if you are really crazy about total calender minutes out of your pack, you can always use 10% DOD and get something like 2000 cycles from it. :lol:

Also, charging rate has alot to do with it as well, same with operating temp (big time)... so the newer cells that run cooler and can handle 5C charging are definitely going to last a good deal... if kept to running your typical load along with 1C charging.

Yep, I figure you can get at least 150 cycles, but even at 100 cycles the cost savings over nitro is massive.

I know I can blow out $5 of nitro pretty easy if I take the Sav out during lunchtime. Frickin truck eats more expensively than I do.

OTOH, the downside to BL is usage, if you don't run the truck very often, natural decay of the batts eats up lifespan w/o use. Unfort there are a few lipos I have for trucks I barely run anymore (little free time w/ 2 little kids now) so those batts are basically rotting away. Least nitro is a pay as you go. This is what's holding back the BL conv for the sav at this point. ~$150
for a motor and ~$200 for a couple sets of batts buys quite alot of fuel, esp at my current burn rate (1.5gal YTD.)


As far as LVC goes, I set @ 3.2 IIRC, but as soon as the batts feel a little drop in I power I kill it. Rarely hit the lvc this way. So far so good on lifespan (2-3 yrs on batts, who the F knows how many cycles that was)

Yeah, agreed with the usage aspect... but on the same hand, the "calender life" of lipo's is at least 6 years (if maintained). A123's are 10+ years calender. So after all, it shouldn't come into play in RC, as you would most likely replace the battery before that time anyways... you know.

BTW, does the Quark 125 have a 3.2v/cell cutoff? thanks.

Nope, highest is 3v per cell.

Well this is the email I got back from Bryan at SMC when I asked him about this


Bryce,

For starters, I would def. raise the cutoff on the ESC. I feel safe with mine set from the factory. I don't have the castle software to change mine, but when the truck goes into LV mode, the packs are coming out of the truck reading around 6.60 to 6.70 per each pack. As for the puffy packs...If you let them cool down and wait a while they "should" shrink back to their normal size. If they do not, there is damage done beyond repair. If you would like, you can send them in for us to test if you do indeed feel they are damaged or you no longer get maximum power and runtime from them. I know it doesn't help but we do have a 50% off the MAP price for warranty of a defective pack. $42.75 per pack for a replacement is still not cheap, but it does help a little if the consumer makes a mistake, intentionally or not. Please let me know if you would like us to check out the packs and keep me informed on the swelling issue. Did they go back down or are they staying puffed up?

Thanks,

Bryan @ SMC


Its really hard to tell if packs are puffed or not now, if not near impossible. So i'm just gonna keep running and keeping an eye on them and take this as a important Lipo lesson learned. Changed the LVC to 3.2v. Damn that Castle link is godsend for these kinda things.

Thanks Linc, what external LVC should I use? I could also just do it by minutes of runtime and then just shut it down. But to be safe, lvc might be in order.