Lipo cutoff, and charge question
 

I have some new turnigy nanotech ultimate shorty's 4600mah 90c. I ran them a few times in my mbx7 Eco with an rx8 gen 2. I don't know my exact runtimes but it seemed a little short. I have the lipo cutoff set with the buttons on the rx8 at the 4s setting, which I believe is 3.2v per cell. I was thinking of increasing this to 3.4 but felt like my runtimes were already short. Anyway here's my issue. After a run to voltage cutoff I probably within an hour or so I put them on the charger to storage charge. It has to discharge down to 3.8v. I understand that packs voltage decreases with load and can increase at rest, but it seems a little much. It seems like I'm not getting what I should out of my packs. I just got some promatch 6500mah 70c, I need to switch back to 4mm bullets before I can compare.

How many mah are you putting back into the packs when you charge them?

1/8 scale buggies can be really hard on batteries, especially if you are the type of driver that has a lead trigger finger. Things like not slamming full throttle just because you can, gearing, and ESC setting all can have a great effect on run time. You really need to hook your ESC up to the computer and see what your settings look like. The current limiter is a good setting to play with to help with run time. Start a timer on your phone or radio when you run, and see what kind of time you are actually getting. When you're just running practice with no clock it can be deceiving how long you're actually running.

You are right about the voltage drop thing. An 1/8 scale pulls a lot of current, so the voltage drop is going to be more significant. Also the opposite is true when you are charging, putting energy back into the battery is going to make the voltage go up, so the voltage you see when you start charging isn't really the resting voltage of the pack. Really if you want to see the true resting voltage, you need to check the packs with a multimeter when you get done running.

As for cutoff voltage, I always run it on a custom voltage, and a bit high. It helps protect the cells as you get to the end of the pack. Being that the ESC doesn't see each cell, if there is a slight mismatch in cell voltage, and you run the voltage cutoff on the low side, you run the risk of damaging one of the cells. That can happen more easily on a higher voltage pack, as there are more cells to compensate for one being weak.

"It has to discharge down to 3.8v"

I don't understand this. Do you mean you have a higher voltage after a run ?

i noticed that even with a cut off at 3.4 volts my nanotech show 3.6 approx. after a run.
what voltage do you read after a run ?

by the way, some infos here : http://www.rchelicopterfun.com/rc-lipo-batteries.html

You're local hobby shop probaly has some sort of cheap Voltage Checker you can pick up, so you can have a quick check after a serten run time, just to get an idea were you are at . I have several brands for my 8.2e . turnigy , rb ad dinogy, With mah ranging from 5400 to 7000, so before I get the 'feel' for the run time , and also since I have been fooled by the ESC in my boat , I like to pull over once in a while and quickly plug in the V Reader to get a read

I think I found the issue. After 1 run at the track today I immediately put the pack on the charger individually. The first pack was greater than 3.8v per cell. I removed it and placed the second one on and it had one cell down to 2.89v wtf. So I may have a bad pack with a bad cell.

On another note before all this occurred I was really looking at the packs and they all seem to be slightly thicker in the middle, not perfectly flat. I have 4 packs which I aways run together and don't mix. Also keep in mind all brand new, all have 2 runs on them, always balance charged at 1c, always storage charged, stored in a cool basement. Also not really ran that hard as trying to make it around the track on all 4 wheels. I showed a knowledgable guy at the track and asked if they looked puffed and he said absolutely not. I was being paranoid, but then this crap happens. Wondering if I should try to get my money back from hobbyking.

They have a 30 day return policy on batteries. I would at least get the one with the bad cell replaced.

Looks like my weak cell which won't balance and is considerably higher resistance than the other, isn't considered defective according to hobby king.

"During the first 5 to 10 cycles it is normal for there to be an imbalance and also less power due to the storage chemical in the cells. Lipo batteries require a break in period and during this time the storage chemical will break down and the cells will balance better and make more power. You should put minimal load on the battery and only discharge around half way during this time. Please put more cycles on as I described and see if it improves. In order for the battery to be covered under warranty the imbalance would have to be .245 volts or greater."

I find with nanotech lipo I have to set the cut off at 3.0v otherwise they temporarily drop to 3.2v under hard load and go into dump mode even though there's still plenty left in the tank

If I set my lvc at 3v per cell it probably would have dropped to 2.5v. There is something wrong with 1 cell. They are actually 2s2p batteries so technically 4 cells in each pack, but just one could be my problem.

Making me nervous over here.......lol
 

I just ordered two (waiting on delivery), 2-cell 7500mah 90c Ultimate Nano-techs and just stumbled on this post. After reading this I will be monitoring both batteries like a hawk for the first 10 cycles once they arrive. I run two Hobbywing SCT-Pro v3.1 ESC in a Losi SCTE & SCTE/Pro8 buggy conversion and from what I've read on here people recommend running the HW SCT-Pro ESC LVC @ 2.8v per cell due to overly sensitive voltage sensors.

I am now second guessing running at that 2.8 LVC setting, I was apprehensive to go that low to begin with but at the 3.2v LVC setting I was experiencing the early LVC kicking in due to voltage sag under load (550 2-pole motor). In fairness I was running inexpensive 2-cell 50c 6000mah Zippys, so they could be a factor. I'll report my findings in a couple of weeks once I get some cycles on the new 7500mah Ultimate 90c Nano-techs.

Sir_CrashAlot.

Honestly you may want to run the lvc even higher, especially at first. If you are running just a 2s battery (not two 2s batts like a 4s) then it's less likely for the pack to dip too low before triggering the lvc. A lot of other battery companies reccomend not discharging below 3.4v. My lcv is now set at 3.6v per cell. You should still have good run times with 7500mah packs with a higher lvc.

Thanks for the feedback, Yes, I am indeed only running a 2s setup in my SCTE 4x4 with a 550 can, 4150kv 2-pole motor. I do believe I am going to move that lvc up until I get several cycles on the packs and get a chance to evaluate exactly how they are "breaking-in" & performing (I.R./balancing, charge capacity input etc).

Funny thing is, I have had zero issues with the inexpensive ($27) 50c 2s 6000mah Zippy batteries with about 20+ cycles on each. Typically I bring it off the track before LVC kicks in, so maybe that is why I've had no issues with them to date.

I bought the new 90c Nano-tech batteries for the fact I just built a SCTE MIP Pro8 buggy conversion too, and I may be giving a 4-pole motor a try soon. So the higher C & Mah ratings should better handle the higher 4-pole amp draws, That's my hope anyways.

Sir_CrashAlot.

I really truly think I just had some bad luck. It is the lack of customer support and denial that there is a problem that I'm upset about. I'm sure you know this, but the heavy 4x4 short course trucks with 1/8 electronics are harder on batteries. It is essentially a 1/8 buggy running on 2s, which draws more amps than on 4s.