New to lipo's. Is It overcharged?

[adamb]

I've only been running lipo's for a few days. I have a turnigy nano tech 2650 2s pack that charged to 8.4v and 2660mah! The voltage is right (4.2 per cell) but what about the mah? Is it overcharged? I ran it this morning until the LVC kicked in.

[LiPo Power]

Take care of your LiPos and time your boating. Try not to drain them down to LVC kick in. They are charched fine. Little bit higher mAh is fine. Make sure to use balancer when charging sometimes or all the time.
Robert





I've only been running lipo's for a few days. I have a turnigy nano tech 2650 2s pack that charged to 8.4v and 2660mah! The voltage is right (4.2 per cell) but what about the mah? Is it overcharged? I ran it this morning until the LVC kicked in.

[785boats]

What it means is that you over discharged the pack during the run . You should leave 20 % of the capacity in the packs at the end of your run.
In your case 530mah. So the pack should take on around 2120mah during the charge.
Start to time your runs.
Don't rely on the cutouts.
If they are set at 3.0V/cell I think you should raise them to at least 3.2v/cell. Maybe higher depending on the C rating of the packs.
With the higher C rating packs , the voltage stays up higher for longer under load & the capacity of the packs is drained before the voltage drops to the LVC.
This can cause the chemistry to change in the packs & degrades their performance.
Try not to do it .
Were the packs hot?

Paul

[adamb]

The pack wasn't even warm. I'm gonna time my runs from now on.

The LVC is 3.0v per cell.

[sailr]

Did it just charge back to 2260 or did you actually put 2660 in it? You shouldn't be able to drain the pack completely with an LVC unless you just kept hitting the throttle after the LVC kicked in.
Don't do dat!

[JimClark]

What charger are you using?

[Fluid]

You shouldn't be able to drain the pack completely with an LVC unless you just kept hitting the throttle after the LVC kicked in.

Not necessarily. An LVC of 3.0 volts has a tolerance so it could be only 2.9 volts. Even at 3.0 volts there is virtually no usable charge left in the pack - it is well below 20%. And packs don't always hold what the label says they do - a 4000 mAh pack may actually hold only 3850 mAh, or maybe 4200 mAh. The only way to tell is to discharge the pack in question to 3.0 volts and check.


.

[adamb]

It's a GT Power A6 charger. It said It put 2660 into the pack. As soon as the LVC kicked in I brought it back.

[adamb]

I think I will discharge to 3v and check it tonight

[keithbradley]

Not necessarily. An LVC of 3.0 volts has a tolerance so it could be only 2.9 volts. Even at 3.0 volts there is virtually no usable charge left in the pack - it is well below 20%. And packs don't always hold what the label says they do - a 4000 mAh pack may actually hold only 3850 mAh, or maybe 4200 mAh. The only way to tell is to discharge the pack in question to 3.0 volts and check.


.

A lot of the turnigy packs I have used in the past seemed to hold more than the capaciy stated on the label.

My question is this:
How do you know what the pack actually holds so you can calculate excatly what an 80% discharge would be? I've been running into this with my NeuEnegry packs, which I have never hit the LVC with. I dont even run them close. I run (6) 3s packs as 9s2p. When I quite running the packs they are at 11.0-11.1v (immediately after run and an hour later, they dont seem to recover any voltage). They are 3600mah packs and they are taking around 3400mah to charge. Does this make sense to anyone? I can believe 3.6-3.7v/cell is over-discharging:glare:

[boatinjoe]

a question to one of the above posts, fluid you are saying I can discharge to 3 volts and recharge to specified mah and or cutoff voltage and the total mah put in is what my pack is truly holding?

[785boats]

Kieth.
The old voltage /capacity scales change with the newer High Discharge packs. As stated earlier the voltage stays up higher longer as you discharge the capacity.
You are over discharging your packs. This is reflected in the lack of 20% capacity left in your packs.
Shorten your run times, or you may ruin your batteries.
3.6Volts/cell resting voltage can drop to around 3.1V-3.2V under a load of about 80Amps, so you are probably closer to the LVC than you think.
I consider my packs flat if my resting voltage is 3.75V/cell. Less than that & I know I'm killing them.
After two 5 lap races my 40C 5000mah 4s packs are usually between 3.75-3.85 V/cell. That's flat in my book. They take on between 3800mah-4200mah. Those numbers are good enough for me.
The packs aren't hot or squishy.
These are just my experiences. Others will differ I'm sure.

These are a handy little item at the lakeside. It gives you individual cell voltage but also capacity remaining in the pack expressed as a percentage. And many other features too.
http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=6232&Product_Name=Cellmeter_8_for_Lithium_Polymer_Packs

Boatinjoe.
Yes. I believe that is what Fluid is saying.
Discharge to 3.0V/cell & recharge with a balance charge at the appropriate cell count & amp setting. The charger will tell you how many milliamps the pack takes on.
Use the charger to discharge the pack. It will keep them balanced & it is a light load which gives a better discharge.

Cheers.
Paul.

[keithbradley]

Kieth.
The old voltage /capacity scales change with the newer High Discharge packs. As stated earlier the voltage stays up higher longer as you discharge the capacity.
You are over discharging your packs. This is reflected in the lack of 20% capacity left in your packs.
Shorten your run times, or you may ruin your batteries.
3.6Volts/cell resting voltage can drop to around 3.1V-3.2V under a load of about 80Amps, so you are probably closer to the LVC than you think.
I consider my packs flat if my resting voltage is 3.75V/cell. Less than that & I know I'm killing them.
After two 5 lap races my 40C 5000mah 4s packs are usually between 3.75-3.85 V/cell. That's flat in my book. They take on between 3800mah-4200mah. Those numbers are good enough for me.
The packs aren't hot or squishy.
These are just my experiences. Others will differ I'm sure.

These are a handy little item at the lakeside. It gives you individual cell voltage but also capacity remaining in the pack expressed as a percentage. And many other features too.
http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=6232&Product_Name=Cellmeter_8_for_Lithium_Polymer_Packs

Cheers.
Paul.

Thanks for the advice Paul. I ran the boat again Sunday. I stopped running it just based on the idea that I thought I had ran it a decent amount of time (hard to actually time because I am trying different battery/prop combos so stopping and checking temps, ect) and because I felt the boat had lost some power. I know that may sound silly to some but .5v per cell on 9s makes a pretty big difference.

The batteries were at 3.8v per cell. After charging, they took just under 2000mah, so I definitely didnt over discharge them this time. The batteries are brand new and only have a couple runs...I wonder if that could have played a part in the large amount taken to charge them last time? I do understand what you mean about newer batteries. A large change in capacity may only net a small change in resting voltage. These are only 25C batteries though, and I really thought I ran them as hard this time as I did the time they took 3400mah:confused2:

[785boats]

Good move to bring it in when you 'Feel' it lose a bit of power. That's not silly at all.
You are probably right about the fact that being new played a part in the large amount of discharge the first time. They generally don't take on a full charge for the first few cycles. The next run will probably last a bit longer too.
With my 25C packs a resting voltage of 3.65-3.7V/cell usually leaves the required 20% capacity in the packs. So yes you still have a bit of run time left with your resting voltage at 3.8V/cell on 25C packs .
It'll take a few runs to get to know your packs & how long you can run them.
But I strongly suggest you try one of those battery checkers that show the percentage left in the pack, like the one I posted a link to previously. Takes all the guesswork out of the equation.
Can you set the LVC to 3.4V? That way if you hit it (before you felt like you needed to bring the boat in) you can check the resting voltage & capacity remaining. If both the numbers are still high you can drop the LVC to 3.2V.
I've done that before to gauge how a setup runs.
All the best.
Paul.

[keithbradley]

I havent found a way to program my SF 240HV in a way that would change per cell voltage. I can change # of cells, but it is pre-set at 3.0v/cell, which to me is virtually useless. I guess I use it as a safety to keep from running the packs completely dead in the event of an accident, but I dont depend on it to do much other than that. I will get into the program again and see if I can change the per cell voltage but if I remember right I think I tryed once and couldn't.

That battery check is definitely cool. Do you know if they sell any in the states? I hate ordering from HK this time of year because boating season is almost over as it is:(