One brand new Tenergy 3s 5,000 mah battery is fully charged with a balance charger and flown in an arducopter quad for 16 minutes. My battery alarm goes off at 10.8 volts (3.6 volts per cell on a 3s lipo) and I promptly land. Before re-charging I check the battery under no load and see that it is 11.1 volts. Nothing unusual. It goes onto my Thunder AC6 charger with a charge current of 5 amps (1C). The balance plug is used. The battery fully charges to 4.15 volts per cell. The charger tells me it put 4,998 mah into the battery.
How's that possible? Is Tenergy labeling the batteries at only 80% of their capacity? The cords and battery were not warm after charging. I'm I doing anything wrong? The only thing odd is that the charger indicates a maximum current of 4.5 amps during charging instead of the 5 amps expected.
Thanks,
Mike
Replies
Unless the charger charges through the balance lead it will balance cells by discharging the high cells.
So the charger is the unit dissipating the heat and this is why you will see more mA go in than the stated capacity sometimes, especially if the battery is unbalanced or has a lazy cell.
Newer LiPo's seem to 'dump' quickly at the end compared to older generations. I used to have my low voltage alarm set to 10.4V but found with my new packs that in the short time between the alarm and me landing the voltage had already dropped into the upper 9's or lower. Have set the alarm higher now.
I found also that charging with a balance program rather than just a normal charge puts in a lot more mAh than normal as presumebly some mAh is used to alter the balance.
LiPo batteries are created by mixing several chemicals together and mixing process is not 100% accurate. Because of this manufacturers usually put a bit higher grade mixture to their batteries to fullfil capacity that is on their sticker. Also you need to remember that capacity is shrinking slowly after every charge.
Making LiPo batteries is not actually so easy and fast thing that you would guess. I have been visiting several factories to see it's process and nowdays I treat my batteries with high respect.
PS. Did you know that it takes 32-37 days to make one good battery :)
jani / jDrones
A standard thing for batteries is that the open circuit voltage will always be higher than the load voltage.
When plugged into a system, and drawing power from the battery, the voltage will drop. Disconnect the battery and the voltage will rise.
A few things:
With all of these things taken together, I don't think what you've described is terribly unusual.
I do recommend that if your charger is capable of logging various parameters, you take a look at the data. You might also run a discharge cycle on your pack to see how much capacity the charger believes it measures during that.
If you check out the quality chargers you will see that they ramp down the charging current when they get to 12.6 volts, and keep ramping down while maintaining 12.6 volts.
Usually the cutoff charge point is set by the mA level, less that 200 to 500 mA would denote a fully charged battery.
Not all chargers are designed or programmed correctly.
After letting the battery sit for about 2 hours I put it back on the charger. It put an additional 168 mah onto it and brought the voltage to 12.6. I have seen this with 2200 mah Tenergy batteries too. The only way to get a 12.6 volt charge is to let them "rest" a short period and then put them back on the charger again.
LiPo batteries don't warm up when charged, worry if they do.
The clue here I think is that the charger only takes the batteries to an indicated 4.15 volts whereas a full charge on a LiPo is 4.2 volts.
If you have access to another charger I would try that and compare your findings.
I would suspect the charger more than the batteries.
Just a guess here, but one factor could be the balancer: I know that some balancers work by comparing the cell voltages to each other and discharging the higher ones until the voltages are equal. This could account for a some of the energy.
There are a variety of other explanations that come to mind; lithium ion chemistry is a little less than 100% efficient at charging.
Somebody else might know for sure.