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.
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.
All three cells were within a few hundredths of a volt at start of charge. I know there must be some heat generated in the wires and battery during charging, although it wasn't much because the battery was cool to the touch during and after charging.
That is the battery, yes. I also have two of the 2200 mah batteries. At 30C I could discharge the entire battery in 2 minutes, but I'm not using nearly that much power. On the 5000 mah battery the quad flew 16 minutes, which means it was being discharged at 3.75C. So why do I need a 30-40 C battery? That higher C rating actually adds weight that produces little value.
The Tenergy batteries I use are rated at 25C.
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.
For the sake of discussion, what if a lipo will not charge to the full 4.2 volts but something less like 4.05/4.10. Is that an indication the lipo has seen its better days?
4.10 is solid, 4.05 just means there is some loss from use over time. However many times you can charge a 4.05 cell at lower C and bump it back up. I always tell people if you charge at the 1C rate sometimes on bigger batteries it will cause the charger to end the charge early. So example, 5000mah 3S lipo charged at 5amps all cells get to say 4.01 per cell, but charger sees 12.60v sustained charge and calls it finished. This isn't a bad battery issue, it is the charger thinking due to extended 12.60v indication it assumes the charge may be completed. But in fact the per cell levels are only at 4.01 - 4.05. In cases like this either the charger is a cheaper brand and does not look at per cell as to when the charge should complete, or the battery was drained beyond its minimum and just needs some bump charge to get it back up to normal levels.
Now if the bump charge at 1amp doesn't get the cells back to say 4.11 - 4.15 then you can assume the lipo is loosing its power ability on a per cell basis. Sometimes its just one cell losing strength, sometimes its all 3.
I have lipos over say 4 years in use that still get to 4.05 regularly. I use them, and make sure I know they are weaker. So I adjust flight time etc....so I am aware I am using a older battery. Unless Lipos are extremely abused i.e. running beyond amp rating etc.... then they can last well beyond the cycle limits the manufacturers tell us. Just my 2 cents. Try charging that battery at lower amp to see if you can get the cell levels higher, might work out for you - might not :)
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.
Interesting point and I will have to try this.
Yes this works as well, but make sure since the end of the first charge that the cells have not lost energy while sitting for the 2 hrs. If they have that is a tell tale signal of cell degrade, chemistry degrade. I have 2200 that I do the exact same thing, some of them get to 4.15 and hold others when plugged back in show 12.10 - 12.15v total and I know they have dropped cell levels since I let them rest. Those lipos I sit aside and lable degraded. I may still use them in flying wings and gliders, but not in my quads,octos,hexes since multirotors really need the best batteries for safety sake.
It does take time for the ions to diffuse away from the electrodes in the cells, and this manifests itself in some interesting ways, such as the voltage "settling" slowly after disconnecting a load or charger.
Ah ha. The battery claims to be 3C fast charge capable. I charge at 1C. It sounds like 0.5C or even slower will produce the best results.