Lipo capacities. Are all lipos over rated in terms of capacities?

[LittleGiant]

Got 2 3s 1500mah lipo packs. Charged and discharged for 2 cycles fully. Cells were discharged from 4.2V to 3V each. Total charge and discharged capacities are constant and values are very close (1290mah - charge vs 1285mah discharge). Discharge rate was tested at 1C and 2C (both discharge capacities are similar) But isn't the lipo rated at 1500mah? Why is the battery over rated by more than 200mah?

Will there be such a problem with more expensive lipos? I mean are expensive lipos over rated as well in terms of capacities?

[HotDogBun]

From my experience with lipos, 2s1p to 6s1p, once each cell hits 3.68V or below, they will be unbalanced. usually.
That is why many flyers always discipline our flying such that each cell is about 3.7V when landed.

I have encountered such an incident before on my 3s lipo for my enginer starter. The voltage dropped till all cells are unbalanced, below 3.5V each. When I charge it up, the capacity charged in shown on my charger was 2215mAh, when the lipo was rated at only 2200mAh. I was using ImaxB5 and 3E lipo.

Unlike Nicad, it is unwise to discharge lipos to 3V per cell. We usually discharge to 3.8V per cell, for storage purposes. Other than that, few will actually condition them.

Thats my opinion so there may be others who does things differently.

[LittleGiant]

From my experience with lipos, 2s1p to 6s1p, once each cell hits 3.68V or below, they will be unbalanced. usually.
That is why many flyers always discipline our flying such that each cell is about 3.7V when landed.

I have encountered such an incident before on my 3s lipo for my enginer starter. The voltage dropped till all cells are unbalanced, below 3.5V each. When I charge it up, the capacity charged in shown on my charger was 2215mAh, when the lipo was rated at only 2200mAh. I was using ImaxB5 and 3E lipo.

Unlike Nicad, it is unwise to discharge lipos to 3V per cell. We usually discharge to 3.8V per cell, for storage purposes. Other than that, few will actually condition them.

Thats my opinion so there may be others who does things differently.

I have an ETEC 3S 1700mah lipo. When I first got it, it was having a capacity of around 1600mah. But I left it on full charge each time I store it. I used it for less than 30 cycles but when I tested it recently, the capacity dropped to around 1200mah. So are the cells damaged now?

[johndyl]

lipos degrade rapidly(ie capacity drop) with full charge at room temp.

if u need to store at full charge, it is best to store them in your fridge(vege or freezer if u like), that will slowly down the degradation very significantly.

else if u have to store at room temp, store at 3.7V to 3.8V per cell.

have a look at the lipo/Li-ion article at "battery university"

[HotDogBun]

You need to charge it up and use it to know if it is holding the voltage well or not.
For example, previously for that lipo you can use for 10min on our electronics before it becomes 3.8V per cell and you put back say 1200mAh. Now you do the same and see if the voltage can hold that 10min, if it can, then monitor how much you charge back.
Usually if lipo is faulty, there are few symtoms like
- you cannot use that long as last time and the voltage drops to very low even before you can reach the usual time you put it to strain.
- the cells always unbalanced after each flight.

3.8V seems to be the storage voltage used globally. Almost all the NIB lipos always comes around that voltage, maybe at that voltage the chemical reaction in lipo is not that much perhaps.

[HotDogBun]

if u need to store at full charge, it is best to store them in your fridge(vege or freezer if u like), that will slowly down the degradation very significantly.

Be very careful when you do that because when you bring it out of the fridge, condensation will take place and will cause wires within to short, when is very dangerous.
What you can do is, to wrap the lipo in think cloth the moment you bring it out of the fridge. This will slow the cooling process and lessen the condensation.

[HotDogBun]

Not only do I stammer, my bloody grammar sucks.
Pls let me repeat

Be very careful when you do that because when you bring it out of the fridge, condensation will take place and will cause wires within to short, which is very dangerous.
What you can do is, to wrap the lipo in thick towel the moment you bring it out of the fridge. This will slow the cooling process and lessen the condensation.

[LittleGiant]

I mean I know about the optimal storage charge. I have been using lipos for over a year now. I know that capacity will drop if the lipo is held at full charge for prolonged periods of time. The thing is new lipos (china brand) that are freshly made dun even meet their rated capacities. Do more expensive lipos have problems like this?

BTW, HotDogBun, how is the charger working?

[LittleGiant]

BY the way when i say full charge, I mean having my lipos charged from 3V to 4.2V. And full discharge means from 4.2V to 3V (under load - usually cells go back to 3.3 to 3.5V once load is disconnected).

[HotDogBun]

The charger is serving me well
Used it once to charge my 6s lipo so far, the fan is actually on thermosat, so it will only activate when the temp is above the limit, a function to lengthen lifespan of fan

I'm quite surprised you discharge your lipo to below 3.5V per cell. From my experience, at this voltage, all the cells will go crazy and be unbalanced if they are discharge through dean, not sure if using balancer to discharge individually.

I have been using reputable lipos like Flightpower when I first started. When I switched to other brands like 3E,ZippyR, Rhino, and now Vplus, I realised their discharge is as good as one needs. The do not bloat like what some reputable lipos like FP and TP do.

I am not sure which lipo is from China, but I have heard most of the lipos from market originated from Korea. You can name some brands to see if anyone has used them?

[johndyl]

Not only do I stammer, my bloody grammar sucks.
Pls let me repeat

Be very careful when you do that because when you bring it out of the fridge, condensation will take place and will cause wires within to short, which is very dangerous.
What you can do is, to wrap the lipo in thick towel the moment you bring it out of the fridge. This will slow the cooling process and lessen the condensation.

Not only do I stammer, my bloody grammar sucks.
Pls let me repeat

Be very careful when you do that because when you bring it out of the fridge, condensation will take place and will cause wires within to short, which is very dangerous.
What you can do is, to wrap the lipo in thick towel the moment you bring it out of the fridge. This will slow the cooling process and lessen the condensation.

been doing that for all my lipos without using any towel for more than a year and no probs encountered.

if u open up modern lipo packs, u'll notice that each cell is well sealed and the internal wires(balancing) and tabs(cell) are well insulated.

In fact frankly, i have quick rinsed some lipos b4 under running filtered water without any shorting as filtered water is bad conductor. Similarly condensed water is ion-free/pure and a v poor conductor. Note that water still can conduct electricity(as can wood) but that is at very high voltages; and not at the voltages we run operate 3s or even 6s packs.
(Some additional myth to debunk: Most ppl think tat they will feel a burn if they physically touch both the +ve and -ve's of a pack. This is UNTRUE from personal experience, at least for up to 6s packs)

Submerging the pack in salt water is another story though, because salt water is a relatively gd conductor and the contacts are constantly shorted thus killing the pack.


With that being said, one can still dry off the packs first b4 using if kiasu,,, but condensation will still occur until the pack reaches ambient temp.
And wrapping them in a thick towel(alot of trapped air - bad heat conductor) will slow down the natural evaporating and ambient warming of the pack(ie the pack stays cold and likely damp longer) ..

Disclaimer: U still have to use Lipos carefully and know what u are doing

[johndyl]

FYI most Lipo packs are from China, and most packs from there are fully rated nowadays.

In fact some of the best brands/lipos that we know of in the market use these cheap China cells.

The most impt thing abt Lipos is proper usage and handling.

[HotDogBun]

Thanks for sharing Johndyl
But on safe side I will discourage anyone from putting lipos in the fridge. The least I want is for moisture to cause wires to oxidise and short in the end.

[HotDogBun]

Using the towel is not a fool proof plan to prevent condensation. But it will definitely reduce the amount of condensation taking place inside and outside the lipo.
With the towel being dry, it also helps to absorb the moisture to a certain extend.
The entire purpose of using the towel is to reduce the condensation and prevent aftermath.

Or maybe I am wrong in my theory?

[HotDogBun]

Just to share some acknowledgement of lipo storing in the freezer.

But condensation is still my biggest worry. Having moisture is ok, but having condensation in the lipo is definitely a big worry still, at least for me.

Not being KiaSu, its being KiaSi