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

[johndyl]

most likely they are overused. Lithium batts do not like to be deep-cycled(meaning running them to 3V) unlike NICAD batts, contrary to popular belief.


As a sidenote, NiMH should not be deep-cycled as well. Deep cycling causes substantial capacity drops.

[zennith]

most likely they are overused. Lithium batts do not like to be deep-cycled(meaning running them to 3V) unlike NICAD batts, contrary to popular belief.


As a sidenote, NiMH should not be deep-cycled as well. Deep cycling causes substantial capacity drops.

Lipo does not like deep cycling - agree.

But when you go queenstown you will see deep cycling of NIMH (during competition and normal days). Their batt use and throw...just wack... serious rugged racer

[LittleGiant]

most likely they are overused. Lithium batts do not like to be deep-cycled(meaning running them to 3V) unlike NICAD batts, contrary to popular belief.


As a sidenote, NiMH should not be deep-cycled as well. Deep cycling causes substantial capacity drops.

But manufacturer always state do not discharge below 3V so what kind of 3 V do they mean? 3V at 0.5C discharge or 1C/2C/0.5xmax cont discharge????

[johndyl]

Lipo does not like deep cycling - agree.

But when you go queenstown you will see deep cycling of NIMH (during competition and normal days). Their batt use and throw...just wack... serious rugged racer

for NiMH think that will be at the cost of cycle life maybe that's why see alot of NiMH packs being sold after abt 30 cycles :P

[johndyl]

But manufacturer always state do not discharge below 3V so what kind of 3 V do they mean? 3V at 0.5C discharge or 1C/2C/0.5xmax cont discharge????

3V is worse case scenario for Lipos... if it goes below 3V... most likely it has been permanently damaged after that "cycle".

using lipos from 4.2V(full cell voltage) to abt 3.7V(or 3.6) is best at prolonging the lipo usable cycles.

That is other than storing at low temps and 3.8V ;)

if u need more run time, I would suggest getting a bigger capacity lipo or more packs. This will be more economical over the long run...

[johndyl]

i meant "discharging to below 3v is the worst case scenario for lipos"

[johndyl]

for NiMH think that will be at the cost of cycle life maybe that's why see alot of NiMH packs being sold after abt 30 cycles :P

OT abit more................oops should be lost capacity

"Over-discharging
A complete discharge of a cell until it goes into polarity reversal can cause permanent damage to the cell. This situation can occur in the common arrangement of four AA cells in series in a digital camera, where one will be completely discharged before the others due to small differences in capacity among the cells. When this happens, the "good" cells will start to "drive" the discharged cell in reverse, which can cause permanent damage to that cell. Some cameras, GPS receivers and PDAs detect the safe end-of-discharge voltage of the series cells and auto-shutdown, but devices like flashlights and some toys do not. A single cell driving a load won't suffer from polarity reversal, because there are no other cells to reverse-charge it when it becomes discharged.

Irreversible damage from polarity reversal is a particular danger in systems, even when a low voltage threshold cutout is employed, where cells in the battery are of different temperatures. This is because the capacity of NiMH cells significantly declines as the cells are cooled. This results in a lower voltage under load of the colder cells." Source Wikipedia

[zennith]

Interesting for other made lipos

A:RC AIR TECH MAGAZINE Vol.19 page 15, #1 RC hobby magazine in Taiwan, has performed destructive testings of KongPower battery. It concludes that KongPower battery does withstand overdischarging without damage.

Could a 7.4V Li-Po battery been overdischarged to 4.4V( 2.2V / cell )?
2.2V per cell tested link:

http://www.kongpower.com.tw/english/index.php?option=com_content&view=article&id=126:could-a-74v-li-po-battery-been-overdischarged-to-44v-22v--cell-&catid=47:all&Itemid=62

Also many FAQ can be interesting and MFG claims

http://www.kongpower.com.tw/english/index.php?option=com_content&view=category&id=48&Itemid=101

In field I saw people discussion on the sending back to MFG for bloat.

[LittleGiant]

3V is worse case scenario for Lipos... if it goes below 3V... most likely it has been permanently damaged after that "cycle".

using lipos from 4.2V(full cell voltage) to abt 3.7V(or 3.6) is best at prolonging the lipo usable cycles.

That is other than storing at low temps and 3.8V ;)

if u need more run time, I would suggest getting a bigger capacity lipo or more packs. This will be more economical over the long run...

The thing once the cell is disconnected from the load, the voltage across the cell will jump back to around 3.5V (depending on the make of the cell) so is this considered safe?

[johndyl]

The thing once the cell is disconnected from the load, the voltage across the cell will jump back to around 3.5V (depending on the make of the cell) so is this considered safe?

my loadless voltage per cell is usually abt 3.7V(3.6 as a min)

btw, mind sharing the brand of lipo that u seem to be having problems with?

[Ghostfit]

I usually dun bother with the voltage when discharging them, I'm more concern about not draining more than 80% of their rated capacity.

Most lipo start to get really hot when discharging beyond the 80% mark and it is this catalyst/heat which will kill your packs.

Another lipo killer is allowing them to be charged beyond 4.25V

[jansonfinn]

I usually dun bother with the voltage when discharging them, I'm more concern about not draining more than 80% of their rated capacity.

Most lipo start to get really hot when discharging beyond the 80% mark and it is this catalyst/heat which will kill your packs.

Another lipo killer is allowing them to be charged beyond 4.25V

But i'm using the voltage as a guide after my flights

[johndyl]

voltage is a quick check for the amt of juice left, other than a digital charger..

[LittleGiant]

But i'm using the voltage as a guide after my flights

Voltage under flight dun usually help much because when the lipos are placed underload, the output voltage could be well below 3V if the lvc on the esc is not set correctly.

[LittleGiant]

I have tested the mystery 20C 900mah 2S lipos.

Their actual capacity is only 800mah. But it provide plenty of power. My brushless lama can simply shoot upward by maxing on the throttle stick.

But the weird thing about this lipo is that with my 10A hobbywing brushless esc set at 2 lipo cells, the lama comes down with the lipo at 6.05V. Do note that the LVC kick in during flight (under load) and the voltage didn't rise even after the lipo is disconnected. However the capacity didnt get reduced. It stayed consistantly at around 800mah (tested using discharge at 1C) even after 10 similar cycles. This lead me to think that the voltage across these mystery cells under load is the same as when it is not loaded.

Weird huh. Can anyone explain this?