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dischargering my lipo??? help!!! please

Old 11-14-2009, 07:32 AM
  #1  
huntjulien
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Question dischargering my lipo??? help!!! please

okay guys im still new at this and iv been reading in a bit about discharging my lipo... my triton manual tell me not to discharge it lower than 3.0 volts per cell but im wondering wat i should discharge it to??? theyjust say dont go under... any advice, im new to this discharging concept

ps random question i was also reading somewhere and is it true we have to discharge are new lipo before charging it???
arggg so many random rules to lipos...:c onfused:

by the way its a 3 cell 1300mah lipo
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Old 11-14-2009, 09:24 AM
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You don't need to discharge a lipo (except by using it). There is no useful purpose served and it may reduce the useful life of the battery.

The one exception I can think of is if you want to run it down to the best level for long term storage (a couple of months or more) in which case 3.8V is a good level.

Steve
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Old 11-14-2009, 03:38 PM
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Originally Posted by huntjulien View Post
okay guys im still new at this and iv been reading in a bit about discharging my lipo... my triton manual tell me not to discharge it lower than 3.0 volts per cell but im wondering wat i should discharge it to???
The 'on load' minimum voltage specified by most LiPo battery manufacturers is 3.0 volts/cell. So if you're test cylcing your battery, setting a minimum (per cell) of 3.0v is just fine. In actual use under heavy loads it is not uncommon to allow cell voltages to drop down to 2.9v or 2.8v as once the load is removed, the no load cell voltage will creep up to over 3.0.

Current practice says that LiPos which will be unused for a prolonged time (months) should be put at a 40 to 50 percent charge condition prior to being stored... ...but be aware that there is some disagreement on this...

FWIW... I've had LiPos in storage for a year, put away with a full charge, and when tested they performed just fine at their rated capacity... YMMV...

Just use common sense with LiPos and you'll be fine...

Jim.
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Old 11-14-2009, 06:10 PM
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Storing fully charged lipos in the fridge in a sealed container reduces the capacity reduction to under 5% per year and your batteries are always ready to use as they warm up on the way to the field.


Clint
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Old 11-14-2009, 06:42 PM
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Originally Posted by cbatters View Post
Storing fully charged lipos in the fridge in a sealed container reduces the capacity reduction to under 5% per year and your batteries are always ready to use as they warm up on the way to the field.


Clint
Can someone please explain why a lipo battery needs to be put in a sealed container/baggie when put in the fridge?

I understand about moisture condensation, but the internals of the battery are already sealed (as displayed by a puffed battery not loosing pressure), and the only other concerns could be the wires and connection points, but those are non-corrosive anyway.

Bill
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Old 11-14-2009, 06:52 PM
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Originally Posted by Sir Raleigh View Post
Can someone please explain why a lipo battery needs to be put in a sealed container/baggie when put in the fridge?

I understand about moisture condensation, but the internals of the battery are already sealed (as displayed by a puffed battery not loosing pressure), and the only other concerns could be the wires and connection points, but those are non-corrosive anyway.

Bill
Soilder joints and connectors are not sealed and can suffer from corrosion. Plus, I just don't like wet batteries.

I store mine in plastic bags in a a plastic container. When I take them out, I leave them in a plastic bag until they have warmed up.
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Old 11-14-2009, 06:56 PM
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okay well the thing is i fried my rx from my super cub and i wont get a new one till christmas (hopefully a dx6i with ar6200). i live in canada so flying lipo's in the cold here isnt a good idea from wat i have heard. i will be 3-4 months until i bring it back out of storage... so from what iv got i should fully charge it the baggie and container it up then throw it in my fridge...??
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Old 11-14-2009, 07:11 PM
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Yeah, but you can still get condensation inside the plastic baggie... :o

Where did the 5% per year capacity reduction number come from? What's the % per year capacity reduction number for LiPos stored in a discharged state, and charged just before use? What's the % per year capacity reduction number for LiPos stored in a 100% charged state (but not in a refrigerator)?

In my experience, the battery does not lose CAPACITY over time -- it loses "C" rating over time.
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Old 11-14-2009, 08:31 PM
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Originally Posted by huntjulien View Post
so from what iv got i should fully charge it the baggie and container it up then throw it in my fridge...??
FYI... what temperature has to do with it all...

The rate of chemical reactions which cause internal current leakage - like most chemical reactions - will increase with temperature and therefore the battery self discharge rate will increase as well. At a 20 degree C temp. a LiPo cell will loose 2 to 3 percent of its charge a month... at 40 degrees C it will lose approx twice that.

Opinion follows... I think frig storage is overkill (but won't hurt anything)... I keep my unused batteries in my basement... sits between 12 and 18 degrees C (55 to 65 F) all year. Works fine for me...

Jim.
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Old 11-14-2009, 10:32 PM
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Default LIPO lithium-ion battery storage



Figure 1: Permanent capacity loss of lithium-ion as a function of temperature and charge level.
High charge levels and elevated temperatures hasten permanent capacity loss. Improvements in chemistry have increased the storage performance of lithium-ion batteries.


http://www.batteryuniversity.com/parttwo-34.htm
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Old 11-14-2009, 10:37 PM
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Default LIPO lithium-ion battery storage

Originally Posted by jjw View Post
FYI... what temperature has to do with it all...

The rate of chemical reactions which cause internal current leakage - like most chemical reactions - will increase with temperature and therefore the battery self discharge rate will increase as well. At a 20 degree C temp. a LiPo cell will loose 2 to 3 percent of its charge a month... at 40 degrees C it will lose approx twice that.

Opinion follows... I think frig storage is overkill (but won't hurt anything)... I keep my unused batteries in my basement... sits between 12 and 18 degrees C (55 to 65 F) all year. Works fine for me...

Jim.
How about doing a capacity check on a battery that you have stored for a year at 100% capacity and compare before/after capacity.
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Old 11-14-2009, 11:07 PM
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Yeah -- I've already done that. I can take a 20C LiPo that I've used on a high-discharge rate (20-amp) application (ParkZone Stryker) for one year -- that LiPo no longer keeps the Stryker in the air, but can keep a low-discharge (12-amp) rate application (GWS P-51 Mustang) in the air for 20+ minutes...

Looking at the flight log that I've kept for the last 5 years, the older LiPos don't lose capacity -- they lose "C" rating. The flight log keeps track of mAh put back into the LiPo after a flight. As long as I "retire" a LiPo to a lower-amp-draw application, I can keep the LiPo going AT FULL CAPACITY indefinitely.
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Old 11-14-2009, 11:30 PM
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Originally Posted by Lieutenant Loughead View Post
Yeah -- I've already done that. I can take a 20C LiPo that I've used on a high-discharge rate (20-amp) application (ParkZone Stryker) for one year -- that LiPo no longer keeps the Stryker in the air, but can keep a low-discharge (12-amp) rate application (GWS P-51 Mustang) in the air for 20+ minutes...

Looking at the flight log that I've kept for the last 5 years, the older LiPos don't lose capacity -- they lose "C" rating. The flight log keeps track of mAh put back into the LiPo after a flight. As long as I "retire" a LiPo to a lower-amp-draw application, I can keep the LiPo going AT FULL CAPACITY indefinitely.
How about doing a discharge test and see what the charger says the capacity of the pack is.
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Old 11-15-2009, 12:24 AM
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Originally Posted by cbatters View Post
How about doing a capacity check on a battery that you have stored for a year at 100% capacity and compare before/after capacity.
I've done just that many times... What I typically do before using a battery that's been in storage for awhile is.. (1) cycle it once... (2) bring it to a full charge... (3) check the capacity using my West Mountain Radio CBAII battery analyzer. I have rarely had a LiPo not meet its stated capacity...

In my experience LiPos seem to just gradually lose their capacity with use... the number of charge/discharge cycles has a more significant affect on life than any length of time they are stored... YMMV....

Jim.
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Old 11-15-2009, 03:21 AM
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Hmmmm -- I've never used the discharge function on my Triton charger... I never saw the need to use it (I'd rather just discharge my LiPos by flying them!)...
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Old 11-15-2009, 12:03 PM
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Originally Posted by jjw View Post
I've done just that many times... What I typically do before using a battery that's been in storage for awhile is.. (1) cycle it once... (2) bring it to a full charge... (3) check the capacity using my West Mountain Radio CBAII battery analyzer. I have rarely had a LiPo not meet its stated capacity...

In my experience LiPos seem to just gradually lose their capacity with use... the number of charge/discharge cycles has a more significant affect on life than any length of time they are stored... YMMV....

Jim.
Number of cycles, terminal charge voltage, discharge rate and storage temerature all affect longevity and capacity.



Figure 2: Effects on cycle life at different float charge levels (Choi et al., 2002)
Higher charge voltages boost capacity but lower cycle life.




Figure 3: Longevity of lithium-ion as a function of charge and discharge rates.

A moderate charge and discharge puts less stress on the battery, resulting in a longer cycle life.
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Old 11-15-2009, 01:41 PM
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Originally Posted by cbatters View Post
Number of cycles, terminal charge voltage, discharge rate and storage temerature all affect longevity and capacity.






Figure 3: Longevity of lithium-ion as a function of charge and discharge rates.

Absolutely correct... all factors do have an impact. However, note in the graph you provided above that the discharge rates are relatively mild. In most model aircraft applications theses rates are significantly higher. In my case I typically size my batteries to run at 8C to 12C at WOT... These high rates have a huge impact on life... It's difficult to pull that data out of the graph you provided as it convolves charge and discharge, but notice the capacity degradation rate between 1C and 3C...

As always... YMMV...

Jim.
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Old 11-15-2009, 06:19 PM
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According to those graphs, I should be able to get 500 cycles out of my LiPos. I actually only get about 100 cycles.

I charge and discharge at 0.5C, and my charge voltage is 4.20 volts.

My personal experience tells me those graphs are not correct. :o
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Old 11-15-2009, 06:55 PM
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Originally Posted by Lieutenant Loughead View Post
According to those graphs, I should be able to get 500 cycles out of my LiPos. I actually only get about 100 cycles.

I charge and discharge at 0.5C, and my charge voltage is 4.20 volts.

My personal experience tells me those graphs are not correct. :o
?? What kind of plane do you fly where you are discharging at .5C?
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Old 11-15-2009, 07:46 PM
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Originally Posted by Lieutenant Loughead View Post
I charge and discharge at 0.5C, and my charge voltage is 4.20 volts.
Discharge at 0.5C?!... You must have the most relaxed flying airplanes out there...

Jim.
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Old 11-15-2009, 07:48 PM
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Originally Posted by jjw View Post
Discharge at 0.5C?!... You must have the most relaxed flying airplanes out there...

Jim.
Maybe he enjoys just taxiing around - safer than flying and puts less wear and tear on the batteries!
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Old 11-15-2009, 10:54 PM
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Yeah, okay... I suppose I don't DISCHARGE at 0.5C... My mistake.

Still, I charge at 0.5C, and discharge my 20C batteries at about 10C (which is where I got confused and said it was half a C instead of half of the C rating). Again, my mistake. :o
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Old 11-16-2009, 12:00 AM
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Originally Posted by cbatters View Post
Maybe he enjoys just taxiing around - safer than flying and puts less wear and tear on the batteries!
actually i dont... if he is taxiing around in a parking lot maybe flying would be safer aslong as he is way up there in the sky... just dont crash and i think flying is safer...
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