Usable LiPoly capacity. - RC Groups
Thread Tools
Jan 18, 2007, 09:20 AM
Southern Pride
everydayflyer's Avatar
Discussion

Usable LiPoly capacity.


The recommended maximum capacity to be used from a LiPoly is 80% if one wishes to enjoy long service from said battery.

Most seem to want to use an arbitrary LVC point and this is just not possible in most cases. The LVC is a point reached under load and this voltage varies with the applied load, the true C of the pack the condition of the pack,the temperature and other variables.

I choose a graph of two different 1000 mAh rated packs which were capable of delivering just over their rated capacity at close to a mid range constant load.

This is an old graph and I merely added the line at 800 mAh (80% cap.) point which just happens to be at approx. 3.5 V per cell.

Charles
Last edited by everydayflyer; Jan 18, 2007 at 10:24 AM.
Sign up now
to remove ads between posts
Jan 18, 2007, 10:42 AM
Registered User
Charles, I have been contemplating this question. It never seemed like a good idea for the batteries to discharge their entire capacity.
Jan 18, 2007, 11:16 AM
Southern Pride
everydayflyer's Avatar
Post here is a year old and even the 3.2V per cell I referenced there was really to deep.

https://www.rcgroups.com/forums/show...68&postcount=1

LVC is a moving target. Remaing capacity or the amount required too recharge the battery is a much better indicator. Most current generation LiPolys will have an open cell voltage of approx.3.7 if they have 20% capacity remaining.


Charles
Jan 18, 2007, 11:32 AM
just look at it smokin'
z-matrix's Avatar
Quote:
Originally Posted by everydayflyer
Post here is a year old and even the 3.2V per cell I referenced there was really to deep.

https://www.rcgroups.com/forums/show...68&postcount=1

LVC is a moving target. Remaing capacity or the amount required too recharge the battery is a much better indicator. Most current generation LiPolys will have an open cell voltage of approx.3.7 if they have 20% capacity remaining.


Charles
Charles,
as far as i know under voltage lockout voltage varies with load current, as internal resistance gets connected in series with load, and you cannot directly monitor the virtual 3.6V cutoff voltage.

if you measure your pack voltage after cutoff, you will notice at what voltage will the cell pop back at no-load condition.

then it should be above 3.6V

what is your opinion?
Jan 18, 2007, 11:53 AM
Southern Pride
everydayflyer's Avatar
What we seem to have here is a failure in communications.
To me your post has the same meaning as mine only worked differently and you are using 3.6V where I used 3.7V.

Take a 1000 mAh verified capacity at 50% of its rated cont. C LiPoly and discharge 800 mAh from it .let it set at room temp fro 30 min and measure the voltage.


A now very old post on capacity / volts.

https://www.rcgroups.com/forums/show...1&postcount=11

Quote:
4.20v = 100%
4.03v = 76%
3.86v = 52%
3.83v = 42%
3.79v = 30%
3.70v = 11%
3.6?v = 0%

Capacity below 3.7v "resting" is not usable for flying, it's where the battery voltage dump begins.

Jim
A snip from one of my post in the same thread

Quote:
So my finding are that from a resting voltage of 10.81 to a resting voltage of 11.42 for this pack required 400 mAh charge or roughly 36%.for a 0.2 v per cell increase.
I know the voltage / capacity curve is not exactly linear however.
10.81/3=3.6033 per cell
and adding 36% increaed per cell voltage to 11.42/3=3.8066 .
To me it loolks like 20% remaining capacity would be very close to 3.7 V.

Cells which I have checked were very close to these numbers.



Charles
Last edited by everydayflyer; Jan 18, 2007 at 12:08 PM.
Jan 18, 2007, 11:59 AM
just look at it smokin'
z-matrix's Avatar
Quote:
Originally Posted by everydayflyer
What we seem to have here is a failure in communications.
To me your post has the same meaning as mine only worked differently and you are using 3.6V where I used 3.7V.

Take a 1000 mAh verified capacity at 50% of its rated cont. C LiPoly and discharge 800 mAh from it .let it set at room temp fro 30 min and measure the voltage.


A now very old post on capacity / volts.

https://www.rcgroups.com/forums/show...1&postcount=11






Charles
Acknowledged

hmm, im concerned about 100% capacity,
4.20V is relative more than 100% of the standard charge method,
unless it is a very low internal resistance pack, with short constant voltage stage.
though i have seen 2 standard charge methods, one is charge at 0.5-1C, stop after going below 0.1C current in CV stage,
other is same with 0.03C cutoff.

my fully charged cells are 4.12-4.16V usually.
Z
Last edited by z-matrix; Jan 18, 2007 at 12:05 PM.
Jan 18, 2007, 12:10 PM
Southern Pride
everydayflyer's Avatar
4.16 is my SOP target and IMO is a 96% state of charge.


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Idea CBA LiPOly Capacity Decay - fAct or Fiction? everydayflyer Batteries and Chargers 5 Jul 24, 2005 03:07 PM
LiPoly Capacity @ 4.2 versus 4.1 resting volts. everydayflyer Batteries and Chargers 25 May 06, 2005 01:13 PM
LiPoly capacity ,on the bench / in the air. everydayflyer Batteries and Chargers 3 Mar 15, 2005 08:13 AM