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        Discussion Lets play 'guess the advertised capacity'

#1 Nethole Oct 20, 2006 08:04 PM

Lets play 'guess the advertised capacity'
 
The initial voltage of the 3S lipo was 11.42 volts. The lipo was charged at less than 0.2 C. The lipo accepted 542 mah.

You know the formula for voltage and % full/empty for a lipo. Do the numbers in your head, or cheat and use a spreadsheet, and play
"guess the ADVERTISED capacity" for this lipo.

#2 everydayflyer Oct 20, 2006 08:27 PM

Quote:

"guess the ADVERTISED capacity"
Between 1500 nad 2000 mAh.

Calculates to approx. 813 mah but tht would be an odd capacity.

Charles

#3 wattsup_kz Oct 20, 2006 08:27 PM

Quote:

Originally Posted by Nethole
You know the formula for voltage and % full/empty for a lipo.

Where is that found?

#4 Eagleburger Oct 20, 2006 08:29 PM

~800Mah

#5 everydayflyer Oct 20, 2006 08:35 PM

Quote:

Originally Posted by wattsup_kz
Where is that found?

http://www.rcgroups.com/forums/showp...1&postcount=11

#6 wattsup_kz Oct 20, 2006 08:51 PM

Thanks!

#7 Nethole Oct 20, 2006 09:07 PM

Quote:

Originally Posted by everydayflyer
Between 1500 nad 2000 mAh.

Calculates to approx. 813 mah but tht would be an odd capacity.

Charles


So tell me, if you calculated 800-ish mah, how did you come up with an advertised capacity guess of between 1500 and 2000 mah?

#8 everydayflyer Oct 20, 2006 09:43 PM

It is common for Vendors to rate capaicty and C much greater than their true numbers.

The industry standard for capacity is based on the 0.2C rate.


http://www.rcgroups.com/forums/showp...13&postcount=1

Snip

Quote:

Cycle life is defined as the point in that test at which the cell delivers 60% of the rated capacity (as measured at 0.2C)
Now if you get a typical flight of 5 hour from a single charge this is very useful imformatation. Close to two years ago I stated that capacity based on less than a 3C discharge meant nothing to electric flyers. 3C is 20 minutes and yet many ststed tha a 1C discharge graph/test was necessary to determine a cells true capacity.
The capacity game is much the same as the cycle life game. Manufactures graphs show 500 cycle ilfe but if you look closely the 500 cyclles are based on discharge rate between 10C and 0.5C and they do not say how many at each dicharge rate.

Charles

Charles

#9 HPSOV Oct 20, 2006 11:12 PM

1000-1300

#10 Nethole Oct 21, 2006 06:38 AM

Ok, now if I told you these were brand new cells. At what mah rating from the seller would you feel that you were given 'incorrect information'?

Lets see if I can be a little clearer. Given these cells are brand new, what would be the appropriate mah rating from the manufactuer? (or perhaps, at what rating from the seller would you feel 'ripped off'?)

#11 hoppy Oct 21, 2006 12:20 PM

Charging mah into a battery of unknown initial charge (1/2 charge voltage varies from brand to brand) is of marginal value to calculate the capacity.
Discharge it at 0.2C and also at the maximum continuous duty rating and see what it gives you. The former might be over 100%, the latter probably around 90%. If it was under 90%, I'd be disappointed.

#12 gulio Oct 21, 2006 04:35 PM

What was the ending voltage?

#13 HPSOV Oct 21, 2006 06:48 PM

Quote:

Originally Posted by Nethole
Ok, now if I told you these were brand new cells. At what mah rating from the seller would you feel that you were given 'incorrect information'?

Lets see if I can be a little clearer. Given these cells are brand new, what would be the appropriate mah rating from the manufactuer? (or perhaps, at what rating from the seller would you feel 'ripped off'?)


I dont see that the charge taken from 11.42v to (I assume) 12.6v has much to do with the total capacity claimed of the battery.
Tell us what the battery delivered from 12.6v down to 9.0v and then I'll tell you what a reasonable claimed capacity would be.

#14 tic Oct 21, 2006 06:56 PM

I don't like this "game" just tell us what you bought and how much less than advertised capacity the pack took.. Please? :o

#15 rpage53 Oct 21, 2006 07:30 PM

Right those numbers are meaningless. At .2C you probably used most of the energy heating up the charger.

Rick.


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