Oct 20, 2006, 08:04 PM Registered Lurker Joined Aug 2004 2,613 Posts Discussion 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.
Oct 20, 2006, 08:27 PM
Southern Pride
Haralson County GA. USA
Joined Oct 2004
35,074 Posts
Quote:

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

Charles
Last edited by everydayflyer; Oct 20, 2006 at 08:34 PM.
Oct 20, 2006, 08:27 PM
Frequent Flyer
Kalamazoo, MI USA
Joined Aug 2003
2,891 Posts
Quote:
 Originally Posted by Nethole You know the formula for voltage and % full/empty for a lipo.
Where is that found?
 Oct 20, 2006, 08:29 PM Electric Hippy Brisbane Joined Nov 2005 2,393 Posts ~800Mah
Oct 20, 2006, 08:35 PM
Southern Pride
Haralson County GA. USA
Joined Oct 2004
35,074 Posts
Quote:
 Originally Posted by wattsup_kz Where is that found?
http://www.rcgroups.com/forums/showp...1&postcount=11
 Oct 20, 2006, 08:51 PM Frequent Flyer Kalamazoo, MI USA Joined Aug 2003 2,891 Posts Thanks!
Oct 20, 2006, 09:07 PM
Registered Lurker
Joined Aug 2004
2,613 Posts
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?
Oct 20, 2006, 09:43 PM
Southern Pride
Haralson County GA. USA
Joined Oct 2004
35,074 Posts
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
Last edited by everydayflyer; Oct 20, 2006 at 09:52 PM.
 Oct 20, 2006, 11:12 PM Registered User Sydney, Oz. Joined Mar 2006 441 Posts 1000-1300
 Oct 21, 2006, 06:38 AM Registered Lurker Joined Aug 2004 2,613 Posts 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'?)
 Oct 21, 2006, 12:20 PM Space Coast USA Space Coast Joined Oct 2000 23,157 Posts 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.
 Oct 21, 2006, 04:35 PM That's a funny word NE Ohio Joined Apr 2003 3,720 Posts What was the ending voltage?
Oct 21, 2006, 06:48 PM
Registered User
Sydney, Oz.
Joined Mar 2006
441 Posts
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.
 Oct 21, 2006, 06:56 PM thunderscreech United States, MI, Gaylord Joined Dec 2000 11,300 Posts I don't like this "game" just tell us what you bought and how much less than advertised capacity the pack took.. Please?
 Oct 21, 2006, 07:30 PM Boffin Victoria, BC, Canada Joined Apr 2001 3,412 Posts Right those numbers are meaningless. At .2C you probably used most of the energy heating up the charger. Rick.