Greg Covey
Posts: 4322
Joined: 5/24/2003
From: Rochester,
NY, USA
Status: offline
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Nomadic,
That's a good question. I'm surprised more people don't ask it.
The old ratings method was seen as something like your first example; 15C / 90% It meant that at a 15C discharge rate (or 15 times the pack capacity C) you would still get 90% of the stated capacity. This older rating scheme focused on the capacity left in a pack at a high discharge rate and turned out not be be a critical factor in maintaining cycle life or longevity of the pack. In those days, most vendors (including FMA) had not documented the effects of temperature, cell balance, and discharge rate on the Lithium pack life span.
Today, the new rating scheme looks like this; Ratings: 15C , 11C/140°F , Cell Rating Spec
The first number, 15C, is the maximum discharge current that the cell will handle without puffing, catching on fire, or generally destroying itself.
The second numbers, 11C/140°F, means that the cell can truly be continuously discharged at 11C without loss of cycle life because it remains at or below 140°F. In a multiple cell pack, the inner cells will be about 10°F hotter or 150°F which is ok. The Rule-Of-Thumb is that this second set of numbers is about 70% of the highest C discharge rating without puffing. There are exceptions to this rule but it works for most manufacturers cells.
The last "Cell Rating Spec" is a hyperlink to the information in chart form that plots all the data taken during the cell qualification testing. As FMA is about to release many new cells from multiple manufacturers, the Cell Rating Spec will provide a consistent and more appropriate method for rating the discharge capabilities of Lithium cells.
< Message edited by Fred Marks -- 5/5/2006 2:28:30 AM >
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RE: Welcome to the FMA Direct - Kokam LiPo Support Forum - 
