Quote:
Originally Posted by himalaya
Here in China soft pack LiFePO4 cells has been around for some time, I would say two years at least. Due to its higher IR and the long exsisting superstition to "genuine" A123 cells, they are not selling too well in RC market, but it's pretty successful in electric bikes. Bigger steel case cells for automotive use has also came out.
I have to agree with you that Chinese products quality has been tremendously improved. I still rememeber when I was around 10 years old making my first 6-transistor radio I have to scratch all transistor legs with a knife to get them solderable, now my company has automatic pick&place machine and multi-temp-zone reflow soldering oven making BEAUTIFUL PCB assemblies.
One of my friends is a competitive RC boater, he spoke to a LiPo factory to get the finest cells to win the game. What he was told is they do "filter" their products to several grades, usually called A, B1 and B2. 5Ah 28C cell as an exmaple, they draw a line at 1.9mOhms. In other words, You may get a 1.8mOhms cell with twice the price of a 1.9mOhms cell. There are difference between A and B grades but not heaven to earth, if there are such huge diversity, the production line MUST be stopped to check what has gone wrong.
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The only grades I know of are the ones that sit in stock for longer then expected. As far as fresh cells go, yes they'll vary in resistance and capacity a little, it happens to almost if not everything as it's hard to have two of the same exact thing made. If a pack builder gets a lot of cell, he may choose to check the resistance and capacity on all of the cells to have them match as close as they can and maybe the price increase of some brands is due to that. Now the question is, how many of the pack builders have the machines capable of doing such a job? Most materials used in the lithium battery manufacturing is as pure as 99.99% and I bet the factory will not have other production lines using 85, 90 or 95% pure material just to cut cost and have a grading sytem going. I like to wait and see what's working for everyone and if I feel the need for more lipos, I just go through the ones that are working good.