# LiFePO4 form factor



## NuBlue (Apr 2, 2010)

A new white paper on LiFePO4 form factor and future trends has been posted as a free download by Kriss Motors - click "Automotive ebooks" menu item and then select "Battery Form Factor" download. Download is an 8-page PDF file.


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## EVfun (Mar 14, 2010)

Well, I see an error on page 4. In the 60 amp hour cells shown as "conforming" the "Length" and "Height" are listed backwards in the table. As a result, the CALB 70 amp hour cells is shown as a "non-conforming" size, when in fact it matches up to most of the 60 amp hour offerings. I would consider the CALB 60 amp hour and Sinopoly S2 60 amp hour cells to the the non-conforming sizes. 

I would suggest that length and width are the more important factors with perhaps a 3mm range for fitting in an existing design while the height would be more negotiable, perhaps observing a standard introductory height and allowing anything shorter or up to 5mm taller to be within the norm.

I am also a bit confused as to where you found any information indicating the high market share for Sinopoly over Winston and CALB. I've seen very few people even mention them and since they indicate a max discharge of 3C and don't publish discharge data even at 3C I'm not seeing how they will be poised to penetrate the market so effectively. Winston publishes discharge data up to 5C and allows very high brief currents. CALB doesn't publish discharge data up to high C rates but it has become established that they are capable of it, and they allow for short term high peak currents on the data sheet.


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## MN Driver (Sep 29, 2009)

The Winston, ThunderSky, and Sinopoly; pick your timeframe and brand the graphs look the same as they have yet their specs have changed to look more favorable. I never believed the old ThunderSky specs in comparison to the performance tests people have done and posted on either websites or forums so I can't really take them to value now. Back in the day the TS cells would sag out very low around 50% SOC at even 3C and in comparison to a CALB cell that well outperformed the TS cell down throughout the range. They seem much closer now but still different, for example Jack Rickards published tests made them look closer, but still clearly not the same. I'm curious how the Sinopoly cells actually perform now. Their 9 page specsheet that they sent me implies a 3C constant discharge is safe to 85% DOD and will be 2.8v+ at that DOD. I've said it before and its not hard to test and see that LiFePO4 and all other lithium chemistries get hot at high discharge rates, especially below 30% SOC at higher amperages and 20% moderate amperages but even 10% SOC they get warm and very saggy even with 1C. Heat kills. CALB might just be avoiding adding charts of high current discharge to their spechsheet because of how much internal resistance and therefore voltage sag varies with temperature along the SOC curve.

Sinopoly isn't mentioned much because we've already talked about Winston being the new TS but in the end it turns out the Chinese stock of TS actually belongs to Sinpoly making Sinopoly the former ThunderSky and Winston a separate company but since the facts are now recently presented and the Winston name has been present everyone associates Winston with the ThunderSky name we all remember.

Back on the form factor topic though, Sinopoly says they are shrinking cells and raising density and changing cell appearance. So either it means more capacity in the same package which works out well for those who've designed a package but don't have the cells yet or need a replacement cell albeit slightly different characteristics), or the same capacity with a smaller case which works out for those who don't need higher capacity than what is currently out there but want a smaller(and lighter) package. CALB is changing too, the gray cells have been on their web site for nearly a year now and the specsheets have been available for about half a year(if I'm remembering my time frames correctly) but they are completely different shapes and depending on the cell capacity its better or worse than before in terms of wh/weight.


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## EVfun (Mar 14, 2010)

Some early TS offerings imported by Metric Mind where truly terrible. There was no one else offering these cells from any of the manufacturers at that time. It was a couple of years before I'm aware of anyone else trying again.

That said, how do current Winston, Sinopoly, and CALB offerings compare? Winston publishes 5C data and that was one of the main reasons I went back to them. My experience tells me that the cells are good for 2.88 volts at 5C and 2.63 volts at 7.5C (300 amps and 450 amps, from pre-split LiFeYPO4 ThunderSky 60 amp hour cells.) 

Lots of people here can confirm that CALB (Sky Energy) cells perform well. I don't know anyone I could ask about the high C rate performance of Sinopoly cells at this time. Form factor is only one variable and if a manufacture enters this market with a cell that sags significantly more that its competitors it won't really make much difference if they offer it in a standard form factor. It won't be well received. I sometimes wonder if there is a nickels worth of difference between any of the cells.

Back to my question though, how do they come up with data indicating the Sinopoly has a 50% market share in current conversions?


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## NuBlue (Apr 2, 2010)

A few errors are now corrected regarding the 70ah and 60ah cell dimensions. See version 1.1.


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## dougingraham (Jul 26, 2011)

I can see this being an issue if you are planning on doing the same car over and over ala a conversion shop who specializes in one particular kind of conversion. I can see that if all the manufacturers made a common size there would be an advantage to consumers.

It struck me that it would make sense if the only change was in the cell height between different capacities. This would make it straightforward to have a common size and offer different capacity packs without changing the battery box.

I just went through choosing the 100AH cell from all the vendors and I bought the GBS-100AH which does not have a common platform. I chose this one because I was able to make it fit better in the car than the other companies offerings. Additionally it has a slightly higher wh/kg and wh/liter rating than the other companies offerings. A common platform is a nice idea but what if you have a square hole and a round peg? The characteristics of these batteries might turn out to require they be cubes with the connections on opposite ends for optimum performance.

I had noted that there were common sizes from the different trading companies. I had just assumed that this was because they were made in the same physical plant using the same machines with the only visible difference the color of the plastic.


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