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  #11  
Old 02-02-2011, 03:19 AM
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Default Re: Battery Box Design

I’m still chewing on this: http://www.che.sc.edu/faculty/popov/drbnp/website/Publications_PDFs/Web26.pdf

I hate the authors by now pretty much. With their endless repeating and using sentences that never seem to end. And words they chose to confuse normal people on purpose.

I’ve found a few interesting things so far. But a lot is still not clear to me. Cell formation is one of the interesting things. But is not important in this topic. It’s like formatting a hard disk.

There is a lot about temperatures. The aging test are done at different temperatures: -10, 0, 25 and 50C. The absolute degradation of the cells is the worst at -10. But relatively it’s worse at 50C. The initial capacity at -10 is from the beginning much lower than at 50C.

I haven't read yet what the capacity of these cells that where aged at -10 is at 25C after the >5000 cycles. That's very important. But I’m slow.

My gut feeling tells me: high temperatures (but below 60C) is good for short term performance. You have higher capacity and more power available at that particular moment. But at the cost of earlier long term capacity and power losses.

You have to choose between these two firstly before designing a battery box. Do you want maximum performance right now? Or do you want your cells to last as long as possible?

Also take in consideration that the cells are heaters by themselves. If the insulation is sufficient you don’t need extra heating. Only the first few miles might be a bit under powered.
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  #12  
Old 02-02-2011, 06:15 AM
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Default Re: Battery Box Design

I'm thinking of having some built using aluminum. This time I want boxes with a top too. I'm thinking of insulating bottom and sides with this stuff. Its' 5/32" thick and about R4 I think. Diamond plate is expensive I heard and after a while will be dingy anyway. I was wondering what else I should use. How about billet sheets?

Thermostatically controlled muffin fans with louvers in the top of the sides would help remove heat in summer and soil heaters could warm them in the winter.
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  #13  
Old 02-02-2011, 06:21 AM
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Default Re: Battery Box Design

Quote:
Originally Posted by Jan View Post
My gut feeling tells me: high temperatures (but below 60C) is good for short term performance. You have higher capacity and more power available at that particular moment. But at the cost of earlier long term capacity and power losses.
I agree that up to a point heat is good, as long as you don't get electrolyte break down and stay below that point I'm not sure what the mechanism is that would cause early losses.
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Old 02-02-2011, 06:22 AM
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Default Re: Battery Box Design

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Originally Posted by ElectriCar View Post
I'm thinking of insulating bottom and sides with this stuff.
What about the top where you'll have most of your heat loss?
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  #15  
Old 02-02-2011, 06:34 AM
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Default Re: Battery Box Design

I didn't think about the top as my old box is more of a rack with no top. But yea the top would be good too in winter. In "the video" they say to limit the temp to 55-60C I think. Calb said keep it below 60 which I think you saw that in the post I made with their reply on another thread.

I'm thinking of modifying the rack and setting these boxes on the modified rack frames.
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  #16  
Old 02-02-2011, 09:25 AM
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Default Re: Battery Box Design

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Last edited by ruckus; 02-02-2011 at 02:33 PM.
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  #17  
Old 02-02-2011, 09:31 AM
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Old 02-02-2011, 09:41 AM
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Default Re: Battery Box Design

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Old 02-02-2011, 09:47 AM
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Default Re: Battery Box Design

The manual for the Thundersky LFP260ah batteries shows they only loose about 10-12% range at -25C (-13F) compared to 25C (77F).

They loose about 20% range at -45C (-49F). But that is COLD. (even for Canada)

The small reduction in range doesn't seem like much to worry about.

I am sizing the batts ~25% big so they will still meet the range requirement as they age (or when the temps drop).

LFP seem less affected by cold than lead.


--sorry, that's what happens when U use the back button to edit... :|

Last edited by ruckus; 02-02-2011 at 02:35 PM.
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  #20  
Old 02-02-2011, 10:02 AM
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Default Re: Battery Box Design

Naturally, my thoughts are going to be out on the extreme edges, but maybe there's something in them that can benefit someone. One thing that may help is the fact that I am trying to keep the cost of the cases down to allow for easier adoption of newer technologies. I'm planning on nano-tech LiPo cells, and want heating/cooling because of how hard I want to push the pack.

I'm currently leaning towards liquid climate control. I'm toying with the idea of using rectangular aluminum radiator tubing to build an egg crate-like divider structure that would flow liquid around the individual cell packs. The same system could take care of the controller and battery pack. With a small radiator in a ducted box and a heating element inside, it could cool or heat.
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