Battery Box Design

65698 Views 249 Replies 28 Participants Last post by tomofreno, Oct 26, 2012

DIYguy

Discussion Starter · Feb 1, 2011

I started out wanting this to be about battery heating....but after a little thought, I decided to throw out this title. With the recent discussion of temperature in the BMS "debate" and my impending need to re-stuff my EV full of lithium, I don't really want to pull them out again for more mods.

For a top performing battery, in all climates ( I realize yours may be different than mine) the battery box should control temperature...therefore perhaps heat and perhaps cool as needed (depending where u live)... both when connected to grid or when parked outside/at work/wherever (at least prior to driving).

Charging at temp is also of some concern since many bulk chargers don't have temp compensation.

For all these reasons, I've been visualizing different designs and have a whole bunch of random thoughts that need to get pulled into one (drawing perhaps) place.

Some of the hardware for heating.....
Farnam heating pads, soil cable, water bed heaters (I kind like this one), RV adhesive heating pads, temp controllers....etc etc.

Some of the ideas for cooling....
Forced air in/around/through batts... Sucking air out (opposite - this has some advantages to be discussed) Getting air movement under/through etc.

Other....
Winter vs summer changes to box if any.
Distribution of heat ie Aluminum sheet.
Best materials to use..
What to line box with top, sides, bottom.

Powering...
12VDC
Pack voltage DC
Grid 120AC and/or 240AC
Dual power....?

Yes, this was dumped to get you thinking... it all has to get organized somehow. I'm gonna throw out a caveat up front. Please be aware and thoughtful of others' situations and that what works in Sacramento, may not work as well in Winnipeg. There are lots of ways to skin a cat... hopefully we can gather a lot of what works and what doesn't and perhaps some new ideas all into one place since all my searching has not turned up a lot of info or consensus.

Thank you all in advance.

I'll throw out some of my ideas soon.

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DIYguy

Discussion Starter · #2 · Feb 1, 2011

A couple things that come to mind right away as a basic for heating/cooling is keeping all the batteries at a fairly even temperature. They could be in larger boxes, smaller boxes and mixed. For both heat and cooling.
I'm going to talk about LiFePo prismatics right now since that is my current need (selfish as it is

).
- I can see aluminum sheet under batts for a couple reasons. It will help to distribute the heat in larger boxes as well as when used with heating elements smaller than the battery area sitting on it. It has good thermal conductive properties and is relatively light.

- I can also see the opportunity to use the spacing created by the ribbed battery cases to allow air (heat/cool) to move through the pack/stack or whatever.

- assuming prior point has some value, a space is required between Al sheet and batteries that allows air movement. (have a few ideas here TBD). Space may reduce contact with Al sheet... but heat still rises off of the entire sheet... oh yes... forgot to mention, this sheet/space mentioned is on the bottom!

- assuming prior two points have some value.... I would propose that cooling through ventilation (fan) would be best handled by drawing air out of enclosed bat box as opposed to forcing it in. I say this because I am envisioning the need to distribute forced air along a thin space at the bottom as opposed to venting this bottom space along the edges (and closing off in winter) and creating suction or exhausting possibly out the top. This would draw air up through all the passages between the battery cases.

That's enough for now... Thoughts? holes? flawed thinking??

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rwaudio

· #3 · Feb 1, 2011

I'd like to see where this goes, I haven't designed my boxes yet (for Headways) but I will need some sort of heating. I grabbed a cheap waterbead heater off ebay, it's pretty sturdy, completely sealed slightly flexible I think it would work well when you are plugged into 120, and could probably be setup to run off of pack voltage as well. The one I got is 120V @ 1A, (120w) there are also 350w versions but that might be too much. I've already designed temperature sensors into my charging boards that will be in each battery box, so that might be able to cycle the heater as necessary.

DIYguy

Discussion Starter · #4 · Feb 1, 2011 (Edited)

rwaudio said:
I'd like to see where this goes, I haven't designed my boxes yet (for Headways) but I will need some sort of heating. I grabbed a cheap waterbead heater off ebay, it's pretty sturdy, completely sealed slightly flexible I think it would work well when you are plugged into 120, and could probably be setup to run off of pack voltage as well. The one I got is 120V @ 1A, (120w) there are also 350w versions but that might be too much. I've already designed temperature sensors into my charging boards that will be in each battery box, so that might be able to cycle the heater as necessary.

Yes, I think water bed heaters are one of the better options. Couple things l like about them...as you mentioned flexible and waterproof and readily available as well as inexpensive. Most come with control also. One thing that may need tweaking is the temp range...as most are in the 70 - 100F range. Perhaps an additional thermal switch would do it. The other thing (for me) is that it would work good for my bigger boxes, but I have a couple of smaller ones that may not be suitable.
The other thought I had was to pick up one/some designed for Europe market and be able to run from 240VAC or my pack voltage of 210VDC or so.
Here is another interesting option...although, not quite as cheap.
http://www.kimhotstartheaters.com/category/565146

Ahhhh, look what I found...

http://www.standbypowerservicecompany.com/battery_pads_wraps_specs.pdf

Apparently, the Silicone ones are not for use on batteries..... http://www.standbypowerservicecompany.com/silicone_hot_pads_specs.pdf

Here's another one... but it says not to use in an insulated battery box... http://www.padheaters.com/battery_heater.html

Another one... http://www.alpha.ca/web2/products/battery-accessories/battery-heater-pad.html

http://www.warehouseautoparts.com/Specialty_Line/Kat/kats_battery_pad_Blanket_heaters.htm

and another... http://alpha.ca/Documents/Brochure/Battery%20Heater%20Mats_10_A002.pdf . . and this one.... http://www.alpha.ca/web2/products/battery-accessories/battery-heater-mats.html

DIYguy

Discussion Starter · #5 · Feb 1, 2011

Maybe some radiant floor heating stuff will work also... ??

http://www.archiexpo.com/prod/cbs-radiant-heating-systems/underfloor-heating-mat-9811-24026.html

rwaudio

· #6 · Feb 1, 2011

I bet those silicone ones would work nice under an aluminum heat spreader. Otherwise it might be tricky finding a size that really works well for even one persons variety of battery box sizes.

TheRedBaron

· #7 · Feb 1, 2011

To switch to cooling for a sec., you could created/buy an aluminium heat sink and computer fan combination. I don't know how big your box is going to be but you could easily run a comp. fan off of 12v.

Yabert

· #8 · Feb 2, 2011

Hi canadian guys!..

Yes the cold wheater will be an issue.

You can see bellow a parts of my future headway battery pack.
I will use 3/8 lexan at the end, at base and for the upper. Both side will be aluminium sheet metal.

For hot temperature, I will think use two small 12v fans. I plan the holes, but i'm not sure to use it because overheat will maybe not a issue with a small car like a Smart.

Concerning cold winter, I think use Easy heat roof de-icing cable or Pipe Tracing Heating Cables. They are rated at 7w/feet and I think use 18' for 126w and less than 1A at 156v. They cost 30-40$.

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EVfun

· #9 · Feb 2, 2011

Have you considered heating the air you are moving? It could be a recirculating system when heat is needed, with the air drawn out by a fan and heated then directed back in the other side. When cooling is needed open the loop drawing fresh air in and exhausting it (heater off naturally.)

Tahoe Tim

· #10 · Feb 2, 2011

EVfun,
I was thinking the same thing. If you are going to add ventilation fans, simply heat the same air.

Jan

· #11 · Feb 2, 2011

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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ElectriCar

· #12 · Feb 2, 2011

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.

JRP3

· #13 · Feb 2, 2011

Jan said:
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.

JRP3

· #14 · Feb 2, 2011

ElectriCar said:
I'm thinking of insulating bottom and sides with this stuff.

What about the top where you'll have most of your heat loss?

ElectriCar

· #15 · Feb 2, 2011

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.

ruckus

· #16 · Feb 2, 2011 (Edited)

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ruckus

· #17 · Feb 2, 2011 (Edited)

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ruckus

· #18 · Feb 2, 2011 (Edited)

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ruckus

· #19 · Feb 2, 2011 (Edited)

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... :|

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toddshotrods

· #20 · Feb 2, 2011

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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