# Canadian battery boxes



## Jarrad (Oct 19, 2013)

I am ready to build the battery boxes for my 2002 mini cooper conversion. I live in Kingston Ontario Canada and this endless winter is making me think about cold weather driving. My morning commute has been consistently below -10 Deg C and frequently <-20

Looking at the lousy performance at low temps for my LiFe battery. Its clear that heating my battery boxes is required. Before I start my questions about design I have a question about operation:

Do I need to keep the batteries constantly warm or can I allow them to freeze and bring them back up to temperature without capacity loss?

Insulated box design.

My main box will be located below the rear seat so a design with a removable top will not be possible. The batteries will be in sealed insulted boxes. I have calculated the heat loss assuming a 40 deg C temperature difference for my main box with 1" of R 5.5 (aged) insulation to be approximately 60 Watts. The car could sit on a -20 Deg C night for 12 hours with a penalty of only 700-1000 Wh

Given the sealed boxes the heating becomes simple but the cooling gets fairly complicated. Here are the two mechanical systems I have in mind.

Design 1 - Restive heating with forced air cooling

This system would use a restive wire in the battery boxes for heating. The boxes would require duct work connecting them and a fan to cool the batteries in summer. The input and output duct work would require an insulated damper that could be removed in summer.

This system would be simpler to build but would require the dampers to be manual changed and would be bulkier than design 2. I would also be concerned that warm winter days may cause the batteries to overheat.

Design 2 - Liquid heating and cooling

The car will have liquid cooling for the motor controller using the car radiator and liquid heating for the cabin so I could expand these systems to heat and cool the battery boxes. I am thinking of a simple coil using copper tubing soldered to some copper sheet at the base of each battery box.

I am also considering using a heat pump to assist with heating and cooling. If required (phase 2)

This design would mean the battery boxes could remain sealed and temperature would be maintained more precisely. The efficiency would be lower than design 1. The cost and complexity would be somewhat higher.


Please let me know what you think/how you are dealing with this.


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## Hollie Maea (Dec 9, 2009)

I would go with design 2. It will take more work, but if you are putting the effort in, might as well do it right.


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## skooler (Mar 26, 2011)

What kind of cells are you using?

With the prismatic LiFePO4 cells, there's not any need to cool them as they are actually more efficient at warmer temperatures. if they are getting warm enough to need cooling then you are doing something wrong!

In terms of box design, I'd go for a well insulated box - insulation board around the edges would probably work well. With something like soil cable underneath the cells. The spec in the example below states that 10m is 100w and covers 1.6 sq meters. in such a small space it will keep the cells quite warm.

http://www.harrodhorticultural.com/...html?Aff=GPL&gclid=CMiohNnkl70CFUsUwwodHbMA-w

Cheers,

Mike


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## Jarrad (Oct 19, 2013)

I am using HI power LiFePO4 cells. I notice the efficiency goes up at higher temperatures. The spec sheet for the cells shows the top operating temp is 60 deg C and top charging temp is 45 deg C. I would also note that the spec sheet shows a test at 85 deg C where it was normal for the cells to leak.

In a sealed insulated box in summer I would think the heat produced by the cells would bring the box above 60.

Does anyone know how much heat these cells produce so I can do a heat loss calculation?


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## skooler (Mar 26, 2011)

Jarrad said:


> I am using HI power LiFePO4 cells. I notice the efficiency goes up at higher temperatures. The spec sheet for the cells shows the top operating temp is 60 deg C and top charging temp is 45 deg C. I would also note that the spec sheet shows a test at 85 deg C where it was normal for the cells to leak.
> 
> In a sealed insulated box in summer I would think the heat produced by the cells would bring the box above 60.
> 
> Does anyone know how much heat these cells produce so I can do a heat loss calculation?


My Sinopoly 100AH cells used at 6c don't get above ambient after a long drive according to my laser thermometer. temperature here at the moment is about 10 degrees and I have zero insulation (other than the battery box wall)


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## Jarrad (Oct 19, 2013)

I assume you mean 10 deg F so abut -12 deg C. How much is your range reduced at these temperatures?

Un-insulated boxes would be simplest. I could heat them when at home on the charger but I am worried about leaving the car at work all day without heat then not having the range to get home.

This brings me back to my first question. If I preheat the batteries to room temp after freezing will I loose capacity?


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## skooler (Mar 26, 2011)

Jarrad said:


> I assume you mean 10 deg F so abut -12 deg C. How much is your range reduced at these temperatures?


Sorry no, I meant 10 Celsius. The point I was trying to make is that you really don't need to cool these cells.



Jarrad said:


> Un-insulated boxes would be simplest. I could heat them when at home on the charger but I am worried about leaving the car at work all day without heat then not having the range to get home.


Are you able to charge at work? If so then I think the answer is to have something to warm the boxes while plugged in. If not it will need to run off the pack. but how you get it to pre-heat the cells prior to a drive without being always on isn't easy.

You might also want to think about how to heat the cells prior to a charge?



Jarrad said:


> This brings me back to my first question. If I preheat the batteries to room temp after freezing will I loose capacity?


Afraid I don't know the answer to this. I suspect that no damage is done to a battery with no charge and no load at the kind of temperatures we are talking about but I'm purely speculating.


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## grip911 (Dec 14, 2011)

forget about the cooling, you don`t need it. A well insulated battery box with a heating wire underneath the batteries inside the boxes works well. I usually find that if the wire is bonded to the underside of an aluminum plate, it acts as a heat sink and dissipates heat evenly to all the batteries. I have not noticed any capacity losses in freezing the batteries.Using an AC source independent of the pack voltage to heat the batteries is the the way I do it. 
Never found the need to heat them while driving.


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## dougingraham (Jul 26, 2011)

Jarrad said:


> In a sealed insulated box in summer I would think the heat produced by the cells would bring the box above 60.


I was concerned about this as well but it turns out it is not an issue. I tried several times on hot summer days to get them hot and it just doesn't happen. I have insulated boxes (somewhere between R3 and R5). This is with LiFePO4 cells. Other types behave differently and you may need cooling.

I could imagine a situation where you have insufficient voltage due to pack design and must operate the cells at max C rating all the time. In this situation you might manage to overheat the cells in an insulated box. Say you have 100AH cells rated at 3C and you are driving 60 miles per hour in a vehicle that gets 300 wh per mile. If you had only a 60 volt pack you would have to pull 300 amps continuous to maintain speed. You could do this for 20 minutes before the pack was exhausted. In this case I could see it happening. However if you have 120 volts the current would be 150 amps (1.5C) and the batteries are essentially loafing.

If you lived in a place like Phoenix or Tucson AZ I would be concerned. I don't think this is an issue for you where you live.


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## grip911 (Dec 14, 2011)

[QUOTEIf you lived in a place like Phoenix or Tucson AZ I would be concerned. I don't think this is an issue for you where you live.[/QUOTE]

I wonder how those better place batteries will react in hot weather without a cooling system hmmm.


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## Jarrad (Oct 19, 2013)

Ok, resistive wire it is then. My system is 144V 80A I am hoping to be close to 1C most of the time.


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## Batterypoweredtoad (Feb 5, 2008)

grip911 said:


> [QUOTEIf you lived in a place like Phoenix or Tucson AZ I would be concerned. I don't think this is an issue for you where you live.


 I wonder how those better place batteries will react in hot weather without a cooling system hmmm.[/QUOTE]

If you are talking about the EVTV/renault/leaf cell style packs they looked like they had a fairly good forced air setup that might be reusable.


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## Yukon_Shane (Jul 15, 2010)

grip911 said:


> forget about the cooling, you don`t need it. A well insulated battery box with a heating wire underneath the batteries inside the boxes works well. I usually find that if the wire is bonded to the underside of an aluminum plate, it acts as a heat sink and dissipates heat evenly to all the batteries. I have not noticed any capacity losses in freezing the batteries.Using an AC source independent of the pack voltage to heat the batteries is the the way I do it.
> Never found the need to heat them while driving.


I'd second all the points made above by grip911. I use the EVDashboard android display and hardware to monitor my battery pack temperature. My battery box is insulated with 3" of ridged foam and has never gotten close to 60 degrees C even on the hottest summer days when the sun is beating in the windows and the cab feels uncomfortably warm.

I've gotten into the mid-high 40s and the batteries seem to perform very well at that temperature. 

I also use a resistive heating wire bonded to an aluminum sheet under the batteries to keep the pack warm during the coldest months. It works well but I wouldn't try it without insulation. My first winter I had no insulation and the pack would not hold temperature at all so I was constantly having to plug in the heater, with the insulation the pack holds it's temperature quite well. I would suggest the more insulation the better.

I've allowed my batteries to got below 0C several times and haven't seen any decrease in capacity to date.

Once you get this sorted out you can start on the real winter driving challenge...the cab heater


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## Frank (Dec 6, 2008)

Resistive heating and insulation. Do you have a garage? This would help even more.


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