# 50 Watt pre-heated battery boxes will do the job in winter ?



## Ziggythewiz (May 16, 2010)

Hard to see anything in your pic. Why not just post it here? 

A grid-tied heater at each location would be ideal, but you may be able to heat the pack after work without wasting too much power.


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## kennybobby (Aug 10, 2012)

*More like 300kg ?*



Nabla_Operator said:


> Driving the Nissan Leaf for the first time in winter ... Next will be a transient calculation: How long does it take to heat up 100 kg of batteries from -10 Celsius to +5?


Couldn't view the image either, but there is a quite a bit of metal surrounding the leaf batteries that will affect the thermal time constant. 48 modules with 4 cells per module takes up quite a bit of surface area too. Good luck to you i'm interested in your successful solution...


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## Nabla_Operator (Aug 5, 2011)

The attached illustration should be readable now, and maybe even understandable.
---nablabla---


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## Ziggythewiz (May 16, 2010)

Yes, much more readable. Is that A=1m^2 for a single face, or all 6 sides of the batt box?


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## Nabla_Operator (Aug 5, 2011)

One square meter for the entire surface of the battery box, Ziggy. 
I want 2 of these boxes in the car. 
---paul---


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## Ziggythewiz (May 16, 2010)

That's a small box! Mine only holds 120 lbs of cells and is more than double that.

Is T2 5 deg or 0?

What's the R value of your insulation?


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## tomofreno (Mar 3, 2009)

Ziggythewiz said:


> What's the R value of your insulation?


 The thermal conductivity of the polystyrene is given on the left hand side of his notes.


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## tomofreno (Mar 3, 2009)

Very good to do up front calculations. Even better if you have data to compare. I have 35W heater pads (Farnum, from kta-ev) under each group of 4 or 5 cells. These are taped to the back of an aluminum pan that the cells (180Ah CALB SE) sit on in each box. Transient heating: about 3 F/hr as measured with a TC on a clamp on a group of cells. They kept the cells at set point temperature of about 60 F on two successive nights of -5F. Don't know the duty cycle. Boxes have 1/2" polyurethane insulation, about R2. I now keep the cells at 65F. They will drop to low 50's F from 65 if the car is left outside with heaters off for about 5 hours in mid 20's F temps. They perform about the same in winter and summer in this temperature range, just a bit more V sag. Heaters only on when vehicle is plugged into wall.


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## Ziggythewiz (May 16, 2010)

tomofreno said:


> The thermal conductivity of the polystyrene is given on the left hand side of his notes.


Yeah, I saw that I just didn't want to have to convert it myself.

I get an R Value of 8.6, which seems too high when I see numbers like R 4-8 / in for different polystyrene products.


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## tomofreno (Mar 3, 2009)

R value is thermal resistance per unit area. In the notation used here the thermal resistance is d/A*lambda and R value is d/lambda = 0.005/0.043 = 0.12 degree K m^2/W, or 5.7 degree F hr ft^2/BTU.


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## Ziggythewiz (May 16, 2010)

Haha...reciprocol. So, don't do math after 10 pm?


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## RE Farmer (Aug 8, 2009)

tomofreno said:


> Very good to do up front calculations. Even better if you have data to compare. I have 35W heater pads (Farnum, from kta-ev) under each group of 4 or 5 cells. These are taped to the back of an aluminum pan that the cells (180Ah CALB SE) sit on in each box. ...


Tom, did you use the temp. controller KTA offered or did you come up with another option to power the Farnham pads?


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## tomofreno (Mar 3, 2009)

RE Farmer said:


> Tom, did you use the temp. controller KTA offered or did you come up with another option to power the Farnham pads?


 The kta one. I did balk a bit, as it seemed pricey to me, but didn't want to get bogged down in details like making my own. Enough to do without that. Iirc, the pads are about 430 Ohm and 35W each in case you want to make your own controller. I have 10 connected in parallel. The unit has worked well for 3 winters now.


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## Jesse67 (May 12, 2009)

I've got a ~350W heater that circulates warm air through the air channels of my 24 cell 100Ah TS pack, about 185lbs of batteries and it heats up about 10 deg C/hour. My box is pretty well insulated, 1" on 3 sides, 1/2" on one side and 4.5" on the other two sides (just how the spacing worked out). I think you would be pretty disappointed with only 50W, the warm up time would be very slow. A car block heater is about the same wattage as my heater and my pack and my car have about the same warm up times.

I would get a plug in 110V heater that has a digital thermostat, like this,
http://www.canadiantire.ca/AST/brow.../Garrison+Double+Ceramic+Heater.jsp?locale=en

then use the ceramic core, thermostat and safety switch and fuse to build your heater. I would use something like a 12V bilge blower fan to provide a higher pressure air flow than the piddly heater fan and then you can have it turn on to cool your pack as well if needed. 

Wire the ceramic core to provide the wattage output you want (they usually have multiple elements in parallel) and duct the air to circulate through and around your cells. Position the thermostat in the airflow downstream of the cells and set your temp. A warning though, unless you have very high airflow too high a wattage will make for air that is too hot coming out of the heater and it will melt your insulation! 350W gave me 40 deg C airflow out of the heater with the fan I have, just right.


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