Keeping Batteries Warm In Winter
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How To Make A HOT BOX:
order to ADD heat to the insulated box I decided to use a 40 watt vibration service incandescent bulb, I may down-size that to an appliance bulb if this bulb turns out to be too much wattage - Time will tell.
Because I did not want the bulb on 24/7 I needed to control it. I purchased a digital temperature controller and will set the low and high temperatures for the hot box interior.
I purchased the temperature controller online with the goal to control the beat bulb to a predetermined low / high temperature. The controller controls a power outlet, and I mounted the bulb and plug socket to that.
Hot Box Size
I mainly wanted to build a hot box for my caulking, glue and wood filler. In retrospect, I could have made it larger, and used it for a battery warmer. I still can. But I don’t have a ton of room for a lot of batteries.
To size my box I measured a tube of caulking and added 4-inches to that measurement. The 4-inches accounts for the 1-inch of DOW insulation on each end of the box and air space. I’d be lying if I didn’t also take into consideration what I had for scrap plywood.
The final dimensions were 14w x 14h x 14d.
Making the Hot Box
The hot box construction is not fancy. I used a table saw to size all of the parts, including cutting the ridged insulation.
A finish nailer was useful to quickly put together the box, and then follow up with 2.5” screws.
Once the box took shape I cut and tightly fitted the ridged insulation, using adhesive to hold it in place.
For the side wall I place ridged insulation at the height I wanted my shelf and used 3/8 plywood for a shelf. I purposely kept the shelf 1-inch off the front and back walls, to allow for heat rise and airflow.
I placed the temperature controller in the far back corner to protect it from damage, and allow heat to rise up behind the upper shelf. When placing the controller I kept it high enough to keep the bulb1-inch off the insulation. I may go back and add a piece of step flashing as a heat shield.
I also added a stop in front of the bulb out of ridged insulation to project from glue bottles hitting it.
The top of the half wall was fitted with ridged insulation, as was the door. For the door I added 1-1/4” screws and 1” washers to hold the insulation panel in place while the adhesive dries, as well as, to provide extra support when opening and closing the door.
I drilled a hole through the back of the box for the temperature controller plug and secured it to the back of the box with cable staples. To block the plug hole, I notched a scrap piece of insulation to cover the wire and hole. Afterward I filled any remaining void with caulking.
To finish off the box door, I used a recycled scrap of piano hinge and an extra window sash lock. I like the sash lock because as it closes it pulls the door tight.
Setting the Temperature of the Hot Box - What’s the Sweet Spot?
The ideal temperature for applying caulk to a surface is anywhere between 45 and 80 degrees F, as these temperatures ensure that the caulk hardens correctly and sticks to your surface adequately. It is also recommended that when applying caulk in temperatures below 32 degrees that you prewarm the caulking to 70 degrees.
Wood glue application manufacturers recommended application temperature at 70°F, but it can be applied as low as 55°F.
I’m sure that if you work in colder climates I’m sure your violating these temperatures as well as have trouble keeping your caulking and glues from freezing.
I’m still experimenting but I set my hot box to 60 degrees. The controller will turn on it the temperature drops to 40 degrees and will turn off at 60. When I tested the box in 22-degree temps the light turned on, heated the box up and was off when I checked it 5-minutes later.