Insulated Rear Battery Box

Today I built the battery box for the 4 Discover EV31A-A batteries in the far rear of the Honda. From start to finish, it took me about 9 hours, not including breaks! My wife was helping me for about the last 3 hours, too. The tasks included: Unwiring the 4 batteries and removing them from the car. Cutting a 1/2" styrofoam sheet to go under the 4 batteries. Wiring up the 4 heater pads and the thermostat. Mounting the heater pads in the car. Replacing the 4 batteries. Cutting and fitting the styrofoam walls of the box. Fitting a lid. Wiring the batteries all back up. Mounting the thermostat. Cleaning up.

Now all of my battery racks are running at a nice toasty 90'F!

Some pics:

The box, about 1/2 finished, putting together an inside corner.

The corner after it's been slid into place

Buttoned up with the cover.

[Yes, I remembered to get the scissors out! :-)]

The thermostat hides under the block sticking out. Hot water heaters place their thermostats under the insulation, so that the entire body of the thermostat heats to temperature. I mounted the thermostats on the batteries the same way, surrounded and covered by insulation.

Insulated Front Battery Box

The last couple weekends, I've been working on building insulated, heated battery boxes.

Here are a couple pictures of the battery box that has the two batteries just behind the front grill of the car.

The completed box.

The thermostat on the rear of the box.

Here is the group of 4 Farnham battery heater pads, mounted on a sheet of styrofoam, ready to be placed underneath the four batteries I installed Oct. 31st (see previous post).

New batteries & battery heater pad

Today I performed a temporary install of the 4 new batteries I've purchased for the Honda. These are in addition to the 6 it already has, thus making it a 120V system with ~12kWh pack (2o hr. rate). These four batteries plus the other two under the hood will be charged by two Dual Pro Recreational Series 3-Bank 6-Amp chargers. Each charger has 3 independent, isolated, microprocessor-controlled chargers capable of pushing 6 amps, which may be used in series or in parallel with each other. Here's a picture of the batteries wired up into a temporary 48V bank, with the Dual Pro chargers sitting next to them.

Also, I found out about a very economical way to control the temperature of batteries being warmed by battery heater pads: Water heater thermostats. These thermostats switch 120V AC, and handle the wattage of normal hot water tank heating coils. Perfect for the battery heater pads I've bought, which don't come anywhere close to the wattage of a hot water tank. And they cost less than $10 each, so you can afford to put one on each bank of batteries you'll be heating. That's important because different banks will have different thermal properties depending on their isolation from the outside environment. Here's a picture of a water heater thermostat I bought at Lowes, sitting on top of a Farnam battery heater pad I bought from KTA Services. The thermostat can control in a temperature range of 90'F - 150'F. Which is fine for lead acid batteries, since you probably want them warmed to about 100-120'F for best performance.

One thing Dave Cloud warned me about with the hot water tank thermostats, is to do one's best to isolate the thermostat from any possible gas the batteries might vent. This is due to the possibility that the contacts inside the thermostat could spark when making/breaking the circuit, which could ignite a concentration of hydrogen gas. While I assume this is more of a concern for flooded batteries than the AGMs I'm using, it's a valid point and one I will have to consider.