Battery musings

While I wait for the motor I need to do some thinking about battery location. I'm hoping that once the motor is in I will get a sudden insight as to how many batteries will fit up front comfortably. Once the motor is in I can make a decision about whether the A/C unit lives or dies. I'm really hoping to take it out: it takes up space, adds weight, and adds more details to the project. But Faith would like us to try it, so we'll see. The other thing about the A/C is that I don't want to vent the freon into the atmosphere: we get enough of that without doing it on purpose. Unfortunately everyone I call says they either can't touch it or that I need to drive the car down. I posed the dilemma on the EV List (a mailing list with a good sized community of EV people) and one of the suggestions was to weld a tow bar to the front: he said it's inevitable. Dang!

Typical batteries installed in an EV are six volt or twelve volt. If you have the room and suspension for it, 6 volt batteries give you more current for a longer time, but you'll need more of them to get the ideal voltage levels. In your car everything runs off of 12 volts and is usually happy about it. In an EV the typical DC voltage is 96 to 144, and some of the AC drive systems get into the 200 volt plus range.

I'm considering a 120 volt system at a minimum, and shooting for 144 if all of the other components work out. For a 144 volt system the car will need to hold 12 of the deep cycle 12 volt EV batteries. The smallest one in my price quotes weighs 60 pounds while the popular one weighs 86lbs. That's 720 to 1032 lbs just for batteries! And I don't want to jam them all together and have uneven weight distribution, so I'm hoping to get three or four in the front and the rest in the trunk.

The top picture showed the "stock" trunk in the Mazda. This other photo has been touched up to show the area I'm considering for the battery box. This rendering is based on having four batteries fit up front, with eight here in the back. The plan is to cut out the metal floor in the trunk and insert a nicely built battery box which will hang down about seven inches, about the same distance the spare tire hung down. The battery box will have insulation, a drainage tap, and an exhaust fan.