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Battery Switch Box for Fridge

Some background: I bought a 12V refridgerator for my Odyssey and wanted to be sure that I would not run down my battery to the point where I could not start the car. Some options:

  • Simply plug the fridge into the switched outlets and only run it when the car was on. This means that when I leave the car and come back the cooler warms up a bit, maybe a lot.
  • Plug the fridge into an unswitched outlet so it can run anytime. Install a Priority Start or similar device to protect the battery. Expensive.
  • Add a backup battery to the Ody's system. Also Expensive.
  • Use a cheaper backup battery for the fridge and figure out a way to switch them. This is what I did and the details follow.

Contents of this page:

Schematic (click for better image):

You can also access this diagram in editable form:
BatteryFridgeConnections_v4.sch is the source.
ExpressPCH is the free tool for working with the source


There are only a few parts, all common and readily available at Radio Shack. Click name for package image or part number for RS link


The package:

What's inside:

Button Button Button

Copyright 2007 Bob Bailey. All Rights Reserved.