Mod #6: Battery Cutoff Switch
Submitted on: 06/10/08
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Ever wonder why you take your RV out of storage after a few weeks and find that the batteries are deader than a door nail? You went through your pre-storage checklist and made sure all breakers and lights were off but your batteries are still DOA. You even plugged in the RV and charged the battery for a few days to make sure it was topped up before storage. What’s going on?
Almost every RV has some sort of parasitic current draw on the 12-volt electrical system. The most likely offenders are the LP gas detector, the refrigerator, and the radio. Even an inverter, although switched off, can have a small current draw. Over time, these seemingly harmless draws can eventually bring even the largest of battery banks to their capacity death. A simple device called a battery cut off switch will prevent this from happening.
Battery switches come in a variety of sizes and functions. There is the simple cut off switch that goes in between the positive connection to the battery and the battery itself. One type has a removable key that is turned to break the connection and you can take the key with you. This prevents someone from maliciously switching back on your power when say your RV is in storage.
Other types of switches feature not only a power disconnection from the battery, but also switching between battery banks. These types will make the connection to the battery you are switching to first before breaking the battery connection you are switching from. This ensures that any 12-volt devices that are being powered do not suffer from a momentary power loss. This type of switch, while still straightforward to install, requires a bit more planning to ensure you get the wiring correct. See the example image for suggested wiring configuration using multiple switches.
A battery switch can also be used to disconnect power from an inverter DC connection. Larger inverters are often wired with separate cabling from the battery to the inverter. Even when the inverter is switched off, there can be a small current drain. Placing a switch between the inverter and the battery will prevent this from happening.
When installing a cut off switch, it is generally recommended to place it in the positive side of the DC circuit. There is some debate however on whether to install it on the negative side. There are valid arguments for each way. The bottom line is that you can do it in either the positive or the negative side. It’s your decision.