Circuit Isolation from Battery Charger

Batteries are charged by applying a higher voltage than the rated voltage. Circuits connected to the batteries during a charging cycle will be exposed to this higher voltage. They may also be subjected to voltage spikes when the charge cycle begins.
For this reason, Duffy advises that you turn off the key switch before plugging in shore power.

You can protect against this situation by adding a Normally Closed DC contactor, with a 12V coil switched by the key switch, to the output of your battery charger. The key switch will then need to be off before the charger can begin a charge cycle.

Please contact me if you have additional information or corrections to share.

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