Circuit Isolation from Battery Charger

Batteries need to receive a higher voltage than their current voltage in order to charge. This exposes all circuits connected to the batteries to this higher voltage and may also subject them to a voltage spike when a 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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