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OhioTom 07-22-2009 06:08 PM

Adding battery charger to DC only boat
I have a DC only sailboat with very modest electrical needs: LED nav and cabin lights, VHF, cabin fan, LED compass lights, knot meter, depth sounder.

I have a Xantrex 10A multi-stage battery charger that I want to permanently install to run off shore power. I have no plans to add any other AC circuits, just the charger. The charger has built-in galvanic isolation.

My big question is do I need to ground the AC on the boat? My thinking is to install the shore power inlet, wire the hot and neutral AC through a 15A bi-pole breaker onboard and wire both of those and the AC ground straight to the charger. The DC output side would be wired to the battery - not the DC panel.

Is this right? Thanks.

btrayfors 07-22-2009 06:47 PM

Almost. You need a fuse in the wire to the batteries and the ABYC calls for AC to be grounded to the DC ground at a single point. While there are some disbelievers and naysayers, the weight of expert opinion seems to be in line with the ABYC standard.



sarischipper 07-23-2009 09:32 AM

Buy a galvanic isolator. This prevents leaking and nasty voltages from the AC earth to you boat installation.

OhioTom 07-23-2009 10:21 AM

I'm on the Great Lakes. Is a galvanic isolator useful/needed in fresh water?

eolon 07-24-2009 09:39 AM

A galvanic isolator is essential as far as I am concerned (also Great Lakes). Mostly because of questionable wiring at many marinas, and certain boaters who do their own on-board wiring and have no clue as to what they are doing.

The galvanic isolator is cheap insurance to protect your boat from other boaters.

Best Regards,



donradclife 07-24-2009 04:20 PM

The current ABYC guidelines are a bit out of date, and they will require GFCI breakers by next summer. I think you would provide more protection for your boat and nearby swimmers if you added a GFCI in the circuit to the battery charger and took the AC ground through to the charger, but NOT to the DC negative. That would also eliminate the need for the galvanic isolator.

OhioTom 07-25-2009 12:34 AM

This was what I was thinking as the battery charger operates as an isolation transformer. With an isolation transformer, you don't need to ground the incoming AC with the DC negative, correct?

donradclife 07-26-2009 06:26 PM

The ABYC wants you to ground the incoming AC to protect against the chance that your battery charger gets hit with water and shorts the AC to the DC system. Their rationale is that the short circuit current back through the AC ground wire should be enough to trip your AC breakers. IMHO it would be better to protect against that scenario by using the GFCI, especially if you are using the boat in fresh water.

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