Charger as Isolation Transformer?

[PippaB]

Originally Posted by Jdege

Can you point me to a description of exactly how this is wired?

It's pretty simple. Shore power connector on boat. Right behind that is a two-pole, 25A 240V RCD that serves as main breaker, disconnect, and GFI protection. In the US two hot legs in the shore power cable go to this (neutral gets ignored). If only single-phase 120V available (US) or Euro outlets hot/neutral go to the same place. PE wire gets connected to galvanic isolator (GI). Two wires from RCD and one from GI go to the charger input, where PE also gets connected to case. On the other side the charger outputs gets wired to batteries. Inverter gets wired to batteries as per normal.

Really the only small wrinkle is making sure the ELCI/RCD/GFI you find is rated for 120/240V and 50/60Hz. They are out there, probably much easier to come by in Europe than the US. Might not matter if you know you'll never use one or the other, but for us it allows a set-it-and-forget-it approach. Turn off breaker, re-wire shore power connector or install adapter, plug in to shore power, confirm all looks good, turn on breaker. Done. Batteries charge and otherwise the boat/batteries don't know the difference between alternator, solar, or battery charger providing the juice.

[captstu]

My 3x previous boat was a Voyage 43' catamaran equipped with air conditioning, washer/dryer and such. Not quite your need, but the solution was similar.

She was built in Cape Town, SA, and I went there for several months to commission her with electronics, and tour the country.

Much of the time, I had ample shore power available, but it was 220 Volt 50 Hz and while I could have used an available (from the Cape Town Yacht Club) transfer, the 50 Hz could have severely damaged my motors in the air conditioning and washing machine. :-)

I opted instead, to purchase an automotive battery slopper with a floating ground, common in countries with 50 Hz power. I wired it to the battery, ran my inverter full time, and used the water as a safety ground for my wiring.

It ran flawlessly from the very beginning. I monitored the water/ground/neutral current with a relay set to disconnect the battery charger (both wires) if the neutral current ever approached 5 ma - to protect the boats and any divers around me.

I also posted a sign, "boat on shore power, dive carefully."

The charger and monitor relay were only about $150 - automotive stuff is cheap compared to marine stuff.

Got the idea from the same book.

[Cadence]

Originally Posted by Jdege

I'm refitting an older boat that has a minimal electrical system - starter battery, 100Ah 12aV house battery, alternator, and cabin lights.

No charger other than the alternator, no shore power connection, doesn't even have nav lights, though I'll be installing them before I put the masts up for the season.

What I want, eventually, is a fully electric boat - electric propulsion, electric cooking, solar charging, etc. The current propane oven/range is non-functional, and the diesel needs a full rebuild.

I can't, of course, do everything at once, so I've been thinking about what smaller projects might move me towards where I want to be.

I'd been thinking that I might start by installing a shore power connector, feeding an inverter/charger, but something I read in Nigel Calder's "Boatowners Mechanical and Electrical Manual, 4th Ed." rather an interesting possibility.

He suggests that if your batteries and invertors are sufficient to power your AC loads - which I intend mine to be - that connect shore power AC only to battery chargers that are electrically isolated from the boat. That, in essence, you configure your chargers to act as isolation transformers.

From his chapter 2:



He discussion of this points out that this violates ABYC standards, but it's within ISO.

Is this commonly done? I'd think that as battery capacities increase and inverters improve, there'd be more choosing this route, particularly with the advent of multi-input chargers that will accept 120V and 240V.

God bless you!

[goboatingnow]

For multi voltage I think the charger invertor idea is excellent as well as providing the appropriate isolation from AC and DC