diy solar

diy solar

Charger+inverter, instead of charger/inverter&isolation transformer?

jdege

New Member
Joined
Dec 16, 2020
Messages
138
I'm reading Nigel Calder's "Boatowners Mechanical and Electrical Manual, 4th Ed.", and I ran across an idea I'd not seen before - inverter-based boats.

That is boats that don't rely on shore-power AC at all, so that all of their AC circuits are powered by inverters running off the batteries. Any boat intended as a live-aboard is going to aim for this, to be able to spend weeks on the hook in beautiful places, instead of stuck in a slip.

But if you don't depend upon shore power AC, why connect it?

From his chapter 2:

Shore-power benefits of an inverter-based boat.You can wire an inverter-based boat so that its shore-power cord is connected to a large bank of battery chargers and nothing else. The shore-power circuit now terminates at the battery charger(s). The onboard AC circuits create an entirely separate (electrically isolated) AC system that originates at the inverter. When plugged into shore power, the boat’s AC system will run off the inverters, as at sea, but with the battery chargers recharging the batteries.
IOW you plug into shore power only to charge the batteries. And since there are marine chargers that accept pretty much any frequency and voltage (45-70Hz, 90-270V), and that act as isolation transformers if not tied to the boat ground, this seems like a reasonable way to go. Particularly if you planned on having a beefy inverter, anyway.

Thoughts?

I'd been leaning towards installing a Victron inverter/charger. Now I'm not so sure.
 
I guess the benefit is electrical isolation from shore power.
I further guess this is about not having a current path through the water back to the transformer on the shore.
Might also be about galvanic corrosion but I'm not really up on that subject.

The drawback is the conversion efficiency penalty of converting ac to dc then back to ac.
 
Shore Power (AC) -> Charger -> Battery Bank(s) -> Inverter -> AC Loads.

When connected to Shore power, you would be incur more losses as you convert AC to DC then back to AC.

Not sure what the losses are, but it's not zero.

Regarding Galvanic effects: If the boat is plugged into shore power, you'll still need a Galvanic Isolator.
 
Shore Power (AC) -> Charger -> Battery Bank(s) -> Inverter -> AC Loads.

When connected to Shore power, you would be incur more losses as you convert AC to DC then back to AC.

Not sure what the losses are, but it's not zero.

But not really relevant. If your house bank and inverter is sized to handle the load, everything else is just a matter of charging. And losses or not, shore power is a far more efficient source of charging than an alternator or generator.

Regarding Galvanic effects: If the boat is plugged into shore power, you'll still need a Galvanic Isolator.

A galvanic isolator is a poor second choice to an isolation transformer, and a marine AC->DC charger can serve as an isolation transformer. If the shore power ground isn't connected to the boat, there can be no galvanic effect.

Or so says Nigel Calder. Though he does say that it's not the usual practice.

Which is why I'm asking questions.
 
If you want your own boat's AC power isolated, the Iso Transformer is the way to go. Correct there is no Galvanic effects, regardless if on shore power.

But more pricey though.

I'd be very hesitant to not connect the ground if you stuck with the charger route, to act like an Isolation Transformer. Think like a lawyer.
 
If you want your own boat's AC power isolated, the Iso Transformer is the way to go. Correct there is no Galvanic effects, regardless if on shore power.

But more pricey though.

I'd be very hesitant to not connect the ground if you stuck with the charger route, to act like an Isolation Transformer. Think like a lawyer

I'm reading Nigel Calder's "Boatowners Mechanical and Electrical Manual, 4th Ed.", and I ran across an idea I'd not seen before - inverter-based boats.

That is boats that don't rely on shore-power AC at all, so that all of their AC circuits are powered by inverters running off the batteries. Any boat intended as a live-aboard is going to aim for this, to be able to spend weeks on the hook in beautiful places, instead of stuck in a slip.

But if you don't depend upon shore power AC, why connect it?

From his chapter 2:


IOW you plug into shore power only to charge the batteries. And since there are marine chargers that accept pretty much any frequency and voltage (45-70Hz, 90-270V), and that act as isolation transformers if not tied to the boat ground, this seems like a reasonable way to go. Particularly if you planned on having a beefy inverter, anyway.

Thoughts?

I'd been leaning towards installing a Victron inverter/charger. Now I'm not so sure.
On my new boat ,power vessel, that is what I am going to do. Being a power vessel with a hard top canopy it will have sufficient solar that I normally won't need shore power. Having only a charger connected to shore power you effectively have an isolation transformer. Your charger should not have the ground and neutral combined that only happens ashore.
 
People keep insisting that a battery charger provides effective "isolation transformer" this is simply not true in most modern battery chargers.

If you have an older heavy marine charger with a real 120/12 volt transformer yes.

But the multi frequency/multi-voltage chargers today often do not they are "switching" power supplies.
They will often have a common battery negative and neutral in the design (especially if not "marine" approved).
Some may have a small high frequency transformer, some may only have integrated circuit isolation such a FETs. These can easily fail along with other diodes, capacitors or resistors resulting neutral to ground connection.
It would depend on the quality and design of the charger. Don't assume.

If you doubt this is probable, this why a real isolation transformer is preferred over "galvanic isolation devices" which are solid state and can fail in this manner. Leaving the vessel with no protection.
 
No, it won't provide isolation. But it is still useful if you sail to other countries. It's much easier to have a universal battery charger that accepts 90-250V AC at 50-60Hz and just plug it in wherever you are and not worry about voltage or frequency at the marina. The ideal imho would be an isolation transformer, feeding a universal charger.
 
US boats bonded to ABYC have a greater risk of corrosion effects from leakage currents in the shore PE , this is made worse by the lack of RCBO in marina circuits in the US. Furthermore ABYC effectively makes up for electro shock risks that should be addressed in the NEC not the boat.

European circuits are far less likely to be affected as bonding on the boat is isolated and whole boat and marina RCBO are mandatory.

Galvanic isolators are useful in my opinion they should be fitted along with a while boat 30mA RCBO. That way failure of the GI is not a genuine safety risk , I build my own 230vac GIs from sets of bridge rectifiers , in my case I use 4 diodes in series to increase the blocking potential.

Most modern switching chargers are isolated as this is required in European codes. There is no no common neutral point etc.

The Calder approach has its advantages but these days the equipment has moved on and his advice is dated.

Grid tied power assist invertors offer the best of both worlds and are readily available. In fact the solar hybrid invertor has a future on boats. Ie combining charger invertor and mppt.
 
@wholybee
Good solution if you wanted to go the all on battery/inverter route. Even a large battery charger would only be around 600 watts (12V x 50A).
Since the batteries/inverter are handling the house peaks the charger would catch up in between. Even I could find space for a 600 watt transformer; smaller, lighter, cheaper. A whole boat transformer would need be 4 KW or more.

@Goboatingnow completely agree with this and did it.
1994 Sea Ray 300 Sundancer that had extensive corrosion of the lower units when I bought it. The miserly OEM 120v 30A (3600 watt) service could not even handle the existing A/C, stove and water heater at the same time. Upgraded shore to a 240V 50A (11,000 watts) service all heavy duty RCD and shore connection. Upgraded the water heater from 6 gallon 120v to 11 gallon 240v with engine heat exchanger and stove to 240v. Threw out the cheap 22 year old GI and installed a new 50A Quicksilver GI with monitoring.

In the photo below the "Generator" is now a self contained 48V 200A LifePo4/6000 watt 240V inverter system, that's a whole other thread.

IMG_0436.JPG
 
I'm reading Nigel Calder's "Boatowners Mechanical and Electrical Manual, 4th Ed.", and I ran across an idea I'd not seen before - inverter-based boats.

That is boats that don't rely on shore-power AC at all, so that all of their AC circuits are powered by inverters running off the batteries. Any boat intended as a live-aboard is going to aim for this, to be able to spend weeks on the hook in beautiful places, instead of stuck in a slip.

But if you don't depend upon shore power AC, why connect it?

From his chapter 2:


IOW you plug into shore power only to charge the batteries. And since there are marine chargers that accept pretty much any frequency and voltage (45-70Hz, 90-270V), and that act as isolation transformers if not tied to the boat ground, this seems like a reasonable way to go. Particularly if you planned on having a beefy inverter, anyway.

Thoughts?

I'd been leaning towards installing a Victron inverter/charger. Now I'm not so sure.
 
Plan for the unknown. If you needed a battery charge and had an on board generator. You would want an inverter that would auto sense shore power or a means to charge the batteries from a shore powered source.
 
Old thread revived here.

An advantage to separating the charger from the inverter is that the inverter is only ever seeing voltage from the batteries and not shore power.

The charger is the only device that sees shore power and charges the DC battery bank.

That DC battery bank is a big sponge and wont let dirty power through to the inverter. So if you are in some far away place that has a less then stable grid and you get dirty power (low voltage, over voltage, frequency variations, harmonics, transients etc (ask me how I know this) you would only blow the charger - the transients will not get through the batteries to the inverter and blow your inverter. Sure you lose your battery charger but your inverter will survive and you wont lose your AC source onboard (until the batteries go flat of course - but you will have time to deal with that scenario).

Some of these small countries we visit have really really poor electric grids. Separating the charger from the inverter is a way to protect your inverter.
 
Back
Top