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Old 02-12-2018, 03:09   #1
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Do I need an isolation transformer?

Hi, I am re-doing the electrics on my boat and I am now looking at shore power and how to use it. I have a well contained AC system running off a victron multiplus inverter/charger and plenty of solar to charge the batteries. Any shortfall in solar will be made up using a portable generator that I'll plug into the shore power connection back to the victron multiplus to charge the batteries. If we're at a marina then I'd obviously like to use their connection.

So basically, the only connection from shore power or portable generator will go directly to the multiplus charger.

So, do I need an isolation transformer?
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Old 02-12-2018, 06:10   #2
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Re: Do I need an isolation transformer?

The short answer is no, but.. A ISO will help clean up any noise from the generator output, which some chargers would like.

An ISO is also good insurance against galvanic corrosion when you do plug in to shoreside power. BTW, the genny should not try to make up what solar doesn't, you it for the bulk phase in the charge cycle.

With an ISO you can switch between 115 and 220 in a few minutes. (Depends on the type and brand)

Draw backs they aren't light nor real cheap. I have a Charles ISOG28-1 3.8KVa 115/240 50/60 Hz and it weighs 27kg and cost $600 USD
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Old 02-12-2018, 07:30   #3
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Re: Do I need an isolation transformer?

You already have enough money tied up in your electrical system to make the cost of a transformer not quite trivial, but not overwhelming, either. I would go for it. The advantages of a transformer over a simple galvanic protection circuit are obvious. Especially if you can get by with just a single 30a (U.S.) shore connection. A 30a or 32a isolation transformer only weights around 70 to 75lb, typically. For a toroid type transformer (not UL Marine approved) weight is even less. So don't let weight scare you unless you positively need 50a 240v service. That size transformer will be between 175lb and 230lb. Used transformers pop up occasionally on fleabay and less commonly on CL, for cheap.



Do you need a transformer? Do you need galvanic protection? YES YES YES!!! One or the other, certtainly, and I would go with the transformer in your case. It increases safety considerably and makes your electrical system a little more beer proof. Much safer for divers in the water, too.



FWIW I just bought a used 3.8kVA Charles transformer for the Bruce Roberts 44 I will be fitting out when I get home from this job. It was kind of a no brainer. Cost was less than a basic AC panel. I can quickly change a few connections and be able to hook up foreign shore power. My zincs will last longer. It's a nice thing, yes.
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Old 02-12-2018, 13:22   #4
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Re: Do I need an isolation transformer?

Thanks for the response. I was leaning towards getting one mainly for galvanic corrosion, but I wasn’t sure plugging into one device (charger) was worth the added cost and complexity.

Thanks again.
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Old 03-12-2018, 11:54   #5
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Re: Do I need an isolation transformer?

If you have enough solar power to charge the batteries why bother with shore power at all? I avoid it altogether as my boat is totally self sufficient.
It avoids a host of issues as some marinas are very fussy what you plug in and rightly so.
I just don't use shore power, carry a 2kw generator just in case and hence don't need an isolation transformer. Ironically there were a few shore power outages lately while boats like mine had power.
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Old 03-12-2018, 14:23   #6
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Re: Do I need an isolation transformer?

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Originally Posted by Ironman162 View Post
If you have enough solar power to charge the batteries why bother with shore power at all? I avoid it altogether as my boat is totally self sufficient.
It avoids a host of issues as some marinas are very fussy what you plug in and rightly so.
I just don't use shore power, carry a 2kw generator just in case and hence don't need an isolation transformer. Ironically there were a few shore power outages lately while boats like mine had power.

Depending on house usage and how long at the dock, a shore power charger will maintain the batteries at float voltage and run the house. Solar will cause a (partial) cycle on the batteries, something that is a finite quantity.
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