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Old 25-08-2023, 04:55   #16
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Re: galvanic isolator, which one? 16amp or 32amp

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I am not great with electrical but need to put in a GI as recomended by my surveyor. It seems like a 32 would cover it? I have a 30 amp shore cord if that means anything?

I wonder why the recommendation was for a galvanic isolator instead of an isolation transformer?

-Chris
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Old 25-08-2023, 05:11   #17
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Re: galvanic isolator, which one? 16amp or 32amp

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I wonder why the recommendation was for a galvanic isolator instead of an isolation transformer?

-Chris
Money. The GI is more likely to be fitted than simply ignoring the problem after pricing up a transformer.

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Old 25-08-2023, 05:13   #18
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Re: galvanic isolator, which one? 16amp or 32amp

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For this reason one shouldn’t have these isolators at all and use an isolation transformer instead, which doesn’t have any of these problems, which is why I have it in all the reference diagrams .
An isolation transformer is roughly the size, weight, and expense of an inverter charger. While there's no question it's good kit, may be a bit much for many small boat owners.

https://www.fastboatparts.com/shop/v...3bd134d3158581
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Old 25-08-2023, 05:41   #19
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Re: galvanic isolator, which one? 16amp or 32amp

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An isolation transformer is roughly the size, weight, and expense of an inverter charger. While there's no question it's good kit, may be a bit much for many small boat owners.

https://www.fastboatparts.com/shop/v...3bd134d3158581
I agree but not for a 40’ boat. If one connects to shore power regularly then an isolation transformer is the #1 option to spend money on. Even with a 30’ boat I would attempt to find a spot.
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Old 25-08-2023, 07:15   #20
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Re: galvanic isolator, which one? 16amp or 32amp

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I Even with a 30’ boat I would attempt to find a spot.
Or use solar instead. Know anyone building a large installation at the moment by chance
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Old 25-08-2023, 08:22   #21
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Re: galvanic isolator, which one? 16amp or 32amp

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Or use solar instead. Know anyone building a large installation at the moment by chance
Ha! Just saw my panels have actually shipped!
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Old 25-08-2023, 09:30   #22
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Re: galvanic isolator, which one? 16amp or 32amp

I agree with s/v Jedi, an isolation transformer is the best option. Yes, it costs more, but in my opinion worth it. It blocks both DC and AC stray currents and protects against shock.
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Old 25-08-2023, 10:19   #23
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Re: galvanic isolator, which one? 16amp or 32amp

We looked at a Isolation Tranformer, but Victron's big ones are 230v.

I don't understand how it would block DC current. The ones we looked at from Victron have no DC connections at all. Just AC in/out.

Cheyne

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I agree with s/v Jedi, an isolation transformer is the best option. Yes, it costs more, but in my opinion worth it. It blocks both DC and AC stray currents and protects against shock.
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Old 25-08-2023, 10:30   #24
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galvanic isolator, which one? 16amp or 32amp

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We looked at a Isolation Tranformer, but Victron's big ones are 230v.



I don't understand how it would block DC current. The ones we looked at from Victron have no DC connections at all. Just AC in/out.



Cheyne


DC cant be transported from primary to secondary. Low frequency AC can, but only “normal mode”. “Common mode” currents are blocked, since they are not causing coil current and therefore no magnetic flux is induced.

Bottom line is unwanted power is blocked at the transformer. They are a wise investment.
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Old 25-08-2023, 17:17   #25
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Re: galvanic isolator, which one? 16amp or 32amp

Both Galvanic Isolators and Isolation Transformers are used to block stray DC currents when plugged into shore power.

Galvanic Isolators do this by utilizing diodes in their circuitry which blocks DC but allows AC to flow. Isolation Transformers do it by isolating your vessel from shore ground by passing power through a magnetic field.

They both perform the same function by blocking DC current from having a path back to shore ground.

The added advantage of an Isolation Transformer is the simple fact that it breaks the shore ground connection. Thereby protecting the the boat from both DC and AC stray current as well as preventing a shock hazard aboard the boat and from the water surrounding the boat. It is the best way to protect your boat.

Victron makes a Toroid Isolation Transformer that works on either 120 or 230VAC. The 3600W model is the one you want for 30 Amp shore power.
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Old 25-08-2023, 17:37   #26
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Re: galvanic isolator, which one? 16amp or 32amp

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Originally Posted by Cheyne View Post
We looked at a Isolation Tranformer, but Victron's big ones are 230v.

I don't understand how it would block DC current. The ones we looked at from Victron have no DC connections at all. Just AC in/out.

Cheyne
You would select the Victron 3,600W transformer. You set jumpers for 120V output voltage (can select 120 or 240) and then you can buy a manual version where you set input voltage (from shore) at either 120V or 240V, or you can buy an automatic version that chooses the correct setting automatically.

The transformer galvanically isolates the boat from shore power via it’s magnetic field. The transformer output is like a new power source, like a generator.
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Old 25-08-2023, 18:19   #27
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Re: galvanic isolator, which one? 16amp or 32amp

Would the 3600w unit be enough for a 50amp shore power? We normally just pull around 2200w from shore power, but when we cook it can go over 4500w. Right now we have a VDI-64 GI from Victron.

Cheyne

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You would select the Victron 3,600W transformer. You set jumpers for 120V output voltage (can select 120 or 240) and then you can buy a manual version where you set input voltage (from shore) at either 120V or 240V, or you can buy an automatic version that chooses the correct setting automatically.

The transformer galvanically isolates the boat from shore power via it’s magnetic field. The transformer output is like a new power source, like a generator.
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Old 25-08-2023, 19:50   #28
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Re: galvanic isolator, which one? 16amp or 32amp

If you have a 230VAC/50 AMP shore power connection the 3600W will not work. The 3600W is for 30 AMP shore power connection. For a 50 AMP system you would need the 7000W which only comes in 230VAC.
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Old 25-08-2023, 20:02   #29
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Re: galvanic isolator, which one? 16amp or 32amp

In actuality the 7000W on supports 32 amps at 230V. When you have higher voltage amperage is less.
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Old 25-08-2023, 20:15   #30
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Re: galvanic isolator, which one? 16amp or 32amp

Use Ohm's Law to calculate your needed wattage/voltage requirements.

P=E x I Where P is Watts, E is Voltage and I is Amps

So if you require 4500 Watts at 120 Volts your amperage would need to be P/E=I
4500 Watts/120 Volts = 37.5 Amps 4500 Watts/230 Volts = 19.56 Amps

Why do you draw 4500 Watts when cooking? Do you have an electric stove? It's rare to see an electric stove on a 40 foot sailboat.
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