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marc-jackson avatar image
marc-jackson asked

Autotransformer for Boat application - not getting correct L1/L2 voltage

I have a USA boat with 2 line 120V/230V and now the boat is in Australia.

I fitted a autotransformer so I can input 240v to convert to 2 x 120v .

I have attached the drawing my wiring.

The problem is on shore power I'm getting 240V on line 1 (should be 120V) and getting 120V on the white neutral wire (should be 0V) and the red, L2 0 volts (should be 120V) between the ground bus bar and the same reading between the white bus bar.


If I turn the generator on the system operates normally. all the voltage reading are below.

This wiring is uncommon and I have to wait over 3 months for a technician just to come have a look, so hoping someone might have the answers for me.

I found the problem after my Freezer stopped working, its 120V and with a multi meter had 240V on line 1 and 120V on the neutral.

Shore Power.pdf

Autotransformer
shore-power.pdf (128.6 KiB)
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klim8skeptic avatar image klim8skeptic ♦ commented ·

It is probably best to look at the schematics on the product page.

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Mike Dorsett avatar image
Mike Dorsett answered ·

The problem is on shore power I'm getting 240V on line 1 (should be 120V) and getting 120V on the white neutral wire (should be 0V) and the red, L2 0 volts (should be 120V) between the ground bus bar and the same reading between the white bus bar.



AU / Shore power will be 240V on active, ~ 0V on Neutral measured with respect to ground. After the auto transformer, you will have :

L1/G 240V, L1 / N 120V, L1/L2 240V

N/G 120V, N/L1 120V, N/L2 120V

L2/G ~0v, L2/N 120V, L2/L1 240V

If you want to get back to 120/0/120 you will also need an Isolating transformer - in AU standards, the N terminal is grounded at the distribution box, rather than American standard of 120/0/120 having 2 active lines and a centre ground. On a boat you ought to have an isolating transformer in any case, to prevent galvanic corrosion.

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marc-jackson avatar image marc-jackson commented ·

Thanks Mike, I'll follow up and add a isolation transformer and let you know the results.

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