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Isolation transformers

Dear Sir.
I have recently been revisiting an article in your December 2009 issue regarding earthing boats, and isolation transformers.
My boat has a domestic bank of two 110Ah batteries and uses an inverter for supplying onboard 240V. Could you please tell me if a mains operated battery charger (from shore power supply) to directly charge the domestic battery bank can be regarded as an isolation transformer, both from the safety point of view and also from the electrolytic corrosion point of view. I take it there would need to be a shield between primary and secondary windings. Is a standard automotive charger likely to have this or some special marine version required.
Many thanks for your help.
Kind regards
Paul Rawson

Asked by: paul rawson  | 11.34pm, Thursday 8 November

WW says:

Most battery chargers do not have transformers any more, they use switch mode technology which does not provide any isolation. Even if you can find one with a transformer the output will be earthed to ensure safety.
The onboard mains wiring must be earthed to the hull, otherwise the RCCB (also known as an earth leakage circuit breaker) will not work to protect against electric shock. An isolation transformer is undoubtedly the best way to prevent electrolytic corrosion from connecting the boat to the network mains earth, a galvanic isolator fitted between the hull and the onboard mains earth will however also provide protection.

Rupert Smedley  | 10.38AM, Friday 9 November

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