While b0atg1rl and I plan to be continues cruisers for a while, but when we are hanging around in an area for a while we hope to also be able to use shore supplies, nbSteven came with 4 x Single sockets on a 230 circuit that would be useful to use when we need 230V while cruising.
When we bought nbSteven there was no inverter, only a few 12V sockets, it looks like the previous owner mostly used her in a marina, so without further ado here is my cunning plan for re-wiring her (hopefully by peer review I can get my design sanity checked!):
- RCD (Residual-Current Device) this is a magic box that should stop me from getting killed if there is any current leak from either the Live, or Neutral.
However this is currently a 2 x 63 A Isolator, which according to §3.5.2 (Best Practice) of the BSS Essential Guide1
If your boat has a 230/240V supply, we strongly recommend having a residual current device (RCD) to disconnect the supply automatically in the event of a fault, which may help protect someone from an electric shock.
is not the recommended option, but I will retro-fit the RCD at a latter date
- Inverter – a little Nikkai 600W power inverter, not the most powerful of devices, but should keep our 230V up and running for a laptop or two
- Mobitronic battery charger, this has two outputs, each independently capable of supplying 25 A (currently wired up to only our domestic 12V, however I will be wiring up the other output to look after our Engine Start).
The Mobitronic 925 012TD is also happy to supply all our 12V items as it runs as a Transformer.
- This magic switchIt’s set out as drawn in the diagram above, so it took a bit of poking (and lateral thinking) to get the diagram to work around it.This should allow me to switch:
- Between 230V from the Shore Supply, and 230 V from the Inverter
- Between 12V to the Inverter, and turning the battery charger off
- The fridge will also be turned between 12V and 230V automatically (unless we get it back on Gas soon) I will have to check to see if the fridge is happy with having this done to it.
The spare way on the switch is going to be used by me at some point to allow the boat automation system to know what position the switch is in (nbWaiouru has EmpirBus, I plan to have an Arduino and lots of I2C).
- The small box beneath the RCD is a Galvanic Isolator, it is to provide Galvanic Isolation between the boat, and the shore.
Galvanic isolation is a principle of isolating functional sections of electrical systems to prevent current flow; no metallic conduction path is permitted. Energy or information can still be exchanged between the sections by other means, such as capacitance, induction or electromagnetic waves, or by optical, acoustic or mechanical means.
Galvanic isolation is used where two or more electric circuits must communicate, but their grounds may be at different potentials. It is an effective method of breaking ground loops by preventing unwanted current from flowing between two units sharing a ground conductor. Galvanic isolation is also used for safety, preventing accidental current from reaching ground through a person’s body.
Because nbSteven is a metal object sat in a semi conductive liquid, with other metal objects, she can act as one plate of a battery, with all the other metal objects acting as the other plate, this can set up a small electrical current on the shared earth (less than a volt). however this will cause pitting on our hull due to electrolysis.
The Galvanic isolator is fundamentally two diodes in series, in reverse bias with two more, blocking DC voltages up to ~1.4V (not huge) from flowing along our earth cable in either direction. this will prevent nbSteven from acting as either plate of a cell.