T-Pain Is On A Boat: [Electric Boats] Grounding an electric conversion in fresh water

Thursday, July 31, 2014

[Electric Boats] Grounding an electric conversion in fresh water

I am close to finishing my conversion.
I have given little thought to grounding up until this point.

Super short version:
I have 3 electrical systems on the boat -- 48V DC, 12V DC, and 120V AC.
How do I treat the grounds for each of these?

So what are my grounding requirements?
- For the 48V:
- For the 12V:
- For the AC:

What are my grounding options?
- For the 48V:
- For the 12V:
- For the AC:

Facts:
As it stands now, my prop and shaft are isolated from the drive through
a flexible coupler.
All my through-hulls are bronze and are isolated.
In my 6 seasons in fresh water, I have had zero corrosion issues.
The mast and rigging is not bonded to the keel.
There is no RF counterpoise or ground-plane in the boat.
There is currently no Dynaplate of any kind.
The system was formerly grounded only through the engine
block-->transmission-->coupler-->shaft-->prop.
There is AC in the boat but it only interconnects with the DC system via
a battery charger.
The dock supplies a grounded 15A circuit which feeds into an AC panel
over the galley that has 3 breakers:
- GFCI over the galley counter (next to the AC panel) used mostly for
phone chargers and tools at the dock.
- 48V charger & 12V charger
- unused.
The AC system is not grounded at all through the boat.

Should the 48V system to stay floating? Meaning that the battery bank
negative connects to the motor controller negative, the DCDC converter
(which provides isolated 12v) negative, and the battery SoC meter. And
that is all.

The 12V system should be attached to some kind of ground, yes?
In that case, I should connect the negative bus bar in my 12V "battery
distribution panel" to a Dynaplate or some equivalent metal mass in
contact with the (fresh) water, right?

If I also connect the negative bus bar of my 48V system to this
dynaplate, will bad things happen?

Since I am sailing in fresh water, I will need more contact area between
the metal and the water in order to sink the same current, right?

Thanks in advance for your input.

Cheers,

/Jason

--
Jason Taylor
--
S/V Fugu
1978 Beneteau First 30
Electroprop PM-20