SHORE POWER
Ali Wood gets a crash course in reverse polarity and smart charging when Project Boat Maximus’s shore power gets trippy
More than once while our Maxi 84 Project Boat was kept in a marina last year, I arrived at the berth to find our battery voltage had dropped to 12.4V, despite having connected it to shore power. Each time it would appear to have tripped –though never while I was on board.
When Adam McMenemy of ACM Marine next visited Maximus, I asked him to take a look. We flicked the breaker back up on the RCD box and reconnected the shore power. The charge jumped to 14.4V on the Victron smart meter, a sign that the battery was going into bulk charge, as all batteries will do when initially charged. We left it a while and moved onto other tasks we’d planned.
Adam’s colleague, Ciaran Vernon, showed me how to check the battery’s charging history on the Victron Connect app on my smartphone. This is where the Victron smart meter gets really clever (see panel over the page).
I hadn’t had any problems at other berths, so one possibility was reverse polarity–where the live and neutral wires are reversed at the shore power connection. That could explain why the battery initially started bulk charging, but once it dropped to float mode (around 13.5V) it would cut out, then naturally discharge over time.
While common in European marinas, reverse polarity is sometimes also encountered in UK marinas.
“Some AC units work in reverse but boat electrics don’t like it, hence the possibility of tripping,” says Adam.
Some boats also have a light on the AC panel to warn when this is the case.
Testing time
It’s not just boats that have problems with reverse polarity. It’s a common issue in Europe for motorhomes and anywhere that might require an outdoor connection.
Adam brought me a socket tester and a 16A male and female plug and socket and three-core 2.5mm cable so we could make our own reversing adaptor, which is simply a short lead with plugs and sockets wired in reverse order. Note, it’s important that the cable is AC and not DC rated.
Sure enough, when we plugged the socket tester into Maximus’s three-pin socket it flashed and beeped indicating reverse polarity.
Ciaran made a reverse polarity adaptor (see over) and we plugged this into the end of the boat shore power cable and then into the marina socket.
Note, for safety, it’s essential to connect the ‘live end’ last and disconnect it first.
The ba
