PRACTICALA fair system of charges
I
n last month’s issue, you might have read Ben Meakins’ account of Hantu Biru’s fi nal sail in
of days’ cruise in the Kyles of Bute following Scotland’s Boat Show was enchanting, but not PBO hands. Our couple
without incident – namely, our engine failing to start when becalmed a cable’s length from the Bute ferry at Colintraive.
here in no way lay with the engine, which hitherto had started with enthusiasm. Excuses are futile – I should point out that the fault
the blame lay squarely with us. Since Southampton Boat Show we had suspected that the solar panel was no longer charging,
as the battery monitor read zero charge where in the past it had shown a charge current of 0.1A or more, even in the dullest
conditions. But, working to a tight timetable of boat shows, we hadn’t found time to check the problem properly. As a result, after
two shows and no charging, the battery voltage was down to around 12.6V, which nevertheless started the engine when we
began our cruise after the show.keep the engine running for an hour or so to give the battery a What we should have done is
decent charge; but delighted by a quartering breeze, stunning scenery and a magnifi cent tranquillity, we switched it off.
Night fell, and with twilight the breeze faltered – and so did the voltage. It was only after several attempts that we fi nally got the
engine going with the starting handle and crept, darkness cloaking our embarrassment, into Caladh Harbour.
Unnerving voltagesFlattening our battery did, however, give us a chance to check out another aspect of a
problem which had been worrying us for some time. When we installed the engine we fi tted a 20A permanent magnet alternator,
as these take up considerably less
room than conventional alternators and space was at a premium. However, despite fi tting the regulator designed to
accompany the unit, the voltage would reach nearly 16V, rising with the engine revs – far in excess of the safe limit.
which can be regulated by varying the current through the rotor electromagnets, a permanent Unlike a conventional alternator,
magnet alternator generates all the time, the voltage rising with the engine revolutions. The regulator has to control the
voltage and dispose of excess power somewhere, which can be done using load resistors or, in some cases, by briefl y shorting
the alternator coils. Our regulator appeared to do neither of these things, but I wondered whether our system would behave more
rationally when it could dump all the power into a flHowever, the voltage remained too high, the only difference attened battery.
being that the battery could accept more current.the same result, so in Scotland we We tried a spare regulator withhad to accept some overcharging, mixed with backing off the throttle until the volts reached an acceptable level. Clearly this was
no long-term solution, so when Hantu Biruthe winter we decided to try fi tting a conventional alternator and fi nd returned to Poole for
the fault with the solar panel.Fixing the solar panelInspired by our problems the night
before, I spent part of our morning at anchor in Caladh Harbour tracing the fault with the solarpanel. The indicator LEDs suggested that the regulator was functioning normally, but on disconnecting the panel there was
no voltage present on the cable.via a plastic box, sealed to the panel with sealant. I carefully cut The connections to the panel are
the sealant away with a sharp knife and dug it out to reveal the connections, which seemed fi ne. A meter confi rmed that the panel
was still producing power – the fault must lie with the cable.Tracing the cable throughAt anchor in Caladh Harbour, cutting away sealant to get at the solar panel connectionsI soldered a new, tinned cable to the panel ... ...and resealed the box with Aquaseal’s mBond 395 high-strength polyurethane sealantFIXING THE SOLAR PANELAfter an embarrassing engine-starting failure on Scottish cruise, we opted to fi t a conventional alternator and Hantu Biru’s
remedy a fault with the solar panel. David Pugh reports