Practical Boat Owner - January 2016

Charging system modifications

PBO conclusion

revealed the fault. The cable passes through the deck under the sliding hatch, almost exactly at the point where the front edge
of the hatch sits when pushed fully back. Unbeknownst to us, the hatch edge had chafed through the cable insulation,
and the salt water had made short work of both cores of the untinned copper cable.The solution was simple. I
soldered a new, tinned cable to the panel and resealed the box with Aquaseal’s mBond 395 high-strength polyurethane
sealant, which will hopefully be strong enough to resist kicking feet. We took the cable around the same route as before,
but this time added a stop to the hatch (right), preventing it from touching the cable.
included a diode within the sealed box to stop the battery discharging through NASA had originally
the panel, but as space is tight I omitted it and soldered in a new diode further down the cable, sealed with adhesive
heat-shrink sleeving. Our solar panel is once more trickling charge
into the battery, and with the engine started the alternator charges at a steady 14.7V, controlling the current
according to the battery’s state of charge. An extra benefit is that the charge lamp, which used to flash on and
off as the regulator struggled to control the power, now behaves as you would expect, lighting when you turn on the
ignition but switching off once the alternator starts spinning.

On the old mounts, the regulator heatsink was too low Swapping the mounts places it on top, out of the way of the starter

I fitted a new diode further down the cable, sealed with adhesive heat-shrink sleeving

A joggle in one of the alternator mounts allows it to sit forward Just enough clearance between the alternator and starter motor!

FITTING THE ALTERNATOR

Fitting the alternatorHowever carefully we measured, it wasn’t until we had our hands on a suitable alternator that we could

be certain whether it would fit. The problem area is around the starter motor and solenoid, which project upwards from the bellhousing just

where our alternator needs to be. A short alternator such as the permanent magnet unit we first fitted presented no problem, but

things were going to be tight with a deeper, conventional alternator.and checked the fit as best we Having downloaded its drawings

could, we bought the smallest alternator we could find: a 40A reconditioned unit from a Kubota generator for

£65 on eBay. We tried slotting it straight onto the previous unit’s mounts, but the

the alternator fouled the heatsink on the back of internal regulator’s protrusion of the

starter solenoid.mounts over so that the alternator pivoted on the opposite side. This Our next idea was to swap the

showed more promise, placing the heatsink at the top and providing what looked like just enough clearance on the

solenoid. However, the alternator pulley was fractionally too far aft to align with the crankshaft pulley – 2mm at most, but enough

to shred the belt. I solved this by cutting one of the steel brackets we had made for the alternator pivot and re-welding it with a

joggle in it, allowing the alternator to move forward by up to 4mm if necessary.We were close to winning now,

but a final offer-up showed we had virtually no clearance with the

solenoid housing. Changing the belt for one just 8mm longer completed the job –

there’s now about 10mm clearance when the alternator belt is tensioned.

Wiring changesThe wiring for the new system is simpler than the old, as we’re using

the regulator built into the new alternator. I was able to strip out the cables which originally

led to the alternator from the regulator, the regulator itself and the output cables from the regulator. At the same time,

I stripped out the solenoid we had installed for our abandoned electric stop system.In their place, a single, short

cable runs from the alternator output to the battery positive on the starter solenoid. The negative returns through the engine

chassis, as before. The old

The engine back in position. The wiring is simpler and tidier than with the old systemregulator had a 12V feed switched

from the ignition, which I reused for the excitation feed to the new alternator.The charge lamp was slightly

trickier: the old regulator provided a voltage to the positive side of the charge light, while the new one grounds the lamp. A minor

modification at the electrical panel (moving the lamp ground to the switched live) solved the problem.