When documenting the various power cables that run through Blue Opal, I checked the output voltage of the alternator, and the voltage flowing in to the batteries. There was approximately a 1V drop, which comes from the diode splitter that was fitted years ago. Since I’m not in a marina, or otherwise on shore power, I decided to replace the splitter with something that’s hopefully a bit better.

My first thought was Sterling’s alternator to battery charger, but that’s a pretty expensive bit of kit, so I opted to get a better splitter first, and see if my batteries will get past 13 volts since the current splitter drops me to a fraction over 13V for charging. Ordered it from Force4, since they had it for a slightly lower price than Sterling directly, and Marine Parts in Ireland don’t carry it.

To ensure I can fit it properly, I wanted a paper template that I could print off and stick to the bulkhead to make my drilling easier. Alas, Sterling don’t seem to supply one, so I made one in Fusion 360. It’s to scale, and is within about 0.25mm – good enough for getting the four holes drilled to mount it. After a lot of muttering, swearing at slot-head screws, and general upside-downedness as I crammed my head and shoulders into the space under the port berth, the Sterling is installed.

It turns out the big terminals on the Sterling are 10mm studs, and the small ones are 5mm studs. The old diode splitter used 8mm studs, so a bit of filing was needed to get the cabling to fit over the new 10mm studs. I’ll do some replacement work over the next few weeks to fit some proper-sized lugs that haven’t been filed – the filing has made the rings of the lugs rather thin and fragile.

The first attempt at firing up charging with the Sterling failed, however. It turns out that it doesn’t read the alternator-in feed to determine if it should be running, and instead needs a separate sense wire connected to the alternator. Trying to connect it via the alternator stud results in the unit being always-on, because it has an electrical connection between the alternator stud and the starter stud…

Sterling ProSplit R mounting template
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