An Overzealous Alternator

Ed Douglass of Sturgeon Bay, Wisconsin, asks:"My Westerbeke/Universal M-35 diesel engine came equipped with a Mando 51-amp alternator. From its appearance, I would say it is an automotive-type alternator. It puts out a constant 14.6 volts, which not surprisingly causes my wet-cell batteries to boil. It does this even after I have charged the batteries to capacity with my
Author:
Updated:
Original:

Ed Douglass of Sturgeon Bay, Wisconsin, asks:

"My Westerbeke/Universal M-35 diesel engine came equipped with a Mando 51-amp alternator. From its appearance, I would say it is an automotive-type alternator. It puts out a constant 14.6 volts, which not surprisingly causes my wet-cell batteries to boil. It does this even after I have charged the batteries to capacity with my shore-power charger. The regulator is internal to the alternator and is machine-sensed. I have looked extensively for a replacement regulator, but it appears none are available.

I have followed the diagnostic procedures described in the 2nd edition of your Boat Owner’s Mechanical and Electrical Manual. Nothing is wrong with the wiring. I took the alternator to a repair shop, where it was mounted in a test jig. It put out a steady 14.6 volts. The “set point” for this alternator, according to the specifications book, is 14.6 volts. The technician was satisfied that the alternator was working properly.

Your book does not mention “set point.” You do say, repeatedly, that an alternator with an output of more than 14.4 volts is bad for wet-cell batteries and deadly for gel-cells. I am concerned not only about the batteries, but about damage to electronic equipment and LED light bulbs."

Nigel Calder replies:

I don’t know enough about the guts of a voltage regulator to know if, or how, you could adjust the regulated output. What you could do is induce some voltage drop between the alternator and your batteries, which is the opposite of what we normally try to do! A voltage drop of 3 percent would knock you down to around 14.2 volts at the batteries. One way to do this would be to insert a battery isolation diode in the circuit. These typically introduce a voltage drop from 0.3 to 0.5 volt, but you need to check this, as some of the newer isolation devices have little or no voltage drop

Related

Lee-Cloths-Lee-Boards-and-single-bunks-on-ISBJORN_by-Andy-Schell_Trans-Atlantic-2019

The Perfect Offshore Boat: Part 2

November, 2009: Mia and I were sailing our 1966 Allied Seabreeze yawl, Arcturus, on our first-ever offshore passage together, a short hop from Wilmington, North Carolina, to Jacksonville, Florida. Our second night out, the brisk northwesterly wind shut down, but the sea state ...read more

210727_JR_SE_Tokyo20_186871368

Tune in for Olympic Sailing

Today marks the start of 470 and NARCA 17 racing on Enoshima Bay, and racing in the other seven fleets is already underway. A few of the American sailors are already off to an impressive start, with Maggie Shea and Stephanie Roble currently in second place in the 49er FX, Luke ...read more

Happy-Cat

Boat Review: Happy Cat Hurricane

I’m not sure what I expected from my daysail on the Happy Cat Hurricane. One thing I do know is that the day didn’t go as planned. The SAIL staff was invited by Alex Caslow from Redbeard Sailing to Gunpowder State Park on Chesapeake Bay near Baltimore. We were to test several ...read more

210722_PM_Tokyo20_4910_5979-2048x

Olympic Sailing Guide

The Opening Ceremony for the Tokyo Games is finally here. From July 24 to August 4, sailors from across the world will be gathering on six courses on Enoshima Bay to race for gold. Ten classes will take part in the event: RS:X (men), RS:X (women), Laser Full Rig, Laser Radial, ...read more

01-LEAD-TobagoCaysHorseshoeColors

Chartering: Voltage is King

For some time now, both in the pages of this magazine and with individual charterers, I’ve talked about how important it is to pay close attention during a charter checkout. The idea is to listen “between the lines,” as it were, to be sure you aren’t missing any hidden red flags ...read more

AC75-No.-1

ETNZ May Abandon New Zealand

Remember when the Kiwis were the young, underfunded upstarts of the America’s Cup world, with right on their side as they took on the Big Bad Americans? Remember the withering criticism leveled at Larry Ellison when, in the wake of “The Comeback” on San Francisco Bay, arguably ...read more

01-LEAD-EX26_1119_dehler_30od_race_2nd_077_web_4zu3_300dpi2048x

Boat Review: Dehler 30 One Design

I’ve long believed that while they may not be as much fun, the best sail trials are the ones that take place in drifters since it’s then that a boat’s performance—or lack thereof—really becomes evident. Pretty much any boat is fun to sail in 15 knots of wind. That said, there’s ...read more

01-LEAD-Opener-DJI_0026-2048x

The Multihull Industry’s Major Builders

It’s a given that boatbuilding these days is a global industry, with sailboats going down the ways everywhere from the icy waters of Scandinavia to the South China sea. This includes the manufacture of multihulls—no surprise given their birthplace in the far-flung islands of the ...read more