Ask Sail: An Explosive Situation

When the engine is under load and moving the boat at a decent speed, the voltmeter is pegged past 16 volts, and after a little while the wires (which are appropriately sized) running to the battery switch from the engine get pretty hot. Am I hurting my batteries?
Author:
Publish date:
Updated on

Jonathan Kirby of Quincy, Massachusetts, asks:

I have a 1976 Hunter 30 with a Yanmar YSE12 diesel engine. The electrical system consists of two batteries wired in through a Guest battery selector. At idle speeds the DC voltmeter at the main panel reads 12.5 to 13 volts. When the engine is under load and moving the boat at a decent speed, the voltmeter is pegged past 16 volts, and after a little while the wires (which are appropriately sized) running to the battery switch from the engine get pretty hot. Am I hurting my batteries? Do I need a new alternator?

Nigel Calder replies:

You are not only hurting your batteries, you are at risk of having them explode! At this high charging voltage, they will be gassing vigorously as the water in the electrolyte is being broken down into hydrogen and oxygen (the batteries will sound like they are boiling), while generating a lot of heat. The batteries will be in a condition known as thermal runaway, with the alternator running at a high output (which is why the cables are hot). If there is an internal or external spark, the hydrogen can cause an explosion either inside or outside the batteries.

NigelCalder

The cause is almost certainly a faulty voltage regulator. The regulator is inside your alternator, so you need to take the alternator off and have it checked out. You should not run the system until the problem is sorted. I regret to say your batteries are also almost certainly toast. 

Got a question for one of our experts? Send it to sailmail@sailmagazine.com

Related

Meridian-X-Spin_2

MOB: A Whistle in the Wind

Mark Wheeler went overboard a few minutes before midnight. He was in the middle of Lake Michigan, 30 miles offshore in 40 knots of wind. As he fumbled for the lanyard to inflate his lifejacket he watched his racing sailboat, Meridian X, disappear into the night at more than 18 ...read more

TOTW_PromoSite

SAIL's Tip of the Week

Presented by Vetus-Maxwell. Got a tip? Send it to sailmail@sailmagazine.com Slapper stopper  When I came on deck at 0800 to hoist my colors on a visitors’ mooring recently, there was an awkward slop running in. This doesn’t trouble my Mason 44, which has a traditional counter ...read more

Tilly-1

Gear: Tilley Polaris Hat

A True Blue Tilley Sailing is all about fun in the sun, but it sometimes doesn’t take long to get too much of a good thing, especially when on a prolonged cruise or offshore passage. Enter the Tilley Polaris, the latest lid developed by iconic Canadian hat-maker Tilley. ...read more

Sand-TOWEL_MODEL-3

CGear Sand-Free Beach Towel

Sand Be Gone! The summer is hot and full of terrors—not the least of which is the sand that sticks in your beach towel in the hopes of a free ride back to your car or boat. Fortunately, there's now the CGear Sand-Free Beach Towel, engineered in polyester to not only dry quickly ...read more

01-Blowup-Tiwal2_sailing-(3)

Gear: Tiwal Inflatable Sailing Dinghy

Blow-up Boating A few years ago, the French company Tiwal arrived on U.S. shores with that most improbable of products, an inflatable sailing dinghy that actually sails the way a boat is supposed to. Now, nearly 1,000 Tiwal 3’s later, the company is back with its Tiwal 2, an ...read more

Koozy

Gear: 22 Below Koozie

Killer Koozie For all that sailors love the warmth of this time of year, that same warmth can also wreak havoc on their otherwise icy-cold beers. (Unless, of course, you drink them very, very fast. But we won’t go there.) To help deal with this terrible hardship, North ...read more

Cool-Specs

Gear: Gill's Race Fusion Sunglasses

Wicked Cool Specs Is there anything in the world of sailing more fun than a cool pair of shades? Heck, no! And it would hard to find a cooler pair than these new Race Fusion specs from longtime weather-gear manufacture Gill. In addition to looking great, they include a number of ...read more

North_new

Gear: North Sails Waterproof Pack

A few years ago, North Sails made a big push into the apparel business with all kinds of sharp-looking button-down shirts, shorts and fleeces. That doesn’t mean, though, that the North Sails Collection isn’t still plenty practical, as is evident in its new roll-over waterproof ...read more