Ask SAIL: Battery Power Drain

I recently bought a share of an older boat, a Cape Dory Intrepid 9-meter, and put new 12-volt AGM batteries in her. Something, however, is draining the batteries.
Author:
Publish date:

Peter Letson, Greenfield, Massachusetts asks:

What the heck is this? And what is it doing there?

What the heck is this? And what is it doing there?

I recently bought a share of an older boat, a Cape Dory Intrepid 9-meter, and put new 12-volt AGM batteries in her. Something, however, is draining the batteries. At one point, after a couple of weeks absence, they were down to less than one volt. I have traced out the wiring and found an unidentified object (see photo) between the battery selector switch and the distribution panel. The two lighter gauge wires in the picture connect to the output terminal of the selector switch and the ground. Power to the distribution panel has been a “sometimes thing.” My questions are: What does this thing do? What functionality would we lose if I took it out of the circuit and connected the selector switch directly to the distribution panel?

Nigel Calder replies:

You are looking at a solenoid, an electro-magnetic switch. When you turn on your selector switch it energizes an electro-magnet, which pulls together two heavy-duty points to close a circuit between the larger cables that supply power to your distribution panel. Given that the energizing side of the electro-magnet is connected to the output side of your selector switch, the solenoid should be disabled when the selector switch is off. It therefore should not drain your batteries when the switch is off, so this is probably not the cause of your problem. However, I can think of no reason to have the solenoid in the circuit (it duplicates the function of the selector switch), so I would take it out. If this does not solve the power drain problem, you definitely need to deal with it, as it will rapidly wreck your expensive batteries.

NigelCalder

Solenoids normally serve as remotely operated switches in high-current circuits. Typically, there is a switch to supply power to the electro-magnet through the small wires, closing the circuit to the bigger cables. This way the big cables don’t have to be brought to the switching location. The most common use is in an engine-cranking circuit. In the old days solenoids looking just like yours were mounted independent of starter motors. Now they are mounted on the starter itself.

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

Related

shutterstock_543237994

The Slow Route to Cabo

Each November, cruising boats start leaving California for “a winter of fun in the sun down Mexico way.” And having spent the summer and autumn on a leisurely passage down the West Coast on board Distant Drummer, our Liberty 458 sloop, my husband, Neil, and I were now in San ...read more

MHS-GMR_3549

New Multihulls 2018

Farrier F-22 New Zealander Ian Farrier ushered in a new genre of sailing with his folding-ama trailerable trimarans, the best-known of which are the Corsair designs. Farrier’s last project before he passed away last year was this sweet little tri. Available in three versions, ...read more

shutterstock_373701682

Cruising: Island Comeback

The U.S. Virgins Islands have surged back from the devastation of the 2017 hurricanes, with new infrastructure plans that will benefit charterers and cruisers alike. After hurricanes Irma and Maria roared through the Leeward Islands in September 2017, it was impossible to ...read more

albintoilet

Gear: Albin Pump Marine Toilet

Head Start Is there room for a new marine toilet? Albin Pump Marine thinks so, having just introduced its line of Swedish-built heads—ranging from compact to full-size models—to the American market. The toilets feature vitreous porcelain bowls and either wooden or thermoplastic ...read more

07n_45R2699

Multihull Sailor: Classic Cats

If you’re looking for a decent sub-40ft cruising cat, you have few choices when it comes to new-boat offerings. It is a well-known fact that the multihull market has taken off in a way very few could have predicted. Despite Hurricane Irma’s recent destruction of a large part of ...read more

TOTW_PromoSite

SAIL's Tip of the Week

Presented by Vetus-Maxwell. Got a tip? Send it to sailmail@sailmagazine.com Thanks a bunch  This scene is very calm and seamanlike. No frantic rope throwing or shouting. As he passes the line to the gent on the dock, the crew on the boat says, quietly and clearly, “Would you ...read more