Ask Sail: Voltage Drop

When I turned on my recently installed chartplotter, I got a “low voltage” message. Using a digital voltmeter, I measured 9.7 volts at the circuit breaker on the load side. Voltage on the battery side was 12.5 volts.
Author:
Publish date:
Updated on


 If your circuit breakers are corroded on the inside, you may have no choice but to replace them

If your circuit breakers are corroded on the inside, you may have no choice but to replace them

David McMillin of The Woodlands, Texas asks:

When I turned on my recently installed chartplotter, I got a “low voltage” message. Using a digital voltmeter, I measured 9.7 volts at the circuit breaker on the load side. Voltage on the battery side was 12.5 volts. I removed the breaker and measured the resistance across it. Each time I turned it on, I got different readings, ranging from 4 to 11 ohms. This breaker supplies power to several other electronic systems (wind, speed, backup chartplotter, etc.), and as more equipment is turned on the voltage gets lower. A check of the seven other breakers on the panel also showed various resistances. Any idea what could cause this?

Nigel Calder replies:

You are apparently dropping 2.75 volts from one side of the breaker to the other (12.5 to 9.7). Let’s say the chartplotter draws 0.5 amps. (They typically have a low power drain.) Ohms law gives us a resistance of 5.5 ohms, which is consistent with what you are seeing. If this is correct, there is high resistance in the breaker, probably due to corrosion or damage to the contact surfaces. The breakers are almost certainly not designed to be taken apart, in which case there is not much you can do about this.

You could try turning the breaker on and off repeatedly to see if this will clean up the points, but I don’t hold out much hope. The resistance when closed should be well under an ohm.

Related

101218BTSC-9887

Just Launched: Little Big Boat

Peter Nielsen looks at Beneteau’s latest entry-level boat and a new cruiser from Tartan Group Beneteau’s commitment to entry-level boats has been reaffirmed over the last year with the assimilation of the sporty Seascape line of pocket cruisers and the ...read more

TOTW_PromoSite

SAIL's Tip of the Week

Presented by Vetus-Maxwell. Got a tip? Send it to sailmail@sailmagazine.com No chafe, safe stay  If you’re leaving the boat unattended for a longish period, there’s a lot to be said for cow-hitching the shorelines, as this sailor did. They’ll never let go, and so long as the ...read more

belize600x

Charter Special: Belize

It would be hard to imagine a more secure spot than the Sunsail base on the outskirts of the beachside community of Placencia, Belize. The entire marina is protected by a robust seawall with a channel scarcely a few boatlengths across. It’s also located far enough up Placencia ...read more

DSC00247

DIY: a Top-to-Bottom Refit

I found my sailing “dream boat” in the spring of 1979 while racing on Lake St. Clair in Michigan. Everyone had heard about the hot new boat in town, and we were anxiously awaiting the appearance of this new Pearson 40. She made it to the starting line just before the race ...read more

01-oysteryachts-regattas-loropiana2016_063

Light-air Sails and How to Handle Them

In the second of a two-part series on light-air sails, Rupert Holmes looks at how today’s furling gear has revolutionized sail handling off the wind. Read part 1 here. It’s easy to look at long-distance racing yachts of 60ft and above with multiple downwind sails set on roller ...read more

HanseCharles

Video Tour: Hanse 348

“It’s a smaller-size Hanse cruiser, but with some big-boat features,” says SAIL’s Cruising Editor, Charles J. Doane. At last fall’s Annapolis Boat Show, Doane had a chance to take a close look at the new Hanse 348. Some of the boat’s highlights include under-deck galleries for ...read more

amalfitown

Charter Destination: Amalfi Coast

Prego! Weeks after returning from our Italian flotilla trip last summer, I was still feeling the relaxed atmosphere of the Amalfi Coast. It’s a Mediterranean paradise, with crystal-clear waters, charming hillside towns and cliffside villages, plenty of delicious food and wine, ...read more

image005

Inside or Outside When Sailing the ICW

Last April, my wife, Marjorie, and I decided to take our Tartan 4100, Meri, north to Maryland from her winter home in Hobe Sound, Florida. This, in turn, meant deciding whether to stay in the “Ditch” for the duration or go offshore part of the way. Although we had both been ...read more