PxPixel
Ask SAIL: Serious Battery Drain - Sail Magazine

Ask SAIL: Serious Battery Drain

Author:
Publish date:

SERIOUS BATTERY DRAIN

Q: While sailing on a friend’s boat we noticed what we thought was excessive voltage loss overnight. The vessel has five 8D conventional flooded lead-acid batteries for the house bank and one 8D AGM battery for the starter. After running the onboard generator for some time during the day and including what the solar panels put in, we would start the night with close to 13 volts on the monitor. Then in the morning we would find the monitor reading 12.1 or 12.2 volts. During the night we would run the autopilot, refrigerator and freezer, VHF radio, running lights and chartplotter. The radar was on standby most of the time. We were able to lower the loss somewhat by turning the freezer off overnight.

My question is in regard to our attempt to find the cause of what we thought was excessive voltage loss by searching for a ground fault. We did this by disconnecting the positive lead from the battery and connecting the leads from a volt/ohm meter between the positive battery post and the disconnected positive cable. On the house bank with everything shut down we got a reading of zero. However, with the start battery we got a reading of 12.48 volts. After that we disconnected all the negative cables, one by one, from the start battery, and each time we got the same reading, even after all the negative leads were disconnected and the battery switches in the off position. Would a ground fault give the results we found?

Carl Updyke, via sailmail@sailmagazine.com

NIGEL CALDER REPLIES

In theory, with the voltmeter between the positive post and the positive cable and nothing connected to the negative terminal on the battery you will not, and cannot, see voltage. There is simply no circuit back to the battery negative. Where a ground fault would show up is if you have the negatives connected with everything turned off (or pieces of equipment disconnected) and you still saw voltage, indicating that there is a path to ground that bypasses all the switches and equipment.

Assuming your meter is reading correctly, what I think may be happening is you have some kind of a connection between the positive terminal on the house batteries and the cranking battery (maybe voltage sensors attached to the battery posts), and although I am finding it hard to visualize, you are actually measuring from the house battery positive to negative. If you disconnect the house battery positive and the reading goes away, then this is what is happening.

On the broader question of why your batteries are discharging so fast overnight, given you nominally have around 1,000 Ah of capacity (at 12 volts) it would take a substantial ground leak to pull this down. It is more likely that you have a problem with lost capacity, either through generalized sulfation (which may be recoverable with an “equalization” charge) or one or more failed battery cells.

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

March 2016

Related

Josie-helm-2

Chartering the U.S. and Spanish Virgins

Flying into Tortola in the British Virgin Islands one December morning, three months after Hurricane Irma, I felt like a war correspondent dispatched to the battlefront rather than a sailing magazine writer on an assignment to go cruising.As my LIAT plane descended toward Beef ...read more

Crew-North-27M004

Weather Gear for Inshore Sailing

Just because you’re not planning on braving the Southern Ocean this summer doesn’t mean that you won’t have some dicey days out on the water. If you haven’t got the right gear, a little rain or humidity can make things miserable. As with all safety equipment, “it’s always better ...read more

atlantic-cup-trailer

2018 Atlantic Cup Video Mini-Series

Atlantic Cup 2018: TrailerThis past spring, SAIL magazine was on-hand to document the 2018 Atlantic Cup, a two-week-long Class 40 regatta spanning the U.S. East Coast and one of the toughest events in all of North America. The preview above will give you a taste of the four-video ...read more

3DiNordac_webheader

3Di NORDAC: One Year In

One year ago this month, North Sails launched a cruising revolution with the introduction of 3Di NORDAC. The product promised to deliver a better cruising experience for a market that had not seen true product innovation in over 60 years. Today we’re celebrating the team that ...read more

HB96k_EP

Sea Eagle’s HB96 inflatable SUP

What SUP?Dinghies and kayaks are all very well, but there’s nothing like a stand-up paddleboard for exploring interesting new shorelines while giving you a good workout. Sea Eagle’s HB96 inflatable SUP makes a fine addition to your boat’s armory of anchorage toys, either on its ...read more

DSC_0031-43

Charting the USVI and Spanish Virgins

When my friends and I booked a one-way bareboat charter with Sail Caribe, starting in the U.S. Virgin Islands and finishing in Puerto Rico, we were a little nervous about what we would find in the aftermath of hurricanes Irma and Maria—even seven months later.When our plane ...read more

SailRepairKit

Know How: Sail Repair Kit

Despite your best efforts, there will inevitably be times when your sail gets damaged while at sea and needs to be repaired. First, no matter what the job, you will need to do a quick damage assessment, a task that requires a flat wooden surface, sharp scissors and a helping ...read more

01-061018ROAC-8149

Coming of Age at the Atlantic Cup

Midway through the final race of the inshore portion of the 2018 Atlantic Cup, the three boats in the lead—Mike Dreese’s Toothface 2, Mike Hennessy’s Dragon and Oakcliff Racing, representing the Long Island Sound-based sailing school of the same name—suddenly broke free from the ...read more

01_silken_2018-03-08-0052

North U’s Regatta Experience Program

“Want to check the keel?” North U Coach Geoff Becker calls to me from back by the transom. We’ve just suffered our worst finish in the regatta and are absolutely flying on our way back to shore, spinnaker up and heeling at an angle that feels like maybe we’re tempting fate. ...read more