Hard Charging: A New Way to Charge Batteries

When my flexible solar panel gave up the ghost early last summer, I was surprised at how much motoring it took to replenish our Norlin 34’s two Group 27 house batteries after they’d been run down by a week of sporadic bilge-pumping (caused by a slow leak around the keelbolts, ahem).
Publish date:
Social count:
When my flexible solar panel gave up the ghost early last summer, I was surprised at how much motoring it took to replenish our Norlin 34’s two Group 27 house batteries after they’d been run down by a week of sporadic bilge-pumping (caused by a slow leak around the keelbolts, ahem).

When my flexible solar panel gave up the ghost early last summer, I was surprised at how much motoring it took to replenish our Norlin 34’s two Group 27 house batteries after they’d been run down by a week of sporadic bilge-pumping (caused by a slow leak around the keelbolts, ahem). Since a typical day’s sailing for us involves an hour at most of engine work—usually half that—the 55-amp alternator on our little Yanmar 2GM20 just couldn’t pump enough juice to bring the 180 AH house bank up to full charge.

I toyed with the idea of installing a smart regulator to boost the amount of current going into the batteries, thereby speeding up the charging process, but that meant removing the alternator, splitting its case and soldering wires onto the brushes. Aside from the awful, back-wrenching prospect of removing the nearly inaccessible alternator, I have no faith in my soldering skills. The cost of having a professional do the job made my eyes glaze over; more to the point, it was late August and no one had the time.

There was another option—the Alternator-to-Battery charger, made by British company Sterling Marine Products. It seemed a very clever piece of gear, utilizing electronic wizardry to place a load on the alternator to pull its voltage down. In effect this tricks it into thinking there is a heavy drain on the system, so the regulator (which is left in place) works at full current. The resulting voltage, though, is not sufficient to charge batteries; so the A-to-B charger takes this current and amplifies it to charge the house bank at a greater rate than is possible with the standard regulator.


Inside the box is the same circuitry that’s in Sterling’s digital battery chargers and advanced alternator regulator, whose four-step charging regimen brings batteries up to charge in double quick time. Sterling claims it charges batteries 5 times faster than a standard regulator.

All this sounded pretty good, though I won’t say I understood the arcane process by which this electronic nirvana is attained. I did however like the promises of faster charging, and of easy installation; you just need to hook up a few wires and you’re all set.

My biggest problem was finding somewhere on a small 34-footer to install the unit. I eventually settled on a location midway between the start and house banks, and convenient to the alternator. First I removed the Blue Sea ACR split charging relay, as the A to B incorporates its own split charger. This immediately lessened the clutter in my battery box.

I was able to reuse most of the battery cables, only having to make up one longer 4AWG cable, and ran them from the A-to-B outputs to the positive terminals on the house and start batteries. Then I ran another cable from the BAT stud on the alternator to the input on the charger. Following instructions, I connected two temperature sensing cables (supplied), one to the house battery negative and the other to the alternator casing. These shut the charger down if temperature exceeds a certain level, bringing the alternator’s own regulator back into play. The last job was to connect a small negative wire from the charger to the ship’s common negative.


I left in place the three-position (off-1-Both) Blue Sea 9011e battery selector switch, simply to be able to parallel the batteries easily in the event the 65 AH sealed lead/acid start battery gives up the ghost. Otherwise, I’d just have installed a simple pair of cutoff switches in the cables between the batteries and the DC panel and starter motor.

Different types of battery require different charging regimens, so you need to select one of the charger’s eight settings—12V/24V non-sealed lead acid, sealed lead/acid, AGM, or gel. In the boost and absorption phase, a standard lead/acid battery is charged at up to 14.8 volts; a sealed lead/acid or AGM at 14.4 volts; and a gel battery at 14.1 volts. An automatic timer limits the boost charge and then, after the battery has soaked up as much current as it can at the absorption rate, the charger drops into float mode to coax it into sipping the last few amps needed to bring it up to 100 percent charge (more likely, 95 to 98 percent). A string of clearly labeled LEDs on the unit’s fascia lets you know what stage of the charging process—initialization, boost, absorption, float—you’re at.

According to my battery monitor, the house bank—a pair of deep cycle lead/acid batteries totaling 180AH— was at 12.2 volts, about 50 percent discharged. When I started the engine, there was a lag of two minutes or so before the A-to-B started charging, as indicated by a drop in engine revs as the load on the alternator increased. I had never seen more than 13.8 volts go into the batteries, but the A-to-B was immediately charging at over 14 volts. Meanwhile, the start battery was being charged at a lower voltage, though the charger does boost it at full current for three minutes out of every 20 to ensure it to gets a good charge.


After a leisurely 90-minute motorsail during which we ran the engine at around 2,400rpm, we put the boat back on its mooring and went home. The next afternoon, after the batteries had had a day to settle down, we measured the voltage at 12.63—about as close to 100 percent as they’ve ever been. These West Marine-branded batteries are now in their fifth season and have seen hard use and benign neglect—though with this increased charge rate I’ll have to be more diligent about checking the electrolyte levels.

I noticed that the batteries seemed to stay at a higher level of charge for the remainder of the season, seldom dipping below 12.5.volts, even though I was not able to use the boat as every weekend. I’ll keep more detailed records this season and report back at the end of the year, but so far the Alternator-to-Battery charger has lived up to its promise of faster, more efficient charging. Other users report their batteries are brought to full charge 30 to 40 percent faster, and that tallies with my experience.

The charger comes in various sizes to handle 12v or 24v alternators up to 210 amps. The 130 amp charger we installed is priced at $396, about twice the price of one of Sterling’s own smart regulators; but considering that you will most likely have to pay a professional to install the regulator, whereas any competent DIY boat owner could install the Alternator to Battery charger, using existing cables, in less than an hour, there’s not much actual difference. Plus—and this is important if you have a new boat or engine—because the alternator is not modified, there are no warranty issues. Nor does it affect the Electronic Control Units (ECUs) on new engines.


Landing Page Lead

The Volvo Returns to the Southern Ocean

Since the Volvo Ocean Race’s inception, the Southern Ocean has made it what it is. And no part of the race says “Southern Ocean” like Leg 7 from Auckland, New Zealand, to Itajaí, Brazil. The 7,600-mile leg, which starts this Sunday, is not only the longest of the event, but far ...read more


SAIL's Tip of the Week

Presented by Vetus-Maxwell.Got a tip? Send it to sailmail@sailmagazine.comTeak deck paradise  I had a call recently from the man who replaced the deck on my Mason 44 five years ago. He was worried about the way people are wrecking their teak decks trying to get the green off. ...read more


Gear: ATN Multi Awning

THROW SOME SHADEAmong the many virtues of cruising cats is the large expanse of netting between their bows, which is the ideal place to hang out with a cold one after a hard day’s sailing and let the breeze blow your worries away. Only trouble is it can get a bit hot up there ...read more


How to Sail the Med

“After spending so many years sailing the Caribbean, I was frankly astounded at how much more I enjoy the Mediterranean,” says Scott Farquharson of charter brokers Proteus Yacht Charters. “The culture, the history, the food, the weather, friendly people, crystal-clear water—there ...read more


Know-How: Rigging Emergency Rudders

We were 1,100 miles from the nearest land when we received a text message on our Iridium GO: “Rudder gone. Water in bilge. Worried pumps can’t keep up. Please call!”We had been in contact with the owners of Rosinante, a 38ft Island Packet, since they had first announced over the ...read more


Experience: Hard Aground

This is a story of how mistakes are made and judgment is dulled to the point of catastrophe. It is also about how prudent planning, good equipment and a bit of luck can bring you back from the brink.We departed Norfolk, Virginia, on December 15 bound for Jacksonville, Florida, ...read more


Vestas Discusses Fatal Collision, Recovery

Vestas 11th Hour Racing co-captains Mark Towill and Charlie Enright discuss the collision near the end of Leg 4 as well as the efforts the team has made to get back into racing trimJust over a month after 11th Hour Racing’s fatal collision with a commercial fishing vessel shortly ...read more