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Prototype DC-DC converter from Victron better, cheaper than old E motion model
January 14, 2008
Ft. Myers Beach, FL. Tests with a prototype DC-DC converter from Victron Energy show that it does far more than the unit previously specified for the E motion system and costs about $800 less.

Besides performing its main function of reducing 144 VDC from the main battery pack to 12 VDC for the house system, the Victron DC-DC converter (or cross charger) also accepts a wide range of AC as well as DC voltages, charges with a full three-step process, has three separate outputs and comes in12 or 24 volt models .

"It's pretty amazing," says Electric Marine Propulsion CEO Dave Tether, who's been putting the Victron unit through its paces on the company's Lagoon 47 testbed. "Fewer boxes, less wiring, more capability, less money. Cross-charging was never so good!"

The Victron cross-charger is based on the company's Centaur battery charger, which
was designed to handle the variety of power sources likely to be encountered at marinas across Europe and the U.S. The charger incorporates an innovative technology that Victron engineers developed to provide clean output voltage for uninterruptible power supplies.

Rigged for test next to Lagoon 47's main panel
12 volt, 60 amp charger
installed on Lagoon 47
24 volt house power is growing more popular
in Europe, and Victron has a Centaur for it.
A UPS must be able to handle wildly fluctuating input voltages from brownouts, blackouts and power surges caused by lightning strikes and convert them into the smooth, clean voltage output required by computers and delicate electronic equipment.

"Basically Victron wanted a battery charger that boaters could use with whatever oddball power they might encounter in out-of-the-way ports around the world - 120, 240, 50 or 60 cycles, low voltage, fluctuating voltage, voltage spikes," Tether says. "They obviously focused on AC, but their UPS technology is so versatile that it works with DC as well."

Centaur chargers automatically adapt to voltage input ranging from 90 to 265 volts AC at 50 or 60Hz and from 90 to 400 volts DC. Victron notes that unlike other chargers claiming similar input versatility, the Centaur maintains full output power for any input within the specified range.

The Centaur features fully automatic three-stage charging that peaks with a second stage 14.3 volt absorption voltage and tapers off with a 13.5 volt float charge Each model also has three isolated charge outputs that allow multiple battery configurations to be charged simultaneously. Depending on the model selected, charge output can be either 12V or 24V with amperage ranging from 16A to 200A. (See Components / DC-DC Converter for more data.)

The Centaur's many features as a battery charger included a formerly unnoticed capability that only became apparent when the company began working with EMP and its unique 144 VDC system. "We discovered that it made an ideal DC-DC converter that was much better than the one we were using," Tether says.

The Centaur's ability to run on both AC and DC allows two inputs into the 12 volt house system - shore power and ship's power, Tether says. "When you're tied up, you run dockside AC through the cross-charger to maintain the 12 volt system. When you go to sea you switch to ship's power and run the 12 volt system from the main 144 volt battery pack."

Tether is going to add a manual switch to the Centaur charger so he can shift between dockside AC and ship's power DC. But other than that minor modification, the Centaur already functions so well as a DC-DC converter, he says, "We could basically sell it right out of the box."

Link 10 e meter registers 228 volts from nominal
144 volt solar array on sunny day with minimal load
Too much solar energy
When Tether began testing the charger as a DC-DC converter in the Lagoon 47, he uncovered another unexpected benefit: The Centaur withstood the extra-high voltage sometimes generated by the boat's 12 panel solar array far better than the old converter did.

The 12 panels nominally produce 144 volts, which recharges the E motion system's main battery pack. But when the main pack is fully charged, and there's minimal load on the system, each 12 volt panel in the array can produce 20 volts – potentially 240 volts total.

The old cross-charger shut down at 192 volts, which meant the 12 volt house batteries were no longer being automatically topped up – either by the main solar array or the 144 volt battery pack.

That wasn't necessarily a problem - unless people started using the house system without switching the cross charger back on, Tether says.
"Say the boat's on the hook, everybody goes swimming, or we go off exploring in the dinghy. It's a sunny day, the cross-charger shuts down, and nobody's there to notice.

"We come back a few hours later, take showers - water pumps running like crazy - turn on the lights, the stereo, hair dryers. Pretty soon there's no house power."
Lagoon 47 with six 12 V solar panels on one side of boom, six on the other, all in series to produce a nominal 144 volts. Three paralleled panels over stern once topped up house batteries, but now are no longer needed.
To guard against that possibility, Tether connected three extra 12 volt solar panels in parallel directly to the house batteries. "But that's always seemed kind of silly when we have this big 144 volt solar array sitting on the bimini," he says.

With the new Centaur unit, the extra 12-volt panels are no longer necessary. It easily converts the extra-high voltage from the 144 volt array to 12 volts without shutting down, no matter how high it gets.

"We can park the boat and leave the refrigerator on, the freezer on, and then come back and turn everything else in the boat on - and the house batteries always stay charged."

"It's funny," Tether says, "you usually hear about not being able to get enough power from solar energy. With our system, we sometimes had too much. But that's not a problem anymore. The Centaur takes it all in stride."
Electric Marine Propulsion
Ft. Myers Beach, FL
phone 239.463.1824 fax 239.463.1485