Ft. Myers Beach, FL. Results of December sea trials with Nilar nickel-metal-hydride batteries in our Lagoon 47 test-bed were so successful that Lagoon Catamarans has decided to incorporate the advanced storage technology in its E motion-equipped 500 series.
"They performed beautifully," says EMP CEO Dave Tether. "They're smaller and lighter than lead-acid batteries, and they last a lot longer. You can stack them together like Legos to fit the space and weight requirements of the boat."
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| NiMH batteries in the Lagoon 47. Small "S" clips between like poles (pos-pos, neg-neg) connect batteries in parallel in each six-pack building block. Arched cables between like poles connect three blocks together in parallel. Curled red cable and black cable between unlike poles connect triple six-packs in series. |
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Customers eager
Lagoon already has a customer base eager for the E motion Lagoon 500, Tether says. Most buyers want the boat for their own blue-water cruising. Only about 20% are expected to go into charter. "These boats will be going across the Pacific and heading around the world," he says. "That's why Lagoon wanted to go with the most advanced batteries available."
To provide battery-recharge redundancy for long-distance voyaging, the new E motion 500 will have two 16 kw DC generators, one in each hull. The first test boat is expected to hit the water around the beginning of June 2008.
Higher cost but longer life
The retail cost of the batteries is significantly more than the valve-regulated lead-acid AGM batteries that come standard with our system. But with quantity discounts for Lagoon volume purchases and the much longer lifetimes of the NiMH batteries, Tether says, "They're going to be comparable in the long run."
Key to the Nilar batteries' long life is their 80% discharge capacity, i.e., down to only 20% of a full charge. That translates into fewer complete discharges, the main threat to battery longevity. Tether says NiMH lifespan exceeding 10 years seems readily achievable based on his experience with the Lagoon 47's Lifeline AGM batteries, which have a 50% discharge capacity. Tether's first AGM failures in the Lagoon 47 came after more than five years of service, half of it on a daily basis.
Conventional chemistry, breakthrough packaging
Nilar, of Stockholm, Sweden, and Denver, CO, designed the batteries with conventional NiMH chemistry, the same as in the small, rechargeable cells with the green stripes sold for consumer electronics. But Nilar has developed its own unique technology for packaging a dozen two-volt cells separated by conductive membranes into a single, 24 volt, nine amp-hour battery.
The membranes eliminate the need for separate cell casings, allowing a very thin, flat shape. Each battery is only 2.2 inches thick, five inches wide and 11 inches high (55 mm x 129 mm x 279 mm). The membranes also eliminate transport resistance between cells and provide uniform voltage across the electrodes.
Nilar has been selling the batteries for self-propelled wheelchairs that operate on 24 volt motors. It also has developed a 144 volt package of six batteries in series for hybrid electric cars.
Parallel for amps, series for volts
For the Lagoon 47 test, Tether stacked six batteries together in parallel instead of in series, creating a 24 volt, 54 amp-hour building block. "I wanted to make blocks with a safe voltage level that I could lift easily," he says.
The six-pack building block is 13 inches (330 mm) long (plus holding clamp), with the same five inch width and 11 inch height as a single battery, and weighs 52 pounds (23.4 kg). Electrical connections within each block are made with clips bolted between the terminals. Connections between blocks are made with conventional battery cables.
Tether connected three 24-volt six-packs in parallel to increase the amp-hours to 162. Then to get the 144 volt potential required for our system, he cabled six of these triple six-packs together in series. A breaker and cutoff switches were included in the circuit for safe handling.
30% lighter
The completed battery pack contained 18 six-pack building blocks with 108 individual batteries. The total weight was 930 pounds. Total volume was around eight cubic feet. Because of their greater discharge capacity, Tether's 162 amp-hour configuration is equal in performance to 12 AGM 4D batteries in series, but is 30% lighter.
The 162 amp-hours of Tether's test configuration proved to be more than enough capacity for the Lagoon 47 testbed. It has two 9 kw motors that draw 64 amps each at maximum throttle. The same capacity should work fine on the hybrid Lagoon 500s, Tether says. "It's a heavier boat with 16 kw motors, but the waterline is longer so it's more easily driven."
For larger boats, amp hour capacity can easily be increased when needed - either by adding more batteries to the basic building block or connecting more blocks in parallel.
Tether notes that the compact battery packs tucked neatly into the Lagoon's cockpit settee make a vivid impression on potential customers. "It's one thing to give people a brochure full of facts and figures," he says. "But when people can actually see those orderly rows of little grey blocks and realize they provide the power for this big boat, they suddenly realize just how special these batteries are."
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Lagoon 500 |
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Nilar NiMH battery is 2.2 x 5 x 11 in
(55 x 129 x 279 mm), weighs 8.6 lb (3.9 kg) |
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Like poles line up for parallel hookup. Series
segment has cutoff switch (on black cable.) |
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Series six-pack for hybrid-electric cars. Battery orientation alternates so unlike poles line up. |
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Parallel, not series, pack for boats
For the Annapolis 2007 sailboat show, Nilar provided a battery six-pack connected in series. But its capacity was only 9 amp hours.
"That's their hybrid car configuration," Tether says. "It needs a lot of voltage to get started, but the gasoline engine takes over once it's rolling."
E motion hybrid drive is different. Electricity from the batteries powers the motors at all speeds. Plus, Tether says, "A boat needs much more amperage to keep moving. It never gets out of first gear. It's constantly pushing its own weight in water out of the way as it travels."
So Tether connected his batteries in parallel to make it easy to add amp-hour capacity and minimize voltage within each building block.
The parallel configuration also simplifies the insertion of battery cutoff switches and breakers to separate the total string voltage into smaller sections for safety and ease of maintenance. |
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