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Converting the Sailboat Sunflower to Lithium Ion Batteries


This is a project undertaken by a serious cruiser, Micheal Lenci. He successfully converted his boat to lithium by getting ElectroMaax to customize his alternators.

Detailed below are the sequence of events that made this project successful

Sunflower, a 2004 Beneteau Oceanis 523 sailboat, is 52 feet at the waterline and displaces 24 tons and has a masthead height of 76 feet.

Sunflower has been extensively modified for long range, luxury cruising in northern latitudes. It is important to understand the design criteria. The relatively heavy use of AC and DC electrical power significantly impacted the design of the electrical system and the decision to change to Lithium Ion batteries.

“Long range cruising” for Sunflower means the US Northeast and the Canadian Maritimes. She cruises between her home port in Rhode Island to Maine, Nova Scotia, Newfoundland, and Prince Edward Island during the four month summer sailing season. She is outfitted to carry provisions and spare parts such that she can operate for 30 days autonomously with six people onboard without stopping for provisions or services.

“Luxury cruising” signifies all the equipment to support essentially unlimited fresh water (600 GPD Village Marine water maker); “hydronic” heating system supplying hot water heating to all spaces (ITR Hurricane II system); satellite TV, satellite internet and VoIP phones (KVH TracPhone and TracVision systems with 24” dishes); washer/dryer; custom freezer and custom refrigerator with Frigoboat refrigeration systems; ice maker; four power winches; and many ancillary electrical devices.

Typically, crew members each have several personal 120V electrical devices so 120V power is always available from an inverter in all compartments and the cockpit, and from the generator set or shore power when available.

Sunflower’s typical battery discharge rate when sailing is 15 to 40 DC amps depending on whether the satellite equipment is running, the heating system is needed, and on which cyclic loads are running. The other major electrical loads underway are the navigation system and autopilot as well as the following cyclic loads: the freezer, the refrigerator, and the winches. Miscellaneous AC loads supplied by the inverter on average draw 5 DC amps from the battery. Discharge rates at anchor at night are typically around 10 DC amps.

The water maker and washer/dryer require the use of the generator set. Thus, during typical cruising, Sunflower expects to run the generator for a period in the morning and for a somewhat longer period at night at anchor. Normally, when the generator is operating, Sunflower makes water to top off fresh water tanks. There is no attempt to supplement the battery charging capabilities with solar power or a wind generator due to the relatively large amount of electrical powered consumed.

Sunflower was initially outfitted with a house battery bank of six MasterVolt AGM-160 batteries. The six 160 AH batteries provided a total useable capacity of 480Ah (Assuming a maximum allowable discharge of 50%). Charging capability was provided by an 80 Amp alternator on the Yanmar diesel engine (see here) and by a MasterVolt Mass Combi charger/inverter capable of providing 2,000 Watts, AC power and a maximum DC charging current of 100 DC Amps.

The Decision to use Lithium-Ion Batteries

House Battery Bank’s condition:

Sunflower’s AGM house battery bank was approaching the end of its useful life as the boat entered the 2013 summer sailing season. The battery manufacturer advised that the batteries were already a year beyond the useful life that is typically seen. Sunflower planned to cruise 3,500 NM from Narragansett Bay Rhode Island, around Nova Scotia, up the St Laurence Seaway, through the Great Lakes to Lake Superior where she would spend the winter. Test discharges performed on the house battery determined that the batteries would support the planned Great Lakes cruise.

The primary symptom of approaching end of useful life was the percent the battery bank could be discharged before the battery voltage either dropped to an unacceptably low level. During the tests, this occurred at 60% of house back capacity. Three months later near the end of the summer season this rapid voltage drop occurred at 70% of house bank capacity.

In terms of operational use, the condition of the AGM house battery bank meant that the house bank’s effective useful capacity by the end of the summer sailing season was 20% to 25% of its total original capacity of 960Ah. (This assumes the bank could only be discharged to 70%, and would be charged to 90% – 95% to limit excessive low load generator run time). Approximately four hours were required to charge the battery bank from 70% to 90%.

The crew also verified that the time to charge the bank was limited by the charging rate the battery bank would accept, not by the capacity of the battery charger. Additional charging capacity would not result in charging the batteries more rapidly. Therefore replacement of the house bank before the 2014 season was required.

Why Lithium Ion?

The primary objective was to be able to charge the battery bank significantly faster, resulting in a reduction in runtime for the generator and higher load of the generator when running. This was, first and foremost, a “quality of life” objective for the crew (Minimizing generator run time while at anchor) and, secondarily, a desire to eliminate running the generator under light load. AGM (lead acid) batteries limit the amount of current that can be charged into them and this current decreases to near zero as the battery approaches full charge.

The charging current for Lithium Ion batteries is limited by the capacity of the battery charging devices and the charging current remains high until the batteries are almost fully charged (99%). The charging efficiency of Lithium Ion batteries is 90% – 94% (compared with 70% – 83% for lead acid batteries). Sunflower estimated that the Lithium Ion battery bank would charge in one half the time of the AGM battery bank, and might charge even faster. In addition to charging the battery bank faster, the characteristics of Lithium Ion batteries promised additional compelling advantages over AGM and other lead acid batteries:

  • For practical purposes, the voltage of Lithium Ion batteries does not drop as they discharge unlike lead acid batteries. The MasterVolt Lithium Ion batteries use eight 3.3V cells and operate at 13.2V instead of 12.8V with lead acid. Sunflower’s electrical system with AGM batteries required a constant voltage 12 VDC stepped to 24 VDC power supply for sensitive and critical electronic components such as the navigation system (Chart plotter, auto pilot, and radar).
  • The Lithium Ion batteries life is stated as 2,000 cycles to 80% discharge by the manufacturer. Two Li-Ion cells X 180 Ah X 80% discharge X 2000 cycles = 576,000 Ah lifetime. The AGM batteries would have approximately 660 cycles if discharged to 50%. Six cells X 160 Ah X 50% discharge X 660 cycles = 316,800 Ah lifetime. Thus, the new house bank should have 80% longer life than the AGM house bank. (The C20 discharge rate is assumed for the ratings provided by the manufacturer.) For Sunflower, that means a lifetime of 14 or more seasons.
  • The MasterVolt Lithium Ion batteries may be discharged to 20% capacity as compared to AGM batteries that can be discharged to 50% capacity. Additionally Lithium Ion batteries have no time constraints on discharge or charging. See the graphs, figure 1 and 2. Sunflower’s AGM house bank had six cells X 160 Ah = 960 Ah total. Thus, the useable capacity (50% discharge) was 480 Ah when the bank was new. The new MasterVolt Lithium Ion bank would be two cells X360 AH = 720 Ah total. The useable capacity is 576 Ah (80% discharge). Thus the new two battery Lithium Ion house bank should have a 20% greater useable capacity compared to the original capacity of the (6) battery AGM house bank.Discharge characteristics for an AGM batteryFigure 2 Discharge characteristics for a Lithium Ion battery
  • Lithium Ion batteries weigh about 30% of comparable AGM/lead acid batteries. Dimensions are also about 30% of comparable AGM/lead acid batteries. Although these were not primary considerations for Sunflower, they may be important in other applications.
  • Lithium Ion marine battery technology appeared sufficiently mature. The owner (with an electrical engineering background) had been following Lithium Ion battery technology and in particular Lithium Ion batteries in the marine industry. In his opinion, the technology of the batteries, control systems, and other major electrical system components produced by Mastervolt had developed sufficiently to justify the large investment in this technology. The crew planned to do all aspects of the extensive work required to convert to Lithium Ion batteries.
  • The purchase price of the Li-Ion batteries was a cost consideration. The Lithium Ion batteries would cost five to eight times as much as an equivalent capacity of AGM batteries. At the time this article was written, the manufacturers suggest retail price was $6,350 for a MasterVolt 12 V 360 AH Li-Ion battery. However, Lithium Ion batteries expected service life is three times that of an AGM battery – 2,000 cycles compared to 660 cycles. Over the lifetime of the battery the cost per cycle for Lithium Ion batteries is significantly lower. There are other cost factors to consider over the battery life time such as the cost of labor and other components required if upgrading rather than building new with Lithium Ion batteries, the cost savings of half or less generator run time, and the removal and installation cost of AGM cells two more times during the Lithium Ion batteries life.

The design of Sunflower’s electrical system with Lithium Ion batteries

The manufacturer (Mastervolt) is very clear that the conversion from AGM or other lead acid batteries to Lithium Ion batteries (Hereafter referred to as “Li-Ion”) is not a “drop in” replacement. The Sunflower crew affirms that the upgrade to Li-Ion batteries requires a fundamental re-engineering of the power generation portion of the DC electrical system.

This section discusses the characteristics of the Li-ion that drive the technical design of the DC system, the practical implications of the characteristics on the design, and further describes pertinent aspects Sunflower’s DC electrical system design for Li-Ion batteries.

Mastervolt Battery Management System:

Batteries of all kinds have some imbalance in the battery pack. During charging, one or more cells will reach maximum charging voltage before the others. During discharge, the cells that are not fully charged will be depleted before the other cells in the pack, and can potentially cause an under-voltage situation.

To avoid this, each Mastervolt Li-Ion battery has a cell management on the battery. The cell management system does the following (From the Mastervolt Li-Ion battery user’s guide):

  • Balancing between the eight different cells within a single battery. Mastervolt uses an “active” system that transfers current up to 20A from the stronger cells to the weaker cells during charging and discharging.
  • Protection of each separate cell from overcharging or discharging by voltage monitoring of each cell.
  • Prevention of over discharge e of each battery with a required external cut-off relay.
  • Monitoring of temperature. (Each of the eight cells, the external temperature of each battery pack, and the printed circuit board are monitored.)
  • Communication with Mastervolt charging devices via the MasterBus network and control of charging devices (stop charge, reduce charge, etc.).

Technical characteristics that drive the design of the DC electrical system:

Two technical characteristics drive the redesign of the DC electrical system. First, the charging requirements of Li-Ion batteries are different than AGM/lead acid batteries. Second, the operating voltage of the Li-Ion batteries are different than AGM/lead acid batteries.

The Li-Ion battery uses a modified version of the three-step charging algorithm used for AGM and other lead acid batteries. The modifications to the three-step charging requirements are (From the Mastervolt Li-Ion Battery user’s manual):

  1. Bulk & absorption voltage setting: 14.6 V as opposed to 14.4 V bulk phase charging voltage and 14.25 V for the absorption phase for AGM/lead acid batteries.
  2. Float voltage setting: 13.5 V as opposed to 13.25 V for the float voltage phase for AGM/lead acid batteries.
  3. All charging devices can receive a “stop charge” command from the Li-Ion battery allowing cell balancing: Each Li-Ion battery sends out a “stop charge” command to the AC powered battery chargers and the regulator for the engine alternator. This command switches the charging devices to the float stage.

Practical implications of the Li-Ion technical characteristics for a sailboat’s DC electrical system:

The technical characteristics of Mastervolt Li-Ion batteries result in three significant implications for design of the power generation portion of a sailboat’s DC electrical system:

  1. All devices that charge the Li-Ion batteries must be able to be adjusted to deliver the charging requirements for Li-Ion batteries. Additionally, all devices that charge the Li-Ion battery must be able to respond to the “stop charge” command from the batteries delivered via Mastervolt’s “MasterBus” control network.
  2. Other AGM/lead acid batteries in the DC system will require a separate charging device that delivers the proper three-step charging profile for those batteries.
  3. The charging devices that charge the Li-Ion batteries should have sufficient charging capacity to take advantage of the high charging rate of the Li-Ion batteries.

The next portion of this article will examine these three points in detail. Charging devices must have the charging requirements for Li-Ion batteries and must respond to a “stop charge” command:

  • AC powered battery charger(s), engine alternator, & the control system:
    • Charger/Inverter: Sunflower started this project equipped with a Mastervolt 12V, 2000 watt inverter/100 DC amp charger (“Mass Combi”). This device was monitored and controlled by an older Mastervolt control system (MasterLink MICC – Mass Inverter Charger Control). The older control system could not support the newer “MasterBus” interface of the Li-Ion batteries. The older control system and its associated DC shunt were removed. A new Mastervolt “MasterShunt” was installed. A “MasterView Easy MkII” monitoring and control panel replaced the older inverter control remote control panel. Since the Mass Combi charger/inverter only has a serial interface for control, a Mastervolt “MasterBus serial interface” device was installed to connect to the new MasterBus control network.
    • Diesel engine’s alternator:
      • At the start of the project Sunflower was equipped with the original 80A alternator for her 100 HP Yanmar diesel engine.
      • In order to meet the requirements for the charging profile, “stop charge” event and to be able to adjust the charging algorithm for Li-Ion batteries, a Mastervolt “Alpha II Pro” external regulator was purchased. This regulator connects to the MasterBus network.
      • Since the existing alternator needed to be removed and its control system modified to permit the use of an external regulator, the decision was made to evaluate the purchase of a new, higher capacity alternator, which would accommodate the Li-Ion batteries greater charging rate.
      • Sunflower preferred to use a Mastervolt alternator in order to minimize system integration challenges. It was determined that significant custom work would be required to devise mounting brackets for the Mastervolt alternator and to upgrade the two pulleys on the Yanmar engine. An initial objective was for the crew to do this project themselves, so using a Mastervolt alternator was deferred.
      • Sunflower found that ElectroMaax (view site) provided high capacity alternators and engine pulley kit specifically for Yanmar engines. ElectroMaax was willing to remove their built in regulator system and configure the alternator per the guidance provided from Mastervolt’s technical support team. The decision was made to purchase a 160A alternator configured for the Mastervolt Alpha Pro MB regulator and Yanmar pulley kit that employs a serpentine belt from ElectroMaax.
      • Comment: ElectroMaax provides an excellent video for the installation of the alternator and pulleys that estimates the time required for the installation of the alternator and pulleys is less than an hour with basic tools. This statement proved to be correct. The installation was completed easily in 45 minutes.
      • Comment: ElectroMaax was quick to caution Sunflower that the design of alternators has not changed to reflect the ability of Li-Ion batteries to draw full capacity from the alternator for extended periods while charging. They cautioned that the alternator temperature sensor of the external regulator (Attached externally to the regulator casing) was critical to prevent overheating of the alternator. Temperature control of the alternator would turn out to be one of the most significant lessons learned. (See the lessons learned section of this article.)
    • “MasterBus” CAN-bus control network: Mastervolt’s MasterBus data network is CAN- bus with a proprietary overlay that connects different Mastervolt devices via Ethernet cables. This network enables central monitoring and control of connected devices. The network also enables connected devices to be programmed to send commands to other devices to initiate various actions. In Sunflower’s design, routine monitoring is done using the MasterView Easy MKII monitoring and control panel that is mounted into the boat’s custom electrical and control panels. However, more extensive capability than is provided by the MasterView Easy is required to program devices and analyze their performance. MasterView provides “MasterAdjust software” as free downloadable software for this purpose. A Mastervolt “MasterBus – USB interface” was purchased to connect the boat’s laptop to the MasterBus.
  • Charging AGM/Lead Acid type batteries in the boat’s DC system:
    • Sunflower’s DC system has three AGM batteries – one diesel engine start battery, one generator start battery, and a bank of two batteries in the bow for the bow thruster and anchor windlass.
    • Sunflower’s new design provides automated charging of these batteries using two Mastervolt 12V to 12V, 20A MAGIC (Multi-purpose Adjustable Galvanic Isolated Converter) devices configured as three-step DC battery chargers. One charger normally charges the diesel engine start battery and if needed, the generator start battery via an “A – Off – B” switch. The other charger charges the thruster/windlass battery bank. Both chargers draw 12V power from the main DC bus.
    • The two MAGIC chargers operate fully automatically. They charge the AGM batteries in three stages when the Li-Ion batteries are being charged. The chargers have the optional capability to be switched off remotely by a push button. The chargers can also optionally be connected to the MasterBus network for advanced configuration, monitoring and control. This connection requires the purchase of a MasterBus Serial Interface unit for each charger. Sunflower did not need either of these optional capabilities so they were not implemented.
  • Sufficient charging capacity to take advantage of Li-Ion battery’s higher charging rate:
    • Sunflower purchased a Mastervolt “ChargeMaster 12V/100A battery charger to double the charging capacity of the system’s Mass Combi 2000W/100A inverter/charger. The ChargeMaster connects directly to the MasterBus; thus, no network interface device was required.
    • Comment: Sunflower considered replacing the installed 2000W/100A inverter charger with a Mastervolt 4000W/200A inverter/charger. After analyzing AC loads on Sunflower’s inverter bus and reviewing operational experience, it was determined that there was already excess inverter capacity so the additional expense of a larger inverter/charger versus the ChargeMaster charger was not merited. However, if this were a design for a new boat, a single high capacity charger/inverter would have been the preferred option. A design with two chargers could be considered to provide redundancy.

The following diagram is a simplified view of Sunflower’s DC power system. Please note that important fuses, disconnect switches, loads, and most of the DC negative cabling is omitted for clarity. Sunflower's DC power system

Operational Experience with the Li-Ion batteries

At the time this article was written, Sunflower had completed 70 days of continuous cruising operations and covered more than 3,000 NM. Key observations about the reengineered DC system and Li-Ion house battery bank are:

  • The primary objective of reducing generator run time 50% was exceeded. Sunflower has actually achieved a 70% – 75% reduction of generator run time for charging batteries.
  • The new house bank was sized correctly. The two 12V/5000W Li-Ion batteries provide sufficient capacity for 24 hours of sailing, and still have at least 35% capacity remaining.
  • The re-engineered DC system performed flawlessly from initial lift off onward.
  • More automated operation has been accomplished. Less crew time is required to monitor and charge the batteries.
  • Li-Ion battery voltage is a constant 13.2V for all practical purposes through the normal range of battery discharge
  • The crew was able to do all aspects of the project including modifying the engine pulley system, installing the new alternator, installing and configuring all Mastervolt components, and the extensive cable modifications. Excellent technical support from Mastervolt and ElectroMaax was essential and the crew was unusually well skilled in these areas. (See lessons learned for a more detailed discussion.)

Lessons Learned & Recommendations

  1. Mastervolt Li-Ion marine batteryLi-Ion batteries are “ready for prime time”: The Mastervolt Li-Ion batteries, their battery management, monitoring and control system, and the other major components required are mature and ready for production use. The battery monitoring system appears to work very well in the practice. Extensive monitoring capability is provided with MasterBus network and monitoring software. Each battery has a safety relay that can automatically disconnect the battery for safety events. The operator can also remotely or manually open these safety relays. The batteries and components are built for the marine environment, for example, the battery monitoring system is in a waterproof enclosure. All necessary system components are readily available. Manufacturer’s technical support is very good. The batteries and supporting systems operate reliably and consistently.
  2. Li-Ion batteries should be incorporated when a boat is built or, if done as an upgrade, the project should be viewed as a complete re-engineering of the DC power system: All sources of DC power (Batteries, chargers, charger/inverters, alternators, etc.) must be modified or replaced. A sophisticated monitoring and control system is required. This would seem to be cost effective if done when a boat is built. In the case where this is undertaken as an upgrade to an existing DC power system, the decision to use Li-Ion batteries and re-engineer the DC power system will be made based on whether the benefits are worth the significant cost of the project. In the case of Sunflower where the generator run time was reduced 75% or more and the existing bank needed replacement, the upgrade was worth the cost.
  3. Use a single vendor for the batteries and DC power generation equipment to the maximum extent possible: Sunflower’s upgrade was successful at initial lite off to a large extent because of the use of all Mastervolt components and the Mastervolt network control system. This is due both to the smooth “plug and play” integration of the components and very importantly, due to excellent and extensive technical support. Having one vendor who “owns” the integration is essential in this crew’s opinion. There are innumerable details in the integration of the component and the design of DC new DC system. The project would be significantly more difficult to accomplish and would likely have integration issues if one primary vendor was not used for the major components.
  4. Vendor technical support is essential: Outstanding technical support from Mastervolt and ElectroMaax (alternator) were key elements in the success of this project.
  5. Carefully consider whether to do it yourself or hire it out: This project is quite extensive. It really is a complete re-engineering of the power generation portion of the DC electrical system. The development of the system design requires in depth knowledge of lead acid and Li-Ion batteries as well as DC power generation components such as chargers and alternators. The actual execution of the work requires specialized tools, experience, likely modification of structural components that support components, and so forth. It is worth noting that Mastervolt’s technical support commented that they had not worked with an owner/do-it- yourself installation of Li-Ion batteries before. (Sunflower’s crew includes a former captain of a nuclear submarine who is also a very experienced sailor and has extensive electrical engineering/battery experience.)
  6. The alternator and its external regulator are the weak link in the system: In the opinion of the Sunflower crew, generally speaking marine alternators and their control systems have not caught up with introduction of Li-Ion batteries.
    1. Alternators were designed for lead acid batteries where the charging current builds up relatively quickly then tapers off to a float over the period of the charge. Li-Ion batteries, on the other hand, will take the full charging current capacity of charging devices for the entire period that they are engaged. The alternator simply cannot handle this high current for an extended period and overheats. The temperature sensor of the external regulator senses the alternator casing temperature and reduces the charging current. However, the alternator temperature monitor was designed as a safety mechanism for potential over-temperature, not as a primary method of controlling the alternator output.
    2. In Sunflower’s case, these events occur in a five- minute cycles. The alternator charges for about two minutes at its full current, then the regulator stops the charging due to alternator casing temperature reaching its limit, the alternator cools down for three minutes, and the cycle repeats.
    3. Sunflower has noted using a handheld pyrometer that there is a time lag between when the windings reach the design temperature limit and when the casing temperature reaches the same temperature. If the engine is brought up to speed quickly with the alternator cold (As is typical when starting the engine and getting underway), there is a distinct possibility of exceeding the temperature limit of the windings before the casing reaches the temperature limit. Through experimentation, Sunflower has determined that the limit of the temperature as measured on the alternating casing must be set at 60% of the manufacturer’s stated winding temperature limit in order to avoid overheating the windings.
    4. The alternator/regulator bottom line: The issue of overheating an alternator due to high current drawn during the entire Li-Ion battery charging period needs to be addressed. In lieu of even larger alternators with more cooling, it seems to the author that modification of the Mastervolt regulator software would be both easier and apply universally regardless of alternator manufacturer. The Mastervolt regulator already monitors the field current of the alternator. The software could be modified to allow the operator to set a limit on alternator field current and thus limit the alternator output. The default could be the maximum field current the regulator can supply (no change from the present mode of operation). If the operator sees that the alternator reaches its maximum temperature the operator could adjust the maximum field current downward so that the alternator would reach a steady state and not overheat. In the author’s opinion addressing what appears to be a simple fix should be a top priority for Mastervolt in order to remove the only weak link in an otherwise effective and robust system.
  7. Miscellaneous items and observations:
    1. The monitoring and configuration capabilities of the MasterAdjust software are essential. The software is a free download however a USB interface device is required.
    2. Additional cooling may be needed for the cabinet or area of the battery charger(s). Sunflower already had thermostat controlled cabinet cooling fans for the container that houses the two battery chargers. These cabinet cooling fans seldom ran when charging the AGM batteries. However due to using the full capacity of both battery chargers for the Li-Ion batteries, the cabinet cooling fans now kick on in every battery charging cycle.
    3. Sunflower found it challenging during the design phase to determine how large to the AC battery charger(s) should be in order to obtain their goal of greatly reducing the generator run time. Based on Sunflower’s experience, 100 DC amp charging capacity per Li-12V/5000W Ion battery seems about right.
    4. The measured charge efficiency has been 94% as the manufacturer’s literature states compared with 73% measured on the previous AGM batteries.