Tech Blog: The 48vDC Lithium Electrical Refit – Part 1: Requirements and Design

Over the past 7 months living aboard our boat with the new electrical system installed we have been testing its functionality and evaluating performance. With this new system, we are able to run our electric SCUBA compressor, 30 gallons per hour desalination watermaker system, electric kitchen appliances (microwave, induction cook-top, kettle, stand mixer, etc.), and 16,000 BTU air conditioner, all directly off of the lithium house battery bank and inverter, and without the assistance of a generator. We can rapidly recharge our large 20 kilowatt house battery bank through a 130 amp-48 volt alternator and 1300 watts of solar. We often can go more than a week without needing to burn diesel to generate power.

This post is very technical, and is intended to document in detail our marine electrical system for others to consider when designing for their own boat, RV, or home system. It’s also a long post as it’s really 2 documents in 1 (Requirements and the Design).

Why Upgrade the Electrical System?

We are serious about long-range cruising where we don’t intend to be at marinas connected to shore power very often, we wanted a system that would provide for some creature comforts to ensure we feel at home and at ease away from the dock. Having the capabilities of a small apartment may not be the most salty sailor path, but this setup allows us to stay away from shore and marina life and continue our journey in comfort without feeling like we’re camping for years on end. (Nothing wrong with camping, it’s just not how we want to live every single day.) This project was not cheap, but we think it was money well spent to ensure our dream stays alive for as long as possible with minimal compromise. It also adds considerable value to our boat if the time eventually comes to sell her.

Why 48 volt DC?

Initially, one of the primary drivers for the upgrade was the ability to run an electric SCUBA compressor which are notorious for being difficult to start because they require a large electric motor inrush current. Compressor manufacturers will claim an 8 kilowatt (kW) generator is required to operate the compressor, and they generally do not mention any ability to operate it via battery power. Our boat came with a 5 kW generator, and most other boats we looked at in the past either didn’t have a generator or also had a less than 6 kW generator. If automotive companies can make batteries work for cars (and at much higher power levels), there must be a better way to run a compressor without any generator!

Once you start looking into supporting other large loads off of battery power, it quickly becomes apparent that a higher voltage house bank (than the conventional 12 volts) is beneficial due to the high amperage required to function over 12 volts. The main limitation at high power levels using 12 volts, is the largest size battery cable you can buy (4/0 or 0000) supports a maximum of 400 amps, so loads over 5 kW aren’t possible. This is at least according to the American Boat and Yacht Council (ABYC) safety specifications: no double cable runs, other than for voltage drop prevention. Wire size requirements at 48 volts are a quarter than what is required at 12 volts, which can be substantial in terms of wire cost and weight. And 48 volt devices are often cheaper and generate less heat due to the high voltage requiring less amps to create the same power, which in turn requires less copper internally for connecting components (our 230v Quattro inverter is cheaper than the 120v equivalent for this same reason). With the advent of electric propulsion on boats, hybrid diesel-electric engines, electric outboard motors, and newer load-heavy marine systems (watermakers, etc.) being available in 48 volts, it made the move to a 48 volt system from 24 volts very appealing. During Mark’s 12+ months of researching how to setup SCUBA compressors aboard boats, he met an ex-cruiser, now living in Fiji, who had re-powered his compressor with a 48 volt BLDC motor (https://www.goldenmotor.com/), making it a viable backup option to get the compressor powered by battery.

High output 48 volt alternators are available on the market that generate 5-10 kW of power, enabling generator removal a real possibility. 48 volt alternators have an ~20% efficiency gain over an equivalent 12 volt alternator, per Balmar white paper. When running the boat under power of the diesel (in and out of marinas, anchorages, dead wind zones, etc.) we make very efficient use of the diesel energy by powering the boat and recharging the house battery bank.

The last piece of the puzzle was how to power the 12 volt systems from the 48 volt side, as we want to slowly migrate loads to 48 volts over time and as required. Victron makes 48-12v ‘converters’ but they don’t have a charging profile to charge a battery (which we’ll get into later as to why we still need a battery) as they only provide a constant voltage (not good for a battery). Mastervolt had very recently released a 48-12v 50 amp charger (Fall 2023), but it was priced at $650. Then we learned about the ‘hack’ of using Victron MPPT solar controllers for the DC-DC conversion (100/50 MPPT controller is half the cost of the Mastervolt charger for the same output). We also learned that some boat manufacturers have been using this method in boats with double and triple DC voltage boat systems. Having the 48-12v charger solution resolved and having an alternate option to power the compressor locked in the migration to 48 volts.

Design Requirements

It took a couple of years of occasional research, with the last 6 months being very in-depth research to figure all this out the proper way. Mark spent countless nights researching batteries, refreshing electrical concepts, searching various online forums, building high level designs, and challenging assumptions and choices to find the right path forward. Of course our decisions may not align with others looking to do a similar upgrade, but this can serve as guideline of what works well (at least for us) and hopefully clearly explains our decision process.

The 48 volt battery bank size depended on what we could fit in the existing battery compartment area of our boat, which is larger than most sailboats of our size (thank you Outbound Yachts). Through a ridiculous amount of research across the lithium battery market, we decided our battery bank would be approximately 20 kWH, based on current market availability of 24/48v batteries and their dimensions.

Lithium Iron Phosphate (LFP) battery chemistry was a given considering our use case, as it can support the heavy loads with ease, when compared to conventional lead acid batteries with voltage drop and the Peukert effect with heavy loads. LFP also allows for the ability to rapidly recharge with minimal losses. There are many other advantages to go LFP over lead acid, but we won’t get into all that here (it’s a no-brainer now with price reductions in the past couple of years, so long as the whole electrical system can support LFP).

The 12 volt house bank should ideally use LFP for the same reasons as the 48 volt house bank, however, this battery is largely just a ‘buffer’ battery to handle amperage bursts from the electric windlass and winch. It can also provide backup power to critical navigational equipment and lights in the event the 48 volt system fails. For this reason, the battery capacity should be at least 100 amp hours. The 12 volt ‘starter’ battery, used for starting the diesel engine and generator, will remain as a Lifeline AGM battery, and is charged via the 12 volt house system via a 12v-12v charger.

Since we plan to travel worldwide, we also wanted the ability to use 230 volt AC appliances, alongside 120 volt AC. 230 volt AC SCUBA compressors are also the preferred motor type as they are slightly easier to startup. (Even easier with a 3-phase 230 volt motor, which we’ll get into later.) We also wanted the ability to plug our boat into any shore power outlet ranging from 120-240 volts at 50-60 hertz, with minimal effort to change between voltages. AC shore ground should be isolated from the boat’s grounding system to prevent electrolysis of underwater metal parts (propeller, propeller shaft, etc.) The AC inverter should have enough output power to support 1 heavy load appliance (2000+ watts, i.e., compressor), plus another medium load (1000-2000 watts, i.e., watermaker).

With all this power stored up to be used, we still need a (fast) way to recharge the bank. Solar power upgrades are one – we fit 2 large rigid panels (470 watts each) on our solar arch on the stern of the boat, plus another 4 flexible panels (100 watts each) were easily mounted on the bimini and hard dodger. The primary recharge method should be via a high output 48 volt alternator, with enough output to recharge the full house bank in less than 3-4 hours. The alternator regulator should be either the Wakespeed 500 or Arco Zeus for smart lithium charging profiles, with fine tuning of configuration options and ease of management through a Bluetooth-connected phone app. Recharging from shore power can be done through the inverter or via a separate battery charger.

Redundancy of the system is of high importance to us considering we plan to be weeks if not months away from a city with repair capabilities, and the importance of running navigational equipment and lights. We are using the following list of items to ensure redundancy in our system: 2 separate 48 volt batteries in case a single battery fails (cell failure, etc.); MPPT solar controllers for each rigid panel that can be rewired to support both panels if one fails; N+1 redundant 48-12v chargers wired into the system; ability to cross connect 12 volt house bank with 12 volt starter bank to start the diesel engine or provide buffer amperage for the electric windlass and winch; flexible solar panels to power the 12 volt house system; and rigid solar panels to power the 48 volt house system. In the event of failure of the 48 volt system, the 12 volt LFP house bank can power critical boat loads, and can be recharged by the solar panel system.

Lastly, the lithium systems should all adhere to the ABYC E-11 standard for lithium batteries on boats, and should be easily manageable through good software. The battery management system (BMS) managing lithium banks should be able to actively control charging and discharging of the bank for safety (electrical fires are the #1 reason of boats sinking).

Our Requirements List:

• 48 volt DC for the primary house bank for future proofing the boat, and all the technical benefits.
• At least 20 kW of house battery bank capacity (must fit within existing battery compartment).
• Keep the existing 12 volt DC system largely intact, as we don’t want or need to migrate loads over to 48 volt DC immediately, and 12 volt DC loads are expected to exist for the foreseeable future.
• 12 volt DC house system still needs to support the high amperage of the 1.4 kW windlass motor and electric winch.
• Retain Outbound factory 12 volt house and starter on/off switches and 12 volt house bank to starter cross-connect switch.
• LFP battery chemistry for both 48 volt DC and 12 volt DC house systems, except for the engine starter battery (AGM).
• 12 volt house LFP battery to be at least 100 amp hours in capacity for reserve power in case of 48 volt bank failure.
• Fast recharging ability, and not requiring recharging the batteries to 100% every day (benefit of upgrading to LFP over lead acid).
• Ideally be able to remove the generator, but will keep it installed for the next 6-12 months after upgrade to evaluate its utility.
• High output alternator for fast recharging a 20 kW bank, regulated by smart regulator (Wakespeed 500 or the new Arco Zeus).
• Global shore power connectivity (120-240 volt, 50-60 hertz) where we ideally won’t need to install a second set of shore power outlets, and only will need a pigtail adapter for the local plug style.
• Dual voltage service for the boat 120 volt AC and 240 volt AC.
• AC shore ground must be isolated from the boat ground – either through isolation transformer or all shore power runs through to only a battery charger to prevent electrolysis.
• Management and visibility into all of the main electrical components through software.
• At least 2 layers of redundancy for critical components and layers of the system.
• Smart BMS to manage the 48 volt DC house bank that adheres to ABYC standards and can actively disable and re-enable charging and discharging of the bank for safety, and communicate with the alternator regulator for ‘allow-to-charge’.

The As-Built Design

The diagram above represents the as-built electrical system on the boat. Details of the design and choices made are explained in the grouped sections below. For this design, we partnered with Justin @ Hullux Marine in Seattle. We were able to bounce ideas off of him, and he reviewed the design, and made improvements to it.

48 volt DC

Victron SmartLFP Batteries, Lynx SmartBMS, and Distributor

We ultimately went with a full Victron setup for two reasons. First was the price. Through shear luck, a few months before kicking off the project, Victron had significantly reduced their pricing across the board, by 40% off in many cases. This brought the price of their SmartLFP batteries within $200-$300 of good quality Chinese LFP batteries that were under purchase consideration. Second was to get the benefit of having the whole system integrated with the SmartBMS system. This was a no-brainer for the slight increase in cost over the Chinese LFP batteries. With this setup, there would not be any push back from insurance companies either (we have heard of insurance companies refusing coverage for lithium systems installed by a DIY’ers or batteries from companies without a US presence). At the time, the standard SmartLFP batteries were all that Victron offered. They only sold them in 12 volt and 24 volt models. So to create a 48 volt battery we wanted, 2 had to be wired in series.

Side note: As of a couple months ago, there are new versions of these batteries – SmartLFP NG (Next Gen) – that are available in a 48 volt native model, utilize digital signals for battery communcations rather than analog, and offer a few other nice features. Our layout works fine as-is, but for others, the advantage of having a 48 volt native battery would be that if 1 battery were to have a premature failure, it could be removed individually rather than our setup which would require both batteries in series to be removed (thereby losing half capacity).

Another key feature of the SmartBMS is it’s ability to output Allow-to-Charge and Discharge (ATC/ATD) signals for smart charging and discharging devices to track. This is primarly important for the alternator regulator, solar charging, and any other loads we can add a Victron BatteryProtect to. This provides a significant safety factor for the LFP bank over most other lithium systems out there, as it can actively disconnect devices if there’s a problem, and charging devices like the alternator can be notified a few moments in advance to stop charging before the BMS disconnects to prevent a load dump condition which would blow up the diodes in the alternator (rendering it unusable). Additionally, the centralized management (CerboGX) that is closely tied to the SmartBMS allows this solution to have multiple charging sources active at the same time (i.e. solar and alternator charging).

The Lynx Distributor is a nice-to-have ‘smart’ fuse distribution box, as it can communicate with the Victron software if a fuse has been blown. We were a few months too early for the brand new Lynx Class-T Power-in module, so we went with the standard of directly connecting Class-T fuse blocks to the SmartBMS input. This worked out in our favor in the end, as we likely wouldn’t have had the space available on our boat for the new module anyway.

Solar

The 48 volt house bank is solar charged via 2 Maxeon® MAX3-470W-COM from www.sunpoweredyachts.com. Each panel has a dedicated Victron 150/35 MPPT controller to maximize solar production, and they are controlled via the Victron Cerbo GX that manages the 48 volt system.

48-12v Charging with Victron 100/50 MPPTs and BatteryProtect 48-100

Three Victron 100/50 MPPTs are setup for the 48 volt to 12 volt conversion/charging. We went with three for the install in order to have 2+1 redundancy. One can fail and we still have plenty of headroom to run everything 12 volt from the 48 volt bank. One of these could also be repurposed for a failed solar controller. Victron doesn’t recommend using MPPT controllers in this fashion (DC-DC charger), as they’re not designed to be outputting power 24/7 and the heat that would create. However, in our use case, they are rarely outputting power anywhere near their maximum, and typically are just seeing short bursts of higher amperage. To help combat any longevity concerns, each MPPT output has been detuned from 50 amps to 40 amps through the VictronConnect software. With 3 MPPTs in parallel, this gives us 120 amps at 13.7 volts. This provides way more energy than we really need with a buffer battery. These MPPTs are also very efficient in their power conversion, rated at a maximum of 98%.

To protect the 48 volt bank in case of a discharging issue, a Victron Battery Protect 48-100 module is inline with the power source to these MPPT chargers. The Lynx SmartBMS can then disable the signal for Allow-to-Discharge, which will automatically disconnect these chargers from the 48 volt bank. Additionally we have installed a separate remote switch through the BP-48-100 module to allow us to manually disconnect these chargers if needed for any other reason. So far that has only been needed for preventative maintenance discharging of the 12 volt LFP battery.

Victron Quattro2 5kva (Charger)

The Quattro2 5kva inverter/charger is a bit of a beast, but it’s what allows us to run everything without needing a generator. For this section, we’ll focus on it’s 48 volt battery charging functionality. When the boat is plugged into shore power or the generator is running, it receives an AC power source input, which it then uses to charge the 48 volt bank up to 70 amps. When we are plugged into shore power, that AC source runs through the isolation transformer (more on this later), which is limited to 3600 watts. So when charging via shore power we’ll get closer to 60 amps which is configured through the CerboGX settings for the Quattro. This slower charging rate is a moot point when plugged into hore power as you’ll likely have all the time you need to recharge by staying plugged in 24/7.

48v Alternator and Arco Zeus Regulator

The primary battery charging method when not connected to shore power is to run the Yanmar 4JH3-TE with the new APS HPI 48v-130a alternator. This alternator can be pushed to generate 7 kW of power at full tilt (normally 6 kW running in ‘generator’ mode), which is massive for an alternator and quite a bit more than our standalone 5 kW generator. It is also more efficient than the generator as every watt of power it generates is absorbed by our large battery bank – versus needing to run a generator loaded up with appliances to get the efficiency and make the generator engine happy (since the battery charger can’t output that high of amperage). Of course this amount of alternator power takes quite a bit of horsepower from the diesel engine, and generates a considerable amount of heat which needs to be smartly managed by a regulator. The alternator can use somewhere in the neighborhood of 10 horsepower (HP) out of the 75 HP (max) from the diesel engine, which is a lot of power to transfer through a belt. The alternator required a J10 belt (10 rib serpentine belt), so we installed a Balmar serpentine belt upgrade kit to convert the flywheel and fresh water pump pulleys to J10.

We chose the Arco Zeus for its ease of configuration and management through their iOS/Android app and Bluetooth. The Zeus also integrates with the Lynx SmartBMS through the ATC signal and more recently via CANBus to the CerboGX. Since all of the Victron integration is still a work in progress, this install required dedicated wires for battery temperature sensing, and a battery shunt. We utilized a ‘hack’ of using the internal shunt of the Lynx SmartBMS rather than install a separate battery shunt, which has been working perfectly fine. The Zeus also has a shunt monitoring amperage leaving the alternator, as well as an alternator temperature sensor, which is critical to keep the alternator from overheating. Lastly, there is a Balmar APM-48 alternator protection device for extra insurance in the event a load disconnect causes a voltage spike which could fry the diodes in the alternator. The Victron ATC/ATD signals should prevent this from ever happening, but the APM module is cheap backup insurance.

Cerbo GX / GX Touch 70 System Management

To manage the 48 volt system, we installed the CerboGX which integrates the 48 volt batteries, LynxBMS, Arco Zeus, 48 volt solar MPPTs, Quattro2 5kva inverter/charger, and the BatteryProtect module. The GX Touch 70 is the display for the CerboGX, which fit perfectly in the cutout at the navigation station where our old Magnum inverter interface had been. Sadly, only a 12 volt SmartShunt in Energy Meter mode was able to connect to the CerboGX for monitoring, as Victron has developed the CerboGX to be authoritative for devices that connect to it. So if you try to connect 12 volt MPPT controllers (i.e., our 48-12v chargers), the Cerbo doesn’t know how to control a 12 volt device in a 48 volt system (they would connect, but the whole system became so slow it was unusable). For non-48 volt device management, we just use the VictronConnect app.

12vDC

Epoch Dual-Purpose LFP 120ah ‘Buffer’-House Battery

The heart of the 12 volt house system is the Epoch Dual-Purpose LFP 120 amp hour ‘buffer’ battery. In our use-case the battery is more than dual-purpose. In another turn of luck, this brand new Epoch battery was released two months before our project kicked off, and it is why we were able to use an LFP battery for this piece of the puzzle (rather than an AGM). The reason we dub it a buffer battery is because during normal system operations, the only time it’s actually being used is during in-rush current from 12 volt motors inside the boat (i.e., electric toilet macerator, etc.) or during the startup in-rush current of the anchor windlass and electric winch motors. It absorbs the tiny bursts of power that our 48-12 volt chargers and 12 volt solar chargers may not be able to react quickly enough to or with enough amps to kick-start those motors.

This LFP battery was designed as ‘dual-purpose’, meaning it can also be used to start a large engine whereas most other LFP batteries don’t have BMS’ that can handle the amps to start an engine (500+ amps). This battery can output 800 amps for 10 seconds, which is impressive, and since it can output those amps at a higher voltage than a comparable AGM, it works even better for electric motors. Online reviews show this same battery is able to start an old, large Caterpillar bulldozer diesel engine faster than its stock 8D lead acid battery. This should be enough for our relatively small Yanmar diesel engine, and it is why we wanted to keep the factory Outbound 12 volt battery switches and cross-connect switch between the 12 volt house and starter systems. If the AGM starter battery ever fails, we can cross-connect over to this Epoch battery to start the Yanmar diesel engine (no need to buy and install a second AGM battery to achieve this redundancy).

The third purpose in our design for this battery is to serve as a 12 volt battery bank to power critical navigation systems on the boat if the 48 volt Victron system ever shuts down. With the 12 volt solar charging this battery during daylight, we can indefinitely run the boat system lights and navigation, until we can get to a city to repair it.

Solar

The 4 flexible 100 watt panels, also from Sun Powered Yachts, were a great fit for the space available on our hard dodger and bimini, as well as very economical. The voltage of these panels are designed for connecting to a 12 volt system. If we wanted to use them to charge the 48 volt bank, we would have to connect all 4 panels in series to be able to connect them to an MPPT. Even then each panel would have to have good sunlight to have a high enough voltage to reach the +5 volt delta over the charging voltage (55 volt charging voltage; so 60 volt minimum for a Victron MPPT to charge a 48-54 volt bank). Instead of going that route, we connect these panels to our 12 volt house system. This gives us two benefits: 12 volt devices (which is the majority of the boat) are powered via this solar during the day (therefore not drawing off of the 48 volt bank through the 48-12v chargers); and it gives us very good redundancy in the event the whole 48 volt system were to fail. The downside to this setup is that we inevitably lose out on some extra solar power to charge the main house bank. To assist with the 12 volt solar chargers being preferred during solar production, the charging voltage has been set .2 volts higher than the 48-12v chargers.

48-12v Charging and Backup Victron 12v-30a AC Charger

As described in the 48 volt section, the 48-12v MPPT chargers are the primary power source for the 12 volt house system. They are configured in software to synchronize their charging with each other. In the event of any issue with these MPPTs, we have a cold spare Victron 12v-30a 120vAC charger partially wired up to provide additional power if required.

SmartShunt Energy Meter

To monitor 12 volt power utilization, we installed a SmartShunt configured as a DC energy meter to assist with visibility into how much power is being used on the 12 volt side (since there’s no CerboGX for the 12 volt side). To ensure this energy meter can ‘see’ all the amps being used, the DC cables for the 48-12v chargers and 48-12v DC-interconnect also connect to the battery side of the shunt. This ensures all 12 volt loads using battery power are ‘seen’ by the shunt – except for loads powered from solar. So it gives us a window into when 12 volt loads are drawing from the 48 volt bank (or 12 volt battery if the 48 volt side is down). We can then see any 12 volt loads on the solar controllers themselves if we need that data. Since this device doesn’t require any control by the CerboGX (it’s a monitoring-only device), it seems to function just fine when plugged into it, so we can see it’s status remotely through the VRM app.

12v House to Starter Battery Charger – Victron Orion XS 12/12-50

The 12 volt starter system is very simple, it’s just a Lifeline AGM battery that connects to the Yanmar diesel starter motor and to the starter motor of the NextGen Generator. We opted for the brand new Orion XS 12/12-50 DC-DC charger primarily for it’s very small size and power efficiency (98%). Victron’s older offerings were double the size and are notorious for running hot (i.e., <90% efficient). It’s 50 amp output is overkill for this purpose, though we were able to fit it snugly behind our system panel next to the 12 volt cross-connect switch, making the installation very simple.

120/240vAC

Victron Quattro2 5kva (Inverter) and Autotransformer 100a

The heart of the AC systems on the boat is the Victron Quattro2 5kva (4200 watt) 230 volt (EU version). We opted for the 230 volt EU version since we planned to use an Autotransformer to provide the boat with 120/240 volt service, and meshed with our plan to transform 120-240v shore power into the system (more on this below). Having the 5kva/4200w output from the inverter allows us to power everything we want on the boat. We can do most things simultaneously, without the need to wait for one thing to finish before starting another. Through the Quattro configuration software, we bumped it’s output from 230 volt to 240 volt to better align with the Autotransformer split-phase output.

The 240 volt output from the Quattro is directly connected to the Autotransformer, which creates 120/240 volt split-phase (2 120v legs 180 degrees out-of-phase; combining the 2 legs creates a 240v circuit). The output from the Autotransformer connects to the factory electrical panel with 120 volt AC breakers, and we split the 2 legs to provide 120 volt service for one half the breakers each (load balancing). These 2 legs also are fed into our new 240 volt breaker panel to power the SCUBA compressor and any other new 240 volt appliances in the future (such as an induction cooktop and stove).

Shore Power and Victron Isolation Transformer

Our plan to use a 230 volt Quattro was part of the solution to obtain global shore power connectivity, and also have the boat grounding system isolated from shore ground through an isolation transformer. The Victron Isolation Transformer (3600 watt, manual version) is able to transform the input voltage from 120 volt to 240 volt and vice versa via jumper wires. We went with the manual voltage switch version of the Isolation Transformer (Victron makes one that will auto transform input voltages) since there are reports that the auto version has troubles with shore power that has a high voltage (i.e. greater than 130 volts), whereas the manual version isn’t as picky with the input voltages. Justin @ Hullux had the great idea to use a transfer switch to eliminate the need to swap jumper wires. So to connect to 120 volt shore power, the transfer switch is set to the 120 volt setting, and we use the same shore power cables. When we connect to shore power in a country with 230 volt service, we only need to use a pigtail adapter on the shore power cable to adapt to the new plug and then turn the switch to the 240 volt setting. Output from the Isolation Transformer then is always 240 volts towards the Quattro. One issue that came up during installation that was tricky to isolate was that 120 volts was being seen on the AC ground throughout the boat. The fix was to remove the GFCI jumper wire that bonded AC neutral to ground in the Isolation Transformer. That jumper wire isn’t needed since the Quattro+Autotransformer ground relay manages this for the boat.

NextGen 5.5kw Conversion to 240v

While we very much would like to get rid of our generator, we decided to keep it around for another 6-12 months to evaluate its utility. To integrate it into the new design, we opted to convert the generator output to 240 volt, and connect it to the Quattro second AC input (intended for generators). We chose the Quattro in the first place so that it could support the generator, otherwise the Multiplus equivalent would have worked just fine. The $200 cost increase of the Quattro over the Multiplus was about the same as installing a new transfer switch to manually switch between generator and shore power, so Quattro it was. It also gives us an the option to add a secondary 240 volt input source if we chose to replace our existing generator with a smaller portable generator option.

Bauer Junior 2 SCUBA Compressor (3-phase 230v) and Invertek ODE-3-220105-1F4B VFD

With the new 240 volt AC breaker panel, we can serve 240 volt appliances, including our Bauer Junior 2 SCUBA compressor! However, to startup the compressor, the best way (or only way) to do this on an inverter is if you have a 3-phase 240 volt motor and use a variable frequency drive (VFD) to slow start the motor. This modifies the frequency of the sinewave sent to the motor to prevent a large current inrush. VFDs are ubiquitous now in industrial use-cases, as the electricity savings from slow starting easily pay for themselves in the long run, but they are rare in the marine world. We sized the VFD based on the motor specs of the Bauer J2 (3HP), and chose the Invertek ODE-3-220105-1F4B as it is rated for 3HP with single phase 240 volt input and 3-phase output, has an IP66 rated enclosure, has a manual frequency speed knob (so we can run the compressor slower if we want), and a manual on/off switch capable of handling high power disconnects. Thankfully, after all this time and money spent, the compressor worked on the first try with default settings on the VFD! This gives us the opportunity to dive as much as we want, where ever we sail.

Next up:

In Part 2 of this series, we’ll cover the speeds and feeds of how the system has been working for daily usage over the past year, updates we’ve made since the install, and upcoming improvements.