A little over a year ago, we worked our way south from Fanning Island, Kiribati towards Nuku Hiva in the Marquesas Islands. We were on a long, fuel-constrained run where we would cover 2,600 nm without fueling. For most of the trip, we were heading up-current and into 30 kts of wind on the bow. The waves were fairly well-developed and spray filled the air day after day. The outside temperature was well over 80F, and the master stateroom was 88F, which made sleeping more difficult. With the doors open for ventilation, a thin layer of airborne salt soon covered the boat interior. But we were not crazy about closing the boat up and running the air-conditioning, because that consumes more fuel and would be a couple of weeks of generator run time at very low load.
As we neared Nuku Hiva, we concluded that we had far more fuel than we were going to use, so we might as well be comfortable and run the air conditioning. I’m not crazy about extended run times on the generator at under 20% load, but it’ll live with it, and it was so wonderful and relaxing to finish the last few days of the crossing sleeping well in air-conditioned comfort. This convinced us we needed to find a way to air-condition the boat underway without running the generator.
In the Tuamotus, we were diving daily and just loving it. It’s just amazing to look up from 140′ down and be able to clearly make out our dinghy floating above us and then look down and see 150′ down to the ocean floor and be surrounded by beautiful fish, sharks swimming by, and a sea turtle making a pass through the area. It was incredibly beautiful, but we found ourselves wondering what would happen if our generator failed. Without the generator, we can’t fill SCUBA tanks, can’t make water, and can’t use the washer, dryer or oven. The inability to make water when that far “out there” is not at all appealing. Our goal is to never have a trip ended early or be redirected by a fault and it would be very difficult to get generator parts flown into some of the obscure, uninhabited islands we visited on this trip. We needed a backup to the generator, but really have no space for another generator on Dirona.
As we continued across the South Pacific we spent the vast majority of the time on anchor. But when we did go to a marina, the shore power was rarely better than 15A. Some of those 15A connections could only reliably deliver 12A without the breaker triggering, and in some places the shore power capacity was over-taxed by the visiting boats and, consequently was sagging badly. Also, they were often 50-cycle connections and Dirona is a 60hz boat, so we couldn’t run most 240v appliances without running the generator. We really felt we needed some way to draw what the shore power had to offer, but to not trigger a breaker and not have to manage the boat to a consumption of less than 15A. Both Atlas and ASEA offer shore power frequency converters that would handle the cycle difference, but they are expensive—friends have spent as much as $50,000 on shore power conversions—and they still don’t allow running the boat well at over 25A while drawing under 15A on the shore power connection. The frequency converters didn’t look like a good solution for the entire problem.
After many nights of thinking through options on passage, and planning and drawing up different solutions during the day, we came up with a solution that appears to solve all the problems outlined above. We installed the new design when we arrived in Whangarei, New Zealand and, having used it for the last year, it really does seem to nail every requirement listed above and a few more. Summarizing what the system delivers:
Backup generator: If our generator fails, we need to be able to operate all 240V appliances including the water maker and SCUBA compressor and produce up to 8kw of power, without installing a second generator. This is super important were the main generator to fail (it never has), and is also very useful for quick 240V loads like running the oven for 10 min without bothering to start the generator.
Efficient light 240v loads: Light 240v loads, such as running a single HVAC while underway, is not an efficient use of the generator. While light loads generally aren’t ideal, our bigger concern is that running the generator 24×7 increases the maintenance frequency. Changing the oil and filter every 10 days is not where we want to be.
50hz/60hz invariant: We have a 60 Hz boat, but more often than not are plugged into 50Hz power. We needed to be able to connect to 50hz or 60hz and run all appliances without restriction and not have to start the generator.
Very low amperage shore power invariant: We want to be able run all appliances regardless of draw without any restriction, without having to run the generator, and with only a single shore power connection that might be as small as 10A at 240V or 20A at 120V. Boats are getting bigger and better equipped all the time and many marina shore power systems are not up to the draw they are asked to deliver. It’s not unusual to see shore power voltage drop down 20% below nominal line voltages. Voltage sags can damage equipment, so we needed isolation ensure that our equipment gets clean, voltage stable power even when the shore-side system is sagging under the collective load.
110v failover: If the 110v inverter fails and we’re not connected to 60hz shore power, we must start the generator to get 110v power. We wanted a backup for a 110v inverter failure without plugging in or starting the generator.
Battery protection for shore power loss: A big concern when leaving a boat unattended at a marina is the shore power could get disconnected, unplugged, the breaker may trip, or a variety of other mishaps could leave the boat unpowered and drain the house batteries. This is bad for the batteries and might result in other problems such as spoiled freezer food. We want the system to ride through a shore power fault by failing over to the generator, running it if needed to save the batteries, and return automatically to shore power if it comes back.
I’ll start with the equipment we installed and how the different components work together to solve the requirements we have itemized above.
1) Install 240V, 60Hz Inverter: This is the most important part of the design. Install a sufficiently large inverter system such that all appliances in the boat can be run off the inverter. On Dirona, we have a 4kw inverter to feed the 110V appliances, so 6kw is sufficient to support the 240V equipment we have on board. In our case, we installed 2 paralleled Victron 3kw 110V inverters to achieve 6kw of 240V power. We particularly like this inverter choice because they are simple and don’t include a charger—all they can do is invert—and are capable of delivering far more than their specification. The inverters are specified to deliver 6kw at 240V, which is roughly 25A, but they can deliver peak loads over 50A and can operate for extended periods at or even beyond their rated output without sag, over-temperature, or cutting out. They are tanks, and just keep delivering no matter what. I’m amazed to report they can start the SCUBA compressor, where the required inrush current at startup can exceed 50A. After a year of use, we just love these units. The key to making this design work is to ensure that the inverter capacity is sufficient to run the boat without restriction, using whatever combination of 240v equipment you need. So, if you chose to duplicate this design, ensure you have adequate inverter capacity. 6kw is enough for us but you can get 240V inverters in a variety of sizes up to 20kw. And if your boat is 60hz, you’ll need a 240-volt split-phase inverter–some appliances need that neutral connection.
2) Upgrade Ships Service Selector Switch: The Ships Service Selector switch as delivered on Dirona (leftmost of the three in the first picture below) allows the operator to feed the 240V breaker panel from either shore power or the generator. We replaced this switch with one supporting a 3rd input (2nd from left in the second picture below) so we can feed the 240V panel and all 240V appliances on the boat from 1) shore, 2) generator, or 3) inverter. This third position runs the entire house system off the new 240V inverter.
3) Install Battery Charger Selector Switch: As delivered, the battery chargers on Dirona draw power from the 240v panel. In other words, one of the 240V “appliances” are the two battery chargers. It would be a very bad configuration indeed to be running the 240V appliances off the inverter and have the battery chargers taking power from the inverter, using it to charge the batteries, which are then feeding the inverter. To support many of the use cases above, the chargers must be powered separately from the 240V panel. We want, for example, the 240V panel to be running off the inverter while the chargers are running off shore power. So we separated the battery chargers from the 240v panel and added a Charger Service Switch (leftmost of the four in the second picture above) to supply the chargers from either shore power or the generator.
An electrical diagram showing these first three modifications is below.
4) Upgrade Start Battery Alternator: The final component upgrade to complete the system is replacing the 85A start battery charger with a 190A @ 24V alternator and installing heavier cabling for this larger alternator. The house battery bank already has a 190A @ 24V alternator so, in this new configuration, we have two 190A @ 24V alternators on the main engine. With the two alternators in aggregate, we have 9kw of power generation on the main engine. But, you probably wonder why we would ever want a 190A charger on the start battery system. The original 85A alternator was arguably already far more than would ever be required. Well, it turns out that bigger is not really a problem in that a large alternator with a high quality smart regulator can produce whatever the start batteries need regardless of how low. So, having an extra-large alternator does no harm but is unnecessary. When this second large alternator becomes very useful is when we parallel the house and start alternators onto the house battery bank. In that configuration, we can produce over 9kw of charging for the house battery bank. In our standard configuration, with only a single house battery bank alternator, we have 4.5 kw of power available all the time. We can run air conditioning units, the water maker, and charge the batteries. If we need more power, we can parallel in the start alternator and have 9kw available. This is useful if we have a generator failure but there are times when it’s nice to be able to charge the batteries at 300A for an extra fast charge and still be able to run the water maker or air conditioning system.
To make it easy to parallel in the start alternator when needed, we mounted a switch and warning light on the dash that closes a 200A continuous duty relay to make the second alternator available to supply the load when needed by just flipping a switch.
With these four sets of new components and changes installed, we can solve all the problems we outlined above by combining these components in different ways. Repeating the requirements list above, we’ll see how each is solved.
Backup generator: The combination of the 6kw 240V inverter and the 9kw of main engine charging capability allows us to have a backup generator without giving up the space. Generators are reliable and we have never experienced a disabling fault, so it’s hard to justify giving up the space for a second generator in a small boat. If we do end up needing the backup, the hours on our main will go up marginally, but the trip will be saved. It’s nice to not give up space for a second generator and yet still have the redundancy protection that comes from one.
Efficient light 240v loads: There are times when you’d like to run the oven for just 10 minutes, but it’s just not worth starting the generator for such a short period. The 240V inverter is happy to deliver the power and although the battery draw is high, it’s short enough that it doesn’t really consume that much power. It’s a nice efficient way to deliver the power for short periods without having to start the generator. Another usage model is low loads when underway. A single air conditioning unit draws less than 8A. It’s not worth having the generator on 24×7 and having to change the oil every 10 days if you only need a small amount of power. The combination of the 6kw 240V inverter and the large on-engine alternators allows even fairly large 240V loads to be run any time without needing to start the generator.
50hz/60hz invariant: The combination of #1 (install 240V inverter), #2 (upgraded Ships Service Selector switch), and #3 (new Charger Service Selector switch) allows the boat to be run entirely on the 60hz inverter, while dual redundant 100A @ 24V Mastervolt ChargeMaster 24/100s charge the batteries. The Mastervolt chargers will run happily on either 50 cycle 60 cycles, so the batteries stay fully charged even on 50 cycle power while the boat continues to operate at full capability as a 60hz system. We never need to start the generator to use the oven or laundry for example. The combination of the chargers and the inverter can run any appliance at any time.
Very low amperage shore power invariant: Extending on the 50hz/60hz invariant point above, we can run on shore power connections as low as 10A at 240V or 15A at 110V even though our peak draw is often nearing 30A at 240V. Because the shore power is charging the batteries and the inverter is powering the house, instead of needing the shore power to provide the peak power requirements of the boat, we only need the average requirements. Often when a hair drier comes on and, say the water heater is already on, the sudden additional 8A draw will cause the shore power breaker to disengage. This is because the shore power is insufficient to meet the peak requirements of the boat. But, if running using the battery charger and inverter pair, as little as 10A is enough to power the boat even though our draws are often approaching 30A. Shore power only needs to supply average power draws rather than peaks. It’s amazing what a relief it is to not have to manage loads, worry about what is running when, and not have to go out and reset the breaker multiple times each day. Suddenly shore power “just works.” And there will be times when old shore power breakers can’t deliver their rated output. I’ve often seen 16A breakers that will pop at anything over 12A. That’s fine too. We just set the charger draw to what is available on shore and forget about it, knowing we will take what we need but never more than the shore power system can provide.
Shore sag invariant: The 240V power systems in many US and Canadian marinas is actually 208V. And, when overloaded the “240” can sag down below 200V, which can damage electrical appliances. With the combination of a 240V inverter powering the house and only the battery chargers connected to shore power, the boat always sees rock solid 240V power through the inverter, while the battery chargers deal with voltage sags and other shore power problems. The Mastervolt chargers will charge on just about any voltage and frequency in the world, so it all works without exposing the boat systems to sags, spikes and other shore power related anomalies.
110v failover: Our boat has both a 240V system and 110V system. The 110V system has a 4kw inverter and, if it fails, the only way to get 110V is to plug into 100v, 60Hz shore power or start the generator. With the 240V inverter, we can still get 110V anytime without running the generator via the 240V inverter. It feeds single phase 240V to the 240V system just as the generator would and the Nordhavn standard step down transformer will just keep producing nice, clean 110V output even if the 110V inverter fails. You might ask why bother with the 110V inverter at all? It could be eliminated without giving up any advantage described here but a larger 240V inverter would be required if we gave up the 4kw of 110V inverter. If we were doing a new build today, we probably would opt for a larger 240V inverter and omit the 110V inverter entirely.
Battery protection for shore power loss: Our battery selector switch (#3 above) has 3 input options: 1) shore, 2) generator, and 3) auto. Auto is an interesting configuration. In this mode, a large 120A continuously-rated relay is used to select between shore power and the generator. If shore power is available, the battery chargers are run from the shore power system. If the shore power system fails, is unplugged, a breaker pops or any other fault causes a loss of shore power, then this relay switches the battery charger source to generator.
Since the generator is not running, you might wonder what value there is in switching to the generator. Dirona is equipped with generator auto-start so, if the batteries are discharged to 50% capacity, the generator starts, the load is brought on after 2 minute warm-up, it charges the batteries back up, the load is removed for 1 min of cool down, and then the generator shuts off again. The auto-start system is a simple extension of the Northern Lights Wavenet system. The normal use of auto-start is to take care of the batteries and ensure they get charged when needed rather than when I remember. Jennifer and I are often late getting back to the boat after shore-side exploring. Rather than allow the batteries to discharge excessively, shortening their life, the generator just turns on and gets the job done without attention. Auto-start is a personal decision where each owner needs to weigh off the risk of running a generator without attention against the risk of allowing the batteries to discharge. Our take is well-maintained equipment works well and, just as most people wouldn’t think twice of having their furnace kick on to prevent frozen pipes when they are not at home, we think auto-start is good for the boat. Even if you don’t decide to install auto-start, the Northern Lights Wavenet system is strongly recommended. We love it.
The combination of the “auto” position on the Charger Selector Switch with generator auto-start/stop means that if something goes wrong with the shore power, the generator will start a day or so later, charge the batteries up, and then shut down and wait for when needed again. If the shore power comes back, it switches back to shore power and uses it again. We will also get email notification if the shore power gets disconnected and there are on-board alarms that signal this event but it’s still good to have backup to protect the nearly $8,000 worth of batteries.
Even if we weren’t cruising in 50hz countries, or remotely, where a generator failure would be difficult to deal with, we’d still install a 240v inverter. In fact, we’ve become so dependent on the system that we’re considering getting a spare. In the past, we needed to run the generator underway or at anchor to make water, do laundry or for baking. We now only run the generator at anchor, either to charge the batteries or for extended large 240v loads. The 240v inverter and either shore power or the main engine can handle the rest. A shore power connection anywhere in the world is now effectively the same as if we were in the US, with the added advantage of isolation from low or sagging supplies. And having air conditioning while underway in hot weather is wonderful.