Power Management

We’ve had quite a few requests over these several years, both public and private, to talk about power management aboard Buffalo Nickel.

Every boat has its own inherent logic in this area. Between the goals of its systems designers and the capacities and limitations of the component hardware, there emerges a pathway where, if we don’t stray too far from it, we can live hassle-free lives that require little forethought about use of appliances, whether at anchor or underway. As cruisers, we learn the pathways over time that work for our particular boats, and then they become second nature. Until we get a new boat, at which point we are overwhelmed all over again. We struggle to make sense of the new-to-us system for a while, wondering if we’ll be able to get hot showers in sequence and dinner prepared, without blowing up an inverter.

My aim in this post is a minimum of discussion about the logic of our electrical generation and distribution, focusing instead to how we live our typical day-to-day in various situations. But you’ll still need a basic picture of the set-up.

In general terms, Buffalo Nickel is a 24 Volts DC, 240 Volts AC boat. On the DC side, there are only a few minor exceptions: our main engine starter battery is 12V (though the generator start battery uses 24V) and perhaps a couple of our helm instruments are 12V.

There are some 120V consumers: our automatic dishwasher, a few small US appliances like our navigation displays at the helm. But even most of our store-bought galley appliances like our bread maker and toaster were purchased in New Zealand, so they are 230V. The boat is designed around 240VAC, though since it was sold to us Yankees, most the domestic electrical outlets aboard are 110V.

100% of the 115VAC power used is inverted power, coming from a stand-alone Victron 2500 Watt inverter, plus a small dedicated inverter under the helm for electronics requiring 115V like our three 19” displays and our Mac Mini nav computer.

The major AC consumers aboard, though, are 230V. High amp draw items are mainly: air conditioning, oven, induction cooktop, water maker, clothes dryer, and water heater. Bulk house battery bank charging is, of course, also an E-ticket ride, and our dive compressor, which will fill two tanks simultaneously, is an astronomical power hog.

We can more or less leave AC frequency aside. AC power in general can be 60 Hz (or cycles per second) as in the U.S.A., or 50 Hz as in practically everywhere else. Our generator and inverters happen to be set to 60 Hz. But all the AC consuming equipment aboard our boat is designed to take either one, so we don’t need to pay much attention to this no matter where in the world we plug in to shore power. And if we plug in to a dock power source in the that is 30A 120VAC, our isolation transformer will step that up to 15A 240VAC for consumption aboard the boat (though it won’t affect the frequency.)

24VDC is used by hardware such as our anchor windlass, our aft deck winch, our bow thrusters, lighting, refrigerator and freezers, fresh water pumps… most of the onboard electrical equipment that is manufactured for marine use.

Our primary breaker panel, divided into sections for 240VAC, 115VAC, 24VDC and 12VDC, is partially visible below, outboard of the helm chair. These are the functions we are likely to access on a regular basis. A secondary panel with less trafficked functions such as fuel pumps, lights, fresh water pumps, etc. is located in our office, near the engine room door.



Several of the usual suspects supply all of the fine juice referenced above:

Shore power: we have 30 and 50 amp inlets in both the forepeak and on the aft deck.

Alternators: while underway, two alternators, each 150A @ 24VDC continuous duty, provide plenty of power from the main engine for our typical underway activities and battery charging. Remote mounting of regulator and diodes, with fan, helps prolong the lives of these components by protecting them from high heat produced by the alternators. Below, you can see our main engine. One of the alternators is visible (that red thing,) its twin is hidden from view on the engine’s other side.



Generator: a 13.5 kW Cummins/Onan (seen below, with one of its cover panels removed) will give us about 58 amps.



House battery bank: 1200 Amp Hours @ 24VDC supplied by our bank of Hoppecke traction batteries. These are sealed and maintenance-free, and well suited to the long term, heavy discharge and recharge profile typical of cruising. (Engine and generator start batteries are AGM, which is more advantageous for the high cranking amps required for that purpose.)

Solar panels: two panels, 345 Watts each, are mounted on our house roof, just forward of our flying bridge. We always intended to install more, but haven’t gotten around to it. Our solar power will take care of what we call our “basal metabolism.” In other words, our house battery bank will maintain a steady battery charge state while the boat is off shore power and we aren’t around. In fact, Buffalo Nickel is, as I write this in Seattle, sitting in a marina in New Zealand with shore power turned off. Our friend who is checking on her periodically reports that her house bank is floating happily at 100% charge.

Inverters: In addition to the 115V inverters noted already, our ‘big’ inverter/chargers are a pair of Victrons in a Master/Slave arrangement with a 7500 Watt capacity (32 amps) that convert 24VDC power from the batteries into 240VDC for consumption throughout the boat. The inverters are set up to ‘assist’ in contributing extra power from the house bank if, for example, we need to consume more than a modest shore power connection is providing.



We can interrogate our power generation and consumption in all kinds of predictable ways via panel displays. But there’s one bit of hardware we make use of that does bear mentioning specifically: our current limiter. This little gizmo allows us to dial in a maximum current that consumers can draw from the power source in aggregate, so that the power supplier itself doesn’t get overloaded. We adjust the value depending on where we are drawing our power from at the time.

So how does this arrangement translate into practice? One concept we should address is the idea of ‘generator dependence.’ On the majority of boats with gensets, there are certain activities that are generator dependent, meaning either you wouldn’t dare operate that appliance on inverter power only, or you literally could not. Our prior boat, a Selene 53 trawler, was designed so that we had to engage the generator if we wanted to operate the power winch to launch or retrieve our large dinghy, or chill our holding-plate freezer every other day, or operate the washer/dryer, or run the air conditioning in some zones of the boat. And we considered ourselves fortunate: many of our friends cruising aboard trawlers in the tropics do not have the option of any air conditioning at all at anchor or underway without running the generator.

On Buffalo Nickel, the only system we have that is generator dependent is the big, beefy dive compressor we chose to install. Of course, running the water maker on inverted batter power alone makes no sense in the scheme of things. But at anchor in the tropics, it’s not uncommon for us to awaken in the middle of the night, hot because the breeze has died, and turn on the air conditioning in our stateroom for a while (sometimes a long while, if we fall asleep!) to cool off. We don’t think twice about using the oven or the cooktop to prepare dinner, or powering our 1,000-lb dinghy on or off our aft deck, while on inverter power.

The concept of “Nice Things”

If we are at anchor on inverter power, our inverters have a capacity of 32 amps, so we proceed accordingly. We can cook a meal, or dry a load of laundry; but we wouldn’t do both simultaneously. We pay some attention. During a long shop-talk session in an Irish pub in New Zealand in 2013 with fellow FPB owners Pete Rossin and John Henrichs, someone advanced the term “nice things” to identify high-consuming systems (15-20A-ish) aboard our boats. The bottom line is: while on inverter power, we only get to have one nice thing, and we don’t get to have it all day long. By the way, I am in no way trying to patronize anyone here. Without the “nice things” talk, it would have taken me far longer to get educated and comfortable with our power management habits, not to mention the repeated jolts to our inverters. It might have necessitated Questioning The Captain for information, or even the Reading Of Manuals.

The inverters themselves draw a not insignificant amount of power. It’s a good idea to turn them off when you go to sleep when possible; though frankly, we only rarely avail ourselves of this savings option.

While underway, our alternators are enough to maintain our batteries even when the inverters are pushed to their limit, so the same “nice thing” rule applies. This typically means that once the batteries have been sufficiently charged underway, we will run the water maker, though we probably won’t start it up while boiling a pot of water for pasta. After the water maker has been running for a time, if sea state precludes leaving a hatch open for decent ventilation from the outside, we can kick on the air conditioning in the great room. Our habit on multi-day passages is to shut the water maker down when it’s time to cook dinner, leaving it off overnight. During the night, hatches are usually closed and in the tropics, we will have air conditioning running in both the great room and whichever stateroom(s) have anyone asleep.

Our water maker, by the way, puts out 58 gallons per hour, and our fresh water tankage is around 1600 gallons. So while we do prefer to arrive in an anchorage with lots of fresh water, it’s not as if we need to run the water maker all the time while underway. When we do run it, it’s typically for at least 6 or 8 hours.

On shore power, we set our current limiter to just below what the dock connection is supposed to provide, and proceed accordingly. Again, if the dock power falls short of its advertised output, the inverters will kick in the difference. If we have 50A at our disposal, we set the current limiter to about 48 and we can enjoy at least TWO NICE THINGS!

Running our 13.5kW generator gives us about 58 amps. We set the current limiter to 47 and try to maintain a load of at least 32 amps. We get our two nice things going, and once draw has leveled out or as bulk charging consumption drops off, we check the displays to see whether we should add more of a load.

This brings us to the most common question we get about our power management: “how often and for how long do you need to run your generator?”

The answer depends, of course, on our cruising grounds. Which is to say, it depends on whether we are using air conditioning. So here are two scenarios:

In more temperate climates or where it’s breezy enough that we don’t need air conditioning, we might run the generator for up to 3-4 hours at a time, about every other day. Whether we are off the boat for part or all of the day, or aboard being lazy, our solar panels will adequately keep up with our background power consumption. On a generator-free day we are cooking dinners but maybe not with 3-burner ambition. I hate having to tend more than two things cooking at once, anyway. My brain only has one- and two-burner settings. We will listen to music through our Sonos sound system and probably watch a movie.

If we are sweltering at latitudes near the equator, we will likely want to turn on air conditioning by around mid-day if we are staying aboard the boat, or on our return to the boat later in the day if we’ve been out. We have UV-blocking mesh, and Sunbrella window awnings, and blinds, and those adorable and quiet Caframo fans. But let’s just say we are neither of us known for our tolerance to heat. Once we turn the generator on to support the air conditioners, we will keep it running through dinner, supplementing the genset load as needed with laundry or another “nice thing” once the batteries are satiated.

I’ve got another post dropping tomorrow with some Big News. It’s why we are a) in Seattle right now instead of out cruising, and b) so behind on our blog. Okay, so b) is a stretch. But let’s go with that anyway! The best way for me to reach the threshold I need for self-forgiveness is a longer list of excuses, right?


4 thoughts on “Power Management

  1. great interesting read! that’s a decent amount of power from only the sun, it looks a bit huge but it holds a lot of power, great job guys

  2. we are converting our European Canal Barge to induction cooking, did you used a specific cooktop, or just any general one ? yes we have 2 Victron Multi’s in parallel

    1. Hi Jan, We have used two different induction cooktops on two different boats. Our first was a Miele, 3-burner. It worked great for us. One of our sister-ships, however, had some issues with theirs and the boat builder, Circa, had big problems getting warranty service from them. So on our 70, they decided to switch to Bosch. Same footprint approximately (about 54 x 58 cm) but has 4 burners, we love it. Both flush-mounted. Have not detected any difference in power consumption between the two. They use substantial power especially at the beginning, but are very efficient. You wouldn’t want to turn the boost feature on to boil pasta water, while 2 other burners were running, without having your generator on. But we don’t tend to cook this way and have never had to turn on our generator to do any cooking. Routinely run the microwave or oven, one cooktop burner, and a toaster simultaneously, for example. Good luck with your canal barge… we would LOVE to do that one day!

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