Online Book: Electrical Systems For Cruising Boats

Most production cruising boats are fitted with inadequate DC electrical systems. Let’s fix that.

Electricity, batteries and how to charge them are the source of more confusion in the cruising world than just about anything I can think of. But suppose you could really understand electricity? Now you can, and it’s not hard. Read on.

The details of how batteries charge and how voltage regulators work together…or not. Practical information that will help make sure you have electricity when you need it.

Just because the battery-supplied systems on cruising boats are low voltage, that does not make them safe. Here are some tips to reduce the chances of a nasty injury.

It’s a common misconception that battery-supplied electrical systems are safe because they are low voltage. That’s wrong. In fact, there are high fire risks. Here’s why, and what to do about it.

Two core decisions we must make when designing a cruising boat electrical system for living aboard full time and making offshore voyages, are the size of the battery bank and which charging sources we will need: generator, solar, main engine, wind, etc. But the first thing we need to do, before getting into all that fun stuff, is think about electrical consumption and how to keep it reasonable.

In the last chapter we looked at some big loads that take electricity from our battery. In this chapter John covers watermakers and diesel furnaces and shows how system thinking can save us from having to install a silly-sized battery bank.

In the last two chapters we took a deep and considered dive into analyzing the electrical loads on our boats and thinking about ways to reduce said loads through smart systems thinking. Now we get to the payoff: How to calculate optimal battery bank size or, alternatively, how to live with the battery bank size we already have. I have built a spreadsheet to make the whole process easier.

It’s easy to assume that the bigger the battery bank and solar array the better, but there’s a much better way to optimize the system for a live-aboard cruising boat, which will save a bundle of money too.

These days we are seeing more and more gear added to boats, much of it AC supplied through inverters from the battery, that demands current (amperage) way higher than even dreamed of a decade ago. But will our electrical system buckle under the load? Here’s how to figure that out ahead of time.

So which is better, 12 or 24-volt DC systems for live-aboard cruising? Like most things, it depends. Here’s a definitive way to determine which is best for your boat and usage.

In Part 1 we learned that it was inefficient, and often impossible, as well as potentially dangerous, to supply the high-load equipment, that so many cruisers seem to want, with a 12-volt system. And, further, that the solution to this problem is either to forgo all very high-current (amperage) gear, or select a boat with a 24-volt system. So let’s look at that.

We all know that any cruising boat should have the engine and house banks separated, but that’s just the start of what we need to know.

Selecting battery master switches and deciding how to wire them is a fundamental part of a good cruising live-aboard electrical system.

A well set up cruising boat electrical system separates the house and engine start batteries. Here’s how to make sure both are properly charged.

Cross-bank battery charging with DC/DC chargers or alternator-to-battery chargers.

How to buy and install a real live-aboard cruiser’s alternator that will be reliable over the long term.

One of the biggest snow jobs in boat gear sales is the myth of the smart three-stage alternator regulator. In fact, the alternator regulators that have been available to us cruisers for about the last 15 years are not that bright…OK, they’re downright stupid. But, finally, we now have a truly smart regulator. John takes a look and comes away impressed.

The WS500 alternator regulator was a great option for cruisers a year ago. It’s even better now. Here’s why.

Most marine battery chargers are, in fact, battery killers. Yes, that includes most of the fancy three stage units we all pay so much money for. Here’s why and what to do about it.

Can we replace diesel fuel generation (main engine or separate) with wind, solar and/or hydrogenerators? Yes, but there’s stuff to know to avoid wasted money and disappointment.

So far in this series of chapters we have been looking at the benefits and drawbacks of the renewable options. Now let’s pull it all together.

An analysis for any live-aboard cruiser who is considering a lifestyle that will require more than about 250 amp-hours at 12 volts (3 kWh) of electricity daily.

These days, most boats with AC generators have significant DC (12- or 24-volt) battery banks that need to be charged regularly by the generator. But often that process is horribly inefficient. The good news is that the fix is easy, simple, and relatively inexpensive.

Many cruisers have already made the jump to lithium. But what if we would like to delay the considerable expense and complications of lithium, but want to be ready at a later date?

Load dumps are an intrinsic danger with lithium batteries installed on cruising boats. Here’s why, and why we need to fix it.

Load dumps on a cruising boat are dangerous. Here’s how to prevent them, including some special tips for “drop in” owners.

Lithium batteries have many benefits, but are too complicated and fragile, and not fault tolerant enough, to be relied upon exclusively on an offshore boat. Here’s how to fix that.

Choosing the right BMS is the first and most important task when buying a lithium-battery system for an offshore voyaging boat.

Before laying down hard-earned cash for lithium batteries, we need to calculate the peak current we will use and think about optimal voltage.

Lithium batteries have very low internal resistance and so we must think carefully when choosing fuses.

So far in this buyer’s guide, we have covered the technical aspects of upgrading our offshore cruising boat to lithium. Now let’s compare three relatively high-cost options and the cost and benefits of each.

In the last chapter we examined an ideal fully integrated lithium system at a big price, now let’s see if we can save some money without sacrificing too much.

I have been frequently asked for my thoughts on systems where lithium and lead-acid batteries are connected in parallel. Here you go.

Charging batteries fast has all kinds of benefits: less engine wear, fuel savings, less carbon. But how far can we go?

Regularly equalizing our lead-acid batteries can save us a lot of money and aggravation by extending their useful lives as much as five times.

Fully charging your batteries after each discharge on a live-aboard cruising sailboat is simply not practical. Instead, most of us will cycle our batteries between 50 and 80% of their capacity. The bad news is that this will ruin your lead-acid batteries (regardless of type) in a distressingly short time due to sulphation. However, there is a solution: equalization. In this chapter we cover what it is and how to do it.

Through a combination of planning, frugality, solar and wind power, Colin and Lou have never had to run the engine of their OVNI 435 to charge their batteries when at anchor. How did they manage that? Read on to find out how.

Should you install a wind generator on your boat? Find out from someone who has cruised with one for 5 years—invaluable real-world experience.

There are very few cruising boats these days that don’t have a solar panel fitted somewhere, and many have some pretty substantial arrays. Based on five years of real-world experience, Colin gives some tips and recommendations for how to get the maximum benefit from solar.

Does buying a Watt & Sea make sense? It’s complicated, depending on boat size and type, as well as usage profile.

It’s tempting, when selecting a complex piece of gear like a battery monitor, to dive straight into the details and features, but that’s a near-sure route to a bad decision. First let’s take a giant step back and look at the two main types of monitors and decide which is right for each of us.

Being able to accurately monitor our batteries is a vital function for all cruisers, but which of the multitude of systems offered should we buy and install? John defines the functions we actually need, and then recommends a monitor.

The single biggest bitch we hear about battery monitors is that they are always wrong. John shares how to fix that and make your batteries last a lot longer too.

Most production boats have battery boxes that are nowhere near strong enough for use on an offshore boat. Let’s fix that.