Size does matter: the story of a narcissistic inverter!

Instead of going straight to the subject, let’s talk a little about the management of electricity on board of a sailboat. Except when docked in a marina, a sailboat cannot be constantly connected to the public electricity distribution grid. Imagine this endless virtual cable that can feed your needs for electricity when you are crossing an ocean? Well this virtual cable actually exists, it’s simply called batteries! Could we do without electricity on a sailboat? Going back to the centuries before us we could, but then there would be no navigation instruments, we would have to rewind the anchor chain by hand, we would need to light candles to be seen at night. But worse, we would be forced in drinking warm beer onboard!

So batteries are the storage compartment where we put in all our electricity reserves. They play an essential role in the operation of a sailboat, when you loose them you loose a lot: unable to use the radio, unable to start the engines, unable to read the depth measured by the sounder, and the list is long. Unlike the distribution grid ashore that provides our homes with AC (Alternating current), batteries can only deliver DC (Direct current). It means that all our onboard appliances need to be tailored to that. It is not really an issue for things like navigation instruments and lights but who has ever come across a DC 12V fridge? Marine appliances are just that, they are tailored to the maritime salty and corrosive environment, but they essentially designed to operate at low DC voltages like 12, 24 or sometimes 48V. Another thing you might ask yourself: why not simplify things and use DC at sea and on land, or do the same with AC? Well, it would certainly simplify things but it is a major physical challenge. Batteries use chemistry to produce electricity and the chemical reaction taking place in these sealed compartments is a continuous process, i.e. it delivers a constant current we call DC. It also does this at a low voltage, this is why a lot of cells in cascade are required to produce higher voltages should this be required. The electricity plants ashore use alternators instead to produce electricity at much higher voltages. An alternator is a device where a rotor spins inside a fixed cage called a stator. Each time one of the windings of the rotor meets a sister winding from the stator in this spinning process, it produces a current that rises, reaches its maximum and then decreases again. This phenomenon is repeated 50 times per second provided the alternator carries two of these windings and spins at 3000 RPM. Electricity at home is therefore 220V @ 50Hz typically in Europe. In the US it is 110V @ 60Hz, a federal choice.

So by now we understand that on a sailboat electricity “looks” different compared to our homes. This brings us to the case where we go for a week long sail and the captain of the boat would like to use his electric shaver he brought with him onboard? Or his wife would like to use a coffee machine? Though our sailboat only preaches DC religion, there are cases where the need for higher voltage AC might be required. This is where the inverter comes into play. This device is an electric and electronic regulator that modifies the voltage from 12/24V to 110/220V and chops this constant voltage into something that ressembles as much as possible to a beautiful sine curve.

The magic of the inverter is not unlimited, one of the core limitations is not the device itself but its source of power. Let’s talk about power: in electricity it is equal to the product of voltage (V) with current (A). So, if your hairdryer needs 1000W of power, at 220V it will draw a little less than 5A, but at 12V it requires over 80A! The current can be compared to the flow of water in a river while the voltage is the height difference over a certain distance of that river. A lot of water in a river will cause a lot of erosion, in electricity high currents cause a lot of heat dissipation. For that reason, electricity is always transported over land at high voltages and never at high currents for a set power. Onboard batteries can deliver high currents but it is at the expense of their own chemistry and the wiring will be the cause of losses because of the heat dissipation. On a small size sailboat, the inverter will range from 2000 to 3000W in the 12V electrical systems. Higher powers require batteries operating at a higher voltage as well.

When I bought this boat, I looked at the structural condition in general but also at the onboard equipment that was OK to take over for a new life. The inverter was one of them. These are the pictures that were posted on all the internet sites the boat was exposed for sale.

The right side inverter is only good for very small equipment like a laptop or USB charger. The ProSine on the left could have been a good compromise for the boat, there are lots of things you can do with 1800W of power. I could even operate my electric iron rated at 1500W. So I elected to include this device in the electrical system mid life update (actually a total new installation :-)).

As part of the dismantling of the device and the connector cables, I performed a general visual inspection plus cleaning: paint from a messy previous paint job of the interior and a lot of dust inside! In addition, a part of the front plate (vent inlet) was broken: most probably an unfortunate collision with a shoe or a knee, knowing the device was mounted just underneath the chart table in front of the seat.

A bit of broken plastic is not the end of the world… I thought! Until I noticed the complete casing had become weakened, a bit like a plastic that was exposed to direct sunlight (UV radiation) for years. Quickly, the little area of broken plastic expanded… to this!

Thinking further about the origin of this phenomenon, if UV is not the guilty party, heat could have been another good candidate. Maybe the device had been operated at its limits for prolonged durations and generated a lot of heat therefore. OK, so far so good, as long as the inverter works properly. It does not have to be part of the cabin furniture, right? Just stay hidden in some technical compartment and everybody is happy. But then came another surprise…

The megafuse is located between the DC inlet connectors and the large winding on the lower right corner of this picture. Found it!

This simple discovery has an significant impact on the electrical system design. 1800W would have been just enough, 1000W is definitely not enough! If I want to operate AC on board I will have to purchase a more robust device. Feeling framed a bit, but also curious to know how a 1800i cover had ended up on a 1000i device. The answer to this question will not make the difference though, money will have to come on the table regardless. At least this way I will have the option of selecting another type of inverter or go for an inverter/charger. Inverter/chargers are more and more being used on newer marine installations. It brings the benefit of a further integration of the AC management knowing the charger also uses AC power as a source.

Keep reading the upcoming posts for some other surprises like this one!