A strange way of living

Our strange way of life begins with the batteries, because the boat runs on batteries (ha! You thought this was a sail boat). The stove's propane valve, the lights, the watermaker, the instruments, the radios, even the wall sockets are supplied by an inverter that makes 110v AC power from the batteries' 12v DC. And they are basically plain-old lead-acid batteries but augmented with fancy stuff like sealed cases, absorbed-mat gel electrolyte and valve-regulated inter-cell transfers, etc, which makes them vrAGM batteries. Which all means that they work better and last a lot longer than the old stand-by car batteries that you had to feed with distilled water and generated hydrogen when being charged (BTW accumulating hydrogen inside a closed boat is generally not a good thing). Which means that they have to be charged in stages and are damaged if deeply discharged, and lose charge just sitting around, and letting them sit partially charged damages the internal cells, etc. Batteries are not just a gas tank that contains electrons.

Filling the batteries takes some tactical maneuvering and thinking ahead because we have only two ways to fill them when we are off the dock. The first is our diesel generator. It can produce up to 40 amps of 120v AC power. But if you get close to that, you'll pop its breaker and have to shut it down, go pull the spinnaker and fenders out of the locker it lives in, open the sound-deadening housing, then climb down inside to reset the breaker that is mounted on the generator head.  We try to avoid that. So, 40 amps AC. That feeds the battery charger's AC input, which converts it to 12-15v DC and applies that to the batteries to drive 'juice' into them. But remember that these fancy vrAGM batteries have to be charged in stages. That means when they are deeply discharged, they can accept a lot of current, so the charger can crank up the voltage and drive as much current as it can muster. Typically this means upwards of 100 amps DC. That is a lot of current. Which means that the cables running in/out of the batters are about the diameter of a garden hose. And it means the batteries get hot, remember those exploding lithium battery stories?, so there is a thermistor on the batteries that is connected to the charger to slow it down if the batteries get too hot.

Once the batteries start to fill up, their voltage comes up, and as it comes up, the charger shifts to Stage 2, called 'absorb' mode, where it down-shifts to deliver only 14.2 volts for a fixed length of time to make sure the batteries have really been filled thoroughly. Only they aren't really filled. Stage 2 kicks in at about 80% of the capacity of the battery, and will usually add about 10% to the battery. Then Stage 3, 'float' charging, begins. Float delivers about 0.5% of the battery capacity per hour and slows down as the batteries approach full charge, ie it takes a looong time to fill the batteries from their 90% state to 100%. This means that the batteries rarely get filled to 100%.

Remember that they don't like being left partially charged? And that they don't like being deeply discharged? So, to efficiently charge them, they have to be discharged, but not too deeply, and to be kept healthy they also have to be filled as much as possible at every chance.

Now, diesel engines don't like being run without a heavy load, ie they like being run with the generator head pulling hard, ie producing a lot of current. So we use it when the batteries are at their lowest state of the day, in the morning after the night's run when the fridge/freezer, anchor lights, instruments p.r.n., have been going all night without any power being produced. But the neighbors don't think much of generators waking them up in the wee hours. So we try to run it as early as is civilized, typically about 07:30. But before the sun gets high in the sky.

Because our second power source is a bank of solar panels. They are rated at 450 watts, ie nominally 38 amps at 12 volts DC. But typically they put out only about 30 amps when the sun is high over the boat and only a few amps when the sun is low, like morning and late afternoon or on cloudy days. Remember the batteries only accept a few amps in absorb and float modes? And that bulk charging can take as much juice as can be applied?

A few other factoids – the solar panels put charge directly into the batteries with their own charger/controller device, and can put out enough power to bring the bus voltage up to levels that make the generator's battery charger think that the batteries are nearly full even though they aren't. And the generator uses the batteries to run its starter, ie if they are allowed to go too low we can't start the generator. And the generator uses diesel fuel, a limited resource that requires periodic stops at fuel docks. And the batteries don't like to abruptly shift from being charged to delivering current.

Putting it all together means that, on anchor and away from the dock with clear skies and good sun in the forecast, we have to run the generator as early in the morning as we can to ensure we use it efficiently and with a good load on its engine. 100 amps DC is only about 10 amps AC (remember the generator can produce upwards of 40 amps AC?). So there's lots of available current. Which means we also run the water heater (8 amps AC), the water maker (3 amps AC), charge all our iThingees using the inverter (3 amps AC), run the microwave (20 amps AC!) and vacuum (10 amps AC), play radios, etc. Which means our mornings are pretty busy. Then we shut down the generator when absorb mode is nearly done and let the solar panels take it the rest of the way. And we hang out in the sun, go kayaking, whatever strikes us.

The end result is a life dictated by batteries. We aren't free spirits, going where we want at a whim, following the wind: your chemistry teacher was right – life is driven by chemistry; in our case, electrochemistry.