Shimshal, as mentioned before and like all cruising yachts has a large appetite for electricity. There are the constant drains on the supplies, the fridge and freezer being the largest of these, but instruments, auto helm, vhf radio, lights, water pump and device charging all add up as well. Then there are the real big users, these tend to only be used for a short period but pull high current when used. Things such as the anchor windless, electric winches and the bow thruster fall into this group. There is also the water maker, run for an hour or so every other day, this is essential when off shore as there are no hose connection points available to top off the tanks. This alone takes about 30 amps at 24 volts.
Storage is mainly in the two domestic batteries, one 420 amp hour at 24 volts, the other 200 amp hours at 12. The 24 volt batterys are relatively new lithium batteries. Lithium has the advantages of accepting a much higher charge rate than the older lead batteries, meaning shortened charging periods and more efficient use of whatever is being used to charge them. Lithium batteries are also much more tolerant to deep discharge so if needed they be used to their full capacity without any problems.
Concern over Li ion batteries becoming a fire hazard if over charged have been overcome with the advent of Li Fe Po batteries which are the type installed on Shimshal. LiFePO batteries have a very low risk of combustion and each battery has its own Bluetooth Battery Management system to protect against overcharging.
The smaller 12 volt bank are AGM cells
You may ask why have 2 different voltages, well most of the items supplied by the 24v system are the higher power devices, they demand large currents and if you run them at 24 volts the current is 1/2 of what it would be at 12 volts. This means you can use much smaller wire diameter. Why not run everything at 24 volts, well, unfortunately many of the smaller powered items are only available in 12 volt.
To keep all these batteries charged and healthy Shimshal has several independent systems.
Firstly when the main engine is running both battery banks are topped up using two alternators, one 12 volts, one 24 volts. The 12 volt alternator also charges the engine starter battery, this battery is independent of the domestic batteries so the motor should always start. Therefore when there is no wind and we have to motor there is an excess of electricity after the first few hours when the batteries are all full. Hence, things like the water maker are used if we have to motor for an extended period.
There is also a smaller diesel engine driving a 240v generator. This generator is run most days to keep the domestic batteries full. When the generator is running the 24 and 12 volt batteries are charged with their own 240 / 24 and 240 / 12 volt chargers.
The last major charging supply is the solar array, Shimshal has several 100w panels configured to charge the 24 volt batteries. On a good sunny day, these panels will supply the whole boats demand and put some charge into the batteries but only while the sun is out. It is unfortunate that as a relatively small boat it is hard to place the panels where they receive maximum sun all day. When sailing the panels can be shaded by the sails for 1/2 the day. They do make a significant contribution though especially when here in the equatorial sunshine. They come into their own when anchored and relieving full sun all day, they cut generator use significantly. The best recorded days output from the panels is 3.5 Kwh.
As the solar only directly charges the 24 volt batteries there is a 240 / 12 volt charger fed from the inverter to support the 12 volt battery from the 24 volt battery. The logic of this is that if you keep the 24 volt batteries well charged then the 12 volt bank will also be kept healthy.
Finally on the charging front is the stern mounted wind generator, this is part of the older system from before the lithium batteries, the wind generator will not support the new batteries so charges a pair 72 amp hour AGM batteries which in turn help to change the 24 volt lithium cells. In this way it provides an independent 24 volt supply which could be used in the event of a failure in the other systems or if needed spare batteries to replace say the engine starter battery if needed.
In addition to all the batteries, if Shimshal is in a marina with shore power available she can be plugged in. There are sufficient transformers on board to enable a 240 volt or 110 volt shore supply to charge all the batteries and provide 240 volts to outlets around the boat.
Finally, both 240 volts and 110 volts can be supplied from the 24 volt battery using an inverter which supplies 240 volts and a 240/110 volt transformer if required. This does however put a significant load on the 24 volt batteries so is not used for much.
Having multiple charging systems and 2 battery banks provide significant redundancy in the event of a single failure, it should always be possible to ensure a power supply from one sauce.
The power demands of a boat like Shimshal require quite complicated systems to support them, in years gone by boats did the same trips without freezers, fridges, watermaker of Internet communications. It is possible to do this with a paraffin lamp and water rations but no where near as pleasant.
All cooking , by the way, is done on gas.
Tim.