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SV-Zanshin
Batteries and more batteries |
 Manuals |
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Zanshin has lots of batteries on board, see the top right chart on this page for the list. Don't let the different voltages lead to confusion, it is a simple conversion from 220Ah capacity at 12V to 110Ah at 24V. In actuality the electrical chemical cells that produces power only generates around 2V and 6 of these are always combined to make a 12V battery. So I've got a total of 1300Ah @ 12V aboard, that is the equivalent of about 20 car batteries! The capacity numbers designate how many amps (named after André-Marie Ampère) are stored in the battery when discharged over a period of 20 hours, if the discharge rate is higher then the total amps available from the battery goes down very quickly. The house bank will last 20 hours when 30amps are removed constantly, but if 60 Amps were to be withdrawn the time would be less than 10 hours. If I were to leave a hair drier at 1800W running constantly that could drain the batteries to 50% in about 6 hours (1800W = 75A @ 24V, the house bank has 400, so 400/75 = 5.9Hrs).
The rate at which electricity can be put back into the batteries depends upon a number of factors, the major one being the battery type. Normal car batteries are so-called “Flooded” lead-acid and they usually are limited to charging at 20% of the 20-hour capacity. The old batteries aboard Zanshin were gel-cells, meaning that there is no liquid sloshing around inside the battery anymore (which has the advantage that there is no danger of spilling acid) but that the electrolyte is fixed in place, the new ones as of March 2015 are sealed normal batteries which don't require topping-up. The Gel-Cells allow faster charging at higher currents, but the new bank will hopefully be kept topped up via the solar panels and won't require me to run the generator very much. The Optima house and starting batteries have (in theory) no upper limit, but the manuals suggest limiting amperage to 4 times the C/20 rating.
In order to keep the batteries working over a long period of time it is recommended that they never get discharged below 50% of their capacity. In addition, charging above 90% takes disproportionately long, so in reality my large 440Ah/24V battery bank only contains 220Ah/24V of usable power in normal conditions when underway. Looking at the consumption table to the right, this is pretty much what I am using daily while sailing. Due to charging losses we need about 25% more power to charge the bank, so the energy deficit is about 300Ah. Luckily I have several means of charging the bank, either through the engine alternator or by using the generator to power the Victron inverter/charger which will put up to 120Amp into the battery bank. At the same time, the boat's 2 chargers are also loading at 60Amps each - a grand total of 240Amps are now being put back into the battery bank and using about 6Kw of power. Since the generator is rated at 9.5Kw this leaves ample reserves while putting the generator under a good load (diesels don't like to run without a load). This formula means that I could run the generator for about 1:15 per day in order to keep up with energy demands without taking solar power into account.
Due to a bad solar panel connection while I stored Zanshin between 2014 and 2015 the main bank went down to 0V for an extended period and this ruined several, if not all, of the 8 batteries. Since a bank needs to be made up of the same batteries, preferably from the same production run, I replaced the whole bank in early March 2015. This was heavy lifting work and batteries do not come cheap, but if I treat these better than my previous ones they should last me a very long time.
The data for chart in the list below was collected in March 2016. The Xantrex LinkPro battery monitor has a serial output which I connected to an Arduino board that I'd put together which has an SD card for data storage and a real-time-clock to ensure that the data is written with a correct timestamp. This chart shows 13 days of collected battery information, the Y-axis shows the time and the chart has two X-axis plots. The top one shows the battery bank state-of-charge in % with 100% meaning that full 440Ah of energy is stored in the bank. The bottom bar shows the corresponding main bank voltage, coloured light blue with light green segments denoting that either the engine or the generator is running.
Overall I'm happy with the performance since I've had the fridge fixed, the bank rarely goes below 80% which means that the batteries will have a long service life. I run one of the two power sources for around 70 minutes a day on average - not too bad considering I sail almost every day and 10-15 minutes to raise the anchor and motor out of the anchorage and about as much time at the end of the journey to motor into an anchorage and lower the anchor. I think I had two long generator operations of 1 1/2 hours which I used to run the dishwasher and washing machine (and to make water if I was in a clean anchorage). All in all the solar panels are doing their job in keeping my battery bank topped up.
