Zanshin I 12V DC Battery system

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Zanshin I Batteries Zanshin I Batteries
(2008-12-14 20:24:52 DSC-N2 [f/2.8, 10/400s] ISO 160)
Zanshin I Batteries

Electrical demands on a cruising and live aboard boat tend to be high and replacing the power consumed is always a problem. Battery and charging technology has come a very long way in recent years but there is a technical limit to how many Ah (Amp-hours) of power a lead-acid battery bank can store and the power demands of modern life have grown so that more space and weight needs to be allocated to the energy stores than ever before..
Lead, apart from being the alchemist's metal of choice and extremely toxic over time when ingested, is wonderfully heavy, inexpensive and easily worked and thus is often used for sailboat keels. But it also has exceptional chemical attributes which allow it, when used with sulphuric acid, to become a 2-way system to store and dispense electric energy and therefore it is the main component of lead-acid batteries. While weight isn't too much of a factor in a stationary battery, in boats (and cars) its weight is a decided disadvantage. The big lead-acid batteries needed to store a lot of electricity are incredibly heavy and cumbersome, not to mention that the acid used is sulfuric and a by-product of overcharging is hydrogen gas (think back to those wonderfully explosive chemistry experiments in high school). A typical car battery will have a capacity of about 40 amp hours and weigh 18 Kg (40 pounds). That isn't all that much electricity per pound and doesn't go that far, my autopilot alone will draw 4 amps, add the displays and radar and that is 10 amps, meaning the battery would last for only 4 hours (and at discharge rates that empty a battery in less than 20 hours the batteries only give out a portion of their rated energy).
Marine batteries are bigger than car batteries, and one has quite a few more of them. The standard setup for a Jeanneau 49DS is to have 3 “house” (for all loads apart from starting the engine) batteries and 1 “starter” battery. The 2 separate circuits are common on boats, designed so that if you manage to drain the “house” bank you will always have enough power left to start your engine (and thus re-charge the house bank as well as the starter battery via the alternator). The batteries are rated at 110Ah and one extra one was installed at the factory, so Zanshin I has 440Ah of house power available. While 440Ah is nothing to scoff at (particularly with a weight of about 130Kg), if it were converted to AC power without loss (which it can't) it would contain barely enough power to run a vacuum cleaner (12A/230V = 2880 watts) for an hour and thaw a small meal in microwave!
To add to the problem, batteries don't give out all their stored Ah energy when drained quickly, the published Amp-hours are for discharge rates of 20 hours, use power any faster than that and the batteries don't even come close to their potential output. Then, to add insult to injury, batteries don't accept all the electricity that they are charged with and deteriorate over time. The closer a battery is to being full , the slower the recharge rate. Modern chargers use temperature sensors (picture boiling sulphuric acid blowing out of your batteries on a small boat) and complex digital circuitry to try to get optimal charge rates.
My power demands are generally pretty low, but that pesky Espresso machine and the inverter I installed to power it without having to fire up the diesel generator are very power-hungry and mainly for this reason I went and added 4 more batteries to Zanshin I I in order to shore up my power reserves to 880aH. While I don't use all that power, I can now charge the batteries at a much higher rate for a shorter period of time and still have a lot of reserves. The downside is that Zanshin I now has 270Kg of lead-acid batteries aboard - mainly in order to satisfy my lust after caffeine.

This is the top layer of the house battery bank aboard Zanshin I. The lower layer has another 4 house plus one starting battery. This is the top layer of the house battery bank aboard Zanshin I. The lower layer has another 4 house plus one starting battery.
This is the top layer of the house battery bank aboard Zanshin I. The lower layer has another 4 house plus one starting battery.
Assembling the bank Assembling the bank
Assembling the bank
565 views since 2017-02-04, page last modified on 2017-04-12.