In his book Boatowners Mechanical and Electrical Manual Nigel Calder writes: Analyzing the DC system, and setting the DC system in order, should be one of the first priorities when taking delivery of any boat, whether it has come straight out of the showroom or is a 20-year veteran of several circumnavigations!
I'm sorry to say that this is true, even to a brand new Southerly and we have had to improve the electrical system. Mind you, the standard system was all right for the average cruising person who has a 220v shore connection almost every night, but if you want to bee truly independent of external power (except for diesel of course) there is a long way to go. We have therefore renovated the system and on this page you can se some rules of thumb, some general and theoretical considerations and a section illustrating the choices we have made in our installation.
Rules of thumb concerning the DC installation
|Most of all you need to be able to control charging and consumption of electricity. For this an AmpHrs-meter (eg. NASA) is imperative||Consumption batteries: 3x 110 Ah/12 volt AGM batteries connected in parallel
||A seperate group of 2x 60 Ah/12 volt Optima spiralcell-batteriesr, for starter engine, windlass and bow-thruster|
|The 100Ah Balmar generator controlled by a 3 step charge-regulator and temprature sensors (batteries & generator)
||The electronic 3 step charge-regulator-lator (left) and the elektronic seperator (right)
||Air intake for the engine is supplied via a large hose. Routed twoards the generator in order to help and improve cooling in the cramped engine compartment|
|One of the 3 solar panels each supplying 55 watts (Sun Ware)
||Charge regulator for the solar-cells (Sun-Ware)
||A 2x20 Ah Mastervolt 3 step-charger (shore-power) (back), and (left) a Mastervolt sinus-inverter|
When planning the electrical installation it is important to create a system with sufficientcapacity and at the same time a balanced system, i.e. a system where consumption, battery capacity available between major re-charges and charging capacity are suited for each other. In my opinion it must to be possible to be self sufficient, once you have reached your cruising ground, ideally it should be enough to charge, only when entering and leaving you anchorage i.e. by using your engine about one hour pr. day. On the other hand, when sailing to and from your cruising ground, when one is often under way for several days using autopilot and charging becomes necessary, it must be as efficient as possible i.e. the generator must be large enough. Most authorities suggest a generator capacity of 25% of the battery bank.
Therefore let us begin by estimating the consumption of electricity from Troldand's domestic battery (theoretical values). The values are approximate and it is worth while to be aware of the relation between consumption, time in use and total load. For instance, if short handed the autopilot will be a heavy consumer; on the other hand plotter does not necessarily have to be on 24 hours a day, and certainly not at open sea, at least if as us you have a GPS that is able to be run separately, thus values below may be in the high end.
Having estimated consumption let us turn to the question of battery capacity where standard for most new yachts, is insufficient with present day electronic equipment. We were aware of that when we ordered Troldand and defined a house battery bank of 3x110 Ah plus a separate heavy duty starter battery of 140 Ah. Capacity of the starter battery is uncommonly large, but it has made it possible for us to connect bow-thruster and anchor winch, items which are any way only used while engine is running and which anyway is only run for very short periods.
Thus, in the following we are only concerned with the house batteries, where ideally a discharge of only 33% is ideal, though a 50% discharge is acceptable and larger discharges than 50% will dramatically shorten the life expectancy of batteries. The table below illustrates the number of Ah available to us at Troldand.
To summarize it may be ascertained that available capacity of Troldands house batteries lies between 165 and 110 Ah, thus fairly consistent (though on the small side) with an estimated 24 hourly consumption of 180 to 110 Ah.
Finally the question of charging capacity should be considered. Shore power is provided via a 20 amps smart charger from Mastervolt (which by the way also works as an 800 W, 220 v DC inverter). Furthermore we have installed 2 x 48 W solar cells and finally charging takes place from the AC alternator of the engine.
The standard Hitachi AC generator supplied with the Yanmar 3YM30F engine is only at 60 amp thus not even close to what is necessary which as a rule of thumb should be 25% of the battery capacity. Furthermore the split charging diodes separating the two battery banks, combined with the build in charge regulator, means that it was impossible to charge batteries to full capacity. In fact, when using engine only, batteries were probably not charged to more than 80% of nominal capacity, which meant that the expected 180-110 Ah wasn't available, but rather 130-90 Ah and that was nowhere close to what was needed.
Firstly: Battery capacity was/is sufficient even though on the small side, and when the battery bank was renewed we choose to upgrade within the limits of the existing battery compartment which would allow 3 x 110 Ah AGM batteries, nominally having the same capacity but allowing for a deeper discharge (50%) and faster recharge than the existing wet, lead-acid batteries.
Secondly: Alternator capacity was insufficient and the alternator has been replaced with a 100 Ah Balmar alternator with an external 'smart' charging regulator. At the same time the splitting diodes has been replaced by an independent charge regulator dedicated to the engine battery, both battery banks beeing supplied with temperature sensors.
Figuren viser sammenhængen mellem generatorens omdrejninger og output i ampere (ved 25°). Ved et udvekslingsforhold mellem motor- og generatoromdrejninger på 1:3 yder Balmars 100 ampere generator over 80 A allerede ved 1000 omd./min. Dette betyder at bruges maskinen til ladning alene, kan den køres med lave omdrejninger og lavt støjniveau.
For at opnå den mest effektive opladning er det bedst hvis der anvendes et elektronisk laderelæ der dels hurtigt bringer ladespændingen (afhængigt af batteritypen) til at maksimum (bulk-charge) som står på i en kortere periode (for ikke at skade batteriet), hvorefter ladespændingen sænkes til et mere konstant niveau (absorption-charge) for endelig når batteriet er fuldt opladet at sænke spændingen yderligere til vedligeholdelsesladning (float-charge). Se ovenstående diagram.
You will find further details on the components used in our installation:
Latest update October 2015 Back to pictures