 I totally disagree that it is the difference between AC and DC. It is the fact that at 12V there is 20 times the current draw for a given power output (watts) that there would be at 240V.
For example, if a 3kW motor (e.g. bow thruster) was operated at 240 V, it would draw 12.5 amps (3000 / 240). At this voltage one could safely use 1.5 mm sq cable as this is good for about 16 amps.
At 12 V the current draw would be (3000 /12)= 250 amps and depending on length of run, would require anything up to 120 mm square cable.
At 12V, volt drop in circuits is critical and this includes both correct sizing of cable as well as the integrety of all connectors. Any corrosion or oxidisation of connectors will increase the resistance of a circuit and thus unnecessarily drain the battery. The main reason why tinned copper conductors are recommended for marine use is that without the tinning the copper rapidly oxidises and the copper oxide creates resistance in any joints.
The main advantage of running at 24V is that there is half the current draw that there would be at 12V.
Any decent supplier of marine grade cable would be able to provide cable sizing charts but if you don't understand them then that is he time to go out to a professional.
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 Don’t know enough about it to comment, but think you should be commended for bringing up the problems in the article. It’s good to hear all the available information and to see someone is keeping an eye on Fred!
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Cheers Pirate
Whilst Fred has covered most things, I prefer to see a little more accuracy and explaination. Statements like ---"You want your stuff to work properly AND be able to recharge? Don't even guess, just multiply your loading by four that ought to do it - which means for a load of 100 ampere/hours, and work on 400 ampere/hours supply."--- aren't necessarilly true. This is not rocket science and there a many books available on boat electrics, most of these will tell you how to do a load analsys, size batteries, cables and general good practice. You can't call in a sparks when something goes wrong 20 miles out at sea but most of the time most people could easily carry out a repair providing they read up a little.
All the best
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 I think it would be good if you have to be able to do basic mechanics and repairs on your boat before you go out, as Chas said, you can’t call someone out when your miles off shore, and imagine how much the call out charge would be if you did!
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 I have picked up a lot about maintenance since I have been sailing, but you hear different things from different people and places, so it can become confusing about who’s right.
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My electrics are terrible. When I bought Talisman over 3 years ago I spent a lot of time removing all sorts of gash wiring that had been added to the basic system installed when she was built. The added wiring was mostly of the average car type of wiring and minor component; in line crimps, terminals, etc. Quite a few of the added items had become redundant, or failed, and subsequently removed but the wiring was left behind! I half filled a supermarket bag with unused wire!
I am still left with a poor system, the basic charging system works, the alternator charges the engine start battery through the engine start panel and also charges the domestic battery through a voltage sensitive (?) relay. I have a third battery, used in series with the domestic battery to provide 24v for the ancient Eberspacher heater (probably fell of the back of a lorry into the hands of a previous owner?). The third battery can only be charged using shore power so the heater is often unusable after a day away from a marina.
Last year I carried out an experiment and tried sailing at night without the engine. With the tiller pilot, echo sounder, VHF, GPS, laptop and tricolour light at the mast head as electrical load supported by the domestic battery - it lasted 1 hour 45 minutes! I find that in order to keep all the gizmos going I run the engine all the time when I am at sea.
I really need to improve the set up but am put off by the cost and am reluctant to interfere with the charging system. Anyone offer any advice?
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Though they can be quite pricey - it may be worth looking into invesing in a small solar panel or wind turbined that can chage the batteries up for you.
To supply you with the power you require for all your equiptment - it would be a BIG investment, but if you look at some of the smaller cheaper stuff - it won't supply all the power, but will give a well needed suppliment that should at least give you an extra couple of hours.
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 | TMS Poloshirt winner |
11/05/06 20:43
 The other alternative is a small generator.
There are some good, quiet, small ones around cheaper than most high amp/hr solar panel too.
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When sailing, a water turbine puts in far more power than a wind genny. The Duogen has had good reviews, and can be converted to wind power when you prefer that mode.
The other thing to do is analyse your power requirements, which means adding up the power used by every item during a typical night under sail, or at anchor etc.
Find the amps used by each item, then multiply the amps by the number of hours to give total amp-hour draw. E.g. 25W navlight draws 2 amps, x 8 hours = 16 amp-hours. Do this for all the things you use. Let us assume you get a figure of 75 amp-hours used in one night sail, and you hope to sail for a week. You need to put 75 amps back into your battery every day.
But, batteries can only safely be discharged to about 50% of their rated capacity, so you would need as a basic minimum a 150 amp-hour battery, and would be sensible to have a bigger bank.
You can work out how easily chargers can top up the battery from their outputs. Solar panels are often quite low, especially in cloud or shadow. Wind gennies vary with the wind. Engine alternators, as you know, are predictable but use up precious resources...
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Hi
I have a assotiated problem, having a partner who is scared of water, We do our cruising in a motor home, we are away 3 months at a time and camp sauvage, ie no campsites..have 2 leisure batteries of 120ah but with lights, computer,some tv can get seriously short of amps after 3 days idleness...have always seeked(qv) an answer, solar panels are not...last trip was to Turkey to see and record the eclipse( 29/03/06) Before going invested in a "Sterling to alternator battery charger"http://www.yachtbits.com/sterling_power/sterling_alternator_to_battery_chargers.php(sorry I can't do hyperlinks.Read it it works, basicly you can charge the leisure 4 to 8 times quicker with the main engine on tickover...if you invest in a better alternator even more.
Oldosc
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Ps
As stated in other threads, I am an ex trawlerman not always dun it ashore
Oldosc
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Hi I'm a newby here but I will make the comment on domestic/leisure batteries.
They do require different different charging from a starting battery.
To extend and maintain the efficiency of a domestic battery a 3 stage charging cycle is required.
Boost phase
Equalise phase
Float phase
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Hi
Fair comment, although on the big boats they have a battery man(qv)Most of the dutch (older) boats we had used Ni/Fe alkali batteries, you have to be very brutal to mess those up, and when (if) They get wet you dont get chlorine but they are very dear and heavy (1.1 volt if I remember) like everything it is cost/time/enjoyment..any two of three. I use sealed glass fibre plates, about 200AH for just on £100 second year of use... still as good as new (nearly)dump when no good.
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Interesting article this. Seldom do we get much info on batteries that applies to me. I am not fond of electrics having been badly shocKed as a child (110 DC as I recall - 1929 ROUGHLY) On my little Felicity I run depth meter and radar in roughly five to eight hour runs. I have two batteries, one a seven year old car type and one a five year old boat type charged by a small generator on my Beta diesel which I use for running in and out of river Dart and then sail out to sea. I have a very small solar panel, badly cracked and lets in water when it rains, as a top up when the boat is idle. I check and top up the battery water regularly. I have had the boat for some time now and only twice have I had to borrow a jump starer to get me out of trouble. That only because I had forgotten to turn off the batteries when I left her and then been away in hospital for a spell. I sail all year round, keeping her on a drying our berth up a creek. Winter cold and damp does not seem to trouble my electrics although it plays merry "H" with mildew and damp down below. Starbrite do a good mildew destroyer and I do my best to keep up the ventilation. Cushions and bunk board set upright when leaving............... er....generally. I suppose I shall have to get some new batteries eventually ...but the prices are way high for my state pension. Guess I will have to start cutting down on the Mars bars Michael
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| TMS Poloshirt winner |
02/03/08 11:36
I bought a Wolf Power cheapo 2 stroke generator. It lasted 4 hours and then seized up. No repair available apparently! If you are going to get one, get a HONDA (but very expensive). Make sure you chain it up too - highly mobile and nickable. I have an Aero4gen on the boat, which works very well indeed in the windy Hebrides. Highly recommended. John G and Vagabond
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| TMS Poloshirt winner |
03/03/08 20:15
 Well dont be put off by those £60- 600watt made in China gens.-mines about 4 years old still going strong including it keeping my house lit/fridge going 24/7 for three days on one occasion.Only problem is that they do not give a very stable voltage output but great for powering up small power tools Phil.
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