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Posted: Thu Feb 10, 2011 8:50am

Post Subject: Adapter plugs

Another newbie question ... could any pls advise, if I use a cigarette lighter adapter with a standard 3 pin plug on my boat, am I correct in assuming that a) the engine must be running and b) if the engine is not running it will drain the battery? Thanks in advance Gill


Posted: Thu Feb 10, 2011 10:52am

Post Subject: Adapter plugs

Dear Gill, This question confuses me because it looks very much as if you are planning to connect a 12V DC (battery) supply with a 240V AC (Mains) supply. If by standard plugs you mean 13 amp square pin plugs like you use in a house then any cigarette lighter plugs MUST NEVER be connected to them. At the best you may end up with damaged equipment and at the worst you may end up dead. Just to complicate things the old mains type small 5 amp 3 round pin sockets and plugs are often used for the 12v supply but which pin is used for which wire tends to vary from boat to boat so once you sort out the pins I suppose you could connect a cigarette lighter socket to a 5 amp round pin plug (wired for 12v DC) to supply things like car type mobile phone chargers etc. Now â if you really are talking about 13 amp domestic plugs this implies (unless a complete idiot wired the boat and if so the surveyor should have warned you) that you have a mains circuit on board for ordinary domestic equipment. This may be fed from the batteries via an inverter, straight from a shoreline, or with an expensive inverter a mixture of both and in the latter case the inverter may well contain a battery charger as well. I trust your survey will clarify this. If the mains supply is from a shoreline only it will not have ant effect on the batteries so just use it but be aware that many marina supplies limit the current you can draw to perhaps 6 or 10 amps. If the mains sockets are fed from an inverter you need to take care â see below. Now the cigarette lighter sockets that are supplying 12 volts DC from the batteries. These together with the lights, water pump, central heating etc. will discharge the batteries and may new boaters run into all sorts of problems because they seem to think their boats are still connected to the mains by a very long 30 amp cable. This can lead to ruined batteries and it seems inverters tend to make the situation worse. The whole area is full of ifs and buts and is also specific to your boat and the way you use it so I would urge you to go to (all on one line) and work through the calculations. You start with a list of ALL the electrical equipment on board and its individual current consumption. You often have to calculate the current consumption from the watts you find on the equipment plate. This will give you some idea about how often and how long you have to run your engine for to keep your batteries in optimum condition. Tony Brooks. PS You will probably find the course notes of help to you â you can print them out if you wish and you may find a course of help in understanding your boat.

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