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bluemist001
bluemist001

Posted: Sat Aug 02, 2008 6:46pm

Post Subject: inverter

i have a 40foot narrow boat and would like to know what size inverter should i install.i just want to run a mirowave small fridge and cabin lights,pumps etc

Tony-B
Tony-B

Posted: Sun Aug 03, 2008 12:47pm

Post Subject: inverter

For goodness sake why do you need an inverter? I have no idea want sort of pump you may want that uses mains power (unless you are intent of fitting a power shower for some reason I can not think of). They are all normally 12 or 24 volts. Again with lights, I can not imagine why you need (rather than want) mains lighting 12/24 volts are the norm. The question of fridges is slightly different but apart from initial cost of the fridge (ignoring the inverter) the balance of power efficiency between the 12v compressor fridges (Shoreline etc.)and high efficiency mains ones is very even. Now we come to a microwave. I really do wonder how well you have researched life on a boat and the implications. The one thing that constantly causes problems is the electricity supply and keeping your batteries charged. Inverters use electricity to work themselves (we typically ignore what the makers say and assume an 80% efficiency, but with a very large inverter plus a small load it may only be few percent efficient (e.g. a 3kW pure sine inverter charging a mobile phone). The "power" most people think of on a microwave is the cooking power, not the power consumed and that is far larger. My domestic microwave made by a German company that tends to produce efficient equipment is a 1000W unit, but its electrical rating is 1680W and it demands a 13 amp fuse. This tells me it produces a large starting surge current. I have checked a small 12v unit and it has similar efficiency/inefficiency. A 600w mains microwave will, ignoring the starting surge) draw about 990W, once we have put that through an inverter it will be drawing 99 amps from the battery. Even though it may only do this for a short time it is still bad news for a boat that has not been designed for this from the start. I can think of nothing a microwave can do that I can not do on my gas cooker. Please, please go into the electrical notes on my website or use the link on the first page to go to the Smartgauge site do some basic calculations regarding your electrical consumption, your battery bank size and the time taken means of charging it. www.TB-training.co.uk. If you want a reliable boat you may then alter your priorities. Now, having gone through all of that you will probably still need an inverter for charging things like camera batteries, battery power tools etc. Try to use a car charger/power supply for any phones and laptops because it will be more efficient. I would suggest something between 150 and 300 Watts would be fine. My 150W "Maplin special" seems fine. If you do decide to go down the mains equipment route please make sure you find out the starting surge current each item of equipment demands and ensure any inverter can supply such a surge - many can not. Finally take care with the type of inverter because there are two types modified sine wave (cheaper) and pure sine wave (expensive) and some equipment will not run on a modified sine wave. In your list I am concerned the microwave might not, and the fridge will certainly produce a large starting surge. Sorry to be negative but it is better to make the situation clear before you start on a route that leads to ever increasing expenditure. Finally, if your mooring has a shore power hookup there is no reason not to use all the equipment you mention whilst you are hooked up, but I have doubts about it when out cruising. Tony Brooks

bluemist001
bluemist001

Posted: Sun Aug 03, 2008 11:05pm

Post Subject: inverter

thanks tony.saving me money is just what i need with an old but great boat

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