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Posted By Discussion Topic: Inverters

Similar Threads That Might Help :
inverter| Inverters| Inverters| inverter| Inverters, transformers and frequency|

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Baz
Apr-12-2007 @ 8:13 PM                           Permalink
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Could someone help me please, by explaining the proper use of an Inverter, describe the NEED for an Inverter, and the differing Sizes and their uses.

Many thanks in advance.

"Man who looks back, Has nothing to look forward to."

Bounty
Apr-12-2007 @ 8:26 PM                           Permalink
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Inverters are used to convert 12v DC (from the boat batteries) into 240v AC like you get at home. This means that you can use your home appliances when on the boat. The differing sizes are used to produce differing amounts of current and therefore power (as in watts).

From memory:   Power(W)=Volts(V) X Current(A)

So, to get 3Kw (an electric heater) you need 12V X 250A. That's a lot of current and a massive drain on batteries.

Inverters have a limited use on boats. Good for charging 'phones and laptops and powering DVD's etc, but really problematic for high power items.

Aclepob
Apr-12-2007 @ 8:28 PM                           Permalink
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Hi Baz
An inverter takes DC,, 12 or 24V from your battery and converts it to something approximating the 240V AC you get out of the sockets in your house.

They are sized by the load they can support e.g 300W.

A couple of things to know.  The output only approximates to a sine wave.  The cheaper versions have a modified square wave output which some equipmet wont like very much. Some TV and radio equipment can be sensitive. Things like the little black 'wall wart' power packs that output DC for laptops, phone chargers etc are usually OK with these.

More expensive inverters will have a better approximation of a sine wave output and will be OK for everything.

Remember that inverters like every other electrical device are not 100% efficient so you dont get as much AC power out as you put DC power in.

Before you buy read the spec sheets and choose one that is sized to provide the amount of power you need.  Remember that highly inductive loads, like electric fires, have a much higher power demand on switch on than their rating plate indicates and some inverters will gib at supplying high instantaneous spike type loads and shut down.

Inverters made specifically for the marine market are often higher priced than their 'domestic' cousins so shop around bearing in mind the environment you will use it in and how much chance it might have of being constantly exposed to the damp.

Hope this helps Baz

Nige

The front of the boat; that's the pointy end right?

Gordon
Apr-12-2007 @ 8:38 PM                           Permalink
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Baz

You also have to bear in mind that even a small inverter e.g a 300W inverter on full load is going to draw 20 - 30 Amps so the 12 volt side needs to be wired accordingly, i.e a short length of adequately rated wire and not just plugged into the boats fag lighter socket.

Gordon

Baz
Apr-12-2007 @ 8:39 PM                           Permalink
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Hiya Bounty/Aclepob, many thanks for the replies. Actually,you've hit the nail on the head by mentioning a DVD. If I were to use one, it would be for this particular item. So do you put a 'normal'socket in the boat to take a 3 pin plug.

Personally, would you put one in your boat. I'm asking these questions now, as I'm nearly in the position to get my own boat, and really need to know if I'm going the right way.

"Man who looks back, Has nothing to look forward to."

Baz
Apr-12-2007 @ 8:42 PM                           Permalink
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Hi Gordon, So really then, my boats batteries aren't going to last long then, when it's switched on.

"Man who looks back, Has nothing to look forward to."

Aclepob
Apr-12-2007 @ 8:43 PM                           Permalink
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Inverters part 2
It is worth knowing that high power items like electric heaters are not usually practical on consumer and boat batteries owing to the very high current demands.  A 2000 watt fire requires about 8 amps at 250V from Power = Volts x Amps. when you do the same sums at 12 Volts you need 2000/12 or about 167 Amps. It gets a bit better at 24 volts but 83 amps is still a lot of current for a battery to supply for anything but a very short time. The inefficiency of the inverter means that you will actually draw more current than these basic equations would suggest.

From this you realise that the Amp hour capacity of your battery is a critical figure to know.

The end result is that inverters, except in specialist installations, are generally only any good for relatively low power consumption items like laptops and small portable audio visual appliances like DVD players and small TVs.

Whatever you do dont run your inverter of the battery that starts your engine!!!

Nige

The front of the boat; that's the pointy end right?

Aclepob
Apr-12-2007 @ 8:59 PM                           Permalink
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Baz
N ot sure I would go as far as trying to fit a 13A socket outlet on the boat.  It might bet you into trouble with BSS if not done correctly.  Most inverters have the socket on them only requiring a 12 volt input. A 12V supply and getting at it will probably be easier to find and attach to. Might even be a spare way on the boats fuse board if it has one. Even at 12 volts the fitting needs to be 'properly' done for safety but I have used inverters with crocodile clips straight onto the battery though not on a boat.

Nige

The front of the boat; that's the pointy end right?

osdguy
Apr-12-2007 @ 9:04 PM                           Permalink
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Hi

We bought a little "coke can" style invertor last year and it is worth its weight in gold.
We don't use it to power major items, just phone chargers, portable (7" screen)DVD player and for charging up general batteries.
Cost about £20 - £25 if I recall.

Didn't appear to take too much charge out of the battery either but then we have an outboard so if I can't electric start it I can pull it.

If you're on the Southern Broads you are more than welcome to borrow it to see if it's what you need before investing in one.


regards

Marc & Karen
(osdguy)

Jonzo
Apr-12-2007 @ 9:11 PM                           Permalink
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Would have thought it would be better to buy a 12v DVD player? They're cheap enough on Ebay and other places.

This message was edited by Jonzo on Apr-12-07 @ 8:13 PM

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