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Old 15-10-2014, 04:43   #1
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I am about to change from an 1981 mono hull to a 2000 Cat. My question is this.

There seems to be mainly AC sockets and very few 12 volt DC outlets. I have lots of DC outlets on my boat now and tend to use these and not the inverter.
Is this "normal" or am I just old fashioned ? The Cat is an ex charter boat .

Does it make any difference to battery life and which is the best way to go?

Any sound practical advice would be appreciated

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Old 15-10-2014, 04:50   #2
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Re: AC/DC ?

It doesn't make sense to use the inverter to power stuff if you could instead power it with DC because there is a power loss in the inverter.

But with that said my boat only currently has 1 DC outlet but has AC outlets in many places.

stop blowing smoke up my rear, blow it at the sails instead
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Old 15-10-2014, 05:40   #3
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Re: AC/DC ?

Just do the math and that will answer your question. Typically when running many AC devices these days you go thru a power supply too. Most of these are cheap and inefficient and many will draw power even if the device is disconnected from them. So you have loss thru the inverter (typically at least 5% even on a high end inverter...low end ones are worse) then additonal loss thru the power supply.

I ran the numbers on an inverter-power supply set up on my boat a few years ago and came up w a 30% loss for that installation! Way more efficient to go direct DC.

You can also get DC-DC power supplies for devices which take other than 12V. More efficient than inverting from DC-AC then back to DC thru a power supply. For example, many devices now take 5V as supplied over USB interfaces. I installed a 12V to multiport USB adaptor last season which we use a lot now to charge/run small electronics.

And my cat, also built in 2000, has a bunch of AC outlets (main salon, galley, and one in each cabin). They do come in handy for occassional use like running a power tool or a guest charging their cell phone, but for normal installed loads on the boat it is way more efficient to go direct DC.

I also control the inverter from the nav station. This way I can monitor power use...especially with guests aboard. I usually turn on when requested and then turn it off when they are done and/or before I go to bed.
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Old 15-10-2014, 05:59   #4
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Re: AC/DC ?

You are a sailor...

And you bought a floating hotel room for tourists... Who don't tend to have a bunch of "sailor type 12v stuff" ...

Just throw in a bunch of DC outlets, and you'll have lots of extra convenient AC outlets!
In the harsh marine environment, something is always in need of repair...

Mai Tai's fix everything...
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Old 15-10-2014, 06:12   #5
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Re: AC/DC ?

I think the lack of DC outlets speaks to the intended use of the boat and by whom.
Good news is DC outlets are easier to add than AC
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