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Old 16-02-2009, 11:49   #1
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Rewiring a relic--power advice? Electrical gurus?

We've got a 1968 Soverel 33 with several generations of kludged-together antiquated wiring and it's a general confusing mess (Lucas electrics FTL); I'm planning to totally redesign and rewire the thing so that it's suitable for fulltime liveaboards (two of us) and eventual cruising.

I'm no expert electrician, but I've rewired cars and planes, and I was an ET in the service. I have the basic skillset but no specific knowledge that is unique to boats. I'm not afraid to get in there and try stuff to get the thing to work.

At the moment it has a 10A charger and no inverter at all; we only have 120VAC while hooked to shore power; it's hardwired to the two AC outlets. No shore power, no AC.

What I want to do is upgrade the charger and install two inverters and a third outlet. The AC power load will mostly be light--two laptops and a printer, a small space heater, and a small fridge; but with occasional large loads from a microwave. The boat has a small DC fridge which we're keeping--ain't broke, so not gonna mess with it--and the DC lighting system, which I'm going to rewire for neatness and switch over to LED light ASAP. We're going to add a second fridge that can store more than a sixpack.

My specific plan is to go with a 30-amp switchable 2-stage/3-stage charger; a single 750W MSW inverter (bought dirt cheap at a pawn shop, not my first choice, but too good a deal to pass up) to power the one V-berth outlet; and a 2.0kW PSW inverter to power the saloon and galley outlets which will carry more sensitive electronic loads.

The 750W MSW inverter will carry an occasional load of ~600W (small space heater, plus a digital clock, plus a small hair dryer (the heater will be turned off while the dryer is on)).

The 2.0kW PSW inverter will carry a steady load of ~250W (two laptops and a printer) and an additional ~350W (second fridge running on AC) plus an occasional load of ~1500W (microwave). We'll power down the printer while microwaving.

The DC system will remain, powering the antique-but-functional minifridge, the interior lighting and fans, depthfinders, radio, cockpit stereo, and all exterior lighting. Again, I'm just going to rewire the Edison wiring and upgrade to LEDs.

First question, and by far the most important: Does any of this sound at all stupid; i.e. am I missing anything obvious?

Second question: Is it preferable to mount the inverters in the cabin, or in the engine space? Are there any regs that specify placement?

Third question: I know this will also require breaker panels, and those I am not as familiar with (not common in cars or small aircraft) but it should not be a major technical challenge; will I need two separate ones for AC and DC systems? Can I go with a "universal" panel that does it all?

Fourth question: Down the road we're planning to add solar panels and a wind jenny; does anything I'm planning now preclude these, or are there things I can set in place now to prepare for these additions later on?

Last question: Anyone in Charleston want to get in on this? I'll buy beer and pizza.

Edit: At the moment we have three batteries and I intend to add more.

Cheers!
Mike
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Old 16-02-2009, 11:58   #2
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Mike,
One serious flaw in the plan that I see: Just where are you gonna get all the power that you envision using? The idea of running space heaters off of batteries ain't gonna work, nor will any of the other major loads that you propose.

Unfortuneately, you are worlds away from being able to support this sort of power drain without running a genset. Period.

Time to rethink your plan.

Sorry to be the bearer of such news, mate!

Cheers,

Jim and Ann s/v Insatiable II lying Gladstone Qld Oz
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Old 16-02-2009, 12:05   #3
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Fair enough, this is stuff I need to know; I have no idea how robust marine batteries are.

At the moment our battery bank is three standard marine batteries. Planning to add more once I understand how long they will last under normal conditions. I'm used to batteries only being used to start an engine.
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Old 16-02-2009, 13:13   #4
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Nigel Calder's "Boatowner's Mechanical and Electrical Manual".

12 volt Bible - don't remember the author.

Blue Sea web site has lots of technical info, you have to look for it.
Blue Sea Systems
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Old 16-02-2009, 13:25   #5
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This is what helped me

-Pull out all the old wiring, Yes All. Start fresh. Saves much time.
- Run conduit (Plastic pipe) along both sides front to rear. Make them twice as lage as you think you need.
-Familiarize with ABYC codes and try to work with them if you ever expect to sell the boat someday.
-Blue seas, Paneltronics are 2 of many primary panel builders with off the shelf -panels. AC & DC
- Check online and or get catalogs from you local retailers/shows
-Size matters.... use the available charts for wire size vs load. Make it bigger.
-Do not start untill you know what AWG is or metric equivelent.
-Draw it out on a big board.

This fourm has some really good electrical folks (not me) so ask about the little stuff
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Old 16-02-2009, 13:27   #6
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there are also limits as to how much battery power you could actually have on a 33' boat. maybe 4 GCs or 2 8Ds could be possible.
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Old 16-02-2009, 13:33   #7
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To get the 15amps AC you need to run a small space heater or hair dryer through an inverter you will draw about 150amps DC from your batteries. If you have a 200amp/hr battery it's not going to last very long. You do not have enough space on a 33' boat to carry all the batteries you would need and if you did, you would not be able to re-charge them.

AC and DC must not be on the same panel and if in the same enclosure must be separated by a dielectric barrier.

Best advice - "The 12volt Bible" by Miner Brotherton
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Old 16-02-2009, 13:37   #8
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Why do you want to power the AC system through inverters? 30A shore power will give you roughly 2700 watts. If you are not plannig on having any shore power by your usage you will be running something like 200 amps through your batteries at any given moment, allowing for an 8 hour day at half that you are going to be running something like 800-900 AH a day, that will require a 2400 AH battery bank. I would worry about the weight of 12 8D's on a 33 footer, its something approaching 1500 lbs!
Do not want to rain on your parade but you need to get your usage down to a reasonable level. In that boat living aboard you will need to be using something approaching 100 AH days, thats about 1100 watts spread over 24 hours so about 4amps per hour.
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Old 16-02-2009, 14:37   #9
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Mike,

Jim Cate and S/V just wrote the Gospel for you
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Old 16-02-2009, 15:01   #10
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DeepFrz: I have Calder's book already. The "12V Bible" is now ordered. Blue Seas bookmarked for research. Thanks!

S/V Antares: Definitely already planning to replace all the wiring with new, terminals and blocks as well. Good idea about the conduit. And I drew out the wiring on green graph paper to start the process.

GoneSail: Not sure what that terminology means. Are those standard types/sizes? Sorry for being ignorant, but that's why I'm asking questions here.

Boatpoker: The heater we were planning to get drew 600W, or about 5A, just enough to warm the V-berth only. We're now--based on replies here and to an identical thread posted elsewhere--planning to ditch the microwave for sure, and the electric heater. Looks like propane is the alternative to electricity.

Rhosyn mor: Well, this is why I asked the questions; I'd rather look like an idiot now online than actually be one later by doing all this and then discovering it doesn't work. We need the inverters to drive the laptops primarily; we'll be working from home online, even out on the water.

Okay, so if inverters are so inefficient, why am I seeing them advertised as 85% to 90% efficient? To me that's not bad at all. I'm just looking at the general inefficiency of DC (massive line loss) versus AC, but if an inverter makes AC as inefficient as DC, should I then just go with an all-DC system? Get a 12VDC-to-19.5VDC converter for the laptops?
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Old 16-02-2009, 16:15   #11
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Okay, focusing on the battery issue for the moment. I'm a big fan of AGM batteries for automotive applications, but that may or may not be of use in marine apps.

So, cutting out the luxuries and going all-DC, using shore power only to recharge but not to power anything, and going all-DC with just the onboard electronics, lighting, fans, plus laptops...looking at some AGM batteries with a 90 AH capacity each and ganging up two or four of them.
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Old 16-02-2009, 16:25   #12
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There are some good diesel space heaters that work well on small boats, such as Dickinson and others. They exhaust out through the deck and supply a "dry" heat. A small DC fan above it will circulate the warm air and keep the boat dry. Much better than an electric space heater on a small boat, unless you are plugged in at the dock all the time in a moderate climate. And I think better (IMHO) than a propane heater because of supply issues mainly.

DickinsonMarine.com - Marine Heaters, Stoves and Barbeques
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Old 16-02-2009, 16:50   #13
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hey Mike,

where do you berth your boat?? We are at mariners cay at folly beach....I've done a bit of boat wiring here in charleston....maybe we can get together for some of that pizza and beer and compare ideas....we are doing somewhat of a refit on our Prout catamaran...including the electrics...

fair winds,

George & Doris
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Old 17-02-2009, 03:01   #14
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Quote:
Originally Posted by captfolly View Post
hey Mike,

where do you berth your boat?? We are at mariners cay at folly beach....I've done a bit of boat wiring here in charleston....maybe we can get together for some of that pizza and beer and compare ideas....we are doing somewhat of a refit on our Prout catamaran...including the electrics...

fair winds,

George & Doris
That would be great. She's still on land at the Charleston City Boatyard. We're narrowing down our marina search; looking at Toler's cove or Bohicket.
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Old 17-02-2009, 07:00   #15
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sinuous,
did not mean to imply idiocy. This electrical stuff can get complicated, I have just finished a complete rewiring., Remember tho' 600watts might draw 5 amps at 110v, but if you are using an inverter you are still using 12volt power, and it will close to 50amps at 12volts IIRC. watts divided by volts equals amps.
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