First, you need to get a clue about 12 VDC electrical systems on sailboats. Running A/C off of a battery bank is really not an option. Get yourself a good book on marine 12 VDC electrical systems, like Charlie Wing's Boatowner's Illustrated Electrical Handbook,
Miner Brotherton's "The 12 Volt Bible for Boats
" or Nigel Calder's Boatowner's Mechanical and Electrical Manual
Much of what you want to do can be done using 12 VDC equipment—refrigeration, wet/dry shop vac, cabin lights, navigation lights, stereo and laptop. The stove should be either a propane unit or an unpressurized alcohol unit, like an Origo.
Running any sort of AC on a boat either requires an engine driven system, which is expensive, or a generator to drive a 110 VAC A/C system—less expensive, but more of a PITA IMHO, or using shorepower to run it.
A basic 12 VDC electrical system will require:
1) Batteries—preferably at least two, one for a starting bank and one for a house bank
2) A main DC panel, preferably using circuit breakers rather than fuses
3) A main DC battery switch—I prefer the BlueSea Dual Circuit Plus series of switches, since they isolate the starting and house loads
4) A main fuse for each battery bank—like the BlueSea MegaFuse
5) A ground bus bar or post
6) Battery cables—I recommend getting them from GenuineDealz.com on the internet. They will crimp the lugs you need on the cables if you ask them to for a very reasonable fee. Use Yellow for the 12 VDC ground.
7) Wire—You can buy wire from many different sources. I like the Berkshire marine wire, as it is better than the Ancor IMHO and far less expensive. Genuinedealz also sells pretty good marine wire. Use Yellow for the 12 VDC ground.
I would also highly recommend getting the following to make the 12 VDC system more idiot-proof.
1) A battery combining relay, like the BlueSea ACR, Xantrex Echo Charge or Balmar DuoCharge. Having one of these will allow you to charge both battery banks without user intervention.
2) A good battery monitor, like a Victron BMV 600, which will let you see how much energy you are using, and what the state-of-charge of your house battery bank at any time.
If you keep the boat at a dock with shorepower, you will also want:
1) A 30-amp shorepower inlet socket
2) A main shorepower panel that has a double breaker for the incoming 110 VAC shorepower line
3) A 110 VAC-powered, three-stage, intelligent battery charger—Iota makes a good unit at a reasonable price
4) A GFCI-type 110 VAC outlet
If you keep the boat on a mooring, or plan on cruising longer term, you will probably want:
1) Some solar panels—to recharge the batteries when not connected to shorepower without running the engine
2) An MPPT charge controller for the solar panels
You should probably read the article on Solar Power on Boats I wrote on my blog.
Tools you will probably need/want:
1) A good digital multimeter—I prefer an autoranging unit
2) A good crimper for heat-shrink insulated crimp terminals, like the Ancor 702010.
3) An ultra-fine tip Sharpie marker
4) 3m White Electrical Tape
5) A good wire stripper, like the Ancor 702030.
You should also read Maine Sail's excellent article
on terminating electrical wire connections.
As for equipment:
—the only choices are either the Engel or the Norcold portable refrigerators. These have consistently been ranked as best for 12 VDC small refrigerators. They’re actually made in the same factory IIRC. I have an Engel MT27 22-quart refrigerator on my boat. The units are dual voltage and will switch from 12 VDC to 110 VAC automatically.
—I’d go LED with the lighting. It will be more reliable and lower draw than going with either CF, Incandescent or Halogen lighting.
Interior Lights—I’d recommend getting SensiBulb LED-based interior cabin lights. They are the best in terms of color, area of coverage and durability.
Navigation Lights—I'd highly recommend getting USCG-certified LED-based navigation lights, like the AquaSignal Series 32 navigation lights. These will be lower-maintenance, lower energy use, and higher reliability than traditional incandescent navigation lights.
—Get a good car stereo, unless you need one that is water-resistant. If you have to mount it near the companionway, get a marine unit instead. Read Camaraderie’s excellent article on stereos and speakers.
—The simplest would be to get an unpressurized Origo alcohol stove. It requires no complex installation... just bolt the mounting bracket for it in place and mount the stove. It is available in both gimballed and non-gimbaled mounts.
—You can either get a small 110 VAC wet/dry shopvac, or get a 12 VDC powered unit. The 110 VAC units are a bit nicer and more reliable IMHO, but you'll need to have either a shorepower connection or an inverter and a larger battery bank.
—Yeah, not gonna happen. And it really isn’t necessary in most areas. Get some good 12 VDC fans and a couple of windscoops. For fans, I like the Hella Turbos and the Caframo Boras. The Hellas are better for bulkhead mounted fans, since they pivot at the center of the fan fixture. The Caframo Boras are nicer fans IMHO, with three speeds, instead of the two and an electronic switch, rather than mechanical.
A Bit About Batteries
Properly sizing the batteries is something that takes a bit of work. An 120 amp-hour battery really isn’t all that useful, especially if you have high loads on it. The higher the load, relative to the battery size, the lower the effective battery capacity will be. This is why the 20-hour rating is always higher than the 5-hour rating for the same battery. For instance. The 20-hour rating on your example battery is 120 amp-hours or a 6-amp load for 20 hours. If you were to put a 20-amp load on the same battery, it would not give you six hours of use. It would probably give you something more like four-hours of use, or 80-amp-hours total. This is due to the Peukert factor or rating.
Now, lead-acid batteries generally do much better if they are not deeply discharged. Discharging them beyond the 50% level will generally shorten their effective lifespan. So, an 120 amp-hour battery really should only be used for 60-amp-hours or so at the 20-hour rate of discharge. This is one reason I recommend getting a good battery monitor. If you know that you’re constantly running the batteries down below the 50% level, you will realize that you really have to increase your house battery bank size to get the maximum life out of them.
—or why you need an intelligent battery charger.
As for how long you can go between recharging the batteries. That all depends on the size of the battery bank and the loads on it. I would point out that lead-acid batteries don’t charge at a constant rate.
—Up to about 80–85% charge level, they charge fairly quickly. This is the bulk charging phase, and on wet-cell batteries is about 20–25% of the battery bank’s capacity in amperage. So, for a 200 amp-hour bank, it would charge at 40-50 amps until it reaches this point.
—Then the amount of current the batteries will accept will drop drastically. This is called the absorption phase. The voltage of the charger will also drop as well. It may well take longer to get from 85% to 99% than it did to get from 50% to 85% because of this.
—This is the third charging stage or phase, and the batteries are essentially nearly fully charged at this point. The battery charger drops the voltage down to about 13.5 VDC and the amperage is minimal. The battery charger’s main purpose at this point is to keep the batteries topped off. Most rechargeable batteries self-discharge and without the float phase, would slowly discharge over time.
Originally Posted by sailguy40
I am a bit confused as to what I need here to get some electric going onboard my boat. I am looking to run a small wet/dry vac, small refrigerator, portable ac unit (or portable air cooler) basic interior and exterior lights, maybe a small stove, laptop and stereo. It seems a noisey generator is not very practical, not to mention it needs to be outside. So I am wondering if a good deep cycle battery with an inverter with do the trick? If so, I wonder how long a 105 or 120amp hr battery will keep me running before I need to recharge. If anyone here has some suggestions, please let me know, thanks.