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Stinkpotter
Master Marine Consultant

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Djibouti
9080 Posts
Response Posted - 01/01/2017 :  21:26:34  Show Profile
quote:
Originally posted by islander

A good rule to follow is that inverters use 100Ah of power for every 1000 watt hrs of use...
A 1000 watt appliance at 120 volts uses 8.3 amps, and if an inverter is 85% efficient (as an example), that becomes about 9.8 amps (call it 10 for a rule of thumb). No?
Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge
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Davy J
Master Marine Consultant

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USA
1511 Posts
Response Posted - 01/02/2017 :  05:44:03  Show Profile
You are referring to AC amps coming out of the inverter. The DC amps at 12v between the battery and inverter, in your example, would be 83.
Davy J


2005 Gemini 105Mc
PO 1987 C25 #5509 SR/SK
Tampa Bay
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islander
Master Marine Consultant

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USA
4024 Posts
Response Posted - 01/02/2017 :  06:02:35  Show Profile
Yes Dave but I think it has to do to the fact that you are up-converting the 12vDC to 120vAC. I got my info from WM advisor.http://www.westmarine.com/WestAdvisor/DIY-Selecting-an-Inverter-or-Inverter-Charger
quote:
The rationale behind this rule is that inverters use about 100Ah of electricity for every 1,000-watt-hours of use. So if a West Marine Slim 1000 were used at its maximum capacity for an hour, it would consume 100Ah. This would discharge a 200Ah battery by 50% if it started out fully charged. This is a recommended minimum: as usual, more battery capacity is better.


quote:
If an inverter is going to run a 500-watt load, it will draw around 50A DC. The math behind this rule is as follows: 500-watts AC ÷ 85% efficiency ÷12.5V = 47A DC. Keep two things in mind: 500W is not very much power (think about a small cabin heater that draws 1500W or a large hair dryer that draws 1000W); and 50A is a heck of a lot of DC current use. Not many DC loads on boats 40' and under would draw 50A or more for more than a few minutes. Therefore, an inverter frequently becomes the largest DC load on most boats, and may require substantial changes in the battery capacity and wiring of the boat in which it is installed.
Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound


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Stinkpotter
Master Marine Consultant

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Djibouti
9080 Posts
Response Posted - 01/02/2017 :  08:54:56  Show Profile
quote:
Originally posted by Davy J

You are referring to AC amps coming out of the inverter. The DC amps at 12v between the battery and inverter, in your example, would be 83.
OK, my brain is working a little better this morning... And at roughly 85% efficiency (reasonable for an inverter), it would be roughly 100 amps.

Most of my cruising friends with electric appliances simply have something like a 2000W Honda portable generator--ideally running on a swim platform or in the open transom where it's down-wind while they're on the hook. It's a little noisier, but it avoids the damage that could be done by drawing batteries down further than intended.
Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge
Edited by - Stinkpotter on 01/02/2017 08:55:57
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Steve Milby
Past Commodore

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USA
5902 Posts
Response Posted - 01/02/2017 :  10:17:36  Show Profile
It's your choice how you set up your boat, but there are much simpler ways that you might consider, other than using 110 v. appliances. For example, good coffee can be made with a French press, and it only requires water heated on a simple alcohol or propane stove. Many of my cruising friends prepare complete meals at home, freeze them and keep them in an ice chest until they use them. Then they heat them on the same small stove. Personally, when I cruise, I don't like to heat up the interior of a small boat by cooking, so I try to have dinner in restaurants along the way, except when gunkholing, and then I like cold foods, like pasta salads, which can also be prepared in advance. There are other advantages to simplifying things. For example, if you use 110 v. appliances and a pressure cooker, you have to find some way to store them when underway. Also, someone has to prepare foods and cook, instead of relaxing. Whether cruising short term or living aboard, the key to enjoying the experience is to simplify your life. If you want to cook a meal, many prefer to do it in the cockpit, so you don't heat the boat's interior.
Steve Milby J/24 "Captiva Wind"
previously C&C 35, Cal 25, C25 TR/FK, C22
Past Commodore
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Stinkpotter
Master Marine Consultant

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Djibouti
9080 Posts
Response Posted - 01/02/2017 :  11:36:30  Show Profile
I've always done it Steve's way, with a butane stove for making coffee and scrambling some eggs, a big cooler with a few days' meals ready to go, a credit card for the waterside restaurants, and some cash for the morning pastry boat on Great Salt Pond (Block Island)--"ANDIAMO!!" I generally have a teapot, non-stick frying pan, and one small sauce pan aboard.

Some of the folks I was referring to spend several months cruising the Northeast Atlantic coast in weather varying from warm to chilly. One couple cooks or re-heats on a 2-burner Origo (with the companionway open under a dodger to disperse the water vapor and fumes). Another has propane in their C-34, plus a microwave, something like 6-8 (?) huge 6-volt golf cart batteries, and a Honda generator. Everyone has their variation...
Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge
Edited by - Stinkpotter on 01/02/2017 11:44:58
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Davy J
Master Marine Consultant

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USA
1511 Posts
Response Posted - 01/02/2017 :  12:21:10  Show Profile
As always threads take on a life of their own......

We usually like to make full meals and actually like carrying the necessary tools to do so while out cruising.

Last Christmas we were out cruising and while docked at Clearwater Marina made a full Christmas dinner including this 14lb turkey we cooked in a Big Easy oil-less turkey fryer...............
Davy J


2005 Gemini 105Mc
PO 1987 C25 #5509 SR/SK
Tampa Bay
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Voyager
Master Marine Consultant

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USA
5377 Posts
Response Posted - 01/05/2017 :  18:24:56  Show Profile
Scott, The math makes sense.
Me personally I would not use 3000 W of electricity to heat food because of the fact that your running the batteries way down in a short amount of time. Could harm the batteries. Recharging them at 4-6A will take 20-40 hours. A Max Burton - style butane stove will boil coffee or veggies or pasta, you can fry eggs, meat and potatoes in a griddle and deep fry in a pot.
If however the coffee maker runs at ~1000 W for 15 minutes, that's ~80A for 0.25 hours or 20AH. That's very doable. And having single serving cups is a great convenience.
Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain — Milford, CT
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michael.anda
1st Mate

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USA
60 Posts
Response Posted - 01/07/2017 :  20:45:06  Show Profile
Where things sit. No solar as yet.
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.