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Old 02-04-2014, 07:41   #1
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Amp usage

Does anyone have or know where to get a list of approximate amperage draw of all the stuff on sailboats? I'm trying to install solar panels naw want to calculate my usage
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Old 02-04-2014, 07:56   #2
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The best resource would be to figure it out based on what's already on your boat. Failing that there's a Good list of ballpark numbers as Well as a Good in depth review of boat electronics including solar in Don Casey's book, This Old Boat. It's a book worth owning.
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Old 02-04-2014, 08:03   #3
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Re: Amp usage

Lots of lists and articles on the net that cover this. Here's one Boat Electrics; How to Calculate Your Daily Amp Requirement

However, the answer will vary a LOT depending not only on your boat and the equipment installed but your usage patterns. Two boats with the same things installed could see 100% difference in actual daily power usage.

Example, the autopilot is a big draw. A boat that is traveling a lot and using the AP vs one that spends a lot more time in port. Some stay up late and use a lot of lights, some cruisers go to bed with the sun. So an power calculator can get you in the ball park but the best way to know is to install a battery monitor and track usage. They're good to have anyway.

Another issue, if you have a refrigeration system it might draw 20-30 amp hours/day for a small, efficient, well insulated box or 80-90 amp hours for a bigger, less efficient box.

Maybe post a list of when you have and some details.

And welcome to the forum.
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Old 02-04-2014, 09:18   #4
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Re: Amp usage

How long is a piece of string? Every boat is different. You need to make your own calculation -- make a list of all the gear you have on board, estimate the number of hours per day you use each device. Make two lists -- one for sailing, and one for at anchor. Pretty soon you will get an idea of amp/hours per day you use on average, and peak amp draw.
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Old 02-04-2014, 09:47   #5
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Re: Amp usage

As a rule of thumb....

Every big thing draws 4 amps
Every small thing draws an 1 amp.


So: fridge 4 when its on, not often
auto pilot & instruments, 4 together
Freezer 4 while its on... Lots
Water pumps etc 4 but they are only on for seconds

All interior LED lights on together 1 amp
Direct battery 12 volt charging of a computer 1 amp

Etc
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Old 02-04-2014, 10:52   #6
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Re: Amp usage

Quote:
Originally Posted by MarkJ View Post
As a rule of thumb....

Every big thing draws 4 amps
Every small thing draws an 1 amp.


So: fridge 4 when its on, not often
auto pilot & instruments, 4 together
Freezer 4 while its on... Lots
Water pumps etc 4 but they are only on for seconds

All interior LED lights on together 1 amp
Direct battery 12 volt charging of a computer 1 amp

Etc


The non-electrical expert's guide to boat batteries. I love it.

Had a good chuckle over this but at the end of the day, it is close enough to get you in the ballpark of your boat's requirements.

One comment, I have a temporary lighting fix with some less expensive (IE cheap) and very bright LEDs and a lot of them (I like it bright when I'm cooking or working on stuff) and if I light up the whole boat at once can pull 3 amps or better.
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Old 02-04-2014, 11:06   #7
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Re: Amp usage

The West Marine Advisors, online and in their catalogs have all that information.

Google boat energy budget and you'll find thousands of posts with that information.

Here's one: The All-Important Energy Budget:
Energy Budget

The 4:1 idea is great, 'cuz it works, close enough.

What comes out is easy.

You also need to understand battery acceptance to realize/learn that it takes much longer to return amps than it does to take 'em out.

Good luck.
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Old 02-04-2014, 11:07   #8
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Re: Amp usage

Thanks for the help and the resources
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Old 02-04-2014, 11:13   #9
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Re: Amp usage

If you want to know for sure without estimating then get a clamp ammeter and measure everything when it is on. For really small loads you will need a multimeter. Then estimate how much the load is on in a given 24 hour period. This will give you the total amp-hours in a 24 hour period. It really is that easy.

If not then the estimates are probably close enough to what you actually use.
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