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  Topic Review (Newest First)
10-20-2013 08:44 PM
Re: How do I calculate my power needs?

Exchange lights you use a lot to LEDs, longer life, and usually less power requirements, although they would be minimal. But every bit helps. Like someone else said, look into a small wind turbine. There are a couple companies out there that sell hybrid kits (2 solar panels, and a wind gen, with chargers/inverters and the whatnot you need)
06-25-2013 10:12 AM
Re: How do I calculate my power needs?

Originally Posted by copacabana View Post
My two 75w panels top up the batteries during the day (12.8v) and I might see a voltage before sunrise of 12.6 or 12.5 volts. Not very sophisticated, but it works.
I think that is pretty sophisticated! Its basically all I need. Coupled, of course, with an on going daily look at the voltages.
Mine is lower than 12.5 at sunrise... Mine is about 12.3, when the fridge cycles on at sunrise it will be 12.15 at its lowest (about 12.24 unloaded)... thats the magical 50%.

If I was getting 12.5 at sunrise I could drop the fridge a degree down... or start my big fridge up for a 10 minutes 4 times per day as a vegetable crisper... Or charge my iPad, phone and shaver...

So instead of some of the metered ways of determaining consumption I just feel and experience.
Today is sunny where tomorrow is cloudy so I better charge my 'extras' today.
06-25-2013 09:10 AM
Re: How do I calculate my power needs?

Chuckles is right concerning battery monitors. Voltage alone only gives you a very rough idea of battery state. To be effective it has to measure voltage on a "rested" battery, which doesn't happen on a boat. However, if it's what you have to go on... A fully-charged battery should show 12.7 or 12.8 volts. The voltage will drop as you use the battery. At 12.2 volts the battery has only 50% charge and should be charged again. I also use voltage on my boat to monitor batteries, but since I make more power than I use, I don't really worry too much about input-output. My two 75w panels top up the batteries during the day (12.8v) and I might see a voltage before sunrise of 12.6 or 12.5 volts. Not very sophisticated, but it works. You might want to add solar panels and/or wind power and then see how much power you can make. Then tailor your consumption to your power generation. The coffee machine may have to go ...
06-25-2013 08:54 AM
Re: How do I calculate my power needs?

Inexpensive battery monitors don't do the trick. Relying solely on battery voltage as a state of charge indicator is fault laden.
Get a monitor that actually measures amp hours in and out, such as the BMV 602s like this one : Need A Battery Monitor ? Photo Gallery by Compass Marine at sold by Maine Sail here on sailnet.

I recommend you do some reading and research, you should combine your two batteries into one bank because a single larger bank is able to accept a heavy charge better, more efficiently and faster.
You'll also need to consult some local experts regarding how many amp hours per watt of solar you can expect to produce in your location.
06-25-2013 07:51 AM
Re: How do I calculate my power needs?

You would need to calculate how many amps you are drawing on each appliance to figure out what your daily draw is. Generally speaking I would say get the biggest pannels that you afford and will fit on your boat.

However, if you are living aboard in England, I would consider buying a wind generator first. I would think you would have more wind than sun on a daily basis.

Here on Yofy we have both and we currently live aboard in a very sunny part of the world. But when we have constant draw, our wind generator will pump up the batteries at night. And of course its great on cloudy days.

06-25-2013 06:20 AM
Re: How do I calculate my power needs?

Thank you everybody, away from Internet connection for a while, will check battery sizes and post back in soon...
06-24-2013 01:23 AM
Re: How do I calculate my power needs?

Download "Battery, Load and generator calculator" by Bill Roosa here: Sailboat Solar Panel News---Information

It will give you something to experiment with.

You can also check your battery voltages after a day and see how the % you have drained the batteries. That will give you another estimate.

Also see the Don Casey Library, "solar panels and calculating demand": Sailboat Solar Panel News---Information
06-24-2013 01:06 AM
chef2sail First do a power condumption diet in amp hours of your equipment daily. Then we can talk. Ie lights, reefer, computers, electronics, pumps, etc.
06-23-2013 04:48 PM
Re: How do I calculate my power needs?

I am watching this with interest as I too plan on spending a few weeks to months aboard (depending on the season) and will need to figure out how much solar I need to keep the batteries in topped up shape.
06-23-2013 04:08 PM
Re: How do I calculate my power needs?

Hi David,

I dont believe anyone can calculate what a boat needs.
I have read a thousand threads and... basically... they are all wrong. A boat will decide herself how much she is going to use. My boat would spit the dummy at the coffee maker! I have too much sugar in coffee so it will suck the battery dry.

A better idea is to tell us how big your boat is and haw many amp hours are your batteries.

Then we will pontificate and try to work out how much money you have and tell you to spend the LOT on as many solar pannels you can before being chucked in Debtors Jail.

When you have all the solar you can get then you will know if you can add useful things like a beer-maker-colder.

Hope this helps.

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