How do I calculate my power needs? - Page 2 - SailNet Community
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post #11 of 14 Old 06-25-2013
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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 pbase.com 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.
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post #12 of 14 Old 06-25-2013
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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 ...

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post #13 of 14 Old 06-25-2013
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Re: How do I calculate my power needs?

Quote:
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.
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post #14 of 14 Old 10-20-2013
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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)

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