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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance > Electronics
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Old 09-12-2010
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Solar power for my MacBook

Hey guys!

I have a 13" MacBook, and I'd like to be able to power it on my boat with solar. I have a 22' Catalina. It currently has 20w of solar, and has two group 24 batteries (I don't know the amphours off the top of my head.) I know this isn't really enough.

Also, I guess it'd need to be enough to actually charge the battery a little too, not just run it. I'm aware of several different options, but I really don't know enough about them to even start researching them.

I'm aware of some power inverter that has a battery built in, so that you could charge the inverter and then provide energy to the MacBook for a few hours. Or perhaps just having enough solar input into the system so that I could charge the MacBook through an inverter. Or at least run the MacBook without losing charge when we have sun?

What do you think?

Googling, I found these:

Apple Juicz solar power for MacBook Air - $700 for a 27w panel (ha!)

And this:

Will Blog for Experience: Patrick: Portable Solar Power for $180

Thank you for any information!
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Additional thought

I haven't researched this but it seems if you can use a dc power adapter, it would be more efficient than an inverter to run an ac adapter. They use them for auto or airplane use.
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Mdbee is right- an inverter will waste tons of power from your battery bank. You can use the macbook in your C22 with the "airline power adapter" which will plug right into the 12v/cigarette lighter plug in your boat. This adapter doesn't charge the macbook- but will run it. Other companies do make charging adapters but usually require a "core" power adapter to cut the connector from.

Where did you mount your solar panels on the C22, and what sort of charge controller are you using? I haven't been able to find a good solution for mine.
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Quote:
Originally Posted by mdbee View Post
I haven't researched this but it seems if you can use a dc power adapter, it would be more efficient than an inverter to run an ac adapter. They use them for auto or airplane use.
Thank you for that idea. For some reason, I believed that they did not exist.

I found this one on Amazon:

Amazon.com: Car Charger Dc Laptop Adapter Power Cord for Apple Mac: Electronics

Now, it says it supplies 85w. That's 4 times what my solar array can provide. So this will still draw a bit from the batteries. Does anyone know how long 2 group 24 batteries would last? I want to say they are both around 100 a/hr.

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The 85W figure is probably for running the computer while it charges. Running it without charging the internal battery could be about half that, 45 watts, and running with the screen dimmed while below, and no spindles turning, maybe more like 35-30 watts average. You'd have to do your own testing.

A brand new group24 battery is unlikely to exceed 80AH and you don't want to cycle them more than 50% in normal use, so with two of them, you have about 80AH of energy to play with. Without knowing what voltage the power supply is rated at...35 watts at 12 volts would be about 3 amps load, if you ran the computer for eight hours that's 24AH compared to the total of 80AH you have available in one battery charge on the boat. Again, you'll have to make your own estimates for the power you need and what other loads you'll have.

A 40-watt $200 solar panel might be the ticket, to put enough energy into the boat's batteries every day in order to substantially feed the computer.
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I'm also looking into this- I use my 13.3" Macbook as a digital chart plotter/viewer on my Catalina 22.

There's just no practical way to fit enough solar panels on a C22 to use a macbook very often. You'll just need a lot of battery capacity, and a 110v charger, generator, alternator outboard, etc.

You get a lot less than the rated battery capacity with high drain rates, plus you should never really let lead acid batteries drain below 50%. If you're drawing 85 watts, that's about 7 amps from a 12v battery.

A group 24 is probably about 70ah, so it should run your macbook for about 5 hours down to 50% charge if it really draws 85 watts (I'd bet it's really about half that).

I think it would be cheaper/easier actually to just get a few batteries for the macbook, charge them at shore, and swap them out, if it's an older model with a replaceable battery.
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I haven't researched this but I wonder if it's more practical to use a GPS chartplotter than a computer for navigation. The fact it's made for a marine environment and it's power use. What advantage is there in using a computer base solution?
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Solar

This is one that I built to hang on my rear rail:



Here is a link:
Solar panel


I also added a controller in the end, as explained in the thread.

Quote:
Originally Posted by casioqv View Post
Mdbee is right- an inverter will waste tons of power from your battery bank. You can use the macbook in your C22 with the "airline power adapter" which will plug right into the 12v/cigarette lighter plug in your boat. This adapter doesn't charge the macbook- but will run it. Other companies do make charging adapters but usually require a "core" power adapter to cut the connector from.

Where did you mount your solar panels on the C22, and what sort of charge controller are you using? I haven't been able to find a good solution for mine.
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Quote:
Originally Posted by mdbee View Post
I haven't researched this but I wonder if it's more practical to use a GPS chartplotter than a computer for navigation. The fact it's made for a marine environment and it's power use. What advantage is there in using a computer base solution?
Well, an old $100 laptop with free plotting software, a USB GPS, and free NOAA charts offers the functionality of large super-expensive GPS chartplotters.

GPSs in this price range have tiny (2") screens, and no nautical chart functionality. I use a small cheap GPS with paper charts usually, but it's nice to sometimes plug that into the laptop to get a more detailed view and position or to plan a route.
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Quote:
Originally Posted by casioqv View Post
Mdbee is right- an inverter will waste tons of power from your battery bank. You can use the macbook in your C22 with the "airline power adapter" which will plug right into the 12v/cigarette lighter plug in your boat. This adapter doesn't charge the macbook- but will run it. Other companies do make charging adapters but usually require a "core" power adapter to cut the connector from.

Where did you mount your solar panels on the C22, and what sort of charge controller are you using? I haven't been able to find a good solution for mine.
I put a 5w solar panel on my front hatch, and I have a 15w panel that I keep on the cockpit seats. When I'm sailing that panel gets moved into the cabin. They are both the type of panel with a black plastic frame. I do not know which charger I'm using. It's not a MPPT (or whatever) - its the one that West Marine sells that can handle up to 80w.

I inherited both of those panels with the boat. Both of their glasses are cracked, but they are keeping my batteries full so that's good. I wish I had some type of gauge to let me know how much I am getting from them.

Honestly, for my C22, what I'm considering is getting a 40w panel that has a metal frame and can be mounted on my stern rails, probably on the port side as I have my dock on the starboard side. But then again I want a BBQ pit, but it sure seems to quickly fill up the rear of the yacht!
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