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post #1 of 14 Old 07-19-2012 Thread Starter
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Solar Conundrum

HOwdy folks,

I have two battery banks. One 48v 400ah bank for my electric motor. One 12v 270ah for the house bank. I want to get some solar panels, but don't fully get it. I have read and read stuff online, but still no definitive answers. So my question is, If I get panels sufficient to charge the big bank, is there some way to switch them to the smaller bank when the big one is full?


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post #2 of 14 Old 07-19-2012
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Re: Solar Conundrum

Do you need auto switching or will manual do.
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post #3 of 14 Old 07-19-2012
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Re: Solar Conundrum

You may need to play the series/parallel game here. It will take four 12V panels to do this. Use your panels in series (4 x 12 = 48) to charge your 48 Volt bank (slowly over time) and configure them in parallel to charge your 12V house battery (rather fast since you will have more current in parallel) This will require you to use 12 volt panels for the entire rig. This is one solution, that only requires 4 panels. My reasoning is most higher voltage panels able to charge 48V will cook your 12v battery if you use them as a direct source. There is bound to be a vendor that has some type of "Smart" switch for this application, but I'm sure its pricey. I'm curious, whats the 48V DC motor you are using? Is this drive something you are making/designing yourself?
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post #4 of 14 Old 07-27-2012 Thread Starter
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Re: Solar Conundrum

Hi TQA, auto would be great, but manual would be fine too. Bruce, the 12v idea is interesting. Trying to wrap my mind around switches to go back and forth between series and parallel. Oh, and I have the Electric Yacht 360ibl. I made an installation video, but it has ads in it but I don't think the moderators like that sort of thing. Private message me if you'd like to see it.


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post #5 of 14 Old 07-27-2012
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Re: Solar Conundrum

Providing the solar panel voltage exceeds the battery voltage ( which you can do by wiring enough panels in series a good MPPT regulator will charge both banks, but you will need to manually switch them over and it will be a bit messy.
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post #6 of 14 Old 07-27-2012
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Re: Solar Conundrum

I've pressed the shower sump after forgetting to open the thru hull and had to stuff a midget in there to change the fuse. I would not want to have that brain spasm, by not manually configuring this charging switch properly, when it comes to a grand worth of batts.

Be sure its simple and absolutely can't be done wrong.


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post #7 of 14 Old 07-27-2012
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Re: Solar Conundrum

I'm thinking one set of solar panels with a nominal 48 (60?) volt output, designed to charge the motor bank. Then, add TWO MPPT controllers, one set to charge the motor battery bank at 48V, the secondset to charge the house bank at 12V.

They should have no problem co-existing with each other except perhaps some fighting over different load conditions. That's something you would want to ask the maker (Blueskies, Morningstar, Genasun) about directly to confirm.

They may suggest putting a "dumber" controller like a plain PWM on the smaller bank, or some other way to prevent altercations, but in theory...one power source, one big solar array, two separate controllers and you should be just fine. And by using MPPT you're not throwing away any power when the '12" volt one has to reduce voltage.
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post #8 of 14 Old 07-27-2012
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Re: Solar Conundrum

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Originally Posted by hellosailor View Post
They may suggest putting a "dumber" controller like a plain PWM on the smaller bank, or some other way to prevent altercations
You cannot do this as the array needs to above the battery voltage. So the array will need to be around 60v if this is to work with 12v the controller must be MPPT.
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Re: Solar Conundrum

While I think it is unlikely he'd find a non-MPPT controller that can safely handle dropping a 60v panel to charge a 12-volt battery, it certainly isn't impossible.

Even a simple three-pin regulator can often handle a 30-volt drop from input to output, diasychain two of those, each with a bootstrap FET or other device to handle the power, and voila, yes, you can charge a 12v battery from a 60v source.

What's on the market? Damfino, someone in China is making and selling almost everything these days, which is why I'd still ask one of the MPPT companies what they have successfully used and recommend in that situation.

And if the answer needs a hundred bucks worth of custom regulator...That's OK, that's certainly possible too. The point being, there are options, the charging CAN be done automatically and safely. Just not conventionally with one device. (Although, I've seen some RV solar controllers designed with two regulators, two outputs, no idea what ratings.)
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post #10 of 14 Old 07-27-2012
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Re: Solar Conundrum

Even if you could find one you would only get 1/3 the power into the 12v that you should do.
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