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Go Back   SailNet Community > On Board > Gear & Maintenance > Solar Conundrum
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Thread: Solar Conundrum Reply to Thread
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Topic Review (Newest First)
07-28-2012 03:34 AM
noelex77
Re: Solar Conundrum

Quote:
Originally Posted by rackham the red View Post
As an engineer, I believe that the only good design is the simplest solution. I think California Switchgear and Solar, a small solar engineering company might be able to give you a fool proof "box" that will do what you want with the series and parallel configuration of panels. Remember to ask for redundancy. The last time I worked with them their number was 707-688-3643. If you have not already purchased your panels, you could do this with configuration switches to eliminate some panels from your 12V charging.

Good Luck
Rather than change the panel configuration. A DPDT switch could be wired to switch between 2 MPPT regulators one charging 48v the other 12v.
07-28-2012 01:05 AM
rackham the red
Re: Solar Conundrum

As an engineer, I believe that the only good design is the simplest solution. I think California Switchgear and Solar, a small solar engineering company might be able to give you a fool proof "box" that will do what you want with the series and parallel configuration of panels. Remember to ask for redundancy. The last time I worked with them their number was 707-688-3643. If you have not already purchased your panels, you could do this with configuration switches to eliminate some panels from your 12V charging.

Good Luck
07-27-2012 12:51 PM
hellosailor
Re: Solar Conundrum

Ah, now you want efficiency as well.

That wasn't part of the original request. Again it comesback to asking the makers how their equipment will behave. If twin MPPTs won't have an issue with load adjustment, efficiency becomes a matter of price. Might be an issue, but wasn't presented as a concern here.

If the makers say "that" equipment is the only way to go, again, efficicency isn't an issue.

Is it something to consider? Sure. But the primary question is, what can do the job? At all, at any price, under any conditions?

Then the choice of solutions (as opposed to "there's no way to do that") can be weighed.

"The ideal way would be to a little box of electronics that would drop the 50v down to say 14v "
Wait, didn't I already say a couple of simple regulators with bootstraps CAN do that? And easily be built if not available on the shelf? Of course today, you could use a DC-to-DC converter to make that more efficient, there's all sorts of IC controllers to do that on the shelf.

Easiest solution is rather obviously to add a second "12" volt panel array, but that also wasn't part of the original question. I'm sure the OP had reasons not to ask it.
07-27-2012 12:50 PM
noelex77
Re: Solar Conundrum

The ideal way would be to a little box of electronics that would drop the 50v down to say 14v this simple battery "charger" could be triggered by most of the solar regulators to engage automatically when the 48v battery bank reached float.
Something like this is not difficult to make, but there are no commercial units available.

Sterling make a 24v to 12v "battery charger" and they may be able to modify this to accept the 48v input.
07-27-2012 12:41 PM
noelex77
Re: Solar Conundrum

Even if you could find one you would only get 1/3 the power into the 12v that you should do.
07-27-2012 12:30 PM
hellosailor
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.)
07-27-2012 12:21 PM
noelex77
Re: Solar Conundrum

Quote:
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.
07-27-2012 11:51 AM
hellosailor
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.
07-27-2012 08:52 AM
Minnewaska
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.
07-27-2012 08:42 AM
noelex77
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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