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Old 18-12-2009, 00:41   #1
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One MPPT Regulator or Two?

I have two 115W solar panels on my boat, one on each side. I am looking at getting a mppt regulator, the cheapest one I can find handles 25 amps which is plenty for both panels.

I am wondering if since the panels can face different directions and can be partially shaded differently, maybe I need two mppt regulators, but maybe not, just wire them in parallel and run at the peak power voltage for both of them My guess is that with a single regulator, I will get 90% of the benefits of mppt, and having two regulators would help a little, but cost much more.

Does anyone have comments or experience with this?
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Old 18-12-2009, 04:45   #2
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Just wire them in parallel and you are good to go. On the other hand, how many batteries are you powering? You may not need an MPPT controller. Is the 5-8% gain in charging ability worth the extra cost. Another panel or better aiming of the panels will result in a higher gain than that claimed by the MPPT control crowd. It is not ascertained exactly how much of the additional effeciency of the MPPT controller is fact and how much is hype. For my money, I would go for more panels and the least expensive controller.
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Old 18-12-2009, 17:59   #3
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MPPT Controllers DO work, and they DO provide significant increase in charging amps..

Quote:
Originally Posted by geckosenator View Post
Does anyone have comments or experience with this?
Yes.....

I've been using solar arrays in remote locales for almost 25 years, and on board boats on and off for almost 15 years....and on my current boat for 3+ years (with MPPT controllers....)
So, hopefully I can help....


1) MPPT controllers DO work.....
I've been using Blue SKy MPPT controllers on board now for 3 years, sailing across the Atlantic with them twice, and staying in some remote spots, etc. and they DO work.....and work well....

I've also retrofitted some Blue Sky MPPT controllers onto some of my remote radio (and TV) installations, and have been very happy with them.....they do make a difference.....

Please have a look at my photos and detailed article about my 520 watt solar array on board my 47' sloop...
Solar Panels

2) You will only need one MPPT controller, as long as it is properly sized for the power of your array......
Whether you decide on parallel (my preference for my application) or series connection.....you only need one....
(note that if you were to decide on series connection, be sure that the controller will handle the combined max voltage of the series-connected panels....)

Sunny Skies!

John
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Old 18-12-2009, 18:29   #4
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I agree that the MPPT controllers work like gang busters ( we got our controller from RV power products before they became Bluesky energy). Makai carries 480 watts (4 *120 Kyrocea's). The rated output is about 28 amps but we would consistently see 32-36 amps in the morning when the batteries were at there lowest.

Like most things you have to very careful with cheap quality. When cruising you are counting on reliabity and losing a cheap controller transiting or anchored out can ruin a great trip.

I would recommend getting the next larger controller if you are near the controller max. This will give you room to expand or upgrade easily in the future, ie adding more panels or higher watt panels, without having to replace everything.

Sun power!
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Old 18-12-2009, 20:39   #5
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Quote:
Originally Posted by geckosenator View Post
I have two 115W solar panels on my boat, one on each side. I am looking at getting a mppt regulator, the cheapest one I can find handles 25 amps which is plenty for both panels.

I am wondering if since the panels can face different directions and can be partially shaded differently, maybe I need two mppt regulators, but maybe not, just wire them in parallel and run at the peak power voltage for both of them My guess is that with a single regulator, I will get 90% of the benefits of mppt, and having two regulators would help a little, but cost much more.

Does anyone have comments or experience with this?
I think you will be better off with one controller. While you can use multiple controllers, one will trip into the next stage before the other. There are controllers that talk to each other to allow them to work together more efficiently.

Previous discussion:
Multiple Charging Sources to the Same Battery Bank

John
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Old 18-12-2009, 20:40   #6
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Quote:
Originally Posted by sv_makai View Post
I agree that the MPPT controllers work like gang busters ( we got our controller from RV power products before they became Bluesky energy). Makai carries 480 watts (4 *120 Kyrocea's). The rated output is about 28 amps but we would consistently see 32-36 amps in the morning when the batteries were at there lowest.

Like most things you have to very careful with cheap quality. When cruising you are counting on reliabity and losing a cheap controller transiting or anchored out can ruin a great trip.

I would recommend getting the next larger controller if you are near the controller max. This will give you room to expand or upgrade easily in the future, ie adding more panels or higher watt panels, without having to replace everything.

Sun power!
I have 430 watts of solar from four Kyocera solar panels and typically get 28 amps. (per Link 20) with a Xantrex C-35 charge controller set at a constant 14.2 volts. It is a matter of math. Open voltage is 17 volts at 7.1 amps yielding the 120 watts. Any change in the operating voltage of the controller will vary the amperage.
The placement of your solar panels to prevent shading under all conditions is paramount. While this is not possible on a sailboat (mast, rigging, radar, etc.) it makes a good case for having more than one panel in various places to minimize the shading, a problem that no controller will solve.
As for cost of the controller, most controllers found in the marketplace that can handle the amperage will fill the bill. Should the controller fail, you can connect the solar panels directly to the battery and keep an eye on them so they don't overcharge as is done with most wind generators. Also, should you need to bypass the controller, they will need to be disconnected at night to eliminate battery discharge through the solar panels.
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