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Old 09-02-2018, 22:03   #1
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Join Date: Jul 2013
Posts: 2
Solar Controllers MPPT 24v - 12v Panels?

Hello Solar Friends,

I have been searching forums and trying to do my due diligence researching but I feel I am stuck.

The main goal is to charge the battery bank with as much power as I can get in, in a day. I own a Lagoon 410 with enough room for about 4 large solar panels. Under passage I will probably use about 400-500 amp hrs per day, at anchor I will use around 250 amp hrs per day. My battery bank is 8, 6volt deep cycle golf cart batteries hooked up in series and parallel to make a 12v system. Thus I have the capacity for about 900 amp hrs and that means I have about 400-450 working amp hours.

I already have an old 12v solar set up on the boat but it is old and I need some more power so I think I am just going to upgrade everything.

My questions?

A. With the new MPPT controllers I understand is can step down the power from the big 24v solar panels to a 12 v battery bank. So when it does this does it actually double the AMPS? (Example for 270w 24V panels?)

270w/24v = 11.25 amps
MPPT 270w/12v = 22.5 amps

270wX4panals = 1080w
1080w/24v = 45amps
MPPT 1080w/12v = 90amps

If so….That is good.

Panal Specifications:
Size: 1640 x 992 x 40mm
Weight: 18kg
Max System Voltage: 1000V
Max Power: 270W
Short Circuit Current: 9.30A
Open Circuit Voltage: 39.0V
Rated Current: 8.57A
Rated Voltage: 31.5V

So I guess the MPPT controller will get 31.5V hitting it turning the power into 12v in sense over doubling the amperage thats on the spec?

B. Does the Mono crystalline vs Poly crystalline debate really matter anymore? I am planning on going Mono right now.
- There may be be a little shade every now from the sail or mast… which would be better do you think?

Also should I buy 2 40amp MPPT controllers and do 2 panels to each one of them do you think?

Thanks for all the help.

Gregory Evans
www.Oceannatheboat.com
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