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Post Info TOPIC: Solar regulator
mezza56


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i'm looking to add port solar panels to our solar setup , we've got 3x80w panels on the van and looking to add 250 watts of port panels my calculations are 490w divided by 12 v giving a max output of 40amps . Would a 30a reg be ok or do I go to say 50a ? 



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PeterD


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First of all, there is a solar forum you should have posted your question in.

Solar panels are not rated at the manner you did your calculations. The output of a panel varies considerably depending upon the current you are drawing from them. The following diagram is for one individual cell but just multiply the voltages by the number cells in your panel and it shows how panels work

Solar Cell Curves.jpg

You will note that the cell voltage is around 0.6 V when you are drawing little or no current (the green line.) as the output current rises you will note that the voltage drops. Note the red line. That shows the output power of a panel (or cell) for different current outputs. You will note that the maximum power you can get from a cell (the top of the curve) occurs where the cell voltage is a little less than 0.5 V. Different panels vary a little. The peak power of a 36 cell panel (the ones we use for 12 V) occur in the range of 17 - 18 V. We generally use 17 V for our calculations. Divide your panel power by 17 and you will get an approximation of your panels capability.



-- Edited by PeterD on Wednesday 31st of October 2018 09:05:11 PM

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Peter_n_Margaret


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The theoretical output power is also calculated at a cell temperature of 25C and very bright conditions. They are usually much hotter than that in full sun, so actual performance will almost always be lower.
Yes, a good quality 30A regulator should be fine.
Cheers,
Peter

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OKA196, 4x4 'C' Class, DIY, self contained motorhome. 960W of solar, 400Ah of AGMs, 310L water, 280L fuel. https://www.oka4wd.com/forum/members-vehicles-public/569-oka196-xt-motorhome
 

 
mezza56


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Thxs PeterD so your saying that a 30A regulator will be ok for 490w of panels ?



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T1 Terry


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mezza56 wrote:

Thxs PeterD so your saying that a 30A regulator will be ok for 490w of panels ?

But will they back that advice with their wallets if you fry a set of batteries?

My advice, with a quality controller I'd look at 40 amps, an evil bay cheapie go 50 amps. I posted the reasons why on a thread in the solar section asking about controllers

 

T1 Terry



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denmonkey


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Forgoing the math, I'd go for the 40.
I'd figure out what I needed and then go one bigger when it comes to electrical. Except for fuses of course :)
That way you're covered for what you have and maybe a little extra latter on.
Panels are getting cheaper and lighter very quickly, so a bit up your sleeve won't hurt.

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