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stmbtwle

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Reply with quote  #21 
It would be "safe" at most any distance, but resistance and losses would go up.  Larger is better.  There are charts out there to determine what size to use for a given distance, amperage, and acceptable loss.

Here's a voltage drop calculator that should work.  Though it's in AWG wire sizes there is a conversion to metric if that's what you need.

Generally you try to keep the voltage drop to a minimum. I try to keep it under 3%.  For some uses 10% is OK.  Bigger wire has less drop, but costs more.

http://www.calculator.net/voltage-drop-calculator.html?


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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay

Aussiemike

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Reply with quote  #22 
Willie I have a hypothetical question. Last for today I promise.[smile]

Is it theoretically possible to attach another completely different array of panels and separate MPPT controller to the same set of batteries?
stmbtwle

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Reply with quote  #23 
Promises, promises [biggrin]

Yes, my guess is it's done all the time.  I parallel an MPPT controller with an engine-driven alternator on my boat.  They "work it out", no switches required.  As the batteries near full charge, one or the other charging systems will shut off first.  Some controllers are designed to be "stacked" with another of the same make.

Another thing you might consider is a voltage converter to run your 12v loads from your 24v battery bank.  It MIGHT be simpler/cheaper than completely separate systems, depending on the load.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Aussiemike

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Reply with quote  #24 

I have already got the 24v to 12v converters on the system I am running at the moment.
Working well.
It's just that I have so many bits and pieces I can easily have a second independent system running.
My problems started when I tried to add to it and ended up with these grid tied panels that did not charge my 24v batteries.
Also I am the one who has been allocated the job of being the solar guru for another 10 cottages on our project so will have to make sure I know what I am talking about before I go ahead.
Thanks to you I am getting there.
7 pm here now so I am opening my bottle of red.
Cheers
Mike
stmbtwle

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Reply with quote  #25 
I have to wait another 5 hours, bummer... 😥

An MPPT controller should work well with your grid-tie panels.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Aussiemike

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Reply with quote  #26 

Morning Willie,

I really think I have the hang of this now.
This below is what I am left with to make a 12v system.
Would you be kind enough to cast your eyes over this diagram and tell me if indeed I have mastered the solar arts.
Cheers
Mike 
solar 12.jpg 


stmbtwle

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Reply with quote  #27 
The controller will only put out 40 amps, so that is your maximum charge. Though at charging voltage, 40a is more than your panels will provide anyway. A 50a breaker would be enough, I think.

12v requires bigger wire than 24v. Check your tables.

You could also configure the batteries for 24v and use those converters.

Otherwise, good.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Aussiemike

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Reply with quote  #28 
Thanks again Willie. The other controller I have is actually 60 Amp. Just forgot to write it in the diagram.
Will take your advice on the 50 Amp CB.
[cool]
Rick H Parker

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Reply with quote  #29 
Otherwise why spend money for the second panel?

With a second panel, one would have the capacity to transfer at a higher rate.

If your load is 100 watts and you have two 100W panels, your transfer rate is 100W not 200W.  The transfer rate is the same for one or two panels. On a tandem bike, the velocity of both riders is the same, that is the analogy.



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Rick H Parker
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stmbtwle

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Reply with quote  #30 
Note: there is some argument whether a fuse/breaker is even necessary between the panels and the controller, as solar panels are self-limiting. Even with a dead short, your 250w panel will output less than 10a, so the 15a breaker would never trip. Some places require it anyway, some don't. Your call.

On the back of the panels you'll find a data sticker. Among other info you'll find the following:

Watts xxx watts under ideal (test) conditions (not likely)
Vmp xx.xx voltage at maximum power
Imp xx.xx amps at maximum power
Voc xx.xx voltage with open circuit (maximum voltage)
Isc xx.xx amps with a short circuit (maximum current)

You'll find the last two mentioned in your controller specs, too, as input limits.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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