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Solar question, existing setup...


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#11 Ladyhawk

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Posted 24 April 2019 - 12:24 PM

KM, lets get it right!

 

AMPs are current flow. Amp Hours are capacity. There is a huge difference in a panel that can give 4-5 amps, and one that can give 4-5 amp hours per 24 hours.....

 

And, your 0.2a draw as above is 4.8 amp hours per day actual draw. There are losses and inefficiencies in charging, you'd really want 5.5-6 amp hours per day out of the panel to keep up with this.  Allowing for crap weather, but still getting this charge, I'd use a panel of around 30w to be certain. That's 30w/13.6v = 2.2 amps x 3 hours useful charge in winter = 6.6 Ah. Thats guessing available sunlight, and using 13.6v as the float voltage for the batts...

and if its for a lithium battery, floating isn't needed, Charge to full and stop.  Cycle the bank down to 80% DOD and recharge only when you have an opportunity or need. If your system is set up well, repeat 2000 +/- times….

But I fear were getting off topic... :roll:


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#12 Knot Me... maybe

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Posted 25 April 2019 - 08:59 AM

but I'm told the maximum output voltage of a new panel must be the same as existing.

Asked a semi guru last evening and he said 'close enough' is fine. With voltages wondering all over the show as they constantly do with solar, a volt or 2 here or there is not a worry.
 


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#13 wheels

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Posted 26 April 2019 - 12:57 PM

It's important to have similar panel voltages. Like 12V to 12V and 24V to 24V. But the differences in Voltage to age of panel is not important. Current output of the panel does not matter. You can have a 10W panel and 200W panel connected together if you wanted. Just as long are both have the same Voltage rating.


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#14 Crazyhorse

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Posted 27 April 2019 - 07:29 AM

It's important to have similar panel voltages. Like 12V to 12V and 24V to 24V. But the differences in Voltage to age of panel is not important. Current output of the panel does not matter. You can have a 10W panel and 200W panel connected together if you wanted. Just as long are both have the same Voltage rating.


Why? The SP regulator simply takes the parallel voltages and combines them? So you are saying if one panel is shaded producing 14v and one is in the sun outputting 21v this is going to cause...what?
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#15 wheels

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Posted 28 April 2019 - 06:47 AM

 

Why? The SP regulator simply takes the parallel voltages and combines them? So you are saying if one panel is shaded producing 14v and one is in the sun outputting 21v this is going to cause...what?

Depends on how they are connected, ie Series or parallel.
In series, the voltage is going to drop to that of the lowest panel. Series is great on a House where there is clear unobstructed view of the Sun and all panels are getting the same light and producing the same output. The Voltage is high and thus a longer length of wire and/or smaller diameter can be used with less loss.
On a boat, because a shadow can fall across a panel, Series is not always the best method. In series, the voltage will drop to that of the lowest outputting panel only when it is shaded. If you have a 24V panel and a 12V panel in series, you will get 36V output
I parallel connection, it does not matter what happens to one or more panels as far as shadows are concerned.The Voltage will also be that of the highest outputting panel. However, if you have a 24V and a 12V panel connected in parallel, the 12V panel will be adding nothing to the batteries. Simply because the 24V panel will be doing all the work.

It is not the reg that combines the panels by the way. The combining is the actual way you connect them. Series is basically daisy chaining. You increase Voltage, but current always stays the same. Parallel always keeps the Voltage the same, but increases the Current. The Power of the panels is the Sum of the Voltage and Current.


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