Author Topic: Adding panels to an existing Midnight Classic 200  (Read 393 times)

0 Members and 1 Guest are viewing this topic.

Gearnut

  • Newbie
  • *
  • Posts: 2
  • Country: us
Adding panels to an existing Midnight Classic 200
« on: September 29, 2017, 07:37:14 PM »
Hello

Off grid system.  SE Michigan.

Currently I have 2 solar arrays consisting of (15) 320 watt panels facing west, and (12) 320 watt panels facing south. Each array
feeds into it's own Midnight Classic 200.  So I have (2) Midnight Classic 200s charging 1 large lithium battery.

However, as we all know, there are days when you have severe overcast and sometimes I must run my DC generator to help out the system.

My average consumption is 18 Kwh's per day

Taking one of those days as an example, looking at my Midnight Classic display(s), I can see where I've only produced say, 10 Kwh's (total). I must make the other 8 Kwh's with the generator.

When we have just light sky (not even any sun), I'm good.  My 10K of solar will keep up, and if we have actual "sun", the battery is charged to 100% in a matter of perhaps 2 hours.

So here's my thought, and ultimately my question. 

I've purchased another (24) panels with the idea of extending the 2 existing arrays, by 12 panels each, and I initially figured I'd also have to double up on the wiring to bring that extra power to the shack.  But then I got thinking, if the Midnight Classic limits the output current, perhaps I don't need to add anything- no duplication of wiring, no additional Midnight Classics   

What I'm thinking is : in a good sun day, wouldn't the Classic just limit the extra available current that it has at it's disposal from the extra panels ?
And likewise, in a bad sun day, the extra panels will just add to the available current that feeds the Classic  ?   (exactly what I want)

Now I realize, if I were to run a dedicated set of wires from the 12 new panels at each array, and buy 2 more Midnight Classics, I could charge my battery in half the time in good
sun---- but I don't need all that power in good sun.   I don't even need all the power in cloudy weather.    I only need that power when it's heavy overcast.   --- thus
my idea of over feeding the existing Midnight Classics 

Does this make sense ? 

What are your thoughts.

Thanks

Mark
« Last Edit: September 29, 2017, 08:03:16 PM by Gearnut »

DamonHD

  • Administrator
  • SuperHero Member
  • *****
  • Posts: 3646
  • Country: gb
    • Earth Notes
Re: Adding panels to an existing Midnight Classic 200
« Reply #1 on: September 30, 2017, 01:42:01 AM »
Some controllers will limit the current, and some will not so would let out the magic smoke.  I am deliberately using my Morningstar SS-MPPT-15L as a limiter for my small off-grid system, with >500W of panels with a reasonable size bank and a tiny average load.

The Morningstar docs are clear that you can provide whatever size of input array you like providing you don't exceed specified input voltage.

There are plenty of controllers out there for which you must not exceed a certain available input power.

For yours, I don't know.  It may be time to read the manual carefully.

Rgds

Damon

joestue

  • Hero Member
  • *****
  • Posts: 1419
Re: Adding panels to an existing Midnight Classic 200
« Reply #2 on: September 30, 2017, 02:14:10 AM »
as long as you don't exceed the input voltage maximum it should not matter. its a buck converter as far as i know.

as long as you don't shove more than 200 volts into it it will suck up whatever power is available and push it into the batteries, but will limit its output current to 79 amps.

Gearnut

  • Newbie
  • *
  • Posts: 2
  • Country: us
Re: Adding panels to an existing Midnight Classic 200
« Reply #3 on: September 30, 2017, 09:10:41 AM »
Thanks guys !

.... yes Damon, I see it now. It's right in the manual, near the bottom in the FAQ area. 

Someone asked:  How many amps can my Classic handle on the input side? OR Can I put too much PV on my Classic?

Answer : *The Classic regulates very well so within reason there is no limit on the input amps or PV wattage. We recommend you not exceed 150% of the capacity. The Classic, just like a grid tie inverter, can be over driven on the pv side it simply produces the max amount it is rated for.

I'll explain why I didn't go looking harder in the manual in the first place. 
Midnight offers a 'sizing tool'.  When I plug my criteria into the sizing tool, meaning, (15) 320 watt panels, 9 ISC, etc, etc,  (3) in series, (5) parallel  it shows  Array Power (Wattage) "EXCESSIVE"
by a factor of 1.2

http://www.midnitesolar.com/sizingTool/index.php

I used this sizing tool back when I was designing the system, and had it stuck in my head that I was at the limit of the charge controller.     

.... but now the fog has been lifted !

And thanks to joestue for the explaination of the buck converter-  makes total sense.

Mark