Midnite Classic 150 limits

vibeline

My current system is:
6 240 watt schott panels
midnite classic 150
magnum PAE4024 inverter/ME-RTR control
600amp/hr forklift battery
I have a chance to buy 6 more of these panels for $1000
can I add them to my system without adding another charge controller?
the 6 I have now face south, the next 6 would face east.
Midnite sizing tool says 2611 max watts.
I cant afford another controller right now.
What are my options?
Thanks for the help folks.

vtmaps

Yes, you can add the panels.  It doesn't USUALLY hurt to be a bit overpaneled.  Since your additional panels will have a different orientation, the entire array will not be at maximum all at once.

There is one change I think you should make, however.  Change your array configuration to a string length of 2.  That will give you a string Vmp of 60 volts rather than the 90 volts you currently have.    The reason to lower the voltage is it makes the controller more efficient which means it can handle more power before it melts.  Realize that when you reach the power handling limits of the Classic, it limits its output to prevent itself from melting.  It is not a good to design a system where the controller spends most of its time on the verge of melting. 

Doubling the array AND lowering the string voltage will both have the effect of requiring a heavier cable between the combiner and controller.  I hope your array is not too far from the controller.

--vtMaps

westbranch

well you can run 3 strings of 3 = 9, or 5 strings of 2 = 10 but that is it!  Why are you running 3 in a string?  2 is more efficient in your case.

vibeline

vtmaps
 I have 6awg solid copper wire running from the combiner to the controller All inside the building, I believe it will handle the amps.
Thanks for the reply.
Cheers,
Jim

vibeline

westbranch
I'm running 3 strings of 3 because I didn't know any better.
I'm learning.
Thanks for the reply.
Cheers,
Jim

2twisty

I run 3 strings of 3 on my 48v system. On 24V, you definitely need to be on strings of 2.

inetdog

The fact that half of your panels will face south and half east will give you good charging over a longer period of time, but you will never get the sum of the absolute maximum power of both arrays. That will help keep you close to or below the maximum for your CC.

vtmaps

vibeline said:

vtmaps
 I have 6awg solid copper wire running from the combiner to the controller All inside the building, I believe it will handle the amps.

The issue isn't whether your cable can handle the 48 combined amps... the question is "how long is that cable?".  A 32 ft (one way) #6 cable will have a 2% voltage drop if you configure the 12 panels to a string length of 2.

--vtMaps

softdown

According to my calculations at pvwatts, a western orientation yields 15% more power than an easterly. I am doing both. Stretches the abilities of the charge controller and eases the load on the batteries since they spend more time charging and less time discharging.

Once you go well over ~2000 watts, 48 volt systems are the logical choice according to my readings. Something to keep in the back of the mind perhaps. Wires lose a lot less power at higher voltages. Perhaps I should refrain from certain suggestions...

travissand

If somebody who knows for sure would confirm my suspicions but I'm worried that the solar array facing the sun would be dragged down to the wattage of the array facing the shade.  

Estragon

Assuming the arrays are in parallel into the controller (not series strings split between arrays), I don't think the shaded array should be a big problem.

My different oriented panels aren't on the same controller though.  Maybe someone doing that (@softdown ?) will chime in.

Tecnodave

I’m doing quite the same thing as others are suggesting to you, my setup: I have several arrays on each of my controllers  for a total of about 2800 watts each Classic 150 and 1000 watts on each of my Midnite Kid controllers with different orientations, I have tried strings of 2 or 3 and I notice quite a bit more controller heating with the higher voltage, on both the Classics and the Midnite Kid controllers. That heating comes at the expense of efficiency and the higher heat is hard on the controllers. I’m using 72 cell polycrystalline Sharp panels on the Classics wired 2 on each string (72 volts) and 96 cell multi layer Panasonic/Sanyo HIT panels on the Kid controllers at the moment wired all parallel (53.5 volts) or 72 cell polycrystalline wires 2 on each string (72 volts).  Not both kinds mixed, that would not work out well. 

Every time I used the Sharp panels wired in strings of 3 (105 volts) or the Sanyo HIT panels in strings of 2 (113 volts) on my 24 volt system I logged much higher temperatures and had several over temp occurrences with the Kid controllers.  I do not have excessive power or heating using the lower string voltages.

I have used as much as 3200 watts of panels on the Classic 150 controllers and 1200 watts on the Kid controllers in my sometimes fowl winter weather, I’m only a few miles from the Pacific Ocean and have severe foggy/overcast weather in the winter months, I switch out extra panels for extended fair weather. 

BB.

If you have a circuit breaker for each "orientation", you could just turn off one array, let reading stabilize, then switch on the 2nd array and turn off the first... And compare the three readings (Both, A, B, and check A+B equal or not equal to Both?).

-Bill