Midnite Classic 150 limits

vibelinevibeline Registered Users Posts: 24 ✭✭
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.


  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    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.


    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    edited October 2015 #3
    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.
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • vibelinevibeline Registered Users Posts: 24 ✭✭
     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.
  • vibelinevibeline Registered Users Posts: 24 ✭✭
    I'm running 3 strings of 3 because I didn't know any better.
    I'm learning.
    Thanks for the reply.
  • 2twisty2twisty Solar Expert Posts: 199 ✭✭✭
    I run 3 strings of 3 on my 48v system. On 24V, you definitely need to be on strings of 2.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    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.
    SMA SB 3000, old BP panels.
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    vibeline said:
     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.


    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • softdownsoftdown Solar Expert Posts: 3,673 ✭✭✭✭
    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...
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • travissandtravissand Registered Users Posts: 5 ✭✭
    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.  
  • EstragonEstragon Registered Users Posts: 4,496 ✭✭✭✭✭
    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.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • TecnodaveTecnodave Registered Users Posts: 437 ✭✭✭✭
    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. 
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Exeltech XP-1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or LiFePO4,
  • BB.BB. Super Moderators, Administrators Posts: 33,002 admin
    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?).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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