Over voltage & amps

billybob9billybob9 Registered Users Posts: 141 ✭✭
My solar array is 2 strings of 8 panels ( 8x300w ) . So 2 strings 2400w ea. VOC per string is 300VDC or 600VDC per system. This is Max for the SMA Rapid Shut Down box. I thought with a DC drop in wiring ( 60' ) I would never reach that point. I was wrong and the RS box now shuts off ( high noon ) one string ( B ) when this happens. To re-boot the RS the system will turn off at night and have both A & B channels on in the morning. So like Tony I need to drop a little DC (from my array). Adding 50' more of PV line might do it but since I have two 160W panels, I might replace the 2 panels (300W) on the end of each string with the 160W panels. This is mixing panels but since this is a series system I thought I might get some advice PRO or CON. The Building Permit will need to be changed and they might not like it ( or not ).


  • EstragonEstragon Registered Users Posts: 4,424 ✭✭✭✭✭
    So this is essentially a single string of 16 panels? 

    I'm a bit surprised it's happening just at noon.  I would have thought early morning when panels are cooler would be more prone to high voltage events.  Anyway, assuming you're in the northern hemisphere, it may get worse as winter approaches. 

    Can you split it into 2 strings for ~300v and 2x the amps?  60' of wire to a parallel connection?
    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
  • billybob9billybob9 Registered Users Posts: 141 ✭✭
    The array is facing south so your right it might have been earlier then noon but I didn't catch it till then. This is 2 strings going into the SMA RS with the same voltage of 300V each max. From the RS to the SMA 5.0 Inverter is 2 strings of 300W max that  is compatible with this Inverter ( so they say ). The users manual did not mention Amperage at all for the Installation but I found INFO on line that MAX AMPS was 18 for the RS.   Many people now are dealing with this same problem of no more 250W panels for sale and going for the 300W. Thanks    
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    What does SMA say?  Does that SMA have 2 or even three MPPT inputs?  In that case, you could spit the array into 2, 2.3 kw strings.  My most recent grid tie system is 6.2 kw, feeding two strings each into a different MPPT L1/L2, and is very happy.  On a good day I see a peak of ~4900 watts, with not perfect orientation.  SMA 5.0 US inverter, also TIGO optimizers on each panel.

  • billybob9billybob9 Registered Users Posts: 141 ✭✭
    I've called SMA to find the cause of no green light on RS controller and other Issues but they don't even want to admit that the RS box is just 2 Relays that can be bought for $13 ea. Yes, there is the 3 MPPT inputs on the Inverter but the RS box only has 2 outlets. It wouldn't do me any good anyway as the SMA Inverter adds up all voltage then divides it in half to send out to L1 and L2 on the breaker box. The SMA TIGO ( thanks ) might be a way out of this as it says it limits the voltage to 600V. So if I put one TIGO Optimizer on each string that might work. If all panels needed to be optimized to obtain the 600V limitation this would defeat the purpose as I have no shading issues.
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