Over paneling the FM80

ApicaApica Registered Users Posts: 22 ✭✭
What are your thoughts? 

I am currently using a 24V off grid setup that consists of 6 260 Watt Panels connected in 2 strings of 3 panels wired to a combiner box. Under perfect conditions which may never happen that would produce 1560 Watts. The FM80 manual states that the 24V system should not exceed 2000 PV Watts.

I now require more pv wattage now that the sun hours are less at this time of year. I purchased 2 270W panels to add to my setup because the 260W panels are not available However a CC Stats check revealed that my FM80 has seen a Max Wattage of 2048W. I have never used this CC on any other system how is this possible?

Based on these findings should I risk adding the extra panels?

3000W Powerstar LW Inverter . 6 x 260W Intenergy Panels .  Flexmax 80A . 2 x 255W Intenergy Panels . 1 x 270W IntenergyPanel . Flexmax 60A  . 8 Trace 6V 255AH  Batteries Wired Series/Parallel for 24V . Trimetric . Midnite E-Panel. Tycon Tpdin Remote Monitor.


  • icarusicarus Solar Expert Posts: 5,355 ✭✭✭✭
    edited November 8 #2
    Most CC will simply “clip” excess production to protect the CC from over current.  That said, if you are running up against the limit quite frequently, instead of “throwing away power” via clipping, consider a larger controller, or a pair of controllers.  The 2000 watt PV limit is a matter of exceeding the 80’s 80 amp design limit.  Consider this...1560 watts of PV plus the extras is 2100 watts.  At 80% nets out to be ~1680 watts, into 27 vdc that would be ~62 amps. Into 24 vdc that would be ~70 amps.  I’m guessing the 2048 peak wattage was short lived edge of cloud event, should have produce just under ~76 amps at 27vdc. 

    My opinion, and it is worth every penny you pay for it...unless you have consistently very low battery voltages and or very cold temps coupled with lots of reflection off of snow, I would think the CC would be fine.  That said, I wouldn’t argue with outbacks documentation, but I will say there is a lot of conversation about this issue on the OB forum:  


    I’ll let other opine.  

  • jonrjonr Solar Expert Posts: 1,331 ✭✭✭✭
    I believe the FM80 specs say "NEC Recommended Solar Maximum Array STC Nameplate".    I would follow the specs.

    I am available for custom hardware/firmware development

  • Dave AngeliniDave Angelini Solar Expert Posts: 4,842 ✭✭✭✭✭
    Pretty common since the days of solar began to overpanel. Usually 20 percent or so. We did this in 1978 at HP. 
     As long as you are not in a metal shed in the desert. Even if you were, if it is offgrid, current limiting probably will not happen more than once a day for a short time.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • VicVic Solar Expert Posts: 2,976 ✭✭✭✭
    Personally would follow OB's recommendation.   (as jonr mentioned).

    It appears that the FM80 & FM60 have a relatively slow-acting  output Current Limit (partially based on these CCs having a maximum input Isc Limit).   For the FM80,  the maximum total Isc input Limit is 64 A,  which would be difficult to exceed with PV strings of 3.

    Have never run any OB FM series CCs,   but it seems that OB should know best about their product  application specs.

    All IMO,   FWIW,  etc,    Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • MakersMakers Registered Users Posts: 15 ✭✭
    how do you plan to add, the panels in your system, (strings panels?)

  • wellbuiltwellbuilt Solar Expert Posts: 416 ✭✭✭
    I think you would be fine you would only be over a little bit . 
    Im sure you are not seeing 2000 watts in day to day use , I’m  a bit over 4000 watts @ 4425 
     on my 48 volt system and it’s working fine
     I use 12 panels most of the year . 
     If I need extra power I turn on my 5th string .
     I have a small fan blowing on the cc and inverter it keep things cool 
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
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