Troubshooting Combinerbox MNPV6

offgridcabin2015 Registered Users Posts: 88 ✭✭
Merry Christmas to all my solar EXPERTS.

I"m looking to get your expertise on the below.

I have a MIDNITE PV6 with 5 150dc breakers
Panels are installed in series to not exceed 150vdc.

My question is inside the box when i use a volt metre on dc to read the volts coming in. 

For ei i have one breaker that reads 63volts . which is the same reading i get on the outback flexmax 80.

i'm trying to understand if i take the reading of breaker 1 + breaker 2 and so on . is this correct . so i'd should be getting 60v x 4 so 240v at charge conroller? is this correct? 

Because that not what im getting. i'm getting 1x 60v. does this makes sense? 


  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    You have to turn the breakers OFF, and then measure the PV panels alone.

    With the breakers  ON, you are measuring the MPPT voltage the controller pulls the panels down to, to produce the best power.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    Some questions...

    What MPPT solar charge controller do you have? A 140-150 VDC max Vpanel input would use an array of Vmp-array~100-110 VDC in a cold (typically well below freezing) to not exceed Vpanel max of the controller.

    Your solar panels... What are their Vmp and Imp?

    How are they wired (how many in series and how many parallel strings)?

    Do you have an AC+DC Current Clamp DMM? It makes debugging much easier... (cheap $50 "Good enough" for simple debugging)

     For example, if you have 4x parallel strings--The parallel strings of "matched" panels should be very similar. If A,B,D have the same current, and C is much less--That is probably the string that has wiring/connections/panel issues.

    Of course, the overall max current at any time depends on angle of sun/weather/and the battery state of charge and controller mode (Bulk, Absorb, Float, etc.).

    Typically, you have one Breaker per series string... And since a "working breaker" is "closed" (short between input and output)... Taking a volt meter to the negative bus (black meter lead), and measuring each breaker terminal (from solar array 'input', to 'output' (positive bus bar to MPPT Vpanel input)... Voltage wise, all connections should measure equal voltage since they are all "tied together".

    If you open the breakers, the input to the breaker should be Vmp-string (roughly +/- 10-20% of Vmp-string-STD) on the 'input' from the string... the breaker outputs should all be the same voltage as the +Vpanel Bus).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,046 ✭✭✭✭✭
    The combiner box is paralleling the 4 strings. In parallel the voltage doesn't change, the current does. You will get the sum of the current of all strings and the average of the 60 = volts of the 4 strings.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.