Forum Discussion

nvreloader's avatar
nvreloader
Explorer
Dec 07, 2016

Problem with the TH solar project

Guys
I have encountered a couple of problems with my solar project.
I am not sure just how to correct/fix or make it work yet.

Problem:
I will have 4-230W PV panels on the roof,
I will have them wired in parallel/series connections,
the spec's of these panels are,

Canadian Solar CS6P-230P Silver Frame
STC Power Rating 230W
Number of Cells 60
Voc 36.8V
Imp 7.78A
Vmp 29.6V
Isc 8.34A
NOCT 45°C
Series Fuse Rating 15A
Maximum System Voltage 600Vistics
Type Polycrystalline Silicon
Output Terminal Type MC connector Type 4
Output Cable Wire Gauge 12 AWG, 2 ft long,
Length 64.5in
Width 38.7in
Depth 1.6in
Weight 44.1lb

It is recommended to use a combiner box,
to reduce the number of pv wires to 2 wires going down to the CC,
pv wire lengths from pv panels to the combiner box is 10-12' each and then 10 to 12' to the CC.

These pv wires will run thru the reefer vent straight down to the equipment bay 10-12' below.

I want a way to disconnect the pv panels, (for any maintenance that may be required) via a fuse or CB etc.

Here lies the problem,

The electrical bay,(22"x 22"x 16") will hold all the solar stuff, CC, possible inverter, major fuses/CB, quick emergency shut off of all the solar stuff/battery bay etc.

This access door, (limited room to work thru etc) is 12" W x 6" high and is located about 12" above the floor level.

I will have all the above equipment mounted to a 3/4" board,
(size unknown yet), prewired etc, for ease of mounting and for vertical attachment to the wall etc.

Is there a way for disconnecting the pv panels at this main equipment board and still have the minimum 1-3% wire loss at the CC, without the combiner box on the roof?

Any suggestions/ideas would be greatly appreciated.

Tia,
Don
  • time2roll's avatar
    time2roll
    Nomad
    Dec 07, 2016
    Just get parallel MC4 connectors and skip the combiner box.

    Connect with #8 MC4 wire to minimize losses. Calculation is at 60 volts not 12.

    You can add a DC breaker or switch to the board for maintenance. It will never trip from overload. Could put the switch in the fridge service area if space is tight on the board.
  • MrWizard's avatar
    MrWizard
    Moderator
    Dec 07, 2016
    he stated series parallel
    he did not name the controller or input voltage limits

    but (4) 36v panels in series would 144v
    this is lethal voltage and probability higher than the controller limits

    he can series (2) panels, then parallel the (2) pairs
    IDK why he wants to eliminate the combiner box, he only needs to drop one pair of wires down the vent to the controller
    with out the box, he may have to drop (2) pairs aka (4) wires down the vent
    depending on connectors available
    put the DC circuit breaker between the panel wires and the CC "where you can reach it"
  • 2oldman's avatar
    2oldman
    Explorer II
    Dec 07, 2016
    MrWizard wrote:
    but (4) 36v panels in series would 144v
    this is lethal voltage and probability higher than the controller limits
    lethal to what? 120vac isn't too safe either.
  • grizzzman's avatar
    grizzzman
    Explorer
    Dec 07, 2016
    2oldman wrote:
    MrWizard wrote:
    but (4) 36v panels in series would 144v
    this is lethal voltage and probability higher than the controller limits
    lethal to what? 120vac isn't too safe either.


    A/C gives ya chance to let go.....DC will not.......
  • nvreloader's avatar
    nvreloader
    Explorer
    Dec 07, 2016
    Sorry guys,
    Thanks for the replies,

    I'll attempt answer all the questions in the order they were posted,

    TT2R
    I had planned on using series/parallel MC-4 connectors,
    but can't find the #8 MC-4 pv type wire yet.

    I will try the Calculations at 60 volts not 12v,
    to see the results I get.

    It will never trip from overload??
    Lost me here..
    ----------------------
    2OM
    Per info received from MS,
    they say to series and then parallel my 230w pv panels,
    to NOT hurt their MPPT 60a CC etc.

    Are you running 920w thru a MPPT 60a CC?
    ---------------------------
    Mr Wizard
    Sorry, I did not include all the info needed,
    my CC is a Morningstar’s MPPT Charge Controller: Tristar 60 Amp
    with Remote Temp sensor for above and Trimetric Battery meter:

    I prefer not going on the roof, if I can do what I want,
    from ground level and to save wear/tear on the rubber roof etc.

    From what I understand (very little a this point, me thinks, LoL,
    I am attempting to under stand the notes I kept in my note book etc,
    and which is not making sense now etc).

    By eliminating the combiner box, that means LESS connections
    and less wire resistance loss, and less holes in the roof etc.

    Tia,
    Don
  • KD4UPL's avatar
    KD4UPL
    Explorer
    Dec 08, 2016
    I find it hard to believe that voltage drop will be an issue for you at all. Running 16 amps thru 1 run of #10 for 25 is well under 2% voltage drop at 60 volts.
    Simply install a DC rated breaker in the wire between your panels and the CC.

    2OM, 120v is lethal as well. Anything over 50 volts is considered potential lethal. But yes, DC is worse as it's constant flow causes muscles to lock making it harder for the victim to let go.
  • Rbertalotto's avatar
    Rbertalotto
    Explorer
    Dec 08, 2016
    I think he wanted a way to disconnect each panel individually from the system. Not sure why. By using a combiner box and one down lead he does not have an easy option. He could use heavy duty relays on the roof to disconnect each panel, but again....why?
    Otherwise four separate downloads to the equipment cabinet with all the extra lose this entails.
  • 2oldman's avatar
    2oldman
    Explorer II
    Dec 08, 2016
    KD4UPL wrote:
    es, DC is worse as it's (sic) constant flow causes muscles to lock making it harder for the victim to let go.
    Then I guess one should be careful not to do that. I have 115vdc and 120vac running around my 5er but I can't say I've ever grabbed those wires.

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