whats the most panels 12 volt you would run to one combiner

hi guys

so i have a combiner that has 12 inlets
is there any problem with running each 75 watt sp75 12 volt panel straight to the combiner

any issues with putting two panels in one inlet

ive been told that if shade is hitting some of the panels the ones in the sun will still produce if wired like this instead
any thoughts???

thanks

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,641 admin
    Re: whats the most panels 12 volt you would run to one combiner
    hi guys

    so i have a combiner that has 12 inlets
    is there any problem with running each 75 watt sp75 12 volt panel straight to the combiner

    Normally it is one string per inlet. If you have 12 panels in parallel--12 panels.

    if you have two panels in series, then you would have 6 parallel strings. etc.
    any issues with putting two panels in one inlet

    Not usually done... For example, you may have panels with Isc (short circuit current) of ~8 amps with a 15 amp breaker or fuse.

    The idea is if there is a short in one string, then if there are two or more other "good" parallel strings, the circuit breaker will pop if there is a shorted string.

    if you put two panels on one inlet--Then you now have Isc from one panel, plus the 15 amps from the other two panels (behind the breaker). So you can have up to 8+15=23 amps into a single shorted panel--Higher than the 15 amp maximum I used in this example.

    People install panels in series/parallel in all sorts of wild and wonderful ways--Generally 99.9% never have a problem. But, there is that 0.1% risk that doing wrong may allow a fire to get started.

    Old risk/reward--How much risk are you will to accept vs the cost/time savings. NEC/Code tries to be conservative (sometimes too much)--To keep insured risk low and prevent loss of life.
    ive been told that if shade is hitting some of the panels the ones in the sun will still produce if wired like this instead
    any thoughts???

    Panels that are shaded will simply not produce any current... Perfectly OK. If you have two panels or more panels in series, a shaded panel will generally make the entire string not produce any current.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: whats the most panels 12 volt you would run to one combiner

    Just to simplify a bit ...

    On a PWM controller and 12 Volt system you are limited to having all panels in parallel. This requires one fuse or circuit breaker per panel to protect against back-feeding a shorted panel. You can not parallel two panels (as in using 'Y' connectors) and then connect them to the over-current protected inlet of a combiner box as it will defeat the protection.

    If you use an MPPT type controller then the array Vmp can be higher than typical, allowing the use of two '12 Volt' panels in series on a 12 Volt system.

    Much of the specifics of wiring depends on the specifics of the components being wired.
  • PhotowhitPhotowhit Solar Expert Posts: 5,825 ✭✭✭✭✭
    Re: whats the most panels 12 volt you would run to one combiner
    so i have a combiner that has 12 inlets
    is there any problem with running each 75 watt sp75 12 volt panel straight to the combiner

    any issues with putting two panels in one inlet

    ive been told that if shade is hitting some of the panels the ones in the sun will still produce if wired like this instead
    any thoughts???

    What you have might be very different from what you need. So what do you want to do with your system?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • solarsquirralsolarsquirral Solar Expert Posts: 54
    Re: whats the most panels 12 volt you would run to one combiner

    well i have 12 plus sp75 75 watt panels that i would like to wire into a 12 position power distubution block from there it hits a 60a dc breaker then the c60 combiner

    i was hopeing to install a diversion load controller to run a dc slow pump while the batts hit float but looking at dc runs in the range of 150 feet to water source at 15 amps im looking at 150 feet of 1/0 yikes kinda sent me back to considering a ac pump off generator

    any tips
  • Ethan BrushEthan Brush Solar Expert Posts: 235 ✭✭
    Re: whats the most panels 12 volt you would run to one combiner
    well i have 12 plus sp75 75 watt panels that i would like to wire into a 12 position power distubution block from there it hits a 60a dc breaker then the c60 combiner

    i was hopeing to install a diversion load controller to run a dc slow pump while the batts hit float but looking at dc runs in the range of 150 feet to water source at 15 amps im looking at 150 feet of 1/0 yikes kinda sent me back to considering a ac pump off generator

    any tips

    I have a few thoughts:
    1) have you thought about wiring them up all in series or 2 strings of 6 (depending on what the voc works out to) and using a MPPT controller? Sure the PWM controller is less expensive, especially if you already have it, but considering the extra equipment and larger wiring, it can pay for itself.
    2) Im not sure about running a DC pump off the pwm of a diversion controller...Id have to think about if the pump would like that or not....maybe others can comment
    3) Not sure what pump/amps you were looking at, but your 1/0 seems pretty big. A surflo 12 v pump would be fine with #2 aluminum which is really cheap....
  • BB.BB. Super Moderators, Administrators Posts: 32,641 admin
    Re: whats the most panels 12 volt you would run to one combiner

    How wedded to the 75 Watt panels are you?

    You could go with 3x 300 Watt panels. 1/4 the panels, 1/4 the connections, 1/4 the combiner box size, etc... ~$900 worth of modern panels. On an MPPT charge controller (Vmp~30 volts on a 12 volt battery bank).

    And sell/re-purpose the 75 Watt panels where smaller panels may be more useful (small remote systems, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solarsquirralsolarsquirral Solar Expert Posts: 54
    Re: whats the most panels 12 volt you would run to one combiner

    well i already have all these panels and would rather not spend another 1000 bucks on new panels
    mostly becase my inverter is 12 volt and most new large panels are 24volt
    id have to rewire the batteriess also

    i would like to use what i have till it breaks and then go from there when this stuff wears out
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: whats the most panels 12 volt you would run to one combiner

    How many more then 12 panels do you have and how big is your battery bank? I agree that running a motor as a divertion load could cause over heating to the motor unless it can be set up as all on for a period and then compleetly off. You could ad another combiner box or fuse the extra panels and combine them with the 12 place combiner out put. If your bank was bigg enough and always loaded or your divertion load was big enough, you could fuse the extra and run strait to the battery. Could you seperate the extra panels off and use them independantly to run your water pumping strait from pv during daylight hour. I have two turbines hooked strait to the battery and I have a little over 100 watts panel hooked strait to the battery and facing a bit east so that they can run unregulated for a morning boost to bulk but add nothing in the afternoon when the batteries get full. They all have independant breaker and don't go through my combiner box, but do take extra wire to get them to the battery.

    Just some thoughts.
    gww
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