how many amps can mc4 wires handle in parallel?

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  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    Re: how many amps can mc4 wires handle in parallel?
    Not a problem. This type of controller is current limiting; it will only pass 60 Amps maximum no matter the amount of panel on the input or the load on the output (save a dead short).
    Even Morningstar's little 15 Amp MPPT controller can be "over-paneled".

    You may have noticed panels don't come in precise Wattages of infinite variety; you always have some leeway to work with.

    The old Outback MX60 is a 60 Amp controller but can actually be cranked up to 70 Amps, for example.





    Thanks everyone!

    So bottom line: no fire hazard running 840w through a 800w max controller...


    I kept thinking the extra watts would overheat something..

    So it just "rejects it" instead?

    Is that correct??

    Thanks

    -cakie
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • BB.BB. Super Moderators, Administrators Posts: 32,018 admin
    Re: how many amps can mc4 wires handle in parallel?

    Technically, the DC to DC converter is "throttling" the energy throughput from the Solar Array to Battery bank.

    It is just normal operation or "the nature of the beast".

    Buck Mode Switch Converters are probably the easiest to understand of the switching topologies. Try reading about them here:

    Buck converter


    Basically there is an Inductor from the input to the output...

    When the "switch" closes, the current starts flowing through the inductor (slowly increasing). At some point the switch is opened, but the inductor wants to keep the current flowing, so there is a diode that supplies current (from ground) and the current slowly slows down again (the inductor is storing and giving up energy). Then the whole cycle repeats... The more the switch is closed, the more energy/current flows form the solar array (i.e., towards 100% closed).

    As the computer decides less current is needed, the switch is closed for less time during the cycle (towards 0% percent), and very little average current flows.

    A buck mode down converter (MPPT type charge controller) uses PWM (pulse width modulation) to control current/energy flow through the converter.

    A pure PWM charge controller---Replace the inductor with a copper wire. And toss the diode. Just an "on/off switch". Cheaper to make, but as you can see, it has now way to "regulate" instantaneous current through the switch. So if you put too large of an array (or a higher voltage battery) on the input to a "pure" PWM controller, you will get current spikes that exceed the current capability of the supply.

    A good quality MPPT charge controller (designed for the job) can actually be connected directly to a higher voltage battery bank and very nicely recharge a lower voltage battery bank (i.e., a 24 volt battery bank => MPPT controller => 12 volt battery bank) and be very happy.

    If you tried this with a PWM controller, it will cook the internal electronics/conductors (no current limiting/regulation possible).

    MPPT charge controllers are also very good at taking high voltage/low current from the array and efficiently down converting to the low voltage/high current needed to charge the battery bank (~95% efficiency). Because the inductor is efficiently converting the energy from the panel to the bank.

    It is the first switch mode regulator I learned about--And I always thought they were very neat.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: how many amps can mc4 wires handle in parallel?
    cupcake wrote: »
    So bottom line: no fire hazard running 840w through a 800w max controller...

    I kept thinking the extra watts would overheat something..

    So it just "rejects it" instead?

    Is that correct??

    Think about it... when your batteries are full and the sun is still shining, your controller is 'rejecting' all 840 watts. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • mike95490mike95490 Solar Expert Posts: 9,362 ✭✭✭✭✭
    Re: how many amps can mc4 wires handle in parallel?

    just like your 100w light bulb "rejecting" the other 29.900Kw sitting in the house wires
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    Re: how many amps can mc4 wires handle in parallel?

    Thanks to EVERYONE who replied with help, suggestions, and positive feedback. I truly appreciate it...

    Be well... all of you...

    --cupcakes
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


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