Lighting / loads

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garynappi
garynappi Registered Users Posts: 105 ✭✭
edited July 2019 in Solar Beginners Corner #1
I am wanting to string lights in front and back of my house but the max 100' cable length for Malibu type lightings necessitates I use two cable runs, one 75' to the front of the house and one 100' to the back yard. 

I'm wanting to use 7 lights in the front yard (4w lamp in each) and 8 lights (also 4w each) in the back yard. I have on order some 1 and 4 watt white LED's to replace the yellowish quartz lamp. 

The Malibu LV transformer instructions indicate that basically any way you connect is acceptable whether it's a continuous 100' string, "T" (of different lengths) or even "hub" (like a wheel spoke) are OK. 

I haven't found anywhere info on whether or not having two cable runs in parallel may present a problem for my 20A Morningstar controller. I read that the Morningstar uses a Mosfet switch which (20A load specs supplied) so my setup load will be way under the specs but without knowing anything about the controller quirks I thought I'd ask and see if anyone else has used a similar setup.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,448 admin
    #2
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    When you place two cables (of the same AWG) in parallel, that is the same as using a single cable that is ~3 AWG heavier (i.e., 2x 14 AWG cables in parallel is approximately equal to a single 11 AWG cable).

    That is the way AWG (and SAE) gauges work... ~3 steps for every doubling of wire cross sectional area. This is assuming the two parallel cables are the same length (same resistance).

    Then you you can use a simple voltage drop calculator to see how much drop/how thick the cables need to be for your application:

    https://www.calculator.net/voltage-drop-calculator.html

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #3
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    If I'm understanding this correctly, you're running 12v nominal lighting off a load terminal on a MS charge controller?

    If so, note that the transformer instructions apply to the output of that particular transformer, which is likely a fixed or very narrow voltage range.  I'm not certain, but the controller output may follow battery voltage (which could range from ~10.5v - 16v).  Some, but not all devices are ok with this range, and you'd want to consider the lower end voltage / higher current in voltage drop.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • garynappi
    garynappi Registered Users Posts: 105 ✭✭
    #4
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    Estragon, yup it turns out that the loads work in a V-E-R-Y narrow voltage range. The split loads on the lighting and water fountain pump worked fine but not for long (only about 4 hours) before the controller protection tripped the shut off of the loads. Funny they set the protect circuit so high, it's bailing out at 12.4 volts which is about at the 80% state of charge.  

    I've been playing with the wattage of the lamps with 1w LED's which are nearly as bright as the 4w quartz. and this cut my current use by a lot, I'm looking at them likely running all night now without issues.

    Unfortunately the LED's are more blue and not as warm as the quartz bulbs but it is what it is. 


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