MC4 cable length ??

offgridoffgrid Registered Users Posts: 20
Hello,
When I bought my system, I had purchased a 100' mc4 cable that I split in half (2 - 50 ' cables). I have about 10' of extra/wound up cable to 1 panel and about 13' of cable to the other panel. Giving the same amount of sunlight, If i cut the cable(s) shorter would I see an increase in amp's to the CC from the panels ? Or, not enough to notice a difference ?


Thanks Tom

Comments

  • mike95490mike95490 Solar Expert Posts: 9,358 ✭✭✭✭✭
    Re: MC4 cable length ??

    Probably not enough to notice a difference. Wait a month and see if you need to re-arrange anything, and then cut. Just to make it neater.
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  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: MC4 cable length ??

    the problem is the voltage drop that would be present at how many amps you are drawing through what gauge number wire and you've not given us enough info to properly answer your question. in general smaller runs of wire do improve things, but we can't say how much or if it is enough to keep v drops within 2 or 3 %. the amps most likely won't increase unless you are experiencing losses to begin with and hopefully these losses are low.
  • GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: MC4 cable length ??

    Niels right. It won't make a difference unless the cable is longer than, say 50'. And depends on what voltage is going through the lines. The more voltage, the greater loss between distances capable. We're talking millivolts or amps if anything.

    A racing trick was done to mini RC cars to increase the speed of the motors . Those who where using this strategy, often won the races. The only thing they did was increase the size of the positive wire going to the RC motor, thus increasing it's speed at the cost of less battery life on one charge, but enough to cross the finish line. So if anything, increase the cable size a notch and check for differences. Bottom line is, the max amp output of the panel is what you'll get every time regardless of size wires except if they're too small.
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  • offgridoffgrid Registered Users Posts: 20
    Re: MC4 cable length ??

    Thanks guys the question has been answered.
    Niel, this was just a general question, I should have been more clear to address that. I should have said -all things being equal- (if thats possible).
    The cables are awg#10 using mc4 connectors that was a 100' cable I bought from NAWS. I cut the wire in half to get 2 - 50' cables. I have extra cable in my run and thought I would ask :)
    The answer I was looking for was "anything longer than 50' would produce a drop".

    Tom
  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    Re: MC4 cable length ??

    You can use the wiring size calculator to calculate the drop--or any program/wiring chart that gives the resistance for copper wire.
    • Remember P= V*I = V^2 / R = I^2 * R
    Without knowing the current through the wiring (and your total power), we cannot really give you any numbers (i.e., you are losing X watts because of the extra length of cable).

    For example, from the wiring size calculator, the resistance of 1' of 10 awg cable at 70F is 0.0010033 ohms. Plugging in the numbers for amps and 23' of "extra cable" results in:
    • P= I^2 * R = (5 amps)^2 * (0.0010033 ohm/foot * 23') = 0.58 watts loss
    • P= I^2 * R = (20 amps)^2 * (0.0010033 ohm/foot * 23') = 9.2 watts loss
    The amount lost is relatively small--but remember this is loss 4-5 hours per day x 365 days per year...
    • 0.58 watts * 5 hours per day * 365 days per year = 105 Watt*Hours per year...
    • Vs, assuming 15 volts * 5 amps * 5 hours * 365 = 137,000 Watt*Hours per year
    Still, not that much loss of power for such a small system (0.08% loss for my mythical 12 volt 5 amp 85 watt system).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: MC4 cable length ??
    offgrid wrote: »
    Thanks guys the question has been answered.
    Niel, this was just a general question, I should have been more clear to address that. I should have said -all things being equal- (if thats possible).
    The cables are awg#10 using mc4 connectors that was a 100' cable I bought from NAWS. I cut the wire in half to get 2 - 50' cables. I have extra cable in my run and thought I would ask :)
    The answer I was looking for was "anything longer than 50' would produce a drop".

    Tom


    all things being equal and you add more wire, the added resistance the wire presents will increase the v drop and thus the losses too. i did answer by the reciprocal before by saying shorter lengths will reduce the v drop and thus reduce the losses. how much that would translate to does depend on the factors i listed.
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