Wire Sizing?

alyaz
alyaz Solar Expert Posts: 114 ✭✭✭
in Solar Beginners Corner #1
Getting close to starting on our second panel array and wondering if I can get some advice on wire sizing for the run from the array to the controller? The wire will be buried and the run is 160 feet. Thanks... Specs are below:

Sharp 240 watt panels (four): Two hooked in series
Panel Specifications -
Voltage Maximum Power 30.1
Current Maximum Power 7.98
Voltage Open Circuit 37.4
Current Short Circuit 8.65

24 Volt System: 12 - 2 Volt Davidson Batteries

Apollo T80HV MPPT controller :
(Maximum output current 80 Amps continuous at up to 45oC/113oF
Battery voltages 12, 24, 36, or 48 VDC nominal
Max PV input current 70 Amps
Input voltage range 16 to 160 VDC operating 200VDC Maximum Open Circuit Voltage
Charge 24v batteries from 34 to 160* volt PV arrays
3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
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Comments

  • TnAndy
    TnAndy Solar Expert Posts: 249 ✭✭
    #2
    Re: Wire Sizing?

    Some reason you're not wiring all four in series since your charge controller will allow up to 160v in ?

    That would cut wire size significantly.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Wire Sizing?

    TnAndy is right: this is a very long wire run. For two parallel strings of two of those panels you'd need 4 AWG to keep the V-drop below 3%. Put all four in series and you can use 10 AWG. The Voc becomes 4 * 37.4 = 149.6 Even with a cold temp increase factor of 1.3 that's 194.48 Volts, still under the controller's listed max of 200 Voc max.
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  • alyaz
    alyaz Solar Expert Posts: 114 ✭✭✭
    #4
    Re: Wire Sizing?

    This is the advice we had received on the Apollo with the four Sharp 240 watt panels, so that is what we were working with:

    'The 240 watt Sharp panels have a Vmp of 30.1 (should be at least 34) which is too low to charge a 24 volt system. The T80 Apollo has a max V in of 72 for Vmp (140 Voc) so it could handle strings of two of the Sharp 240W's in series (60.2 Vmp). Two strings in parallel do not require fuses.'
    3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Wire Sizing?
    alyaz wrote: »
    This is the advice we had received on the Apollo with the four Sharp 240 watt panels, so that is what we were working with:

    'The 240 watt Sharp panels have a Vmp of 30.1 (should be at least 34) which is too low to charge a 24 volt system. The T80 Apollo has a max V in of 72 for Vmp (140 Voc) so it could handle strings of two of the Sharp 240W's in series (60.2 Vmp). Two strings in parallel do not require fuses.'

    That is correct, as far as it goes.
    However, it does not mean you can't put four panels in series on the input side as this must be an MPPT controller anyway.

    However, I do not understand the discrepancy between your first posting of the Apollo's specs ("Input voltage range 16 to 160 VDC operating 200VDC Maximum Open Circuit Voltage") and the statement in this post: "The T80 Apollo has a max V in of 72 for Vmp". Maybe you should consider a different charge controller as there seems to be some confusion as to what the T80 is capable of. :confused:

    So long as the array output does not exceed the charge controller's input maximums all is good; the output side of the controller will take care of itself.
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  • alyaz
    alyaz Solar Expert Posts: 114 ✭✭✭
    #6
    Re: Wire Sizing?

    Thanks.

    I suspect that discrepancy came about because there are two models of the Apollo T80, one is the regular and one is the high voltage model. We have the high voltage model and the specs for the high voltage model are as posted.
    3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #7
    Re: Wire Sizing?

    From the Apollo specs:
    Charge 48v batteries from 68 to 160* volt PV arrays
    Charge 36v batteries from 51 to 160* volt PV arrays
    Charge 24v batteries from 34 to 160* volt PV arrays
    Charge 12v batteries from 17 to 80 volt PV arrays – not recommended to charge 12v
    batteries from over 80 volts of PV for efficiency reasons.
    *Check max Voc from PV modules at low temperature extremes.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • alyaz
    alyaz Solar Expert Posts: 114 ✭✭✭
    #8
    Re: Wire Sizing?

    Can anyone advise, with one series string (from the four sharp 240 watt panels) is a combiner box / fuse required? After reading some threads I get the impression that you only need to fuse more than two parallel runs? thanks...
    3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Wire Sizing?
    alyaz wrote: »
    Can anyone advise, with one series string (from the four sharp 240 watt panels) is a combiner box / fuse required? After reading some threads I get the impression that you only need to fuse more than two parallel runs? thanks...

    That is correct. One panel cannot put out more current than its Isc rating, no matter what. All panels in series acts like one panel; the Isc remains the same but the Voltage goes up.

    More than two parallel connections and you need to add fuses/breakers because two acting in tandem would be able to overwhelm a third with 2X its Isc.

    BTW, if you make parallel connection on even two panels that have dissimilar Isc it is a good idea to fuse them according to their current rating (1.25X Isc) because a higher current panel could cause a problem with a lower current panel should something go wrong.
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  • alyaz
    alyaz Solar Expert Posts: 114 ✭✭✭
    #10
    Re: Wire Sizing?

    Thanks....

    http://www.apollosolar.com/Support/SupportByProduct/SupportT80HV/tabid/150/Default.aspx

    I've been trying to make sense of the wire sizing chart located in the Apollo charge controller manual.

    On page 40 and 41 they chart the various runs etc. Should I assume that my setup would fall into the last category on page 41 (120 volt ?). Just trying to make sense of this and learn something in the process...
    3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: Wire Sizing?

    Using their chart on Page 39 (pdf pg shows 41) your four panels would be: "96 Volt PV array" Actually 128 Vmp. (Really it's 30.1 * 4 or 120 Volts.) The closest to the current level would be 10 Amps. (Really 8 for your panels.) Your distance is 160 feet, which falls in-between 8 AWG for 145 feet and 6 AWG for 230 feet. My calculator says 10 AWG would be a minimum for under 3% loss.

    In short, if you can afford 8 AWG use it. It will take another 1% off your V-drop.

    You might want to do the figures with a more accurate calculator like this one:
    www.solar-guppy.com/download/voltage_drop_calculator.zip
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  • alyaz
    alyaz Solar Expert Posts: 114 ✭✭✭
    #12
    Re: Wire Sizing?

    Awesome ... thanks for all your help.
    3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
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