Wire size & performance questions

I have 3 Kyocera 185 watt panels connected in parallel. 25' away is a Xantrex XW MPPT60-150 charge controller. 30' away from that is the battery bank. The batteries are 3 Mastervolt 4D AGMs in parallel.

My questions are:

1) What kind of performance loss do I have if the whole thing is wired with 10 gauge wire? (10 gauge is what my salesman recommended due to the very difficult 25' wire run between the panels and the charge controller with lots of 90 degree angles through narrow stainless steel scaffold tubing (this is on a boat).

2) If I upgraded the relatively easy 30' wire run between the charge controller and the batteries (goes along hull of boat through lockers and under bunks), what gauge wire would be recommended, and what kind of improvement would I see in performance, if any?

3) On the wire sizing charts when they talk about 3% voltage drop, what does this translate to in terms of charging? If on a given day I get 100 Ah returned to my batteries, does a 3% drop mean I would get only 97 Ah instead?

Comments

  • CariboocootCariboocoot ✭✭ Banned Posts: 17,615 ✭✭
    Re: Wire size & performance questions

    Why are the panels wired in parallel? They're 30 Voc so in series it would be 90 Volts and surely the Xantrex can handle that. Higher array Voltage = less line loss. The 10 gauge should handle it either way.

    As for wiring to the batteries with 10 gauge ... The panels have a potential of over 30 Amps charge current into the batteries, so 10 gauge is too small there.

    Voltage drop refers to how much goes in the wire at one end vs. how much comes out at the other, so to speak. 3% is the generally accepted limit. As in 90 Volts at the array being 87 Volts by the time it gets to the charge controller, with the resultant power loss. It doesn't have anything to do with the Amp/hours per se, except for whether or not you are able to recharge them or use them; battery capacity remains the same.

    I'm not explaining this clearly. It must be nap time.:blush:
  • nielniel ✭✭✭✭ Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Wire size & performance questions

    for these lengths it must be one big boat. isn't there any way you can keep everything closer together?

    1> i don't know your exacting circumstances to know for sure if the salesman is advising well or not, but at a 25ft run this represents better than a 6% v drop loss. we recommend no lower than 3%, but it will still work if one wants to live with the loss.

    2> the voltage drop gets worse after the controller because you are now at a lower voltage with higher current and it is a longer run of wire. the current has at least doubled to 47a through the mppt controller downconverting and through #10 would be a whopping 30% v drop loss. normally it is recommended to keep total losses under 5% from pvs to load, but the pvs to cc alone will exceed that. to keep the cc to battery v drop % loss down under 3% you would need #0 and #000 for under 2%. these percentages are additive just for the record so whatever v losses you get from the pvs to the cc add to the v losses you get from the cc to the batteries. 6% + 30% = 36%.

    3> so what this means is if one would have a v drop of say for an example, 1v from a 17v source like a pv then the voltage x the current it passes represents the wattage lost from it or in this case 1v x 7.84a = 7.84w as watts = volts x amps. for 3 of them you lost 23.52w. now this isn't exactly your circumstance for the pvs you have and i only showed you an example. your v drop losses are worse than 1v.
    now the battery losses from this are extreme and could interfere with the batteries actually charging. if say you put an absorb charge point of 14.4v that by the time it gets to the batteries it will be about 3.6v lower and represents 10.8v by the time it reaches the batteries unless there is some remote voltage indication to the cc of the batteries' actual voltage. this voltage to the batteries is critical and the same losses can be figured as i did for the pvs to the cc, but the cc is more flexible in dealing with the lower voltage. that 10.8v would mean there is no charge being delivered to the batteries as it must be at the 14.4v to even have succeeded in bulk charging to start an absorb charge. this means you have 0 charge to the batteries or a 100% loss of charge.
    the charts are somewhat helpful if you know what you're doing. there is even a voltage drop calculator in the faqs, links, and information section above.
    http://forum.solar-electric.com/showthread.php?t=29
    your salesman should understand the implications of voltage drop losses and if he doesn't then drop him and get somebody else who does know.
  • System2System2 admin Posts: 6,290 admin
    Re: Wire size & performance questions

    Panels are in parallel due to shading problems from mast, boom, sail etc. At any given time one or more panels may have a significant shadow on it, depending on the boat's orientation in the water with respect to the sun (the orientation is constantly changing, whether sailing or at anchor).

    If 10 gauge is too small between batteries and charge controller, what size is best and what will the performance improvement be?
  • nielniel ✭✭✭✭ Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Wire size & performance questions

    i did answer your question. i said you need at least #0 for a 30ft run from the cc to the batteries. this is a large wire due to the distance the wiring is and how much current it needs to pass.
    even at that it will still lose .35v.
  • System2System2 admin Posts: 6,290 admin
    Re: Wire size & performance questions

    Neil - I think it is charging okay.

    This morning (oh dark thirty) the batteries were at 12.42 volts with no load (measured with multi-meter on the batteries). They stayed in Bulk mode for 3 hours, with the Xantrex output showing 14.3 volts with 20 amps going to the batteries after about 2.5 hours. This was in fog and misty sun.

    At 3 hours (around (9:00 am) it went into Absorb with the output voltage still at 14.3 and amps dropping over 3 hours to about 10 amps in full sun.

    Then at about noon it went into Float where it has been for 1.5 hours hours with Xantrex showing output voltage of 13.3 and output amps around 8.

    My questions originated because with no load, when the Xantrex reported 14.3 volts output, my multi-meter on the batteries measured 13 volts. Later, when Xantrex reported 13.3 volts output, my multi-meter across the batteries measured 12.7 volts.

    What I'm not sure is whether I have some phantom loads bringing the batteries down, or if the difference is due to the long run of 10 guage wire between the charge controller and the batteries.

    There is no shorter way to run the wires. All I can do, at best, is replace the 10 gauge between the charge controller and the batteries with something bigger. But before I bother with that I am wondering what the improvement will be.
  • nsaspooknsaspook ✭✭✭ Solar Expert Posts: 396 ✭✭✭
    Re: Wire size & performance questions
    My questions originated because with no load, when the Xantrex reported 14.3 volts output, my multi-meter on the batteries measured 13 volts. Later, when Xantrex reported 13.3 volts output, my multi-meter across the batteries measured 12.7 volts.


    Check your multimeter calibration. If your measuring the voltage at the battery end with no-load it should be pretty close to the Xantrex value. (assuming it's the correct value)
  • mike95490mike95490 ✭✭✭✭✭ Solar Expert Posts: 8,417 ✭✭✭✭✭
    Re: Wire size & performance questions

    What does the heanheld meeter read when measuring AT the controller, compared to the controller ? each could be 2-5%+ - off. Does the charge controller have Remote Battery Sense inputs ?
    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 ,

  • n3qikn3qik ✭✭ Solar Expert Posts: 741 ✭✭
    Re: Wire size & performance questions

    My questions originated because with no load, when the Xantrex reported 14.3 volts output, my multi-meter on the batteries measured 13 volts. Later, when Xantrex reported 13.3 volts output, my multi-meter across the batteries measured 12.7 volts.

    This is the voltage drop of the wire(s). When you add loads, the voltage difference is going to get larger.
  • System2System2 admin Posts: 6,290 admin
    Re: Wire size & performance questions

    I guess the voltage drop is not all that bad after all.

    At the end of the day when the batteries were fully charged and had had no load for a few hours, I measured the voltage at the output of the controller, and it was 13.25 volts (as compared to the reported output voltage on its display that read 13.3 volts). The voltage at the batteries was 12.82. This is a difference of 3.24%.

    I spoke with my salesman again and his take on the whole thing was that the difference with the smaller 10 gauge wire would be in how long it took the battery bank to reach full charge. He suggested that upgrading to 6 gauge wire might allow the bank to reach full charge about 30 to 60 minutes faster than with the 10 gauge wire.

    We'll upgrade if we find that we can't reach full charge by day's end in winter. Thanks everyone for your input.
  • mike95490mike95490 ✭✭✭✭✭ Solar Expert Posts: 8,417 ✭✭✭✭✭
    Re: Wire size & performance questions
    ...This is a difference of 3.24%.

    I spoke with my salesman again and his take on the whole thing was that the difference with the smaller 10 gauge wire would be in how long it took the battery bank to reach full charge. He suggested that upgrading to 6 gauge wire might allow the bank to reach full charge about 30 to 60 minutes faster than with the 10 gauge wire.....

    Best to be below 3% - wire upgrade is needed, I wonder if 8 ga would be enough. Use the voltage drop calculator here http://forum.solar-electric.com/showthread.php?t=29 to see what wire you should use.
    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 ,

  • BB.BB. admin Super Moderators, Administrators Posts: 29,634 admin
    Re: Wire size & performance questions

    The closer you can put the charge controller to the battery bank (short/heavy gauge wire)--the better off you will be...

    Remember, the charge controller is basing its decision of how much current to feed into the battery bank based on what battery voltage it is measuring.

    With high voltage drop between the controller and the battery bank, the charge controller will cut back on current output thinking the battery is already approaching full charge.

    In general, voltage drop between solar panels and the charge controller is just a bit of lost power.

    Too much voltage drop between the charge controller and the battery bank can be a big deal... The difference between heavy charging at 14.2 volts and 13.7 volts (float charging) is only ~0.5 volts.

    0.5 volt drop is 30 amps of current on 7 feet one way run (14' round trip) using 10 AWG wire.

    Will a battery charge at 13.7 volts--yes, but pretty slowly--and for you, that is a waste of solar panel power.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nsaspooknsaspook ✭✭✭ Solar Expert Posts: 396 ✭✭✭
    Re: Wire size & performance questions
    BB. wrote: »
    The closer you can put the charge controller to the battery bank (short/heavy gauge wire)--the better off you will be...

    Remember, the charge controller is basing its decision of how much current to feed into the battery bank based on what battery voltage it is measuring.

    With high voltage drop between the controller and the battery bank, the charge controller will cut back on current output thinking the battery is already approaching full charge.

    In general, voltage drop between solar panels and the charge controller is just a bit of lost power.

    Too much voltage drop between the charge controller and the battery bank can be a big deal... The difference between heavy charging at 14.2 volts and 13.7 volts (float charging) is only ~0.5 volts.

    0.5 volt drop is 30 amps of current on 7 feet one way run (14' round trip) using 10 AWG wire.

    Will a battery charge at 13.7 volts--yes, but pretty slowly--and for you, that is a waste of solar panel power.

    -Bill

    A good reason a remote battery voltage sense option is a good thing on charge controllers.
    I've found the internal voltage calibration on the C40 remote readout data I tried using to be off by +-4% compared to a calibrated Fluke 73 meter (+-0.3% , 20+ years old) which makes it less useful for precise charge measurements.

    If you have accurate meter use it to setup your set-points at the battery terminals. A NIST meter calibration is about $40 at a local cal-lab. It's worth the money to a good meter. http://us.fluke.com/fluke/usen/digital-multimeters/fluke-170.htm?PID=56027
  • BB.BB. admin Super Moderators, Administrators Posts: 29,634 admin
    Re: Wire size & performance questions

    Oh boy--do these solar charge controller need remote (voltage) sense...

    On larger computer systems, most of the low voltage power supplies have remote sense capability. It makes life so much easier (100's of amps and 5.00+/-0.25 volts). It makes the controller to bus connection voltage drop pretty much irrelevant.

    I think I remember seeing a grand total of one solar charge controller that had remote sense... And I cannot remember which one that was.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar GuppySolar Guppy ✭✭✭ Solar Expert Posts: 1,962 ✭✭✭
    Re: Wire size & performance questions
    BB. wrote: »
    I think I remember seeing a grand total of one solar charge controller that had remote sense... And I cannot remember which one that was.
    -Bill

    The Morningstar Tristar's have remote voltage sensing included, both the Mppt and PWM models.
  • BB.BB. admin Super Moderators, Administrators Posts: 29,634 admin
    Re: Wire size & performance questions

    That was it!

    Not listed in the data sheets--But listed in the user manuals.

    Really great to have. Adding a small fuse at the + end of the cable where it is connected to the + bus/battery terminal would be a good safety addition too (if the small sense wire gets cut/grounded--the fuse will protect it).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • halfcrazyhalfcrazy ✭✭✭ Solar Expert Posts: 720 ✭✭✭
    Re: Wire size & performance questions
    Neil - I think it is charging okay.



    My questions originated because with no load, when the Xantrex reported 14.3 volts output, my multi-meter on the batteries measured 13 volts. Later, when Xantrex reported 13.3 volts output, my multi-meter across the batteries measured 12.7 volts.

    What I'm not sure is whether I have some phantom loads bringing the batteries down, or if the difference is due to the long run of 10 guage wire between the charge controller and the batteries.

    There is no shorter way to run the wires. All I can do, at best, is replace the 10 gauge between the charge controller and the batteries with something bigger. But before I bother with that I am wondering what the improvement will be.

    Ok I will elaborate more later on the CC and our thoughts on voltage sense. But this above statement is troubling to me if the controller is not charging and you are seing these numbers I would question the XW I have had 2 that where off one 2 volts and change one 6 volts and change.

    That said upgrade the wire between the CC and Batteries to as big as practical for you. The way the voltage drop works will not really be that big an issue as the Bulk charging ramps up the voltage drop will be at its worst but as the cc sees its target voltage and starts ramping the current down the voltage drop will ramp down as well making the actual battery voltage closer and closer to accurate. then as it goes to float the voltage drop goes almost away. I will revisit this later when I have more time to really explain it better though.
  • n3qikn3qik ✭✭ Solar Expert Posts: 741 ✭✭
    Re: Wire size & performance questions
    We'll upgrade if we find that we can't reach full charge by day's end in winter.

    2X on waiting. If you limit your loads to less than what is currently generated. Then no need to upgrade.

    I am in the same boat so to speak. 1/2 my panels are on a shed 120 feet away. Currently at 13-16% losses. But my loads are so light, 30-50% is pushed into my dump load. So no sense to upgrade the wiring just to heat up more water.
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