confused on wire calculation

mshen11
mshen11 Solar Expert Posts: 185 ✭✭✭✭✭
i thought i had to worry about it but i went to an electrical store this morning and they told me not to worry. here is the problem:

i have the outback FM80 MPPT which supports up to 2AWG. it is 20+5ft = less than 30ft inside the house (to the garage door). furthermore i need 15ft from garage door to mount point of the panels. my panels are kyocera 130TMs which supports up to 10AWG.

in some chart i have it says if i want 80A on a 30ft run i should have about 2/0... which is too big to fit in the controller's 2AWG or the panel's 10AWG for a straight connect. buying 2/0 or 2 AWG is going to cost an arm and a leg which i want to avoid.

the store guy says i dont have to worry about this type of stuff until i am beyond 100ft?

im thinking my ONLY solution is to make the panels 48V but i dont want to because:
* i have to buy 4 panels at a time and i can fit 6 if i am lucky
* shading
* high(er) dangerous voltage

i was thinking my solution be:

(cheaper) run 10AWG at 24V all the way to the controller
(more expensive) run 10AWG to the garage door and 2AWG to the controller [ouch]

but neither apparently will work?


edit:
http://www.powerstream.com/Wire_Size.htm
this talks about voltage drops... so the amps doesnt drop at all?? <confused>

Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: confused on wire calculation

    How many panels, and why use a MPPT controller, if not for the higher voltage /lower amps benifit ? 80amps long distance ? Unreal.
    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

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  • GreenPowerManiac
    GreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: confused on wire calculation

    Exactly. How many panels ?

    My system is set up with a Morningstar TS-60 and I have 1.25kw of panels: http://www.greenanything.net/ . Look at the bottom of the page. At best, I'll get between 5-10 amps output with 72 watt panels. Yours are almost twice as big, however, may be outputting 10-20 amps max depending on the size of your array. Getting a larger charge controller is just giving yourself an opportunity to increase the size of the system, eventually.

    My wiring is 10 gauge to the controller on a 12v parallel system. All the panels are hooked up in parallel with 14 gauge wires. No problems with heating up even on hot days. The stretch of 10 gauge wire goes 50 feet without a hitch.
    Nature's Design & Green Energy on FaceBook : Stop by and "Like" us anytime.. Many up-to-date articles about Renewables every day.
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  • solorone
    solorone Solar Expert Posts: 257 ✭✭✭
    Re: confused on wire calculation

    The store guy is an AC dude, such folks are dangerous, sort of like going to best buy and getting an educated answer about the cameras they sell, don't listen to him, stay with your wire tables and Ohms law, If you need to, splice/solder a short #10 wire to the proper size you need for the run. If anything over size your wire, go to larger wire, then if you enlarge your setup you will not have to replace your wire, also a higher voltage will help a lot. Always look to the future. My solar arrays are 200' from my house, I had to run multiple lines of 4 ought copper, this would of course be incredible $$$ today.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: confused on wire calculation

    mshen11 - the 80 Amp rating on the charge controller is the maximum current output @ whatever system voltage you have chosen. The current on the input side is a function of the panel's output @ whatever voltage you have them configured at. This is one of the advantages of an MPPT controller: higher panel voltage so you use less current on the 'downlead' with less power loss.

    Your Kyocera 130's are a 12V panel. You could wire 5 of them in series and have 650 W @ 60 V. The current on the downlead would then be about 10 Amps.

    With your panel to controller run of approximately 45 feet 10 AWG is capable of handling about 30 Amps.
  • solorone
    solorone Solar Expert Posts: 257 ✭✭✭
    Re: confused on wire calculation
    mshen11 - the 80 Amp rating on the charge controller is the maximum current output @ whatever system voltage you have chosen. The current on the input side is a function of the panel's output @ whatever voltage you have them configured at. This is one of the advantages of an MPPT controller: higher panel voltage so you use less current on the 'downlead' with less power loss.

    Your Kyocera 130's are a 12V panel. You could wire 5 of them in series and have 650 W @ 60 V. The current on the downlead would then be about 10 Amps.

    With your panel to controller run of approximately 45 feet 10 AWG is capable of handling about 30 Amps.

    OK, sorry, I have been talking old school here, so the controller converts back to battery voltage??
  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    Re: confused on wire calculation
    Your Kyocera 130's are a 12V panel. You could wire 5 of them in series and have 650 W @ 60 V. The current on the downlead would then be about 10 Amps.

    With your panel to controller run of approximately 45 feet 10 AWG is capable of handling about 30 Amps.

    Actually, since most 12 volt panels are rated at about 17 volts for Vmp, you would have around 85 volts going to the controller @ about 7.65 amps. With 5 panels and #10 wire, you could go up to 150 feet and still be within the 3% max voltage drop.

    The tricky part is from the controller to the battery, where amperage is much higher - which is why the controller should always be as close to the batteries as is practicle.
  • mshen11
    mshen11 Solar Expert Posts: 185 ✭✭✭✭✭
    Re: confused on wire calculation
    mike90045 wrote: »
    How many panels, and why use a MPPT controller, if not for the higher voltage /lower amps benifit ? 80amps long distance ? Unreal.

    would it be so cock-eyed to say # of panel is variable (varies from day to day - please dont ask)... but no more than 6 (most likely) or 8 (highly unlikely). if thats not an acceptable answer, and i have to give a number - 4 panels.

    MPPT because i am very limited in real estate and want to squeeze power based on that fact (cant do array tracking).

    80amps is the max of the MPPT. "long distance" is just the distance of the garage. dont most people have this problem because their equipment is housed in the garage?

    controller is next to everything, so no problem after the controller.

    it sounds like THE solution is to make it higher voltage? the only thing i would have to say (that is not addressed) is possible shading. what happens if my panels are only producing [some low voltage] each because its not sunny enough, the the distance would be too long?

    also isnt such high voltage dangerous?
  • mshen11
    mshen11 Solar Expert Posts: 185 ✭✭✭✭✭
    Re: confused on wire calculation
    mshen11 - the 80 Amp rating on the charge controller is the maximum current output @ whatever system voltage you have chosen. The current on the input side is a function of the panel's output @ whatever voltage you have them configured at. This is one of the advantages of an MPPT controller: higher panel voltage so you use less current on the 'downlead' with less power loss.

    Your Kyocera 130's are a 12V panel. You could wire 5 of them in series and have 650 W @ 60 V. The current on the downlead would then be about 10 Amps.

    With your panel to controller run of approximately 45 feet 10 AWG is capable of handling about 30 Amps.


    so how do i wire up the input side (isnt it also 80A max input?) assuming i want [gritting teeth at expense] 12V system? i assume the 10AWG wires would consolidate to a buss bar and have a 2AWG from buss bar to controller?

    and on the 2AWG side be short enough to handle 80A; on the 10AWG side, short enough to handle 8A? if thats true, my distance is too long for a 12V system and am wondering if there are solutions other than increasing the voltage?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: confused on wire calculation
    solorone wrote: »
    OK, sorry, I have been talking old school here, so the controller converts back to battery voltage??

    That is correct: the MPPT "down-converts" to system (charging) voltage.

    As Windsun correctly points out, the actual panel voltage is higher than its nominal rating. I always use nominal numbers when explaining basic principals - it keeps people from getting confused. Usually. :p

    When you go into "fine tuning" of a system design, then you need to worry about Vmp et cetera. For instance, the maximum input voltage on a controller may be 150 Volts, so the total output of the panels mustn't exceed that. And whereas 10 * 12V would still be under 150, 10 * 17V isn't!

    The "rule of thumb" for array Voltage is "one step up" from system Voltage: 12V system gets 24V array. The reason for this is that the efficiency of the CC goes down the greater the difference between array Voltage and system Voltage. It's not a perfect way of calculating, but it "gets you "in the ballpark" so to speak.

    So what is your system Voltage?

    For 4 12V panels you could have: 4 in parallel for a 12V system (around 30 Amps on the downlead) 2 strings of 24V for a 12V or 24V system (around 15 Amps) or 4 in series for a 24V or 48V system (about 7.5 Amps). Roughly, and I want to emphasize that, speaking.
  • mshen11
    mshen11 Solar Expert Posts: 185 ✭✭✭✭✭
    Re: confused on wire calculation
    The "rule of thumb" for array Voltage is "one step up" from system Voltage: 12V system gets 24V array. The reason for this is that the efficiency of the CC goes down the greater the difference between array Voltage and system Voltage. It's not a perfect way of calculating, but it "gets you "in the ballpark" so to speak.

    So what is your system Voltage?

    For 4 12V panels you could have: 4 in parallel for a 12V system (around 30 Amps on the downlead) 2 strings of 24V for a 12V or 24V system (around 15 Amps) or 4 in series for a 24V or 48V system (about 7.5 Amps). Roughly, and I want to emphasize that, speaking.

    please clarify - are you saying if i DONT have an MPPT controller and the controller is 12V, i should buy/set up 24V panels?

    what happens if i set it up for 48V in yoru example and its a very cloudy day... and say each panel pumps out only 5Vs? at such a long(er) distance, would i lose everything? [i think i am getting confused between volts and amps generated]
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: confused on wire calculation
    mshen11 wrote: »
    please clarify - are you saying if i DONT have an MPPT controller and the controller is 12V, i should buy/set up 24V panels?

    what happens if i set it up for 48V in yoru example and its a very cloudy day... and say each panel pumps out only 5Vs? at such a long(er) distance, would i lose everything? [i think i am getting confused between volts and amps generated]

    No. With a non MPPT controller (i.e. PWM) there's no down-converting from higher system voltages. You always have to have slightly more Voltage to charge with than the battery's rating. Thus a "12 Volt" panel actually putting out 17 Volts is capable of 'running' a PWM charge controller and charging a 12 Volt battery.

    If you have an MPPT controller, the array Voltage doesn't matter as long as it is above the battery Voltage and below the controller's input maximum. It's just that the higher the difference of in/out on an MPPT the less efficient it becomes.

    One of the advantage of the high array Voltage is as in your example: cloudy day. Knock a parallel 12 Volts array down below 12 Volts (like 11 V) and you've nothing to charge with. But if that same array can be configured for 48 Volts its output under the same conditions would be 44 Volts and the MPPT could still "have something to work with." (This is slightly imprecise, but you get the idea).

    Anecdote: I had a 72 V (nominal) array on a 12 V system. It used to click the charge controller (MX60) on under a full moon! Couldn't harvest enough power to charge with, of course, but it tried. :D
  • mshen11
    mshen11 Solar Expert Posts: 185 ✭✭✭✭✭
    Re: confused on wire calculation

    [No. With a non MPPT controller (i.e. PWM) there's no down-converting from higher system voltages. You always have to have slightly more Voltage to charge with than the battery's rating. Thus a "12 Volt" panel actually putting out 17 Volts is capable of 'running' a PWM charge controller and charging a 12 Volt battery.]

    what happens if you put 24V int a PWM of 12V? it just takes the first 12V and then drops the rest? assuming it doesnt fry.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: confused on wire calculation
    mshen11 wrote: »
    [No. With a non MPPT controller (i.e. PWM) there's no down-converting from higher system voltages. You always have to have slightly more Voltage to charge with than the battery's rating. Thus a "12 Volt" panel actually putting out 17 Volts is capable of 'running' a PWM charge controller and charging a 12 Volt battery.]

    what happens if you put 24V int a PWM of 12V? it just takes the first 12V and then drops the rest? assuming it doesnt fry.

    It puts out 24V, the current goes sky high, something goes "frzzt", the fire starts .... :cry:

    This type of controller puts out what it gets in. In 'Bulk' mode the output is connected to the input. As charge nears completion, it 'pulses' to keep the Voltage at the set levels. Take this with a grain of salt: I don't know the inner workings of absolutely every PWM controller out there - nor every MPPT for that matter. This is just the basic idea.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: confused on wire calculation

    In terms of voltage/current... An MPPT type controller is like a variable transformer for DC--It takes "high voltage and low current" and down converts it to "low voltage and high current" very efficiently (90+%). Very similar to a variable AC transformer.

    Remember the equation P=V*I (power = voltage * current)--excluding losses from electronics, wiring, and battery charging:

    Power from panels = Power to charge battery:
    100 volts * 20 amps = 1,200 watts = 15 volts * 80 amps

    A PWM controller is basically just a switch that connects from the panels to the battery. Charging, the switch is on more than it is off. As the battery approaches full charge--the switch is off more than it is on (PWM=Pulse Width Modulation--100% on--lots of charging. near 0% on--no charging). Most are high frequency on/off (20kHz +/-). Some have the option of only switching on and off on the order of seconds--this can make a PWM controller quieter for use around radios, Audio/Visual equipment, and such.

    PWM P=V*I

    Say 8 "12 volt panels" at 10 amps each for 80amp total (120 watts in 2 series/4 parallel strings):

    17 volts * 80 amps = 1,360 watts from array:
    15 volts * 80 amps = 1,200 watts into battery (wiring/controller losses included)

    Say 8 panels wired in series parallel for "24 volt" 10 amp for 40 amp output:

    34 volts * 40 amps = 1,3600 watts (in theory)

    In practice, the battery will still clamp the voltage at 15 volts:

    15 volts * 40 amps = 600 watts into battery

    Or--over 1/2 the energy loss with 24 volt panels charging a 12 volt battery bank.

    The other issue may be is that the >24 volt input may damage the switching transistors for a 12 volt PWM charge controller. (have to check the controller ratings).

    So--the advantage when BULK charging a battery bank is that an MPPT controller allows you to have high voltage / low current from the array (long distance transmission of power) and efficiently down converter to local battery voltage (low voltage / high current) to keep copper costs lower.

    When the battery is mostly charged, both controllers cut back on current flow and the "difference" in MPPT vs PWM does not matter as much--as both controllers are cutting back in power to the battery--so Maximum Power Point Tracking is not needed as it is reducing power into the battery.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solorone
    solorone Solar Expert Posts: 257 ✭✭✭
    Re: confused on wire calculation
    That is correct: the MPPT "down-converts" to system (charging) voltage.

    As Windsun correctly points out, the actual panel voltage is higher than its nominal rating. I always use nominal numbers when explaining basic principals - it keeps people from getting confused. Usually. :p

    When you go into "fine tuning" of a system design, then you need to worry about Vmp et cetera. For instance, the maximum input voltage on a controller may be 150 Volts, so the total output of the panels mustn't exceed that. And whereas 10 * 12V would still be under 150, 10 * 17V isn't!

    The "rule of thumb" for array Voltage is "one step up" from system Voltage: 12V system gets 24V array. The reason for this is that the efficiency of the CC goes down the greater the difference between array Voltage and system Voltage. It's not a perfect way of calculating, but it "gets you "in the ballpark" so to speak.

    So what is your system Voltage?

    For 4 12V panels you could have: 4 in parallel for a 12V system (around 30 Amps on the downlead) 2 strings of 24V for a 12V or 24V system (around 15 Amps) or 4 in series for a 24V or 48V system (about 7.5 Amps). Roughly, and I want to emphasize that, speaking.

    WOW, I will read up and stop asking repetitive questions, I have my wire in a 200' conduit, with this setup I could pull the 1200' feet of 0000 out and sell it:D