Howdy,
I was just reading my inverter manual and in the wire sizing chart it says to multiple the length of wire x 2 for purposes of calculating wire/size and voltage drop. It is rather poorly written and I am hoping not saying what I think it is saying, because I have never multiplied wire length x 2 in my system design! Have I been doing it wrong?
thank you
Quote from: pablo on October 18, 2016, 05:41:32 PM
Howdy,
I was just reading my inverter manual and in the wire sizing chart it says to multiple the length of wire x 2 for purposes of calculating wire/size and voltage drop. It is rather poorly written and I am hoping not saying what I think it is saying, because I have never multiplied wire length x 2 in my system design! Have I been doing it wrong?
thank you
It is simply that the run is one conductor out and one back!!
Those electrons need a complete path.
It is for ease of calculation.
Cable resistance is generally expressed as ohms per foot so you need all the feet as it were.
Not sure what you are concerned about.
This is DC electricity 101 stuff. And a well established standard for these calculations. Trust me.
Tom
Pablo
If your inverter is 6 feet from the battery bank measuring from the out of the positive to the breaker & then to the Positive in on the inverter And Your Negative is from the battery to the shunt & then to the inverter negative in is 7.6 feet you would use 13 .6 feet or round it to 14 / 15 feet to be safe.
Use that with the Max AMP draw for cabling size.
Your lucky your not asking on the long runs of solar panels to the combiner/CC ..
VT
Thanks guys.
So my array is 75 feet from the charge controller and I used 75 feet to calculate voltage drop and wire size. I should have used 150 feet? You can see my concern. If this is true then I probably have undersized my conductors system-wide and probably have too much voltage drop not too mention possible safety issues... :(
I believe some of the calculators online have the round trip distance already calculated. But if the one you used said to multiply by 2 then it probably didn't.
What voltage and amps did you use for your calculation ? What wire size ?
Larry
Actually the calculators I used did NOT say to multiply by 2. This is just something I noticed later in my inverter manual and made me wonder if I should have multiplied by my lengths by two.
For the run from the panels to the house: 39 VOC, 9 amps, and 4/0 AL conductor.
According to the windsun calculator
Results:
A maximum distance of 556.14 feet will limit the voltage drop to 3% or less with a 4/0 AWG Aluminum conductor delivering 9 amps on a 39 volt system.
So I guess you are okay !
http://www.windsun.com/Hardware/Voltage_Calc.htm
There are lots of Excel calculators on the internet if you do a search
Here is one
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&ved=0ahUKEwiRk8H91-XPAhWM0YMKHRrXCyYQFghJMAc&url=http%3A%2F%2Fw8usa.org%2Fwordpress%2Fwp-content%2Fuploads%2F2013%2F01%2FSolar-and-Battery-Sizing.xlsx&usg=AFQjCNEB3PnVjsAJKP1S1ARS79Ok3nVscQ&sig2=rB-kePXBtpFTL78AJPOExw&cad=rja
Quote from: pablo on October 18, 2016, 08:41:05 PM
Actually the calculators I used did NOT say to multiply by 2. This is just something I noticed later in my inverter manual and made me wonder if I should have multiplied by my lengths by two.
For the run from the panels to the house: 39 VOC, 9 amps, and 4/0 AL conductor.
You have only one string of panels ?
Pablo , what is your array size & wiring configuration as in series & Parallel feeding the 75 foot away or 150 foot in round trip ?
VT
My favorite is http://www.calculator.net/voltage-drop-calculator.html (http://www.calculator.net/voltage-drop-calculator.html)
...errr this doesn't look right.
What happens if the neg to earth tie is used in the Epanel or MNSC and the PV array negatives are tied to an earth as well, at the PV array mounting? Is that insufficient to ensure the negs at the controller and PV array are equal?
In any case how could you ever measure the actual voltage loss in a -ve cable earth ties at both ends?
So you connect a fluke voltmeter at the PV end of both -ve and +ve bus connections eg in PV combiner and take a voltage reading.
Then you measure the voltage at the Classic PV input terminals?
So does that mean that both the -ve and +ve are voltage dropped? the +ve is lower and the -ve is higher?
dgd
Well in our case it is not code compliant to wire it like that. BUT that said If the PV - line was earthed on both ends and you did v drop calculations based on the 2 conductors you would just not have as much drop as the resistance on the negative side would be less
Ok thanks everybody. It sounds like I am ok. Freaked out for a minute there....I'm glad I over-sized my conductors throughout the system.
VT: I'll let you know. Don't have my diagrams with me at work right now. But yes, 1 string of 2 panels at 285 watts each. I believe wired in series.
Pablo
Post 10 11 & 12 do not effect you.
VT
I figured. Thanks.