Ok so the ts-MPPT-60 is on its way, I put the card board cut outs on the roof just to make sure the panels fit as I thought and now on to more planning.I check a few voltage drop calculators for the three 250w polys in parallel pushing 30+ amps Isc at 35v for 35 ft. From various calculators I am seeing everything from 2 AWG to 10 AWG. I say 30a+ because the panels easily exceed their Isc here and even more so at altitude. I can't tell how much because my 10a meters pop as soon as I attempt to check them.I am assuming 2 AWG is going to be pretty pricy. 10 AWG is cheap but the cost comes in voltage drop. The different calculators say different levels of voltage drop.I am not going series and thinner wire for shading considerations and controller efficiency, otherwise the 10 AWG would be fine. The only shade issue from the rig would be when the sun is very low and the trailer pointed in a east/ west direction. Even then only one out of three panels will be affected. ( max air covers are too tall)So what is the happy medium here? What is considered acceptable voltage drop?

You can find the wire resistance per 1000ft and calculate the resistance for your distance. Multiply times two. Positive and negative lines. How much voltage drop are you willing to accept? I thik you answered your own question it will be somewhere in between #10 and #2. I suspect I would run #6 or #8. I ran some #6 the other day for a house line think it runs about $1 a foot. Pretty good quality stranded at Home Depot.

Hi Jim,1% is nice if you can manage it. 3% is the upper limit for acceptable voltage drop.I'm at about 1% but I have 1/3 your wattage.

I would go with 2 gauge marine battery cable. 2ga will cost about $3/ft, 4ga $2/ft and 6ga about $1/ft. If you go with 2ga you will be set for expansion.

The voltage on that path would be less than the Voc at the panel temperature, so your calculation should be for the approx Vmp.Eg, my 230w panel rated at 37Voc is at 34Voc out in the sun, but the measured voltage between panel and controller on mine is more like 29.3v at the panel and 29v at the controller input terminals (1% drop) I believe the 29ish volts is what the controller chose for Vmp at the time I measured. (Rated panel Vmp is 30v)IMO it is not worth fine tuning for AWG on that path, since your panels are flat and so already operating below optimum, which is why to have so many panels, so who cares about a little loss here and there elsewhere in the set-up?I prefer this calculator tenbear posted since it makes it clear the distance is one way for a pair, so you don't have to wonder if you should double it or not like some of those other tables make you wonder.http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=2.061&voltage=12&phase=dc&noofconductor=1&distance=60&distanceunit=feet&eres=8&x=42&y=5

Check with your local automotive audio shops. They have some good braided very flexible wire in the larger sizes.

panel wire AWG to controller | Good Sam Community

WyoTraveler
Explorer
Apr 12, 2015
You can find the wire resistance per 1000ft and calculate the resistance for your distance. Multiply times two. Positive and negative lines. How much voltage drop are you willing to accept? I thik you answered your own question it will be somewhere in between #10 and #2. I suspect I would run #6 or #8. I ran some #6 the other day for a house line think it runs about $1 a foot. Pretty good quality stranded at Home Depot.
pianotuna
Nomad III
Apr 12, 2015
Hi Jim,

1% is nice if you can manage it. 3% is the upper limit for acceptable voltage drop.

I'm at about 1% but I have 1/3 your wattage.
jhilley
Explorer
Apr 12, 2015
I would go with 2 gauge marine battery cable. 2ga will cost about $3/ft, 4ga $2/ft and 6ga about $1/ft. If you go with 2ga you will be set for expansion.
BFL13
Explorer II
Apr 12, 2015
The voltage on that path would be less than the Voc at the panel temperature, so your calculation should be for the approx Vmp.

Eg, my 230w panel rated at 37Voc is at 34Voc out in the sun, but the measured voltage between panel and controller on mine is more like 29.3v at the panel and 29v at the controller input terminals (1% drop) I believe the 29ish volts is what the controller chose for Vmp at the time I measured. (Rated panel Vmp is 30v)

IMO it is not worth fine tuning for AWG on that path, since your panels are flat and so already operating below optimum, which is why to have so many panels, so who cares about a little loss here and there elsewhere in the set-up?

I prefer this calculator tenbear posted since it makes it clear the distance is one way for a pair, so you don't have to wonder if you should double it or not like some of those other tables make you wonder.

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=2.061&voltage=12&phase=dc&noofconductor=1&distance=60&distanceunit=feet&eres=8&x=42&y=5
enblethen
Nomad
Apr 12, 2015
Check with your local automotive audio shops. They have some good braided very flexible wire in the larger sizes.
time2roll
Nomad
Apr 12, 2015
#6 looks like 4% and #4 is 2.5%

750 watts 4% is 30 watts lost.... I would use #6.

http://www.genuinedealz.com/voltage-drop-calculator

The drop only applies during an hour of max bulk charging, not all day.

I did mine in series with #10 MC4 wire.
2oldman
Explorer II
Apr 12, 2015
I'd probably do #8 or #6, but for that little shading, series would not be a problem. Then #10 is fine.
JiminDenver
Explorer II
Apr 12, 2015
I am using the numbers from tracking not flat as they will be. I'll do a flat test on one of the panels today and see what the numbers are here at a mile high. I can tell you that I have seen a working voltage of 33v tracking. Yesterday I was seeing over 18a out of the Eco-w.

It sounds like 4 or 6 AWG will be fine as there is no room for expansion. I'd think bus bars to combine the feeds as MC4 branch connectors are rated at 30a. Running the Ac at high noon may be pushing that limit.

Now to see where the controller is going to see if the 2 AWG will handle the 50+ amps going to the bank.

So far I'm in for just under $1200 for the panels and a respectable controller/ remote display. I'm hoping for a total around $1500 or so but still have mounting, wiring, switches, fuses and probably more to go. (not to mention new batteries) Costly compared to tracking on the ground with Eco-worthys but in the end it will be worth it.
westend
Explorer
Apr 12, 2015
I bought AWG 4 welding cable from Waytek Wire for $1.20/ft. They are local to me, you should be able to find a similar deal in Denver. #4 is a good size for wiring switches, fuse boxes and such because the lugs are readily available in different sizes to accommodate a variety of posts. I think I have 20' left of a 100' roll.
grizzzman
Explorer
Apr 12, 2015
JiminDenver wrote:
I am using the numbers from tracking not flat as they will be. I'll do a flat test on one of the panels today and see what the numbers are here at a mile high. I can tell you that I have seen a working voltage of 33v tracking. Yesterday I was seeing over 18a out of the Eco-w.

It sounds like 4 or 6 AWG will be fine as there is no room for expansion. I'd think bus bars to combine the feeds as MC4 branch connectors are rated at 30a. Running the Ac at high noon may be pushing that limit.

Now to see where the controller is going to see if the 2 AWG will handle the 50+ amps going to the bank.

So far I'm in for just under $1200 for the panels and a respectable

controller/ remote display. I'm hoping for a total around $1500 or so but still have mounting, wiring, switches, fuses and probably more to go. (not to mention new batteries) Costly compared to tracking on the ground with Eco-worthys but in the end it will be worth it.

Your in it 1500 plus and you want to skimp on the wiring?......... just sayin.......

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