Help-Wire Gauge-Load

[Wits' End]

I'm trying to decide what gauge wire to use in a Solar application. I'm currently (no pun intended) looking at 48V 340 watts for 100' from panels to charge controller. I hope to double my panels so I'll have 48V, 700 W for 100'. Will 4 Gauge be enough/too much, can I wisely go with lesser gauge? Any suggestions for DC safety? Source for breakers? Any suggestions are welcome and will maybe help others also. I'm taking a big step from 100W 12V system I had/have.
Thanks, Herb

 

[TigerhawkT3]

In my 600W landing light (LK12), I use 12AWG wire and it works fine. It operates at 28V, 22A. Of course, it uses barely a foot of wire, so I don't know how well it would work for 100'. You might be better off with 10AWG. I don't use that light very often, so I went with a simple fuse instead of a circuit breaker, so I'm not sure where you'd find an appropriate breaker.

Good luck.

 

[Diesel_Bomber]

Wire gauge/distance/amperage calculator.

 

[modamag]

Hi Herb,

For a 48VDC 700W @ 100' system even 6AWG is marginal, and 4AWG should do it with an extra 50% capacity. Check out solar4power.com for their suggestion.

Luckily you don't have to go with high current breakers. They are mulla expensive @ Grainger.

BTW: You should check with Darell, he's the solar guru.

Tiger, your larryk12 is only couple of inches of wire so it's not that significant. Herb need 100 feet which have much higher line loss.

 

[TedTheLed]

at that wattage 4 gauge should do it. you could go to 6, but not wisely and safely.

(bah Darrell shmarryl, what does HE know? )

 

[65535]

The lower guage the better, but since you are running medium current I would say you would want something around 6 guage, if you were doing 12 volts and 700 watts I would say 1# or larger.

 

[blahblahblah]

At 48v and 700w, you'll be at less than 15A. Keep in mind, a nominal 48v solar system can really be putting out 72v, depending on the panel manufacturer. The wattage will remain the same and the amperage will decrease (to under 10A) due to the increased voltage. The charge controller that is near the batteries will handle the charging regulation.

Will 4awg be sufficient??? Yes
Can you go to thinner wire??? Yes, but if you can budget for 4awg, use it.

I just did some 20A 240v AC work yesterday and I chose 8awg over the required 12awg. Why??? If I ever upgrade to a larger AC unit, I don't want to break drywall and stucco again! I also have another welding outlet near the AC.

 

[qip]

on another note i was watching xtreme 4x4 on fx ," tv show" and the guy mentioned about wire gauges for his winch and he said since electricity mainly rides along the outside of a wire not the core it is better to use the strand type wire in the guage you choose like this on the right ...same guage ones thick ones thin wire https://www.expeditionexchange.com/jlaudio/jlaudio002 007.jpg


suppose to be less resistance as a benefit

 

[greg_in_canada]

Skin effect only applies at radio frequencies. I'm too lazy to look up the formula but at 60Hz the current is carried by the whole wire.

Greg

 

[jrmcferren]

Check those wire sizes again, I'm only calculating around 15 amps. 10 AWG should be enough for this, but you guys know a bit more than me when it comes to things under 120 volts.

 

[blahblahblah]

Check those wire sizes again, I'm only calculating around 15 amps. 10 AWG should be enough for this, but you guys know a bit more than me when it comes to things under 120 volts.

Yes, he might get away with 10awg without risking fire or damage to the stucture. But here's another way of thinking about it and of why it is worth it...


If you have 4 x 175w panels valued at $900ea ($3600 total).

Let's say the 10awg costs $50 and the 4awg costs $160 ($110 more).

10awg gives 7.5% loss and 4awg gives 1.9% loss (5.6% difference)

5.6% of his $3600 solar panel is $210 of lost/wasted capacity

$210 is > $110 of added cost for bigger wire

 

[Brock]

Herb you have to come over and check out
http://www.wind-sun.com/smf/index.php
What charge controller are you getting, battery bank, inverter? I currently have stacked Trace SW2412's, 4 KC 120's for 480w of PV, MX-60 charge controller, Trimetric meter and either 8A8D AGM's or 1960A at 12v or or 24kw of battery
check out http://www.uwgb.edu/nevermab/solar.htm
I also have a wire size calc on my site as well
http://www.uwgb.edu/nevermab/voltage_drop_calculator_.xls

As blahblah noted the larger wire you use the less loss and loss is $ in solar. I would recommend at least #6, prefer #2. When you have 4 panels in series you will actually be up around 60v. If you're using a MX-60 for a charge controller you could go 5 in series to get the voltage up a bit more without adding amperage.

 

[TedTheLed]

I'm in accorde with Brock and blahb.b..esp. blahblahb.'s math, a man after my own heart !
..just look at the charts and you can see wire gauge requirement goes down dramatically as the voltage goes up.. I would add only to keep in mind that as the voltage goes up so does the possibility of sparks, so if you're running wire near anything combustible, it would be wise to make sure everything is well-insulated..

...and that in some places building codes may have something to say about installations over 24 volts..

 

[MrAl]

Hi there,

With a constant resistance load (many loads are like this) here are the efficiency
numbers for four different wire gauges when the run is 100 feet one way
(200 feet total wire length):

#14, 93 percent
#12, 96 percent
#10, 97 percent
#08, 98 percent

Number 12 isnt that bad really.

If you have a constant current load (7.08 amps) then the efficiencies will be about
twice as bad, so for #14 gauge wire the eff will be around 86 percent.

 

[Wits' End]

Wow!
As usual I'm blown away by the experienced help available and given. My new system has two 24V 170W panels. I may add 2 more if I feel i need it.
OutBack MX60 MPPT Charge Controller and a Trace inverter (model ??) that allows me to charge from a generator as well.
I was hoping that someone(s) would say no reason to go with 4 Ga. As that was recommended. Any suggestions for least expensive (including shipping) 4 Ga stranded?
I assume that stranded is better overall. Welding cable OK?

 

[MrAl]

Hi there,

I thought my post was self explanatory. Number 12 wire isnt that bad for your
application but if you really want good eff then go with number 10 or number 8.
No good reason to use number 4 wire, just to gain 1 percent efficiency.

Here are the efficiencies referenced to 340 watts for seven wire gauges:

#4, Eff=0.985
#6, Eff=0.977
#8, Eff=0.964
#10, Eff=0.944
#12, Eff=0.912
#14, Eff=0.866
#16, Eff=0.799


This shows #12 losing about 9 percent, while #8 loses about 4 percent.

 

[Wits' End]

These are my thoughts Al (the quote below). However I see Brock and Blahblah talking with some experience of Solar suggesting the 4 or minimum 6. I'm definitely interested in dollar savings and being efficient. But doing so at the cost of power to my batteries isn't a good plan. I'm open to more discussion though

Thanks--Herb

Hi there,

I thought my post was self explanatory. Number 12 wire isnt that bad for your
application but if you really want good eff then go with number 10 or number 8.
No good reason to use number 4 wire, just to gain 1 percent efficiency.

Here are the efficiencies referenced to 340 watts for seven wire gauges:

#4, Eff=0.985
#6, Eff=0.977
#8, Eff=0.964
#10, Eff=0.944
#12, Eff=0.912
#14, Eff=0.866
#16, Eff=0.799


This shows #12 losing about 9 percent, while #8 loses about 4 percent.

 

[65535]

Has anyone ever used a step up inverter or boost transformer to increase voltage so that a smaller wire guage can be used? I know that most cheap (relatively) units are rather inefficient.

 

[VidPro]

Yes, he might get away with 10awg without risking fire or damage to the stucture. But here's another way of thinking about it and of why it is worth it...


If you have 4 x 175w panels valued at $900ea ($3600 total).

Let's say the 10awg costs $50 and the 4awg costs $160 ($110 more).

10awg gives 7.5% loss and 4awg gives 1.9% loss (5.6% difference)

5.6% of his $3600 solar panel is $210 of lost/wasted capacity

$210 is > $110 of added cost for bigger wire

YUP, i second that, if you can deal with the unruley fat guage wires, even with such a high voltage (system), which will be less amperage and therfore less total loss.
Its amasing how much loss can exist via the trail to get it there.
And of good copper quality too, solid will work fine, stranded only if you need to bend it many times (non stable instalation).
fat wire important, especially when it comes to the distances like over 100'.

The voltage differential at the charge point will somewhat determine the charge amperage. so a small minor loss in total voltage, will result in a good loss of charge amperage. so depending on all the parts and pieces, the smaller losses along the way will result in larger changes to the total, because of voltage differentials of the storage and the charge.
(ok so it isnt said right, but Wider is better)

if somone wanted to put that into proper MATH for efficency, take your storage voltage (battery), and your starting voltage (solar cells TOTAL as measured not rated), now if its EVEN, then you have 0 moving electrons. so your efficiency losses, have to be determined from the voltage DIFFERENCE between the two items. math and science only gets complicated severly when put into reality :-(

so calculate your voltage DIFFERENCE, then your "total voltage loss at its maximum amperage" * , and that would be your actual efficiency issues. because your not shorting out the other end., its attached to something that is already at some specific voltage.

*i guess you would have to do the ohms thing to use that guage chart

ok math aint my strong suit, but i seen the effects on the ampmeter.

 

[MrAl]

Hi again,

Some interesting views. One thing to keep in mind though is that we are talking
about full sunlight on a bright day with the angle close to 90 degrees. Even
the slightest deviation from this perfect picture means 1 percent (compared to
a perfect day, regulated angle thoughout the day, etc.) is lost anyway.

It's good to look at the cost difference in wire gauge too as has been done here,
and another thing to keep in mind is the quality of the wire. If the wire has to
be replaced at some point a few years from now that will mean more cost too.
I believe the wire to get is the 'oxygen free' wire, which doesnt corrode inside.
Some cheap wire will corrode inside even when used indoors.

DC DC converters are generally in the efficiency range of 75 to 85 percent efficient,
unless you build your own using high power mosfets and use sync rectification.
If you boost up 2.5 times you'll get 120 volts, and your current would be about
2.8 amps which would be great for the wire choice, but since the booster will loose
more efficiency points than the wire it is not going to be worth doing just for this
reason alone. If your end load requires 120vdc anyway, then it is definitely worth
doing.

Another thing to look into is automatic solar tracking, which keeps the solar panel(s)
pointed directly at the sun. The panel output goes down as the angle is changed
from 90 degrees, and the effect can be quite high losing a percentage of the output
just because the panel is not pointing at the sun as the sun passes overhead from
morning till evening. A solar tracker tracks the movement of the sun (usually with a
set of small solar cells) and moves the panel appropriately. Some are built to track
the sun as it moves overhead (relative to the earth) along one line, while some
others will track the sun as it moves overhead and also tracks as it moves from
side to side thoughout the year.

In any case i hope you keep us posted about this interesting project.
I thought about doing the same many times (mainly battery charging apps) but
i see the solar panels are still quite high priced.