# Solar Question.



## City Bound (Jan 24, 2009)

I read in the manual for the solar kit that I bought that I need to keep the charge controler about ten feet from the panels, the baterry about five feet from the controler, and the inverter five feet from the battery.

My problem is that I need to run a 25 f cable from the panels on the roof down into my apartment, and then connect to the controler, the baterry, and the inverter inside my apartment.

Can I run such a long cable between the panels and the rest of the system?

Can you intersect the line between the panels and the charger with some kind of transformer to boost the signal to make it travel over 25 foot of cable?

Any help would be great.
Thanks


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## 12vman (Feb 17, 2004)

How many watt in panel do you have? What voltage?


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## wy_white_wolf (Oct 14, 2004)

City Bound said:


> ....Can I run such a long cable between the panels and the rest of the system?
> 
> Can you intersect the line between the panels and the charger with some kind of transformer to boost the signal to make it travel over 25 foot of cable?
> 
> ...


Yes to the 25' but you may need to run a larger size cable than came with the kit to compensate for line loss.

No to the second part.


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## City Bound (Jan 24, 2009)

Thanks guys. I really appreciate the help.


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## City Bound (Jan 24, 2009)

12vman said:


> How many watt in panel do you have? What voltage?


12v, I have a 60 watt, 12 volt system.


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## City Bound (Jan 24, 2009)

wy_white_wolf said:


> Yes to the 25' but you may need to run a larger size cable than came with the kit to compensate for line loss.
> 
> No to the second part.


What size wire would you recomend?


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## 12vman (Feb 17, 2004)

http://www.builditsolar.com/References/pvwiring.htm Thanks, Gary!

Quote..
"Maximum distance one-way in feet of various gauge two conductor copper wire from power source to load for 2% voltage drop in a 12 volt system."

Your 60 watt panel will produce ~5 amps of current. Use 6 amps on the chart. It suggests #8 wire to 30' in distance.


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## PD-Riverman (May 24, 2007)

If you got one of the 60 watt kits that has 4, 15 watt panels, you can connect the wires from all 4 panels together in a weather proof box, hooking the positive wires to a 8gauge wire(for the length of run stated) then the negative to another 8 gauge then run these 2 8 gauge wires to your charge controller.




City Bound said:


> 12v, I have a 60 watt, 12 volt system.


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## idahodave (Jan 20, 2005)

I'd have a different answer.

A 60 watt PV for 12 volts normally has a peak power output at around 17 volts. This will be 60/17 or about 3.5 amps. A 60 watt panel will not deliver 5 amps.

To fully charge the battery it takes 14.4 volts. Starting from a partially charged lead acid battery that could drop to 12.5. There is excess voltage that can be used in the wiring and charge controller. 

If the loss in the wire was limited to 0.5 volts that would be 0.5/3.5=.143 ohms of resistance in the 50 feet (25 ft each side) of wire or .143/50=0.0028 ohms per foot. Looking at an ohms/ft table 14 gauge is .0025 ohm/ft. Power in the wire would be (3.5*2)*0.125 or about 1.5 watts.

14 gauge is good, 16 gauge would drop 0.7 volts and work OK.

This calculation is good only for the PV side using a conventional charge controller (not MPPT) because the panels have excess voltage. The load side from the battery out is different and should have minimal loss.


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## 12vman (Feb 17, 2004)

Your correct Dave, but its highly unlikely the voltage coming from the panel will exceed the float/bulk charge voltages. The battery resistance and the charge controller is going to hold the voltage down.

By using 12 volts when figuring wiring, the fudge factor is built in. When figuring the current of a 12 volt panel, using 17 volts usually works out real close.


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## idahodave (Jan 20, 2005)

I reduced the PV current output a little too much...the calculations were at the MPT and the current at that point is about 10-15% lower than a normal operating point. 

Voltage drop in the wire would be closer to 0.57 and 0.8 volt, so the conclusions are the same.


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## City Bound (Jan 24, 2009)

Wow, you guys are great. I really appreciate the help.

I have a 7 amp controler.
I have four 15 watt panels.

The load side of the battery is fine, I have the inverter and the wires that came with the kit.
The trouble is the distance between the panels and the rest of the system which will be located in the only place I can store and use the electricity, my bedroom.

Dave, so when you take length into account you have to double it? Is that because the electricity travels back over the negative wire, forming a loop? If it does form a loop, why would it need to do that?

I am as green as they come when it come to electricty, so please parden my nievity.


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## City Bound (Jan 24, 2009)

There are few different opinions of the wire gauge, I am a little lost there.

8 gauge wire is thicker then 14 gauge, does a thicker wire give less resistance over a long distance?


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## 12vman (Feb 17, 2004)

Personally, I'd go with 8 gauge. It might be a little over kill but when you're dealing with a small amount of current, you need all that you can get to the battery. You can't afford to have any losses.

By installing 8 gauge, you could add another set of those panels and still be OK and not have to fool around with making another run of wire if you decide to expand in the future.

Just my opinion..


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## City Bound (Jan 24, 2009)

Vman, so eight gauge could handle another 60 watts? I might get more panels in the future. These 15 watt panels are very affordable.


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## 12vman (Feb 17, 2004)

Yep.. 120 watts divided by 17 = 7.06 amps. 8 gauge wire is good for ~22.5 ft. @ 8 amps for a 2% loss according to the above chart.

Quote..

PV BATTERY CHARGING CIRCUITS are critical because voltage drop can cause a disproportionate loss of charge current. To charge a battery, a generating device must apply a higher voltage than already exists within the battery. That's why most PV modules are made for 16-18V peak power point. A voltage drop greater than 5% will reduce this necessary voltage difference, and can reduce charge current to the battery by a much greater percentage. Our general recommendation here is to size for a 2-3% voltage drop. If you think that the PV array may be expanded in the future, size the wire for future expansion. Your customer will appreciate that when it comes time to add to the array.


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## idahodave (Jan 20, 2005)

Yes the current flows out one wire and back on the other, so the round trip will be twice the length. #8 wire is big and will work good for a couple of sets...I was trying to save you a little money and make the connections a bit easier as #8 wire is hard to work with. I still think #14 is fine.


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## City Bound (Jan 24, 2009)

Dave, thanks, I appreate all your help. I will look up the price of 8 guage wire and if it is way to expensive, I will consider 14. I like vman's point that 8 gives me the option of adding more panels without reduing the wiring.

What do you guys recomend with the battery? Right now I have one 12v car battery, and I have that just to set the system up and to learn how to use the panels. I was thinking that I may get another car battery and have two batteries in my small system that will be used to charge a computer and run some lights. Do you think two batteries is a good start?

Eventually, down the road, I will get some 6 volt golf cart batteries, because i hear they last the longest.


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## City Bound (Jan 24, 2009)

What do you guys think of this wire?
http://www.solar-electric.com/8-2-tc.html
If I get this, then I dont need two wires right?
Both wires are in the cable, right?


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## idahodave (Jan 20, 2005)

Yep, its a pair of wires and should work good. 

Don't forget something to make connections with if the panels or charge controller have wires for connections. Probably need some big wire nuts (usually would be a grey color) or split bolts.


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## City Bound (Jan 24, 2009)

Ok thanks everyone. I will stop in again if I have any problems during the set up.
Thank you again.


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