Any harm in using thinner gauge wire?

[Wxboy]

After 3 or 4 weeks of owning a Classic 150 I'm finally going to get my first solar panel tomorrow.  I'm piecing this system together on a low budget so I'm trying to work with existing wire to save money.  Currently I have 50 feet of 8 gauge or 25 feet of 6 gauge wire to use from the panel to the controller.  25 feet isn't enough to do what I want so my question is this...Is there any harm in using the thinner wire other than the fact that I will lose more than the recommended 2% line loss?  I know I will get less power to the controller with the 8 gauge wire but I will have more flexibility of where I can place the panel.  For now I don't have a permanent mounting solution(or any mounting solution for that matter) so I will be moving the panel from time to time when I'm home to keep it in the sun.  I'm starting small but I plan to be adding panels as the years go on. 

Panel specs:
SolarWorld SW 255 mono
20V nominal
Performance under STC:
31.4V Vmpp, 8.15A Impp

[Halfcrazy]

If you are running just the one panel and it is say 30ft away I do not see a problem. From a purely safety stand point #8 will handle a bunch of amps so it really boils down to acceptable Voltage Drop. And using what you have and having it work will be better than not using it at all as long as you stay in the safe ampacity of the wire.


Ryan

[Westbranch]

Since he has both sizes, is there any benefit to using #6 and #8 wire?
It may be a bit more efficient than just #8?

[Wxboy]

I should have mentioned in the original post that I have to pick one or the other.  The wire is my father's and I have to return whatever gauge I don't use.

Ideally I want to have a 75 foot run of wire.  So I'm hoping that I can use 50 feet of 8 gauge for now with one panel.  And then if I add a second panel in series that would increase the voltage and I could get away with adding another 25 feet of 8 gauge at that time??

[niel]

for a temporary setup with just the 1 pv it would do quite well as it would be just about 1% on the voltage drop for a total wire length of 50ft. this would include going from the controller to the batteries too. when you go for the bigger system you can plan it out better, but some big systems don't have v drop percents as low as your temporary installation.

[Wxboy]

Finally got the system set up with the full run of wire today.  I did a week of testing with the Classic in the garage with a short run of wire(6ft) and then a medium run(50 ft) and now it's in the house with the full run.  I ended up pushing things farther than planned.  I'm running 50 ft of 8 awg and 25 ft of 6 awg for a total of 75 ft(1 way) from the Classic to the panel.  I didn't test the actual line loss but I was pulling in 205 watts at high noon from the 255 watt panel so I can work with that.  Pulled in over 1 KW today and considering the panel is at ground level and I have trees in my yard I was very happy with that.

[niel]

this is not what you first indicated in your initial post. one way means there is a plus and a minus wire travelling that distance. with 50ft of #8 one way that's 100ft of wire and that doubles things right there.
you also added the #6 at 25ft one way for a total of 50ft of wire and that adds to the total v drop percentage as well.

calculating for 8.15a in both cases i get 2.08% on the #8 wire and 1.71% on the #6 wire for a total of 3.79% v drop. the #6 is much higher than what you might've thought because the voltage is much lower after the controller being 12v nominal. it is also not very desirable to have much more than 1% v drop after the controller as it could fool the controller into thinking the battery voltage is much higher than it actually is because the wires would drop that voltage lower. that could stop you from properly charging your battery. you will lose .2v from the classic to the battery. you don't want to raise the voltage on the classic either to compensate for when it goes to absorb the current diminishes and so does the v drop and it would overcharge some here. if this is an agm or a gel battery you could harm it. you may get away with this amount on a fla type. in reality that added wire over what you originally said puts the setup way out of whack with losses, but it will still work. if you have to add wire anywhere it should be between the pv and controller as the higher voltages there will present a lower loss for the same wire size and length.

[Wxboy]

I had a feeling people misunderstood my first post and that's why I added the 1 way clarfication yesterday.  Sorry for the confusion. 

Just to make sure there isn't any more confusion I'll explain the wiring in a little more detail.  From the controller there is 50 feet of 8 ga. wire + and - and then there is another 25 feet of + and - wire spliced in for a total of 75 feet 1 way between the controller and the pv.  Between the controller and the battery there is about 4-5 feet of 8 ga. wire.  I get the feeling you were thinking I had a longer run of wire to the battery. 

I did notice that at higher current the controller reads low by .1v but under low current it's spot on so I figured that was due to the loss in the 8 ga. wire.  I am using a fla battery so if it's off by .1v it should be ok but for today I turned off the temperature compensation just to be on the safe side with the battery since it is in my cool basement with no ventilation other than the leaky windows.   

My dad did loan me a couple of small agm batteries so I may use those for now just to increase the safety factor related to gassing.  My battery is 6 years old and is nearly useless for storing energy at this point anyway so the agm's would serve 2 purposes.

[niel]

to be sure that you understand, you have high losses for your system.

do not disconnect the bts or you can make things worse for it is there for a reason.

[Wxboy]

Since I am new to this, what is the harm in having 5% loss in the wiring from the pv to the controller?  I know I lose power but will it harm the system? 

[niel]

no it won't harm the system, but it will hinder it.