BajaNomad

Solar wiring ?

Santiago - 4-30-2011 at 09:43 AM

Before you guys pile on, remember "There are no stupid questions"!
I am designing my little solar system and all the tables and interactive programs kick out that I need #6 wire from my panel combiner box to the charger. OK, I can do that.
But, I have available for free, twisted #12, professional crimper and lugs. Can I use two runs of #12 in place of one run of #6? In other words, do two #X wires safely carry as much current as one #X/2.
I realize there are two issues here:
1. Are wire sizes additive or logarithmic?
2. Does the physics of 'lectricity follow whatever the answer to #1 is?

Bob - I KNOW what you're gonna say, but wire is expensive and the #12 and accessories are FREE.:coolup:

woody with a view - 4-30-2011 at 09:49 AM

my stupid answer would be yes. use three strings if you have it.

disclaimer: all i know about electricity is....

#1 it is invisible.
#2 it hurts.

good luck with the project!

BajaGringo - 4-30-2011 at 09:59 PM

Better setup would be to wire the panels in series (summing the voltage) which will allow you to run thinner wire fed into an MPPT controller.

Bob and Susan - 5-1-2011 at 03:54 AM

listen...been there done that...

when it gets HOT there is resistance in the wire
voltage goes WAY down

#2 wire IS the answer
don't cheap-out $$$ with this...
i'm seeing again and again problems when the "heat" starts

even if "the experts" tell you differently they don't depend on their batteries

and others talk about wiring your panels at a higher voltage to reduce the line...
remember the RULE...
"bring it to mexico and it'll break"

with 72v if you lose one 12v panel...you lose 6
with 24v if you lose one 12v panel...you only lose 2

i would wire to 24 volts

remember do it RIGHT the first time or you WILL be doing it again

edit...
i started with #10 wire because the solar guys told me the 20 foot drop wasn't that great...
hahahahhaa
by july i had dead batteries
it took a week of generator time to "bring them back"
mucho $$$ in gas



[Edited on 5-1-2011 by Bob and Susan]

Russ - 5-1-2011 at 06:15 AM

I agree with B&S

BigWooo - 5-1-2011 at 06:26 AM

Follow Bob's advice. I've seen way too many setup's where the owner "cheaped out" and have had nothing but problems.

RnR - 5-1-2011 at 06:42 AM

Quote:
Originally posted by Santiago
Can I use two runs of #12 in place of one run of #6? In other words, do two #X wires safely carry as much current as one #X/2.
I realize there are two issues here:
1. Are wire sizes additive or logarithmic?
2. Does the physics of 'lectricity follow whatever the answer to #1 is?

Bob - I KNOW what you're gonna say, but wire is expensive and the #12 and accessories are FREE.:coolup:


Follow this link to the NEC ampacity tables:
http://www.armstrongssupply.com/wire_chart.htm[/url]

The temperatures listed at the top of the table are for the wire insulation class not ambient air temperatures. The goobledegook of letters in the next row are the insulation designations printed on the wire itself. (One of the most common: THHN)

You can add the ampacities of various conductors to reach your total required ampacity. Looks like you'll need more than two #12's to equal one #6. Parallel conductors are used all the time to acheive required ampacities.

That said, using a single large conductor is always better electricity-wise.

And now, after saying that: FREE IS ALWAYS BETTER!

[Edited on 5-1-2011 by RnR]

[Edited on 5-1-2011 by RnR]

capt. mike - 5-1-2011 at 07:51 AM

the minimums are all published at NEC and NABCEP for wire size load and distance. never exceed the stated specs in the tables, don't be cheap and don't have to over think it - the EE's have already done the calcs.

larryC - 5-1-2011 at 08:49 AM

As several others have already stated "there is never enough time or money to do it right the first time but there is always enough time and money to do it right the second time".
I would use at least #4 but #2 would be better. Gives you room to grow. Solder and crimp the connections, then tape or heat shrink them. I have a hydraulic wire/cable crimper if you need some help.
Larry
PS Did you see the latest deal at sun electronics? Evergreen panels, $1.64 a watt, free shipping.

[Edited on 5-1-2011 by larryC]

Bob and Susan - 5-1-2011 at 09:33 AM

evergreen may be out of business next year
the chineese are undercutting them...

i'd stick with something "made in mexico":saint:

Santiago - 5-1-2011 at 12:08 PM

Quote:
Originally posted by soulpatch
Your runs can't be that far so cut back on a box or two of wine and do it right.

Heh - that's a good one right there.
Looky what I just found in the back of the shed - about 18' of black 2/0 and 19' of red 2/0......AND an 8-ton hydraulic wire crimping tool from the disposable tool company with dies from 00 to 12. Damn 2/0 is so big I'm afraid the 'lectricity will just wander around in there and never come out the other end.....

[Edited on 5-1-2011 by Santiago]

Santiago - 5-6-2011 at 06:49 AM

Cable length is another important factor. Runs should be kept as short as
practical. Longer cable runs increase resistance, thus lowering the overall
efficiency of the system. This is especially true in lower voltage systems (i.e., 12
Vdc) where, depending upon the length of the cable run, it may be necessary to
oversize the diameter of the wire, or parallel (double) the cables.
The above is from the installation manual for the TR1512 inverter/charger.

[Edited on 5-6-2011 by Santiago]

msteve1014 - 5-6-2011 at 07:31 AM

You need to keep in mind when paralleling conducters the ampacity of each. 2 #12 are not the same as 1 #6. paralleling #12 is not legal in the states for 120 volt work, would be considered a sloppy job, and would probably work just fine.:D