Author Topic: wire lengths  (Read 977 times)

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thirteen

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wire lengths
« on: October 16, 2006, 04:13:48 AM »
I am trying to find out how far I can go from a solar panel to my battery banks. Any rule or simple formula I can use? Just a general idea.
« Last Edit: October 16, 2006, 04:13:48 AM by (unknown) »
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ghurd

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Re: wire lengths
« Reply #1 on: October 15, 2006, 10:29:46 PM »
You can go as far as you can afford the wire for.

The higher the amps, the closer it should be.  Or longer runs need larger wire. How ever you want to think about it.

Some people like to keep losses to 2%, others say 5% is fine.  Too small on the wire will really drop the output amps.

Here is a handy chart.

http://www.windsun.com/Hardware/Wire_Table.htm

G-
« Last Edit: October 15, 2006, 10:29:46 PM by ghurd »
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stephent

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Re: wire lengths
« Reply #2 on: October 16, 2006, 08:53:27 AM »
Keeping wire losses low feeding the inverter (or anything from the inverter) is very good practice.

Keeping wire losses low everywhere is rather important for RE systems.

I would try to keep total wire losses to 5% or less from the source to the end use..

This includes solar panel (or wind gen) to controller to battery bank to inverter to end use.

Don't figure each place (like battery to inverter) for 5% wire loss--these add up in a hurry.

Wire loss is easy to figure.

Single Phase or DC Voltage drop = L (length of run one way) x 2 x I (amps) x R (get this "R" figure from a wire table) divided by 1000


L x 2 x I x R

-------------

divide above by 1000


Three Phase Voltage Drop is

L (one way length) x 1.73 (the square root of 3 rounded) x I x R

-----------------------------------

Divided by 1000


Shoot for all the losses added together to be 5% or less (less is better but way more expensive). There's enough losses (I^2 x R) in a 1/2/3/more phase genny to live with without having more inline (unless needed to avoid stall, etc) and solar effeciency is low enough without added losses taking a share of the output.

« Last Edit: October 16, 2006, 08:53:27 AM by stephent »

craig110

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Re: wire lengths
« Reply #3 on: October 16, 2006, 10:46:09 AM »
Here is a handy page I found that might help you:


http://www.powerstream.com/Wire_Size.htm


Not only does it list the wire sizes and maximum amps (which I find to be useless when thinking of long runs), but the bottom of the page has a nice calculator that shows you what your voltage drop will be for a given type of wire, length, and amperage level.


Something else to consider when running wire is whether you might expand in the future.  I recently installed a 40 foot run and ended up using double-ought aluminium that is rated for 150A even though I'm only currently pushing 20A.  The guy at Home Depot was rather befuddled by my choice until I pointed out that given the current copper prices, the double-ought cost only slightly more than if I purchased #6 THHN copper and will handle my future expansion plans nicely.


Craig

« Last Edit: October 16, 2006, 10:46:09 AM by craig110 »