Author Topic: wire loss help.  (Read 1552 times)

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donald77777

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wire loss help.
« on: January 04, 2008, 07:03:18 AM »
Hello everyone. I am building a 12volt solar system that has in my opinon some long runs. I have about a 50ft run from my solar cells to my battery bank. I am running 4 gauage wire for that but I know it will have loss. Can I offset this loss by running an additional 2 lines of 10 gauge for + and - to help with the drop? Or will that just make it worse.

And I know it wasen't the right size of wire but it was all I could get.


Also one other thing I am planning on buying a 300 amp fuse for my battery is this a good size someone recommended it to me since he has a system close to mine. the battery is a walmart everstart 27dc-6 deepcycle(lol) marine battery. the wire to my battery and inverter is 1/0 size.

« Last Edit: January 04, 2008, 07:03:18 AM by (unknown) »

Flux

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Re: wire loss help.
« Reply #1 on: January 04, 2008, 01:48:16 AM »
Adding an extra #10 wire in parallel with a #4 will help, but to be honest it will make little difference. You would need something comparable with another #4 to make much difference.


If you have the #10 around free of charge then use it, but I wouldn't spend money on it for the benefit you will see. I don't know how bad your situation is, you don,t give enough information and I don't have those tables of wire loss handy like some people who are doing this sort of thing every day.


Battery fuse needs to be bigger than the full load rating of the inverter. 300A is probably reasonable, most 12v systems are for smaller installations. 300A should just about handle the surge of a 2kW inverter or even a 3kW inverter that is not overloaded with high starting loads. If you have a much smaller inverter than you could use smaller and have better protection for your cables and battery. Things need to be sized for the individual case.


Flux

« Last Edit: January 04, 2008, 01:48:16 AM by Flux »

wpowokal

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Re: wire loss help.
« Reply #2 on: January 04, 2008, 04:53:20 AM »
« Last Edit: January 04, 2008, 04:53:20 AM by wpowokal »
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donald77777

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Re: wire loss help.
« Reply #3 on: January 04, 2008, 08:56:33 PM »
my inverter is a 3000watt with 6000 watt surge for upto 10 seconds so what would be a better fuse to use than. Oh by the way the 10 gauge wire I just have laying around. So it would be useless to use than.
« Last Edit: January 04, 2008, 08:56:33 PM by donald77777 »

zeusmorg

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Re: wire loss help.
« Reply #4 on: January 04, 2008, 10:15:14 PM »
 The information to calculate your needed wire size isn't given.


You need to know the amperage maximum output of your solar panels, if you're only capable of generating 20 A (@12v dc) then your 4 ga wiring is sufficient, if it exceeds this, then you have a system loss. If you exceed it by an excessive value, the resistance in the wiring can be enough to cause overheating in the wiring.


 You can double up wiring runs to create sufficient capacity. Another good calculator for wiring size can be found at: http://www.powerstream.com/Wire_Size.htm

« Last Edit: January 04, 2008, 10:15:14 PM by zeusmorg »

Flux

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Re: wire loss help.
« Reply #5 on: January 05, 2008, 01:40:37 AM »
In theory a 3000W inverter takes 250A. When you include efficiency it will take somewhat more. The 300A fuse may be adequate depending on the type of fuse. Many fuses age and some will not carry full current rating indefinitely. During the surge rating of your inverter you will be well over the fuse rating but again fuses have a short time overload rating and with the best HRC fuse you would still be within it.


Ultimately the fuse will never protect the inverter, it will only protect the battery and cable if the inverter fails so rather than run the risk of false shut down due to fuse ageing I would look for a 350A fuse if you can find one or even go to 400A.


If you have the #10 wire free then use it in parallel with the #4.  As others have said we have no way of knowing what your cable loss will be. 50ft of #4 should handle most things. It will be about .023 ohms. Adding the #10 in parallel will reduce it to about .018. An improvement worth having if it comes at low cost but not something that you will likely see any improvement from unless you measure carefully when the panels are hot. If you had to buy the #10 at full price I doubt it would be worth it.


Flux

« Last Edit: January 05, 2008, 01:40:37 AM by Flux »

donald77777

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Re: wire loss help.
« Reply #6 on: January 05, 2008, 11:21:37 PM »
Thank you everyone for helping me. Now on to the next topic.
« Last Edit: January 05, 2008, 11:21:37 PM by donald77777 »