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cityconvert
Member
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# Posted: 4 Sep 2012 02:26am
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Hello all,
I am new to this site and I hear great things about it. Anyway, I am setting up an off grid cabin and I have a few solar questions. I would like to begin wiring the outlets, switches and lighting fixtures. What size wire is safe to use with a 24v PV system? I'm fairly new to solar as you may have guessed.
I was thinking of moving up a notch from #14 to 12/2 Romex. Opinions? Any advice is welcome. Thanks.
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sparky1
Member
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# Posted: 4 Sep 2012 07:42am
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here's "some " information/ installing wiring NOW using 24 V.DC and possible later going to AC. do it once and correctly.
sparky1.in s.Va.
http://www.colemanair.us:80/vp_asp/scripts/shopexd.asp?bc=no&ccode=WireCalculator
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MtnDon
Member
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# Posted: 4 Sep 2012 10:38am
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One thing to remember is that a 24 volt device drawing a similar wattage to a 120 volt device draws 5x the current. That means larger wires are needed. However, if the load is LED lighting on 24 volts the amperage is going to be very small. Incandescent lights are another matter though.
Also it should be noted that the usual household wall switch is meant to operate on AC power circuits. DC power can rapidly wear out, burn the contacts inside an AC switch. Possibly if the switches are used for only the very small loads that are normal with LED lighting, this may not be a problem. Or if you can locate AC switches that "snap" when operated, use them. They are made different from the usual silent switches and do stand up better under DC loads. ... This is because AC current flow is easier to break as it is turning on-off 60 times a second as the current alternates. DC switches have to break a steady one way flow of current. This is much harder on the mechanical contacts.
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TomChum
Member
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# Posted: 4 Sep 2012 11:27am
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LED can use such a tiny fraction of the current, they can use very small wires, like small as a thread. I think the biggest concern in wiring a house for 24v, is the possibility that you may want to run 120v in it someday. Or someone else might run 120v thru your tiny LED-sized wires. I plan to run some 12-2 trunk lines, and split off those with my tiny LED wires.
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cityconvert
Member
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# Posted: 5 Sep 2012 02:38pm
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Thanks Sparky1 I'll have to checkout that link.
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cityconvert
Member
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# Posted: 5 Sep 2012 02:40pm
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MtnDon
Are there switches made specifically for handling DC?
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cityconvert
Member
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# Posted: 5 Sep 2012 02:50pm
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TomChum
Can I not wire the LEDs directly with 12/2?
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cityconvert
Member
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# Posted: 5 Sep 2012 03:14pm
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If it helps the system I am designing would include three 315w panels, most likely an Outback Power FX3048T 3000 Watt (for later expansion), Outback Power FLEXmax 60 MPPT Solar Charge Control, Trimetric Battery Monitor, a number of T-105's, and all the other hardware yet to be determined. None of these components are concrete yet so please give suggestions.
My plan was to have 10-12 LEDs and possibly 2 fluorescents for my little office area. Those would be 24v DC. Then through the inverter I would run a 120v circuit for my very small frig, laptop and printer.
A question I have is WHY IN THE WORLD IS IT SO HARD TO FIND A DECENT BOOK ON SOLAR INSTALLATION?! lol
Thanks guys for all your help.
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Dillio187
Member
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# Posted: 5 Sep 2012 03:23pm
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there are so many different facets to solar/alternate energy that the book would be HUGE.
I don't mean to 'pimp' another website, but the northern arizona wind and sun forum has been VERY helpful to me in designing my solar setups, that I would recommend it to all.
http://www.wind-sun.com/ForumVB/forum.php
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cityconvert
Member
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# Posted: 5 Sep 2012 04:07pm
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Dillio187
Wow thanks for the info. I just found out how much I don't know. lol
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exsailor
Member
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# Posted: 6 Sep 2012 12:28pm
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Hi cityconvert
This link was provided by a forum member sometime ago. From what I have seen it is a pretty good primer on a small solar power generation system http://www.outsidesupply.com/cabin-solar-guide.aspx enjoy
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MtnDon
Member
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# Posted: 6 Sep 2012 12:49pm
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Quoting: cityconvert Outback Power FX3048T
That is an excellent inverter; however it does not fit in with a 24 volt system. It is for a 48 volt system. 48 volts is not needed by most of us. I do like 24 volt systems though. We have the 3524M. Personally my feelings are that if there is a top quality inverter in the system, along with a top quality MPPT charge controller, wiring in a lot of DC lines is a waste of time and copper. Having both DC and AC can also be confusing at times, especially to others around you. We have a couple of DC "emergency" lights just in case the inverter craps out. Other than that our cabin is wired just like a regular house with AC circuits.
DC rated switches are difficult to find if it is important to pass electrical code inspections. Otherwise look for a quality made DC switch like those made by Carling switch. I've seen a couple DC rated switches online and they have been ridiculously expensive. Forget where.
Yes, the AZ Wind-Sun forum is a good one. So is the forum sponsored by Outback if you use their equipment.
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GomerPile
Member
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# Posted: 6 Sep 2012 02:04pm
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Per NEC 12AWG is good for about 25 amps depending on factors like temperature etc.....20 amps is a safe bet.
Some basic advice (based on my 12V system):
+ Run the largest wire you can to your PV array to minimize losses and allow for future expansion.
+ If you run an inverter and batteries use *really* large cables from the battery to inverter and make them short. My cables are 3/4 inch diameter welding cable to a 2000W inverter.
+ Use 10 or 12 AWG wire in your lighting circuits (24V you're ok with 12 AWG).
+ Put fuses or breakers on every circuit.
+ Put a DC rated switch on *everything* in an off grid situation you want to turn stuff off when its not in use
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cityconvert
Member
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# Posted: 6 Sep 2012 02:52pm
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Quoting: MtnDon wiring in a lot of DC lines is a waste of time and copper. Having both DC and AC can also be confusing at times, especially to others around you. We have a couple of DC "emergency" lights just in case the inverter craps out.
My main reason for the low volt lighting is simply an attempt to conserve power. I can't really afford a massive solar array. If I wire everything up for AC won't I lose alot when it is inverted?
Do you have any wiring diagrams of your setup? Thanks.
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GomerPile
Member
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# Posted: 6 Sep 2012 03:04pm - Edited by: GomerPile
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Conversion to AC will be at best 90% (average) efficient and probably less depending on your configuration. If you are using a battery, it will likely be closer to 80%. It really depends on how many batteries in your bank and the loads.
I live 100% off grid and run everything from a 12V system. I won't buy something that cant reasonably be run from 12V. For some thats just not an option, and you may need to live with the losses associated with a 120V AC inverted system.
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cityconvert
Member
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# Posted: 6 Sep 2012 03:36pm
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exsailor
Thanks. That link did help alot. I'm a visual learner...lol
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MtnDon
Member
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# Posted: 6 Sep 2012 06:10pm
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Quoting: cityconvert Do you have any wiring diagrams of your setup? Thanks.
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cityconvert
Member
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# Posted: 7 Sep 2012 06:41am
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MtnDon
Thanks. Still taking it all in....lol However, I actually do understand most of it.
So you have two sets of copper rods driven into the ground?
I have to do more research on determining circuit breaker size. Also it seems you always place them on the positive side. Is that simply because electricity flows from negative to positive?
What's the reasoning behind the way you have your battery bank wired up? Forgive me I am fairly new to all this.
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