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Borrego
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# Posted: 27 Nov 2011 08:08pm
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Hey all - here's what's up: I am currently wiring the cabin for down -the-road solar (when I can afford it :-)
So I am running Romex as I would in wiring a 'real' house.... a friend stops by and asks why I am not running 12 v wire as well. I tell him I'm gonna use solar.. His point was that why not have 12 v as well? n case of too many cloudy days, a malfunction, whatever, plus I could have immediate lighting and add the solar later!
So I figure, ok, might as well..... But I know nothing about 12v wiring.
So questions:
1) should I do it?
2 if I just want to run say, 4-5 lights off the 12v system for now, what size wire(s?) do I run? The cabin is 24'x24' so longest run from the battery (for now) would be about 30 ft~
3) any good sites on this? All my searches found was solar stuff, not just DC
4) can I use existing holes with Romex in them? (Heat issues?)
5) Should I just put up 1 panel for now to charge the battery? Or use the generator and a charger?
Thanks!
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Bzzzzzt
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# Posted: 27 Nov 2011 09:33pm
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I'm an electrician and deal with 120V all day every day and 12V stuff almost never. My biggest question about your set up is why run 2 things? I mean, if you're going to wire it with 12/2 romex (or 14/2 as the case may be) why not just hook that into a power inverter connected to your battery and just have 120V lights with LED or CFL lamps in them to have as little amp draw as possible.
Think about this: If you have 24 watts of light at 12 volts that equals 2 Amps, but if you have 24 watts of light at 120 volts, that equals .2 (2/100) amps. I'm not 100% sure about the draw on your battery through an inverter, but I would guess it to be less.
Until you get a solar cell to recharge the battery(ies) you can charge them with a common battery charger when you run your generator.
If you're bound and determined to run some 12 volt sockets throughout the cabin, you can just use some #12 (or 14) and fuse it with car fuses at 20A (or 15A accordingly.) Stranded wire will work better but romex should work for a 30' run. I'd go to the auto parts store and get a spool of that really soft stranded wire they use as it will lessen the voltage drop. Remember that in the cabin you need 2 wires: one for the hot and one for the ground. In auto work you only need one wire lots of times because you use the auto body as the ground. There shouldn't be much in the way of heat trouble with the voltages in the same drilled holes I wouldn't think.
I cant imagine that I'm wrong about this, but like I said in the beginning, I hardly ever deal with 12V DC.
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Borrego
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# Posted: 27 Nov 2011 10:15pm
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Thanks, Bzzzzzt! I'm a General Contractor and have wired my fair share of homes in 110/220. But this is a new animal for me. I get your math, but I thought 12v drew less power? I dunno.... 12v would get me light sooner? Maybe?
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Martian
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# Posted: 27 Nov 2011 10:41pm
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As a yacht rigger and liveaboard, I've dealt with 12vdc a lot. First off, measure the runs there and back for 12vdc. Check online for a wire guage chart for DC to figure your size requirements and work with a 5% line loss, or less. Watts are watts regardless of voltage. Amps are figured by dividing watts by voltage. Buy good wire! Personally, I like Ancor products; they aren't cheap, but neither is doing the job over in four or five years because of cheap wire or terminal ends. If you go to their site you'll be able to gleen a lot of knowledge and find the wire guage chart for reference. Always put a fuse/breaker at the battery, between the battery and the distribution panel, that can handle all the loads, and put a fuse/breaker on each circuit.
Tom
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Bzzzzzt
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# Posted: 27 Nov 2011 11:08pm
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I wanted to add to my comments from before. I was just looking at battery chargers for my own application and noticed that a deep cycle battery charger takes approximately 11 hours to charge a 100 amp hour battery. That might rule out a generator recharge method.
For my own purposes (and I haven't done any wiring at my cabin as of yet) I'm thinking of just wiring the thing for 120V as I normally would, getting a couple of batteries and charging them up at the house and carrying them out to the cabin until I get my solar power set up installed to keep them charged. I will continue to use my generator as necessary but the battery set up might lessen the need for it tremendously.
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Martian
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# Posted: 27 Nov 2011 11:18pm
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The simplest way to use batteries for power is with standard wiring and an inverter; especially if you have a generator available for peak loads. Then all that's needed is a transfer switch to go from inverter to generator. An inverter that automatically switches over to gen power can be had, but they get expensive.
Tom
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Bzzzzzt
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# Posted: 27 Nov 2011 11:55pm - Edited by: Bzzzzzt
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Martian you seem to be knowledgeable in this area. Do you think that a system where you have the generator hooked up to the batteries charging them while simultaneously using them for power would work? What I mean is, to exclude the transfer switch from the equation, plug the 120V stuff into the inverter, attach the inverter to the battery(ies), set up the charger on the batteries and turn on the generator. This method MIGHT generate enough power to power your 120V stuff while also giving some charge to the batteries so that when the generator dies out from lack of gas the batteries keep whatever is going, going. Does that make sense? Or would it not work that way. IE: It would work to run the load but not charge the batteries?
Perhaps a better set up would be to install a contactor with a 120V coil with NO and NC contacts. Wire the contactor to engage by the generator power which would also run your 120V load through the NO contacts while simultaneously running the battery charger. When the generator runs out of gas (or you shut if off) the contactor switches to NC contacts that are attached to the battery which would then run your 120V load. Basically this set up would mimic a transfer switch but at a substantially cheaper price. For most of my own purposes I think a 30amp relay would work just fine. One like this one seems adequate: http://www.amazon.com/Potter-Brumfield-Relay-120VAC-T92S11A22-120/dp/B00316W4QI/ref=s r_1_12?ie=UTF8&qid=1322457163&sr=8-12 (see diagram)
You think I'm barking up the right tree?
Borrego: If you have a power inverter set up then 12V or 120V wouldn't really matter. You'd get light either way in the same amount of time.
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Martian
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# Posted: 28 Nov 2011 08:13am - Edited by: Martian
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Bzzzt, The tranfer relay would work, but it needs to be a make-before-break design to prevent a short interruption every time the gen comes on, and goes off, line.
You can charge the batteries while there is a load on them, but the charger needs to be large enough to get the batteries topped off while they're carrying the load, too, before the generator shut down. Look at marine grade chargers. I would compare the price between an inverter/charger unit and seperate charger and inverter. Personally, I like having them seperate so I don't lose both if one side craps out.
You could build a small DC generator, using an automotive style high output, internally regulated alternator and a lawnmower engine, that would charge the batteries while they are powering the inverter. The only consideration is the draw/charge difference which determines how much charge is added to the batteries during the charging cycle. (One horsepower is the equivelent of 750W.) Realistically, you can only charge at 10% of the battery bank capacity without risking damaging the batteries or starting a fire. Some systems monitor the battery temp and control the output of alternator to protect them.
Marine charging systems are pretty highly evolved. They are the way I'd go despite the fact they are more expensive. I've seen chargers that had survived over twenty years in the highly corrosive marine environment.
Where sailors save the most power is in using systems that limit run time on high draw systems; think refrigeration. The best marine refrigeration systems use holding plates that contain a solution that freezes during generator operation and releases the cold over a long (12hr) period. The biggest factor is size of the box and how well insulated it is. Some even have two seperate plates for freezer and refrigerator. I couldn't afford one of those systems (about $4000) so I had a 12vdc powered compressor with evaporator coil just like a standard fridge, but it was limited to a pretty small box (3cuft) and still cost over $700. I think it pulled about 7amps.
Tom
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Borrego
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# Posted: 28 Nov 2011 12:45pm
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To get a cheap(er) start, should I just get one of the Harbor Freight $149 1 panel packages to charge the batteries and run the lights and forget about 12v?
And do I need 12v at all?, I'm in the desert and get about 350 days per year of usable sunlight and the house is freshly wired for 110....
Now I'm gettin confused............
I just want to have a light or two for now and add more later, what's the best angle here?
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Martian
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# Posted: 28 Nov 2011 01:24pm
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So let's talk cheap and simple. I'm not familiar with the Harbor Freight package, but I'm assuming it contains a panel (wattage?), a charge controller, and an inverter (output wattage?) Since you are pretty much assured of sun most days, a couple of series 31 deep cydle batteries, tied into the harbor freight package, would probably work quite well. If you do need to charge the batteries, and don't have a generator, you might consider rigging up a system that uses your vehicle alternator. I've heard of people who ran wires from their car's battery to the trunk and charged one of the house batteries while commuting. I would reccommend a battery isolator to prevent the house battery from discharging the car's battery, however.
If all you want to run is a couple of small lights and maybe a 12vdc stereo, a two battery bank will last a long time (several days). Using 12vdc flourescent lights, will greatly reduced the draw. Having lived in Yuma, AZ for four years, I doubt you'd go too long without sunshine in the desert.
Tom
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Borrego
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# Posted: 28 Nov 2011 02:26pm
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Quoting: Martian So let's talk cheap and simple. I'm not familiar with the Harbor Freight package, but I'm assuming it contains a panel (wattage?), a charge controller, and an inverter (output wattage?) Since you are pretty much assured of sun most days, a couple of series 31 deep cydle batteries, tied into the harbor freight package, would probably work quite well. If you do need to charge the batteries, and don't have a generator, you might consider rigging up a system that uses your vehicle alternator. I've heard of people who ran wires from their car's battery to the trunk and charged one of the house batteries while commuting. I would reccommend a battery isolator to prevent the house battery from discharging the car's battery, however. If all you want to run is a couple of small lights and maybe a 12vdc stereo, a two battery bank will last a long time (several days). Using 12vdc flourescent lights, will greatly reduced the draw. Having lived in Yuma, AZ for four years, I do
Thanks, Tom - Here's the package: http://www.harborfreight.com/45-watt-solar-panel-kit-90599.html
I'd need to get the inverter and batteries separately. And I do have a generator so that's no problem....
So should I run wire for DC before I seal the walls or just go with AC?
We're only about 75 mi NW of Yuma so you're right, no shortage of sunlight :-)
Bruce
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Bzzzzzt
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# Posted: 28 Nov 2011 02:31pm
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I was considering the 45 watt harbor freight solar kit but after comparing it with the 60 watt kit from northern tool that has name brand equipment and only $100 more I think this is the way I'll go. Northern's kit comes with more of what you need and I believe it allows for expanding to more panels.
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Martian
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# Posted: 28 Nov 2011 04:14pm
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I'm sorry. I missed the part about your cabin already having AC wiring. In that case, forget about wiring for DC. Start by adding up the wattage of everything you want to use and how many hours/day you plan on using them. This is the actual time they are turned on. Watts, like amperes is measured in hours; ie, 60 watt light bulb uses 60watts/hour or 1watt/minute. At 110vac, that is around .6amps, but the battery has to supply 5amps to the inverter at 12vdc to get that .6amps at 110vac. You with me so far?
Once you know how many watts you want to use at one time, then you'll know how big an inverter you need. Then you figure out how many watts you'll be using in a 24hr period. From there you work out how many amps the battery bank is going to need to supply to the inverter, how large the wires from the batteries to the inverter need to be, the size of the main fuse to the inverter, and how big the solar array needs to be to keep the battery charged.
I'd suggest you start reading about solar charging systems and their limitations. For instance, chances are your not going to get a full 45 watts out of the panels from daylight to dark. I think I read somewhere to figure on averaging 50-60% of rated power. That would take your 45watt panels down to averaging around 20watts or 3 amps. Assuming 8hrs of daylight, that's 24amps/day. Anyway, there is a lot of information out there on the internet. Google is your friend!
Tom
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Borrego
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# Posted: 28 Nov 2011 09:00pm
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Thanks!
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Rob_O
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# Posted: 28 Nov 2011 09:18pm
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Quoting: Martian Bzzzt, The tranfer relay would work, but it needs to be a make-before-break design to prevent a short interruption every time the gen comes on, and goes off, line.
You don't want to do this on AC unless you have an inverter generator that can sync up with the waveform from the inverter
The relay Buzz suggested would do the job, this transfer switch comes in a nice enclosure and has a delay to let the genny get up to speed before it switches over. The switching speed on these things is fast enough that most devices will never notice
Quoting: Borrego To get a cheap(er) start, should I just get one of the Harbor Freight $149 1 panel packages to charge the batteries and run the lights and forget about 12v? And do I need 12v at all?, I'm in the desert and get about 350 days per year of usable sunlight and the house is freshly wired for 110.... Now I'm gettin confused............ I just want to have a light or two for now and add more later, what's the best angle here?
You can do better than that harbor freight kit. The cost per watt is high, and the quality is not very good. Sun Electronics has 200ish watt panels for under $300 and they're selling the Xantrex C35 charge controller right now for 90 bucks. That plus a couple T105 batteries gives you a nice little system that can be upgraded as your power needs grow
For a couple lights and a radio, just get a cheapie ~200 watt inverter. Nothing with a fan, it just wastes energy. I have 2 in case one dies, they're cheap enough to keep a spare
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larryh
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# Posted: 28 Nov 2011 11:56pm - Edited by: larryh
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I have exactly the set up your asking about. Granted mine is a rather old system perhaps by todays standards. Way back Home Power magazine had some good articles on 12v power for stand alone systems. I followed what they called the "Bus system".. They did that because 12v loses power if you try to run a load too far. My home is about 40 feet from the battery to the opposite end. They recommended and I installed #6 copper wire for the positive and negative sides the length of the house. That will carry the power without loss for that distance. Off that I soldered standard house wiring being sure to mark the negative and positive sides with red and black tape to let me know I am not getting things crossed. I put in lines in the walls with standard plug ins that I soldered in place to lessen power loss. From that I use standard lamps with 12v lights. I used to use the old type standard bulbs but they were power grabbers for sure. I now use them with the new low energy type 12v lamps similar to those for 110. In some places I installed ceiling or wall lamps where I wanted permanent lighting. In the kitchen I put a regular wall type cigarette type receptacle and use it for small appliances that used that type of plug. For the rest of the house where I wanted to use that type of say fan or radio with the torpedo shaped plug in I converted "Y" plugs and used the one that plugged into the wall by converting that plug to a 110 type plug in. That way each standard plug in will run say a 12v tv and 12v vcr or a fan and tv, ect. At the battery I have a simple fuse in the line incase something should get shorted. But in 25 years now its never had to be replaced. I use it mostly for emergency extra lighting but I do use it daily in the bedroom and bath and stair case where the wall lamp is 12v. If your interested I might be able to find that Home Power article? I think any up to date site would be able to show how to install a simple 12v system.
larry
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Martian
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# Posted: 29 Nov 2011 06:26am
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Quoting: Rob_O You don't want to do this on AC unless you have an inverter generator that can sync up with the waveform from the inverter
You are absolutely right; it should be a break-before-make switch.
Brain fart!
Tom
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Borrego
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# Posted: 29 Nov 2011 02:30pm
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Quoting: larryh If your interested I might be able to find that Home Power article? I think any up to date site would be able to show how to install a simple 12v system.
Yes, please! I've been searching online and everything is geared towards solar w/ batteries
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Martian
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# Posted: 29 Nov 2011 05:00pm
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Don't you want a battery for nightime and those 10 days/yr that you don't have sun? Can you even run a solar array that we can afford without a battery?
Tom
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Borrego
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# Posted: 29 Nov 2011 09:49pm
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When I started this thread I just wanted to go battery, thinking it was cheaper in the short term and get me some lights until I could afford to go solar.
Now I dunno...........
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larryh
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# Posted: 30 Nov 2011 07:29pm
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Just got back to looking at this thread, I will search for that article, I am pretty sure I still have it. I too do not have solar. I use either the house power which you won't have, (but you could perhaps use a friends or neighbors if you paid for the power), or I use my Honda Generator to charge it. I always wanted to get a set of solar panels but the cost seemed to keep me from investing in it so far. I did originally intend to use a windmill but the small one I put up incorrectly quickly self destructed plus the noise it made rather changed my enthusiasm for having one. I like a degree of peace and quiet unless I am creating the noise and the outside yard was a constant whirling which I found not very pleasant. I'll go look for that article.
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MtnDon
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# Posted: 30 Nov 2011 07:41pm
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Solar PV modules make no noise. They just sit there and run themselves (via the charge controller). To me the convenience of that was well worth the expense of the modules. Not to mention no need to buy gas for the generator. The noise from a windmill can be bothersome and is not mentioned in a lot of sales info for them.
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larryh
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# Posted: 30 Nov 2011 09:10pm
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Yes I have often wished the money I spent on that ill fated windmill would have been making solar power all these years. Unfortunately I had a bug to use a wind generator since a relative when I was young had a small home that used an old 12 V wind charger on the roof and it always intrigued me making me wish for one. Another thing I never considered was the huge task installing one high enough and secure enough was. No thanks. We have a large bank of commercial generators a couple hours north of here and I pity anyone that has to listen to and watch those things running. They are like giant invaders on the soil. Funny how one mans green energy is another mans curse.
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AYP1909
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# Posted: 1 Dec 2011 10:12am
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Thank you all for sharing your expertise with the rest of us. This is very informative.
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MtnDon
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# Posted: 1 Dec 2011 11:25am
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If I had good dependable winds where our cabin is I'd put a windmill up far enough from the cabin that the noise would not be an issue. We've enough land but no dependable wind though. The PV modules are 325 feet away; all it takes is larger wire and higher voltages to reduce the transmission losses. We run approx 90 VDC from PV modules to batteries.
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Anonymous
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# Posted: 7 Dec 2011 05:40pm
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One good site is the 12 volt side of life: http://www.marxrv.com/12volt/12volt.htm.
I've found that the panels at Northern tools to be very dependable (and the price keeps dropping) http://www.northerntool.com/shop/tools/product_200422042_200422042
A charge controller can hadle up to four of the panels:
http://www.amazon.com/Sunforce-7-Amp-Charge-Controller/dp/B0006JO0XI/ref=sr_1_1?ie=UT F8&qid=1323297287&sr=8-1
I bought 2 (27) deep cell batteries at Sam's (because they have the best return policy)
This has run my RV for at least a week with no problem (running the water pump, (replacement LED) lights, etc.)
I do have a generator (Honda 2000i) that I very occasionally run.
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pondjumpr
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# Posted: 7 Dec 2011 07:03pm
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I just did a similar set up for a friend of mine at his cabin in Georgia. I used 12.3 wire and wired a standard light fixture to the middle of the cabin roof, just like if I was using 110V. I then rah the wire to a standard switch like you have on a wall in your house. All of it is hard wired. I then went from the switch and ran another section of wire to a couple of battery terminal wires just below the light switch. ( I left some extra length so we could move the battery around if needed) I can always run that switch to a panel box if and when he gets 110V or if he ever converts to run off a generator. All I did then is buy a $2 12V battery online. I have since found the rough service 12V bulbs in local auto parts stores (O'Riley here). I just put it in the household light fixture in the ceiling like you would at home with a 110V medium base bulb. Hook up the single 12V battery and flip the switch. You have light!
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pondjumpr
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# Posted: 7 Dec 2011 07:09pm
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Correction. I said I bought a $2 battery and meant $2 12V bulb....
Another option we have used in the past is to buy one of the silver 110V clamp lights like you would see in a home improvement store. We cut the 110V plug off the end of the cord and replace it with 2 alligator clips. Install a 12V medium base bulb and hook up you clips to a bettery. They have a switch built in so you can leave them hooked to the battery and turn the light on and off.
We started using these several years ago and use them when we are cooking at a campsite. The light is easy to direct and very bright. The entire set up takes about 5 minutes to make and costs about $10-$12 including the bulbs.
In years past, we paid $6 for 100W 12V bulbs. Now we have found 50W 12V bulbs for $2-3 each and you can even get 25W 12V incandescents now.
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pondjumpr
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# Posted: 7 Dec 2011 07:19pm
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I just did a similar set up for a friend of mine at his cabin in Georgia. I used 12.3 wire and wired a standard light fixture to the middle of the cabin roof, just like if I was using 110V. I then rah the wire to a standard switch like you have on a wall in your house. All of it is hard wired. I then went from the switch and ran another section of wire to a couple of battery terminal wires just below the light switch. ( I left some extra length so we could move the battery around if needed) I can always run that switch to a panel box if and when he gets 110V or if he ever converts to run off a generator. All I did then is buy a $2 12V battery online. I have since found the rough service 12V bulbs in local auto parts stores (O'Riley here). I just put it in the household light fixture in the ceiling like you would at home with a 110V medium base bulb. Hook up the single 12V battery and flip the switch. You have light!
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pondjumpr
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# Posted: 7 Dec 2011 08:03pm
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sorry about the duplicate posts above and need for editing. I originally posted without signing up but just signed up for the site.
I am enjoying reading the site.
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