cabin 12v?

ronpozoromoronpozoromo Registered Users Posts: 6
I am planning a small solar system for a 900 sq ft primitive cabin I am building. I'll use propane for cooking & small fridge and a small generator to pump water to a 75 gal water tank located in the attic So I basically will need lights for reading & cooking(i'll use oil lamps for general nighttime illumination), a laptop, and a small bedroom window fan for sleeping in the summer. My question is voltage. Can I just wire this cabin for 12 volts and not use an inverter if I use 12v lights, fan, & the laptop has a built-in inverter? The longest wire run for voltage drop will be 25 ft.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: cabin 12v?

    It should work if the wire size is large enough and the loads small enough. Hard to be specific without specific load info. Think carefully about placement of things and you may be able to shorten the wire runs.
    Specifically be careful about your laptop's input. If you have a "12 Volt car adapter" it'll be fine.

    Almost inevitably you'll end up adding a small inverter, though. When you've got a little electric, you always want a little more! :p
  • BB.BB. Super Moderators, Administrators Posts: 29,696 admin
    Re: cabin 12v?

    The long wire runs (like the 25') can be an issue with 12 volts... If it is a small/non-critical load (such as an LED light)--usually not a problem. Otherwise, you need to measure the current and calculate the voltage drop.

    Another issue with car adapters--Automotive adapters are usually designed to run from about 12.0 to 14.4 volts or so... A solar RE system should be designed to run from 10.5 to 15.5-16.0 volts. Some 12 volt car adapters will have problems (especially at the high end of the voltage range). You should make sure that your loads are disconnected when you are equalizing the battery bank.

    For the above reasons, I really like to get a nice 300 watt TSW inverter like the Morning Star. They are designed for the wide range of battery bank voltage, easier to send power longer distances (lights, radio, fan, etc.) and you don't have to get 12 volt adapters for everything. Just run a 120 VAC power strip to charge your cell phone and run stuff. And you end up with regulated 120 VAC to all of your AC appliances.

    In any case, make sure you have a fuse/breaker off of each 12 volt line from the battery bank to protect against shorts/squirrels, etc.

    For water pumping--you might look at a 12 volt pump (or a 24 volt pump with voltage doubler) to move your small amounts of water... Since pumps typically do not run that long for a small cabin, they can be a very nice load for your solar system.

    Also, it may allow you to reconsider that 75 gallon tank in the attic and use a small pressure tank instead with a diaphragm pump (freezing, weight, overflow control, valve, float switch, size, sedimentation issues, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: cabin 12v?
    I am planning a small solar system for a 900 sq ft primitive cabin I am building. I'll use propane for cooking & small fridge and a small generator to pump water to a 75 gal water tank located in the attic So I basically will need lights for reading & cooking(i'll use oil lamps for general nighttime illumination), a laptop, and a small bedroom window fan for sleeping in the summer. My question is voltage. Can I just wire this cabin for 12 volts and not use an inverter if I use 12v lights, fan, & the laptop has a built-in inverter? The longest wire run for voltage drop will be 25 ft.

    As I understand your post, all you are going to power with the 12-Volts is some sort of LED lighting, a fan and your laptop. If I am correct, then you should have no - or very little problem doing so - IF - as others have mentioned, you take into account the amperage - or the loads.

    I am currently running a small solar panel/battery system - which powers a set of LED lights in the evening. The load that the LEDs present to the battery is either 700mA or 1.4A - depending on if I have one or two of the LED LightTubes lit. The amount of light is 600 Lumens or 1200 Lumens - depending on whether I have one or two LightTubes lit - certainly adequate for lighting a small cabin - as we use it to illuminate our kitchen/living room - which is an area of about 16-foot x 25-foot.

    I can get several hours of light from the battery, which is a 35Ah SLA. It is recharged using my 30-Watt solar panel - which goes through a PWM charge controller. (I would NOT recommend a 'wet' lead acid battery for small-scale-solar. A SLA is maintenance-free, and the last battery I used was a 17Ah SLA that lasted over 3 years - and is still good - just removed from service because my 'load' increased.)

    Yes, my solar panel is too small for the battery, but it seems to be charging it up okay during the day - just at a trickle-charge, though. (I intend to install a larger 68-Watt solar panel when I get the chance.)

    As for the distance in the wiring, I have a run of 12-AWG extension cord (being used for 12-Volt) that is about 40-feet long, and do not have that much voltage drop - for the load.

    Small-Scale-Solar is very doable! Go for it!

    If you need any more info - feel free to contact me.

    Regards,

    James Jackson
  • icarusicarus Solar Expert Posts: 5,345 ✭✭✭✭
    Re: cabin 12v?

    As one who has been there,,, done that,


    A simple 12 vdc system will work fine. That said, as time goes by, loads will grow. We initially did a pure 12vdc system, (lighting, radio, fridge controller, lap top etc.) We then build a new house (600 ft sq) and built a parallel system, since that was what we though made sense. As it turns out, we have nearly abandoned the 12vdc side, except fot the radio and the fridge controller. (We still use a 12vdc paddle fan since it is here, but it turns out a 120 vac model uses less energy for any given amount of air movement).

    As I have often suggested, loads grow with time. People usually underestimate their loads, and over estimate their solar potential.

    We also used to live with oil lamps, but in the net/net the Pv with CFL makes much better sense. Between heat from lamps in the summer, indoor air quality etc, (not to mention being able to read!) the oil lamps are quaint, but not very useful. (Unless you are Amish!)

    I agree with Bill, a small inverter, cfl/led lighting and one can live quite comfortably off grid with little electricity. For example, we use ~600 watt hours a day,, (Now that we have the bed warmers we use closer to 800 whs!) We do this fine with ~400 watts of PV, 450 ah of battery and 300 watts of inverter.

    Just be sure to think things through, and understand what can grow and what can't as your system needs grow. Adding panels, easy, assuming you have a big enough controller, adding an inverter later is fine, or stacking two. Adding batteries to an existing string is a no-no. I would start with the biggest controller you think you might need looking forward ten years. (A lesson it has taken me 4 controllers to learn).

    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: cabin 12v?

    Tony speaks truth.
    That's why I bought an Outback MX60 for big $ back when. It's been reconfigured three times as the system grew and got redesigned to meet expanding needs.

    If I were able to emulate Thoreau I'd have stayed with 12 VDC. :p
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