12v home wiring

photonboy
photonboy Registered Users Posts: 16 ✭✭
Just signed the contract and will begin building off grid this summer.  I am in the beginning stages of thinking about my electric system and am wondering about going through the effort of wiring portions of the house with DC.
I am wondering if I can find enough, lights, fans, etc that I can limit the inverter from coming on.  Am I over thinking this?  Is it legal to have a DC breaker panel?  Going to be putting the system slowly over time, but will make the appropriate investments up front so as to not have to replicate big ticket items.  

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    First question--Do you have your energy needs documented/estimated?

    Modern AC electrical appliances that are Energy Star rated seem to be almost as efficient as DC versions of the appliances. More or less, you just have the ~85% efficiency of the typical AC inverter.

    And, with DC power systems, 12 volt battery buses are pretty much limited to ~1,200 to 1,800 Watts typical "practical" maximum energy transfer. More than that, you are talking about very heavy currents and short/heavy copper wiring:
    • 1,800 Watts * 1/0.85 AC inverter efficiency * 1/10.5 volts battery cutoff = 202 Amps
    And realistically, you can support a voltage drop of ~0.5 volts (wiring drop, fuse/breaker voltage drop).

    So--DC battery bus voltage--Depends on the equipment you want to drive too... Obviously 12 volts is very common. 24 volts for trucks, buses, aircraft, boats... And 48 volt DC appliances/equipment is more rare.

    There is also a question on the "acceptable" voltage range vs what a deep cycle battery bank may see... 10.5 to ~16.0 volts is typical on a solar charger + Deep Cycle Lead Acid battery bank. Many of the "non-commercial" DC adapters (like laptops, etc.) really work around 12-14.5 volts volts--Outside that range--Verification/Testing is required (have had reports of some major brand computer adapters failing >14.5 volts).

    And if you are into 12 volt HAM... Most DC "optimum" power ratings are in the 13.8 volt range (maximum output power)--And you need to get a DC to DC converter to get a stable 13.8 volt DC bus (in all battery/sun/load conditions).

    If you were looking at a 1,000 WH per day system (LED lights, fan, cell phone charger, laptop, RV water pump)... You can probably get away with a 12 volt system pretty nicely (4-6x Golf cart 6 volt @ 200 AH batteries in series/parallel). And running some/all of the appliances from 12 VDC is somewhat practical (RV water pump, some LED lighting)... I would still say get a ~300 Watt PSW AC inverter too to run the other loads, especially if those loads are more distant from the Battery Bank (just wire up 15 amp @ 120 VAC branch circuits around the house, and keep any 12 volt loads close to the battery bank).

    If you are going to run a full size electric refrigerator, and some more loads (solar friendly well pump, clothes waster, LED TV, etc.)--Then you are looking at something like a 3,300 WH per day system, 24 volt @ 650 AH or 48 volt @ 325 AH battery bank... And going at 120/240 VAC loads.

    What would be "legal"? You need to check with your local building department... They are all over the map--From pretty much requiring 120 VAC main panel (we had one poster here that had to put in an empty/blanked utility meter socket even though no utility power within miles of his place) and wiring per NEC, to a shrug of the shoulders and let you do what you want.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • photonboy
    photonboy Registered Users Posts: 16 ✭✭
    Bill,

    Thanks for your detailed answer. I have just begun the process of looking at loads.  I was thinking about running all my lighting at minimum with DC.....Then I started thinking that by the time I bought the extra, box, wiring, plugs, etc, I could probably buy extra batteries/panels and not have two separate systems.   I think it may be wise to keep some DC lighting around in case I lost  my inverter.  I will probably start off with  a simple DC system as you described, with some limited AC.  Going to meet with the inspector to get his take; thinking it will be more like a shrug if i asked him such questions.  Thanks again.   

    Chris
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    edited December 2019 #4
    LED DC lighting draws just a little bit less power than its AC brethern... But if you don't need an AC inverter--It is a power savings (a 300 Watt PSW 12 volt inverter will draw about 6 Watts idling, and about 0.7 Watts in Search mode, has a remote on/off if needed):

    https://www.solar-electric.com/morningstar-si-300-115v-ul-inverter.html

    For example... Say you wire 14 AWG wiring, want to run 2 amps @ 12 volts (24 Watts load) with ~0.5 volt maximum drop... How long of wire run would that be (this calculator uses "one way" wire run):
    https://www.calculator.net/voltage-drop-calculator.html

    https://www.calculator.net/voltage-drop-calculator.html?
    material=copper&wiresize=8.286&voltage=12&phase=dc&noofconductor=1&distance=50&distanceunit=feet&amperes=2&x=75&y=26


    The answer is ~50 feet for 24 Watts:

    Voltage drop: 0.51
    Voltage drop percentage: 4.21%
    Voltage at the end: 11.49

    And how long of 14 AWG cable with 12 amps, and 3% drop at 120 VAC:

    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=8.286&voltage=120&phase=dc&noofconductor=1&distance=50&distanceunit=feet&amperes=14&x=36&y=32

    50 feet, 12 amps or ( 12 * 120 VAC = ) 1,440 Watts with 3% drop @ 120 VAC:

    Voltage drop: 3.54
    Voltage drop percentage: 2.95%
    Voltage at the end: 116.46

    So--Roughly (1,440w/24w) 60x more Wattage on the same wire, same length, same percentage drop...

    Be aware... Starting small can paint yourself into a corner later (too much expensive "12 volt" equipment to dump when you hit the need for 24 or 48 volt equipment).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    I wouldn't bother .keep it simple and run all ac .if your going to run a fridge full time then realiscly you will have the inverter on continuously , so losses are there already anyway .as for having the back up if the inverter  fails , quality inverters are pretty reliable , amd you will most likely have a small inverter gen at your disposal for the remote possibility of a  failure .
    Also as a side note , go to 48 volts to start with , makes for lower currents on dc side and more head room for expansion.
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
  • 706jim
    706jim Solar Expert Posts: 514 ✭✭✭✭
    Scrap the 12 volt wiring. It's just not worth the bother. What would you use for receptacles? IMO there isn't a decent standard one to use. The "cigarette lighter" style common in cars and trucks is a poor design that tends to overheat. And line loss using #14 wire is really bad over any distance. My cabin has a completely duplicated wiring system for 12 and 120 volts. The 12 volt loads that I have now are powered by.......a 120 to 12 volt power supply!
    I simply run my inverter 24/7 with the standby circuit defeated.
    Island cottage solar system with 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 30th year.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    For 12 volt circuits, HAM folks (amateur radio) use a lot of Anderson Power Pole connectors. And I have seen the larger ones on Forklift batteries for quick connects:

    https://powerwerx.com/anderson-power-powerpole-sb-connectors
    https://www.solar-electric.com/residential/wiring-cables/anderson-connectors.html
    https://www.rfparts.com/connectors-powerpole/powerpolekits.html

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    FWIW, I did a dual (12&48v) system.  It does have the advantage of being able to limit running big inverters for small loads, and also some redundancy.  It also let me run a bunch of LED lighting directly off DC without needing 120v transformers and very efficient site built DC refers.

    At the time (~6yrs ago), there weren't many good choices for small 48v inverters, and that's what tipped it for me to do the dual systems.  Now there are some decent choices for small 48v inverters, and the cost of adding a few panels to make up for inverter losses is less.  I'd probably stick with a single voltage system if doing it now.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Yep, when I went looking for smaller 24 and 48 volt inverters in the last year or so, I was surprised there are more options now. Even down to 250 and 400 Watts 48 vdc input from our host:

    https://www.solar-electric.com/residential/inverters/off-grid-inverters.html?nav_inv_input_voltage=439

    Adding to a solar power system is like buying a VW Bug, and upsizing ot a station wagon, then a pickup, then a Mac Truck... It is difficult to do right and preserve the underlying components (cost effectively).

    I would suggest that, roughly, you can up size a system by something like 2x more power/energy... But beyond that, you can end up struggling to mix and match components (both in power/voltage ratings, and even new vs 5 year old hardware/panels/etc.).

    In the end energy usage is a highly personal set of choices... For one person, a 48 volt system with two inverters (one small inverter running 24x7 for lights, computer, cell charger, etc., and a second large unit for shop tools that is only on when needed)... For another, there have been folks that build out a 24/48 volt system, and even have a second 12 volt battery system that is charged from the higher voltage system (some sort of battery charger, DC to DC, AC to DC, or even a small MPPT charge controller). Typically the dual battery voltage system is a bit more common for HAM Radio folks that want "backup power" for their 12 VDC rigs.

    -Bill


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    If you build an offgrid home which in itself is less marketable than a grid home, then you do something fairly dumb like 12V wiring in the home. You will make it uninsurable and even harder to sell later. A building department could require you to open the walls and then take away the certificate of occupancy.

    If none of this matters, there are quite a few like this and if the county has very little teeth in their enforcement, you may be fine. Just make sure it is safely constructed so you do not awake to the smell of smoke. Good Luck!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • Thom
    Thom Solar Expert Posts: 196 ✭✭✭
    I have a very small system . Still I wired like a regular house .  I turn off the 120v at night . Very glad I wired like a grid house. We pump water using a 2400w generator. Just flip a switch to change from generator to inverter. It was cheaper to wire like a grid house. We have a 12v charge capability and our DSL runs off 12v so I don’t need 120v during the day. You will get great help this forum . Good luck 

    Off grid since 1984. 430w of panel, 300w suresine , 4 gc batteries 12v system, Rogue mpt3024 charge controller , air breeze windmill, Mikita 2400w generator . Added 2@ 100w panel with a midnight brat 
  • softdown
    softdown Solar Expert Posts: 3,812 ✭✭✭✭
    If you build an offgrid home which in itself is less marketable than a grid home, then you do something fairly dumb like 12V wiring in the home. You will make it uninsurable and even harder to sell later. A building department could require you to open the walls and then take away the certificate of occupancy.

    If none of this matters, there are quite a few like this and if the county has very little teeth in their enforcement, you may be fine. Just make sure it is safely constructed so you do not awake to the smell of smoke. Good Luck!
    You keep saying that. Of course there are more prospects for grid homes. You seem to be implying that the return on investment of offgrid construction pales - significantly. Which I find markedly easy to believe. But aren't most off gridders building their dream rather than a marketable investment? 


    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    I say that because it is my experience with so many it would hurt your head. Usually a haircut in cost invested is the norm. 

    As long as you have open eyes and make good decisions definitely follow your dreams.

    Relating an offgrid home to a grid home analogy, you definitely want to be the least expensive home on the block.

    I am not sure that most are doing that on this forum either. Seems to be alot of corners being cut or just doing it because it seems inexpensive.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • 706jim
    706jim Solar Expert Posts: 514 ✭✭✭✭
    My electrician friend commented that he would be more concerned about electrical fires from a 12 volt DC system than a typical 120 volt AC system. Learn from my experience and stay away from 12 volt wiring.
    Island cottage solar system with 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 30th year.
  • softdown
    softdown Solar Expert Posts: 3,812 ✭✭✭✭
    706jim said:
    My electrician friend commented that he would be more concerned about electrical fires from a 12 volt DC system than a typical 120 volt AC system. Learn from my experience and stay away from 12 volt wiring.
    I think DC may offer ~10 times the arcing capacity of AC. Maybe only 4 times? 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • softdown
    softdown Solar Expert Posts: 3,812 ✭✭✭✭
    edited December 2019 #16
    I say that because it is my experience with so many it would hurt your head. Usually a haircut in cost invested is the norm. 

    As long as you have open eyes and make good decisions definitely follow your dreams.

    Relating an offgrid home to a grid home analogy, you definitely want to be the least expensive home on the block.

    I am not sure that most are doing that on this forum either. Seems to be alot of corners being cut or just doing it because it seems inexpensive.
    Always the voice of experience. Lets take a closer look at possibilities:
    1) Many are built out of pocket rather than bank financed home loan.
    2) Many are recreational part time cabins.
    3) Solar winds up costing a lot more than anticipated. Goes way over budget. 
    4) Some are bachelor pads with no real family usage. 
    5) Losses in manufacturing from globalization equates to reduced income opportunities for many rural environments. 
    6) Off grid solar takes a very long time to understand just the most important facets. Lots of important facts to unwrap. 

    ***It continues to amaze me how possibly most of the population still see solar as "free energy" from the sun. They actually go in expecting to save money. Not spend $20,000 for even a decent full home system that is owner built.***
    I fight the dreamers every week. "You need to put down the crack pipe" is one of my favorite reality checks. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    Not saying your electrician friend is one, but at least some sort of diss 12v because it tends to be done by another trade (for alarm systems, etc).  They consider the 12v guys as less skilled (at least in terms of skills they have) and vice versa. 

    In my experience it's sometimes just the electrical contractor gets pissed he didn't get the gig to run the LV stuff.  An AC wire run somehow ends up running parallel to a camera signal wire.  Everybody throws rocks at each other.  Next time, the GC gets the EC to run the LV stuff, or uses a different EC, and so it goes.

    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Having built an off grid house, thinking exactly the same way the OP is, i wired my house with significant 12VDC wiring.  I needed 12 vdc for fridge control of LP fridge. I then also wired a 12 vdc paddle fan, a few lights, the radio etc.  In retrospect, the only thing I use the 12 vdc for is the fridge control board, and the radio.  (I live a long way from a station so I use a car radio, with a big Yagi outside antenna to get reasonable reception 100 miles from town.) 

    Perhaps a better way to to consider energy conservation is to use a dual inverter system. One for large loads, and a small one for most “normal loads”.  Consider an inverter like the Suresine 300 from Morningstar.  When it gets right down to it, 300 watts (very efficiently) is enough to power nearly all loads most of the time.  

    Tony
  • photonboy
    photonboy Registered Users Posts: 16 ✭✭
    All,

    Thanks for the great comments......I am not at the KISS stage for this based on all the feedback.  
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    You are welcome. My comments are only based on a normal home and not a cabin or ? I certainly am not saying there is anything wrong with using multiple inverters for starting out. Just keep the 12 volt wiring confined to where all the equipment is. This way one can see it and it is not hidden in a wall.

    If anyone wants to buy an offgrid home, I know of 3 of them right now in the US and 1 in Mexico. None of them can get bank loans and so the seller must carry the loan. I know of this not working out and sellers having to take back properties that cost them more than the lost deposit.

    The moral here is offgrid Homeowners should be able (financially) to walk away from the house, if they need to.

    I really can't imagine not living offgrid up here in the mountains. We love it. Nothing better than just walking around or seeing the weather roll in for 30 miles. 
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    Trouble financing off-grid homes likely involves more than just the source of electricity. 

    As they tend to be remote, comps for appraisals may be less reliable, for example.  Off-gridders themselves may also not "tick the boxes" in terms of employment income etc., potentially making them higher risk for either conventional or vendor take-back financing.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    Not in my experience Estragon. Many are near grid homes with comps. Some of what you said can be true but the lender often asks this. If you lie about it they can make life difficult. I hear it all having done what many here do not. Mostly because of numbers well over 200 offgrid homes. Just keep your expectations reasonable and price realistic if you have to sell.

    Insurance for the offgrid home is even worse, if it is even available. Especially in the southwest US.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • softdown
    softdown Solar Expert Posts: 3,812 ✭✭✭✭
    To be fair a southwestern offgrid home is typically at risk for wildfires. Plus the fire department may be miles away and understaffed. 

    Fire/vandalism is about the only risk I worry about aside from theft involving a truck load. Not because of solar but sometimes weird stuff can happen. Yesterday, for example, I had to reboot a voltmeter by removing the batteries. How does that even happen? 

    Far off the grid but perhaps not far enough. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    To be even more fair a grid tie home can have the same risk in the southwest. Once the fire department fills up their structure protection assets, it really does not matter.

     In this case the offgrid home is able to defend itself and not worry about gensets failing or loss of grid power. I teach this to my folks and they make the decision on staying or leaving. The utility often turns off the power often days before you are threatened to get you to leave.

    I do not think you can get theft insurance for a home without a home policy around here. Another reason offgrid is just a harder to sell. 
    Do you get theft insurance in Co offgrid? I carry liability for my business but it does not require a fire policy.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • softdown
    softdown Solar Expert Posts: 3,812 ✭✭✭✭
    They sent down a city slicker to evaluate my remote place. She insisted that I remove all firewood, boats and campers. I was somewhat inclined to cancel anyway. I pay for Colorado risks that include hail, wildfires, and tornadoes while only having theft and domestic fire to worry about. 

    We had Colorado's second largest wildfire in the near by forests. Hundreds, maybe thousands, of homes were incinerated. I've not heard of that happening in urban homes for a very long time. 

    I'm personally not a huge believer in insurance or government. Or a number of other contemporary institutions now that I think about it. With social engineering being the worst of the worst. Let people be people as long as they don't hurt others. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    Camp Fire. Paradise CA last year. 14,000 homes  84 souls
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • softdown
    softdown Solar Expert Posts: 3,812 ✭✭✭✭
    Encrypted. Message.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Nice summary of the Camp Fire here:

    https://en.wikipedia.org/wiki/Camp_Fire_(2018)

    Warnings about issues decade before, Sounds like so many things done wrong... And the few things that were tried to do right spent lots of $$$, but did not help much (if at all).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • softdown
    softdown Solar Expert Posts: 3,812 ✭✭✭✭
    Appears that extreme drought conditions were a heavy contributor. Along with absolutely everything apparently going wrong. 

    I doubt that professionally logged forests go up like tinder boxes. I've never seen it happen anyway. 

    Speaking of fire - currently wondering what happened to the pin in my main fire extinguisher. Along with all of its contents. I always grabbed it for babysitting my trash pit fires. Ghosts? Same ones that rearranged the cabling of two roof top solar panels? 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries