DC Power Distribution

Horsefly
Horsefly Registered Users Posts: 470 ✭✭✭✭
Our cabin is completely off-grid, but we wired it for standard 120VAC when it was built 45 years ago. Since then, we have run a generator periodically when we needed to.  Now that we are putting in solar, I'm looking at a different conop.

The Schneider SW4024 I'm using allows for a shut-down period daily, and I'm looking at setting it up to shut-down every day from around 11:00pm until 6:00am, saving some tare losses when we don't really need the inverter running. 

There are some things that we will still want to be available during the night. These would include a bathroom light, perhaps some reading lights on each side of each bed, and a USB charger for phones and such.  For that reason I'm planning on running both the nominal 24VDC from the batteries (really varying between as low as 23VDC and as high as 29VDC) and 12VDC from a buck converter.

Although I've looked some, I can't find much about DC power distribution in a home, since it is probably pretty uncommon.  I'm planning on running both the 24VDC and the 12VDC via relatively large 6AWG wires to a central point on both floors of the cabin, and then have separate runs from there to where the loads are. I'm thinking I want a box or panel of some at those central distribution points, but not sure what to look for or where to look for it. I already have some 1/4" insulated terminal posts and can use ring terminals to wire everything, but I'm thinking there must be something out there that would be better.

Anyone have some thoughts about DC power distribution in an off-grid home?
Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 8S (25.6V), 230Ah Eve LiFePO4 battery in a custom insulated and heated case.

Comments

  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    send 24 v to the point of use and then use 24 to 12 v 'transformers'...less line loss
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Anderson Power Pole connectors are common in the HAM radio world. Generally 12 volts, but breakers/fuses/busbars should work at 24 volts too.

    https://www.google.com/search?q=anderson+powerpole+distribution&client=ubuntu&hs=HtW&sa=X&channel=fs&tbm=isch&tbo=u&source=univ&ved=0ahUKEwifyNn4w5_UAhUms1QKHVodBU0QsAQIqwE&biw=1366&bih=626

    Otherwise, there are not a "universal' DC connector. If you want to run 12 VDC adapters (cell phone chargers, etc.)--You are looking at cigarette lighter plugs. Big, low current (typically 10 amps max), and unreliable--Plus, if you have kids, they can stick (relatively large) metal objects into the DC outlet.

    I am not a big fan of 48/24 volt to 12 volt converters in support of DC power distribution. As soon as you look at DC to DC converters--You might as well look at a small AC Inverter to run your small/nighttime loads.

    https://www.solar-electric.com/sa300wa24vos.html

    Of course, the higher the DC battery bus voltage (12/24/48 volt), the larger the minimum wattage AC inverter you can find. Makes it a bit more difficult to power those small AC loads overnight without burning more power.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    What are you worried about losing by shutting down the inverter, just the parasite load? You  might run a small 125 watt inverter instead, would prevent having redundant systems.

    What are you using for a fridge? I'd rather just let mine run, but to each their own...

    Exeltech XP250 is hard wirable and draws just 7 watts, Here's a used 600 watt (draws 8 watts) on eBay for $150, I think it's been on a while, heck offer them $120, I think the rack mount bothers some people.

    http://www.ebay.com/itm/EXELTech-XP600-Power-Inverter-Rack-Mount-/112121916414?hash=item1a1afcabfe:g:yRMAAOSwFe5XzJ9E
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    I doubt I'd run DC at all, but if I did, I'd look at just ~12V with a battery voltage balancer (so that small amounts can safely be taken from one battery).

    I am available for custom hardware/firmware development

  • Horsefly
    Horsefly Registered Users Posts: 470 ✭✭✭✭
    Thanks for the responses guys. 

    @BB., I've seen those kinds of power distribution blocks, and that is kind of close to what I was looking for. If I'm putting a distribution point up in the attic and another one someplace in the basement, I was thinking I wanted an enclosure of some kind too. It may be that just mounting my terminal posts in a plastic junction box will be fine.  I also am not a real fan of the 24VDC to 12VDC converters, but if I am using some DC I'm a bit afraid of running directly off the battery bank since the voltage can swing so much. I did buy a 480W peak / 360W continuous converter on Amazon that seems to be OK.  By looking at marine stuff, there's quite a large selection on-line of 12VDC lighting and such, which also argues for the buck converter.  The car radio we use for music in the cabin and the 5-port USB charger actually say they will work on 12VDC or 24VDC, but I'm not too confident they will work when I've got the batteries in absorb mode at 29.3V.  I already have a dual cigarette lighter socket and a 5-port USB charger that plugs into  it. The place we are mounting it is in a eye-level cabinet, so no problem with the kids doing damage.

    @Photowhit: The tare loss on this inverter is about 26W, which really isn't too bad. For the 7-8 hours I would hope to have the inverter shut itself down, that only amounts to around 200Wh, but the budget I set up for our system was only about 3000Wh, so 200Wh is not insignificant. Given that we don't need the inverter for anything at night, it seems like it might be worth it.  Oh, and our fridge is propane so it doesn't care about the inverter.

    In the end I think the DC stuff is of marginal extra value, but we're leaning towards it right now.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 8S (25.6V), 230Ah Eve LiFePO4 battery in a custom insulated and heated case.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    edited June 2017 #7
    Yes , at 200W just buy anther panel to cover it off... less mess, no fuss

    Add: if you want to have some lights etc at night , what about a small 100W 24V inverter? use a dedicated circuit..
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
    im set up to shut down at night for a long term off grid situation, water is really all thats important and mine does run on 12v, small lights are easy enough to get rechargeable ..not worth it to me to pipe in 12v to the house though, just a matter of planning things to be done during the day ..
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    I've read where the buck converters can fail in a way that lets 12v loads see higher voltage, so I'm inclined to avoid that.

    Marine stuff seems to be designed for the variable voltage, and some is ok with 24v. To run a few lights at night etc., I'd go that route.
    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
  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,039 ✭✭✭✭✭
    Many LED's have a wide voltage tolerance.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

  • Horsefly
    Horsefly Registered Users Posts: 470 ✭✭✭✭
    I'll admit, I'm hoping I can find a way to get only 24VDC distributed. @Estragon and @littleharbor2 are way more experienced than me, and I am hoping you guys are right. If so, I can chalk up the $$ spent on the 24VDC-to-12VDC buck converter as an experiment. However, I'm not sure I am willing yet to try out the stereo and USB chargers on the 28+V battery bank. I'll have to work up the courage.

    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 8S (25.6V), 230Ah Eve LiFePO4 battery in a custom insulated and heated case.
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    To, be clear, I'm suggesting you use 24v marine gear. I'm not at all sold on the notion of bucking to 12v.
    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
  • Horsefly
    Horsefly Registered Users Posts: 470 ✭✭✭✭
    Estragon said:
    To, be clear, I'm suggesting you use 24v marine gear. I'm not at all sold on the notion of bucking to 12v.
    Yep, that's how I interpreted your comment. I'm just pointing out that some of the stuff we have already might work on 24V, but may not like the 28VDC or higher.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 8S (25.6V), 230Ah Eve LiFePO4 battery in a custom insulated and heated case.
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    I'm thinking about the same issue with 12v (can non-marine stuff handle voltage range). The solution in my case will likely be a variable input fixed output 12v power supply for any gear I suspect may not like the voltage range.
    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
  • just starting
    just starting Registered Users Posts: 235 ✭✭✭
    edited June 2017 #15
    One member on this forum made some 24v led lights from ebay components 2-12v lights and a led driver that was converted. With some costom cooling pucks, cant recall his name but he had a very detailed website about his setup. Anyone recall his name.
    200ah LiFePO4 24v Electrodacus Sbms40 quad breaker chest freezer to fridge- Samlex PST 1524 - Samlex pst3024  - 1hp shallow well pump-Marey 4.3 GPM on demand waterheater - mama bear Fisher wood burning stove, 30" fridgarair oven ,fridegaire dishwasher  Unique 290l stainless D.C. Fridge-unique 120l portable fridge/freezer 
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    might be ZoneBlue...?? he has done lots of that stuff
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    edited June 2017 #17
    For Low Voltage DC Panels, maybe research RV and BOATING websites for "Circuit Breaker Panels"

    http://shop.pkys.com/Circuit-Breaker-Panels_c_35.html
  • Horsefly
    Horsefly Registered Users Posts: 470 ✭✭✭✭
    mvas said:
    For Low Voltage DC Panels, maybe research RV and BOATING websites for "Circuit Breaker Panels"

    http://shop.pkys.com/Circuit-Breaker-Panels_c_35.html
    Yeah I found lots of stuff for Boating stuff, but it all is mostly overkill for what I want. This is just going in the attic, and homerun lines will run out fro there to the few DC loads we will have. I think I'll just buy a big PVC junction box and put some terminal posts in there. 

    Thanks everyone for the suggestions.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 8S (25.6V), 230Ah Eve LiFePO4 battery in a custom insulated and heated case.
  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    edited June 2017 #19