Selection of DC Load Center Panel?

midijeepmidijeep Registered Users Posts: 102 ✭✭✭
I have a room that is wired for four 12V DC lights, one USB outlet and one cigarette lighter outlet.  I want to run the DC lights and DC outlets off the batteries directly.
I am grid-tied right now but I am in the process of wiring up the Sunny  Island.

I have a SMA SunnyBoy mounted outside on the house by the meter and the SMA Sunny Island placed down in the basement (about 25' of wire between the SB ans SI).  The batteries are by the Sunny Island and the DC load center box would be about 7' from the batteries.
I am unclear what kind of DC load center box and breakers needed for this setup  I plan to use the The DC load center between the batteries and DC lights/outlets. 
Does any one have suggestions, other equipment I need to purchase or a better way to use the DC lighting and DC outlets?  Please advise.  Thank You.


  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    look into the Square D QO series circuit beakers, they are DC rated, most up to 48 volts and a few at higher voltage than 48... other wise look at Midnite Solar DC circuit breakers...
    KID #51B  4s 140W to 24V 900Ah C&D AGM
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    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • oil pan 4oil pan 4 Solar Expert Posts: 766 ✭✭✭✭
    I have seen avionics back shops use NEMA 6-15 plugs and receptacles for 28 volt DC power.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • BB.BB. Super Moderators, Administrators Posts: 32,235 admin
    Look for HAM radio 12 VDC setups using Anderson PowerPole Connectors.

    Our host also sells Anderson connectors:

    12 VDC for lighting and radios and etc... However, if you send power more than a short distance, or do not want to wire up your own low voltage drop DC power system--I do like to suggest looking at using a small/effecient 12 VDC to AC inverter like this one from MorningStar:

    12 VDC can work OK for smaller systems/power usage--But anything more, and 12 VDC can be a real burden.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • midijeepmidijeep Registered Users Posts: 102 ✭✭✭
    Thanks for all the information.  The only thing I want to run straight off the batteries are four 12 Volt LED wall light at 2.46 Watts each. Here is a link for the example :
    The furthest DC light would be about 15 feet from the batteries.

    I am trying to figure out what I would need between the batteries and the LED lights, USB port and 12 amp female  cigarette lighter connector.  I have 10 AWG wiring going to all the mentioned lights and connectors and  have been ran to a central location to connect to a DC load Center.  I want the setup to be safe and efficient as possible.  I was thinking that I could possibly run copper wire (size?) from the batteries to a DC load center with the appropriate breakers for each light and connector mentioned in the breaker box.  Does this sound like it would work safely and efficiently?  I am nor sure if I would need to put anything else between the batteries - DC load center or between the Dc load center and lights/connectors.  Please advise.  Thanks!

  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Hey BB, how about cleaning up after your delayed/multiple post problem?

    SMA SB 3000, old BP panels.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Whatever you use for a DC plug/connector pair, keep firmly in mind that few if any of them are rated to deal with the DC arc that forms if you unplug them while load current is flowing.
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 32,235 admin
    The duplicates (originally went to spam folder) are cleaned up.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 32,235 admin
    You have it pretty much described correctly... The battery (in most off grid systems) can output 100's to 1,000's of amperes into a dead short. You want to make sure that any wiring (usually the + or "hot" wire) that leaves the battery bus, is fused or circuit breaker (breakers can be very nice--is both protection and an "on/off" switch).

    The battery cables are sized for the maximum continuous current you expect to run--Then size the protection device to protect those cables.

    Typically a large CPD (circuit protection device) between the battery and the DC bus. Then smaller breakers on each "hot wire" that leaves that bus to your loads. (in 12 VDC and solar power, typically we use heavier wire to keep the voltage drop low--you can still use smaller CPDs, or up size to the larger cable).

    The NEC is pretty conservative for breaker rating (remember, the CPD + Wiring should be at least 1.25x larger than the maximum continuous current that you want to run through the cabling. 100 amp max current means at least 125 amp wiring+CPD).

    And marine wiring specifications are less conservative:

    If you can afford to use the NEC ratings (heavier cables)--I would suggest that. It will also help keep your voltage drops lower. For 12 VDC, I would suggest a maximum of 0.5 volt drop (at rated current) for loads. You can use a voltage drop calculator for to figure out the drop:

    For chargers (solar, AC battery chargers, etc.)--I would suggest that you try to keep the charging connections short and heavy--0.05 to 0.10 volt maximum drop (at rated charging current) will help ensure your batteries are quickly and accurately charged.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • midijeepmidijeep Registered Users Posts: 102 ✭✭✭
    Right on Bill!.  Thank you for the excellent description.  I like your suggestion on using heavier cables.  You have given me the frame work I need.
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