Two Negative Buss Bars

I have run out of large connecting spaces on the main Outback negative Buss bar with shunt. Can I use another negative Buss bar for my #4 wires from solar panel array and what size wire should I use to connect the two Buss bar? Will doing this cause any issues?
Steven M

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Two Negative Buss Bars

    I have to say that this question as presented doesn't make sense. Especially if the information in your signature is correct.

    "Outback bus bar with shunt" - the "shunt" implies that this is a bus bar for connecting things to the battery. In that case you have: BATTERY (-) --> SHUNT --> BUS BAR --> CC output, Inverter input.

    There's nothing else to connect there, unless you've got a whole load of DC equipment?

    I'll also stick my neck out and mention that you seem to have a 705 Watts of mixed panels, which not only will not produce 70 Amps of charge current (as per the modification) but also isn't going to do anything much for charging 1000+ Amp hours of battery.

    Does your "sig" need upgrading by any chance?

    Incidentally, this another reason why I don't recommend very large capacity 12 Volt battery banks/systems.
  • fireflyfirefly Solar Expert Posts: 66 ✭✭
    Re: Two Negative Buss Bars

    The system is not mine, I don't always explain myself clearly,hate typing. This system is a FLEXware 500, two VFX2812, two FM80, two 1225 watt arrays and a large 12 volt battery bank. Because of the large arrays, #2 wire is to be used on battery side of controller, this takes 2 of 3 #14 to #1 spaces on the buss bar. The array has #4 wire. The person that installed the controllers used # 4 wire on the positive side, but # 6 on the negative side, of the controllers. Outback want positive and negative on the battery side to be the same size, as they should be to balance the system. That leaves only one #14 to #1 space left to accommodate 2 #4 wires. Hope that explains the reason for the other buss bar. The only other thing I thought of was to change the #4 to #6 from the panels their are enough #14 to #6 spaces left, the run is only short from a junction box, maybe 5 feet. Hope this explains.

    Steven M
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Two Negative Buss Bars

    Or "how not to build a system." :roll: A classic example of why you don't build high-Watt systems around 12 VDC.

    It isn't Outback that wants the positive and negative wires to be the same size, it's that darn Isaac Newton guy and his pals Volta, Ampere, Faraday, Ohm ... you know; The Electric Gang.

    Okay, instead of continuing the lecture about why this is all wrong in so many ways (you've already figured that out) and suggesting it all be replaced with something that makes sense ...

    Yes, you can feed one bus bar off another one. Even though this is in my book as "bad practice". You just have to be sure that the wire running to it is capable of taking the full current. Think very carefully about how you're dividing things up; keep the highest current connections short and near to their sources/destinations. And be absolutely certain nothing is getting skipped/scrimped on circuit protection.

    I really would not want to do this. If the wire won't fit in the space provided, there's something seriously wrong with the design. I will now stop ranting about high-current 12 Volt systems. For now.
  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: Two Negative Buss Bars

    Be very careful to design accordingly. I despise 12v systems for just this reason it does not take long to exceed the amperage of things. I regularly see people without intending to over current buss bars etc.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Two Negative Buss Bars
    halfcrazy wrote: »
    Be very careful to design accordingly. I despise 12v systems for just this reason it does not take long to exceed the amperage of things. I regularly see people without intending to over current buss bars etc.

    I started out with 12 volts, never daring to dream that one day I'd be running my whole house on it, but now I am, and wish I had started out 24 volts instead. Now my 12 volt system almost daily is subjected to 120 amp loads, sometimes much more with the starting surge of power tools.
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