diy solar

diy solar

Bus bar

Grey Fox

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Joined
Jan 23, 2023
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11
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TAOS,NM
I have 4 100w panels, 30amp CC, 4 12V 100AH batteries and 3000w inverter....batteries in parallel. I am going to have a bus bar...actually 2....neg and pos...the bars will have probably 8 holes in each...rated at least 600 amps...my question...in what position do I hook up my CC and my inverter...on the bus bar...what gauge wire? Can I attach my 12v little frig on them also...I will fuse it all....can someone show me a simple diagram or explain simply to me...thanks
 
I'll take a stab.

Bus to inverter wire gauge: Assuming a minimum voltage of 10.5V, 3000W/10.5V is 286A. NEC requires the wire to be sized at 125% of that, so 357A. Assuming the terminals are rated at 90C (I doubt it!), you can use 90C rated wire like THHN or DLO or welding cable. Welding cable and DLO are nice because they very flexible as apposes to the very stiff THHN. Again, if the terminals are rated at 90C, you would use 3/0 copper. This wire size would be appropriate if the bus-inverter wiring is in free air. If in conduit, the size increases to 400 kcmil. A more rational assumption is that the terminals are rated at 60C, which then requires 600 kcmil wire if in conduit or 300 kcmil if in free air. The terminal temperature rating is important and a lot of folks don't understand it. If disregarded, the wire can be fine, albeit hot, but the terminals where the wire is connected (most likely at the inverter) will melt or worse catch fire.

One the charge controller side: 400W of panels will generate around 32A or so at 12V. That is potentially in exceedance of your 30A controller. Cloud edge effects and temperature will drive the 32A higher and might destroy the charge controller. Normally, the panels might generate 80% or so of the total 400W rating, but the wire needs to be rated at 125% of 32A, so 40A wire. Again, assuming 60C rated terminals, that's gonna be #8 AWG.

The frig. It will connect directly to the bus bars. You didn't include any power requirement on it so just size the wire as above once you know its maximum current consumption.

As far as connections to the bus bars are concerned, you just want to keep everything balanced or symmetrical. Since you only have a couple of connections to them, any connection "order" will be fine.

Keep the wire from the bus bars to the inverter (both positive and negative) and the wire from the bus bars to the batteries, again both of them, the same length. This helps the voltage drops the same.

Be mindfull that fuses should be as close to the battery as possible and as close to the bus bar as possible for the wire supplying the inverter. Fuses are there to protect the wire, not the electronics connected. Batteries can develop some incredible short circuit currents!

Symmetry about the battery connections to the bus bars is important also. Somewhere on this forum are discussions about it.

One last thing, you will have cables connecting the batteries in parallel. If you assume that each battery will deliver 1/4 of the total 286A, or 72A, use #4 AWG wire for these jumpers. Problem is, the batteries will eventually become unbalanced so their individual currents will not be equal. If you take one battery out of service, you'll need #3 wire, if two out, then #2. You might consider just using #2 to allow some flexibility in maintaining your batteries.

Hope this helps!
 
I have 4 100w panels, 30amp CC, 4 12V 100AH batteries and 3000w inverter....batteries in parallel. I am going to have a bus bar...actually 2....neg and pos...the bars will have probably 8 holes in each...rated at least 600 amps...my question...in what position do I hook up my CC and my inverter...on the bus bar...what gauge wire? Can I attach my 12v little frig on them also...I will fuse it all....can someone show me a simple diagram or explain simply to me...thanks
Thanks
 
I have 4 100w panels, 30amp CC, 4 12V 100AH batteries and 3000w inverter....batteries in parallel. I am going to have a bus bar...actually 2....neg and pos...the bars will have probably 8 holes in each...rated at least 600 amps...my question...in what position do I hook up my CC and my inverter...on the bus bar...what gauge wire? Can I attach my 12v little frig on them also...I will fuse it all....can someone show me a simple diagram or explain simply to me...thanks
If it's the same ones I just purchased, those are really really nice, but large buss bars. Quality appears to be top notch, and really easy to work with. Plus it has screws on the end for small connectors too.
 
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