Bus Bar Sizing

[hooptie00]

HI,


I'm in the last stages of acquiring all the pieces to start the installation of our solar system.

I need to add a positive and negative bus bar from the solar to the batteries, The existing batteries are 4 Optima AGM's for a total of 220 amps.
Because of the number of batteries and cables required to connect the solar and inverter, I wind up with 3 positive cables attached to the power supply battery.
It seems like it might be a good idea to add a bus bar to get the cable connections down, but what size in amps do I really need.
We plan on installing 2 new AGM's for as total of 400 amps, what size bus bar should I go with. Any ideas would be greatly appreciated.


TIA,


J R

[Chuck Q]

I use 3/8 inch connection
for the batteries.

[rarebear.nm]

I also added Pos & Neg buss bars when I installed solar. I simply do not like stacking more than 2 maybe 3 wires to any one terminal post. I had used 2-0 gauge welding wire for the battery cables to the buss bar. I calculated the cross sectional area of 2-0 wire to determine the cross section area of the buss bar. In my case I bought a couple feet of 1/2 x 1 1/4" (I think it was) solid copper bar on Amazon. I cut it to length, drilled and tapped it for 1/2" brass bolts with brass lock washers. For an insulator I used some HDPE 1/2" stock. Same stuff as plastic cutting boards are made. Its a very good electrical insulator.

I went a step, really a few steps, farther and used two Pos buss bars. The first one has all of the charging sources and the battery Pos lead, also the jacks and slides are attached here. One lead from it goes to a Battery Protect device which feeds the second Pos buss bar. This one includes most of the RV's house 12 volt loads. Power for the propane alarm and couple other items comes off the first buss bar, going to a small ATO fuse box from Blue Sea.

Here's a drawing what my main 12 volt control panel looks like today.

[Beau388]

The bus bar only needs to be only as large as the max amperage draw and charge. Typically the max charge current will come from the alternator 150 to 200 amps and the max discharge will be the inverter. Any were from 100/200 amps for a small inverter to 200/400 amps for a larger one. Solid 4/0 has a diameter of 0.46 in and can carry 195 amps @ 60 C. or about 0.166 sqin. Twice that size or about 0.33 sqin should work fine. (3/8" x 1"= 0.375 sqin) If you are going to put a 3/8" hole in it, I would recommend 1" and 3/8" bus bar.

[hooptie00]

Thank you, once again the great folks on this website come to the rescue.


I found a 300 amp 3/8" bus bar by Blue Sea Systems that should work.


Thanks again,


J R

[John Hilley]

You might also consider using a Power Posts instead of bus bars

Blue Sea Power Posts

[R.B]

Originally Posted by John Hilley

You might also consider using a Power Posts instead of bus bars

Blue Sea Power Posts

I used a bus bar for the primary power tap but many of these for other purposes, and they work well. One tip: pay attention to your torque -- it's really easy to shear the bolts accidentally.

[astrocamper]

I didn't see an inverter on your diagram but if you are considering one later I would use higher rated bus bars. I used four Marinco Power Products 650A 5 Stud Buss Bars for my largest connections that involved the batteries, protections fuse, shutoff and inverter. I used smaller 250 amp rated secondary bus bars for the smaller stuff like solar charge controllers and other things.

My Spartan 2200 watt pure sine wave inverter has a peak of 6600 watts which is about 550 DC amps. I used eight 2/0 cables from each of 4 LiFePO4 100 amp-hour batteries to positive and negative bus bars. I used 4/0 cables from the center of each of the bus bars to the plus side shutoff and fuse negative side shunt and then to a secondary set of 650 amp bus bars that had the inverter connections and 105 amps from AC->DC chargers plus links to smaller bus bars.

[rarebear.nm]

Originally Posted by astrocamper

I didn't see an inverter on your diagram but if you are considering one later I would use higher rated bus bars. I used four Marinco Power Products 650A 5 Stud Buss Bars for my largest connections that involved the batteries, protections fuse, shutoff and inverter. I used smaller 250 amp rated secondary bus bars for the smaller stuff like solar charge controllers and other things.

My Spartan 2200 watt pure sine wave inverter has a peak of 6600 watts which is about 550 DC amps. I used eight 2/0 cables from each of 4 LiFePO4 100 amp-hour batteries to positive and negative bus bars. I used 4/0 cables from the center of each of the bus bars to the plus side shutoff and fuse negative side shunt and then to a secondary set of 650 amp bus bars that had the inverter connections and 105 amps from AC->DC chargers plus links to smaller bus bars.

You are totally correct, I do not have, need or want an inverter on that RV. DW and myself had several long discussions about that point and we opted not to install one. Therefor, there was no need to go to the higher rated buss and cables as you mentioned. If I had designed in an inverter the 12 volt design would have been different. I designed and built exactly what we wanted.

Good point to make for others. The main point of including the diagram was the double Pos buss bar configuration to go with the narrative.