Battery Bank Wire Size

[mitchk]

Originally Posted by sproutroot

This is how I have it on my boat. I use DC breakers instead of switches, but there's one between the batteries and the inverter/converter, another between the batteries and the alternator, and a third between the batteries and solar. There are ways to have it all happen automatically, but I like "operating" my equipment.

But if you switch off the line between your charge controller and your batteries isn't that really bad for your charge controller because its still receiving power from the solar panel but it has no where to put it? Or do you also have a breaker between your solar panels and charge controller?

Thanks for all your help so far!

[Drew Bru]

Originally Posted by mitchk

But if you switch off the line between your charge controller and your batteries isn't that really bad for your charge controller because its still receiving power from the solar panel but it has no where to put it? Or do you also have a breaker between your solar panels and charge controller?

Thanks for all your help so far!

I've got a breaker on either side of the charge controller. I always shut off the solar panels before the charge controller.
Also, about the inverter. I think you can wire your inverter into the distribution panel using the outlet and an appropriate size cord. We've got an ac/dc distribution panel like a normal RV. Our wall outlets are fed by the distribution panel, as are any 12v lines (water pump, lighting, etc).

[sproutroot]

Yes, breaker on both sides of the controller. Drew Bru's method of turning off the panels is correct.

I'd also second the distribution panel. You'll have redundancies with your breakers, but that's not a big deal (just know what the circuit(s) in the inverter are fused to, and don't go above that in your distribution panel). Having all your wall wiring set up like a normal RV will make it easy to upgrade your inverter if you ever want to.

[dzl_]

Originally Posted by mitchk

Alright so I already have run into another question. I will probably use around 8AWG to wire my charge controller to battery bank. I am putting a fuse between the solar charge controller and the battery bus bar. I'm assuming I would want to put the fuse as close to the charge controller as possible since power will be starting in the charge controller and going to the battery bank. Or is their a failure scenario where the power would actually go backwards from the battery bank to the charge controller? If that could happen would I actually want the fuse closest to the battery bus bar?

So I don't have a good answer for you, but it is a good question, and thinking things through at this level puts you way ahead of the crowd. I asked a similar question here and received some useful feedback but not a clear answer. Some charge controllers have internal fuses in which case it probably makes more sense to place the fuse or breaker closer to the battery (this is probably what I will do). I think this is a good place to follow your manuals recommendations if it gives one.

So long as you use properly sized wires for your PV array and controllers max output, and have circuit protection somewhere in the circuit, you should be pretty safe I think, regardless of the precise location.


I think sproutroot and DrewBru are right:

Yes, breaker on both sides of the controller. Drew Bru's method of turning off the panels is correct [disconnect pv array first].

Also I'm assuming I would want a master switch to turn off charging the batteries. I would want to put that switch between the solar panels and charge controller right?

Correct, a breaker or switch between your PV array and your controller is a good idea. I also plan to have a main battery switch to disconnect the battery from the rest of the system.

put fuses in between the batteries and bus bar? I am wiring my 3 batteries in parallel directly to the bus bar and not with each other and then to the bus bar.

As a best practice you want a fuse as close to the battery positive terminal as possible (ideally right on it). What that means in practice will depend on the specifics of your situation.

Originally Posted by mitchk

But if you switch off the line between your charge controller and your batteries isn't that really bad for your charge controller

This is (or was) the conventional wisdom. Victron used to explicitly warn against this, but recently has recently stopped warning against doing this. My recollection of their explanation is that it was a theoretical problem, that turned out not to be an issue in practice. See post #43 here the person replying to my comment is a licensed Victron support tech, and the person he is referring to 'Matthijs' is Victron's CEO, so I trust this answer, at least in terms of Victron products. But always follow the recommendations of the manual for your specific charge controller unless you are sure you know what you are doing! And as a best practice, I think its still best to follow the conventional wisdom, even if its not strictly necessary its still logical to disconnect things at the source.

[kidharris]

Originally Posted by Phatman

Mitch - if you use DLO cable (locomotive cable) the ampacity of #2 is 190 amps. Don't know if they do it where you are but here in the Houston area can rent a hydraulic crimper from Tool Mart. You can go to an electrical contractor and explain what you need and they may be able to help you out if you have all your material. Find a commercial/ industrial contractor not a residential. Good luck.

Don't want to sound like I know what I am talking about, but... in the past I have had good luck going to welding supply places and buying welding cable for bigger wires. Some of them will make the ends for you or tell you someone that will. What I like about welding cable is that it has more and smaller strands which makes it much more flexible and I think it carries more current for a given size and the cables are tougher. However since they are made to use in open air the insulation may not be adequate for running in tight spaces or plenums. Car wiring insulation has its own standards and I am wondering if anyone is familiar with whether it is ok to use in this situation.

[dzl_]

Originally Posted by kidharris

Don't want to sound like I know what I am talking about, but... in the past I have had good luck going to welding supply places and buying welding cable for bigger wires. Some of them will make the ends for you or tell you someone that will. What I like about welding cable is that it has more and smaller strands which makes it much more flexible and I think it carries more current for a given size and the cables are tougher. However since they are made to use in open air the insulation may not be adequate for running in tight spaces or plenums. Car wiring insulation has its own standards and I am wondering if anyone is familiar with whether it is ok to use in this situation.

I believe both the marine electrical standards (ABYC) and building electrical code (NEC) require de-rating the current carrying capacity of wire if its in conduit or bundled with other current carrying wires (I'm positive this is the case with the ABYC, less sure about the NEC) so I wouldn't be surprised if the Automotive and RV standards were the same.

As for welding wire, I bet they list the insulation temperature, I would guess that once you find this out, you can compare it against a similarly rated marine wire or automotive wire.

[Phatman]

Originally Posted by kidharris

Don't want to sound like I know what I am talking about, but... in the past I have had good luck going to welding supply places and buying welding cable for bigger wires. Some of them will make the ends for you or tell you someone that will. What I like about welding cable is that it has more and smaller strands which makes it much more flexible and I think it carries more current for a given size and the cables are tougher. However since they are made to use in open air the insulation may not be adequate for running in tight spaces or plenums. Car wiring insulation has its own standards and I am wondering if anyone is familiar with whether it is ok to use in this situation.

That’s what the DLO cable is for . We use it in tight places in switch gear and motor control centers where it is impractical to use THHN wire because of the amp rating or conduit size.
DZL is correct about derating the wire after so many conductors in the conduit. Conductors are rated in centigrade and the ampacity goes up as the rating goes up. As long as you are not installing the conductors in conduit, you won’t have any problems. Ampacity is all about dissipating the heat. I’ve put a 100 amps on #8 THHN wire in free air with no problem. Just don’t do it very long.