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Old 01-24-2020, 09:32 AM   #1
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RV Solar Specifics

As I get more serious about my rv solar project and start loading components into my amazon cart, there are some issues.

The research seems to point to 8ga awg flexible welding cable, which seems logical.

But this cable may not be able to be jammed into mc4 connectors.

And, this cable may or may not squeeze into the screw connections on normal charge controllers.

Anyone here able to share a solution or a workaround?

Thanks
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Old 01-24-2020, 10:54 AM   #2
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I think(!??) Renogy provides to 4 gauge on the smaller controllers, double check. It will show in the specs on their website. As for other brands, check out the company's website. If they don't show it it could mean that they are embarrassed.

Gauge required will be dependent on your system configuration and if you want to build in "add ability".

Whatcha got cookin'?
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Old 01-24-2020, 11:16 AM   #3
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MC4 connectors are for connecting to the panels. You shouldn't need 8 ga. cable from the panels to the controller - connect them in series. Higher voltage means lower current so thinner wires will suffice. If you are using an mppt controller most will handle an input voltage of at least 70, and many will accept over 100 volts in. Where you need the heavy cable is between the controller and your batteries. The terminals on any controller you buy will be large enough to handle cable appropriate to the controller's maximum output.
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Old 01-24-2020, 02:45 PM   #4
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Don't over think it, back in the days of $5 per watt solar panels it made a lot of sense to optimize wire type and size, today in the era of sub $1 per watt panels, it makes a lot less sense
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Old 01-24-2020, 03:00 PM   #5
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I am running 2600 watts through 8 gauge wire with no problems, but are using a 250 volt mppt controller at 240 volt input, panels are wired series/parallel.
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Old 01-25-2020, 01:09 AM   #6
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8ga wire to connectors?

They're designed for 10ga. We run the paralleled panels with 10ga on roof to a centralized junction box, then 6ga down to the solar controller. Very little loss.
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Old 01-25-2020, 01:49 AM   #7
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I know. Every youtube install I watch uses 10ga.

Here is my math:

(4) 170 watt panel in series is 680W (probably only 80% of that in real life).

Open voltage of 22.5V. Multiplied by 4 makes 90V.

That makes total amperage just about 7.5A, right?

Am I figuring this wrong?
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Old 01-25-2020, 04:10 AM   #8
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10 guage for wires from panels to charge controller
8 guage for wires from charge controller to battery
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Old 01-25-2020, 07:02 AM   #9
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Quote:
Originally Posted by Brianna View Post
As I get more serious about my rv solar project and start loading components into my amazon cart, there are some issues.

The research seems to point to 8ga awg flexible welding cable, which seems logical.

But this cable may not be able to be jammed into mc4 connectors.

And, this cable may or may not squeeze into the screw connections on normal charge controllers.

Anyone here able to share a solution or a workaround?

Thanks
Have a look at the am solar web site. Good videos, info, and solutions. They have really nice kits that are well designed and include most of what you will need at reasonable prices. Lots of help weather you buy from them or not. Here is what I used. We only have 220 amp hr of storage but this may grow.

10ga wire from 3-90 watt panels to roof combiner box
4ga from combiner to controller and controller to batteries
100/30 mttp Victron controller mounted less then 6 feet from the batteries

The 4ga is a little large for charge controller but if you carefully remove a few strands it fits fine. 6ga wire fits. Big wire less loss and room to grow. From what I understand bigger wire is better...read handybobsolar, good info. The 10ga wire from am solar is a good product for the roof and can be used for any solar panel....watch the videos!
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Old 01-25-2020, 07:20 AM   #10
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Also nothing says you have to run all panels through just one pair of wires

I have 1500w in three strings. Each 500w string has a run of #10 to a combiner box with circuit breakers near the controller. That's 3 #10 pairs.

The #4 from combiner/breaker box to controller and controller to batteries.

Victron 150/100 controller.
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Old 01-25-2020, 07:37 AM   #11
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Yes, if those are the numbers for your panels. In series the voltage adds and currents stats the same.

If you have room for a bigger array, suggest to do so. Solar production has lots of variables. I typically advise to put as many watts as you have roof.

Flat mounted in january low sun results in upwards of a 50% reduction.
Quote:
Originally Posted by Brianna View Post
I know. Every youtube install I watch uses 10ga.

Here is my math:

(4) 170 watt panel in series is 680W (probably only 80% of that in real life).

Open voltage of 22.5V. Multiplied by 4 makes 90V.

That makes total amperage just about 7.5A, right?

Am I figuring this wrong?
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Old 01-25-2020, 07:40 AM   #12
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Thanks everyone.
I am grateful.
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Old 01-25-2020, 08:12 AM   #13
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This is where I get my solar advice. https://handybobsolar.wordpress.com He agrees that 8 gauge is enough from charge controller to batteries provided they are close together.

Also, if you happpen to be anywhere near Phoenix there is a company selling used solar panels really cheap. Right before Christmas I picked up 4 panels 250 watts each for $150 total. That’s 15 cents per watt! They also ship them. I found them on eBay.

I’m using those panels on an off grid tiny house that I’m building in the desert. I added a Morningstar MPPT 60 amp charge controller and a Trimetric battery monitor.
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Old 01-26-2020, 07:06 AM   #14
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Interesting, when I read handy bob he mentions that for his 340 watt system he had installed 6ga in his rv and the wire run was only 12 feet from the panels to the controller and 4ga from the controller to the batts. He goes on to say that he wished he had used 4ga in his own rv from the panels to the controller and typically used 4ga in other systems he has designed installed and/or repaired. And I quote Bob,"Resistance or impedance is the enemy. You have to overcome it and get the power to the batteries, not just to the output terminals on your charge controller. The system in my rig is efficient because I wired it with six gauge wire, for a total distance of only 12 ft from panels to controller. I ran #4 from the controller to the batteries." He continues, "Use BIG wire, at least #8 for two panels and, and #6 for three panels and that is only for runs under 20 ft. I have installed a lot of #4 cable and wish I had it in my own rig."

Brianna has a fairly large coach and I suspect will have wire runs of 20 feet or more. Brianna, use larger wire and get the controller as close to the batts as you can. My coach is only 28 feet and my wire run from the roof is close to 30 feet and then another five to the batts. I could of gotten away with 6ga but my system is small as my storage is only 220 amp hours and I wanted my system to be as efficient as possible.
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