diy solar

diy solar

First solar setup advice

Nathannz

New Member
Joined
Jul 9, 2021
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3
Hi everyone, newbie here.
Building a rv system, attached is a basic layout of my proposed system.

Main parts:
Series battery connection 2x 6v 200ah sealed
Series pv 2x 250w 8.32a
60a Mppt controller
Using 3 breakers at applicable amps
800w sine wave inverter
Circuit lengths all will be under 4m

My questions are:

1. The charge controller has a "dc load" output
Can i leave this be and just run load directly from positive poll on my bank. I assume its for individual load monitoring?

2. For dc appliances. Lights,fridge etc.. what is the proper way of circuit routing.
A common ground back to battery earth ? Or individual negitive wires from each appliance.

3. Is it proper practice to ground to the vehicle chassis at any point?

4. What size breaker do i select for between positive poll and fuse box for dc load?

I appreciate any feedback on my schematic or any answers to my questions.
Thanks,
Nathan

Picture of my system: https://ibb.co/Y2HKr97
 
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1. Yes you can leave it be, you don't need to use that load port.
2. Common grounding is fine, unless you run into any noise issues.
3. You can ground anywhere really, in my opinion, more grounds better than not enough grounds.
4. Depends on wire gauge (and max load calculation, which drives decision on wire gauge)... It starts by deciding what 'amps service' the fuse box will provide as a whole to meet the sum of all it's individual fuse loads.
 
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4. Depends on wire gauge (and max load calculation, which drives decision on max gauge)... It starts by deciding what 'amps service' the fuse box will provide as a whole to meet the sum of all it's individual fuse loads.
Hi Samsonite, thanks for reply. does wire gauge factor into breaker size? For example my maximum total amps would be 16A so a 20a dc breaker would be sufficient?
I plan on using 8 awg to fuse box and 14awg to each appliance. With runs all under 2m.
 
Hi Samsonite, thanks for reply. does wire gauge factor into breaker size? For example my maximum total amps would be 16A so a 20a dc breaker would be sufficient?
I plan on using 8 awg to fuse box and 14awg to each appliance. With runs all under 2m.
14ga is good for 15A-20A DC if under 20 or 25 feet of length. You fuse things to protect the wire not to accommodate your load. I use 20A fuse for 14ga for short run, 10-20ft: 15A fuse. I underrate wire- I’ve seen “unlikely” fires; I treat gage very conservatively and use fuses for the load, not the wire rating: none of that has burned.
Your 8ga is only good for like 40A at ~30 feet.
Run this Blue Sea Systems fuse box https://www.amazon.com/dp/B000K2K7VA/ref=cm_sw_r_cp_api_glt_fabc_YGDHKQGSP7QK7NTYR4GC?psc=1 and both negative and positive will be accommodated. The negative “bus” on these fuse boxes is a big deal to me. Not just useful on boats!
Get a bunch of bare spade or ring terminal crimps if you’re anal or want to amaze people, or OCD like me. The ring terminal ends really pluck the harp for ocd needs….

Your 8ga is only good for like 40A at ~30 feet. It will be fine if your cumulative service loads do not exceed 40A

A naturally underrated / safe low-voltage DC load chart is the ABYC wire gage table. https://www.bluesea.com/files/resources/newsletter/images/DC_wire_selection_chartlg.jpg


3. Is it proper practice to ground to the vehicle chassis at any point

no that is not proper practice. Use paired wire +/- and home run it to the fuse box.
Other folks have a different opinion. Mine is based on experience and backed by ABYC guidelines. Sure other stuff ‘can’ work and does but home-runs have never caused I fire that I’ve seen, so…

4. What size breaker do i select for between positive poll and fuse box for dc load?

40A max for the 8ga wires. For the sum of the cumulative loads on the fuse box shouldn’t be made capable of exceeding the feed wire capacity.
 
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Yeah, what he said!

I don't know ABYC guidelines, the idea of ground home runs sounds most logical anyways. I do have an RV and notice all my runs have negative lead wires from the factory (on the house bank circuits anyways, chassis battery circuits do not).

I was more of an automotive mechanic for many years, and not versed well on specific standards for RV house circuits, so if ABYC says do then do it hehe...
 
Your 8ga is only good for like 40A at ~30 feet. It will be fine if your cumulative service loads do not exceed



40A max for the 8ga wires. For the sum of the cumulative loads on the fuse box shouldn’t be made capable of exceeding the feed wire capacity.

Hi there! I have purchased one of the common negative fuse boxes you mentioned, I didint know they existed, makes sense.

I always thought larger wire gauge was better? Less voltage drop, I've already purchased larger gauge. There is no,disadvantage to running larger wire? Such as the 8awg?

The cumulative maximum load of all my dc appliances is 16amps would it not be safer to run a 20a breaker between positive and dc fusebox?
My reasoning being,
It Exceeds the maximum amp draw of load but will cut off well before maximum rated current of wire
 
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Yes that sounds fine. Other than cost, running bigger gage has no disadvantages.

Advantages yes: when I first started solar with a 200W windyNation kit and junk batteries I wasn’t charging as much as I needed. Past experience made me wonder about using 8ga panel cables. I bought some. In totally full sun the max amps on 8ga that I saw was 11.9A!! On 2 100W panels parallel. The most the 10ga (or was it 12ga?) ever did was 9.xA; the day I switched I was like 9.6A and showed 10.8A or something the moment I went in and checked. I was shocked. (I’d turned on a shop vac to ‘force’ the input amps to be as high as possible).

That’s extreme. I wouldn’t claim or predict that drastic a difference but in that case that’s what it was.

Example of gage difference: one of my welders is a 120V mig. On a 12ga extension cord it doesn’t weld as nice at higher settings- and pops 15 and 20A breakers regularly. I have a 50’ 10ga extension cord. It welds well and I can go for hours and never pop a 20A breaker. (15A still trips in a few minutes.)

A little change but a big difference.
 
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