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diy solar

Bobbing for Questionable Apples

Oak_Sandalfoot

? Everybody Loves the Sunshine ?
Joined
Mar 16, 2022
Messages
44
Location
SWFL
Greetings solar community,

I need help setting up my first PV system in my Schoolbus RV conversion. I have the following components:

*12v, 750w PV array (3 x 250 in series)
-Max VoC: 50.9a (Brand: Sunpower)
*2500w PSWI (Reliable)
"50a MPPT SCC (Vic.)
18a DC to DC charger (Vic. Orion)
*Lynx Power In busbar (modded to be a Fuse holder as well) (Vic.)
*412 ah lifepo4 battery bank (2 x 206ah in parallel) (SOK)
*DC fuse box (100a Blue Seas)
*Master disconnect wired at positive output terminal of the Lynx
*Shunt for BM at negative output of Lynx
*Fuses:
-Inverter: 400a mega
-SCC: 60a mega
-Dc to DC charger: 60a (lynx), 50a terminal fuse (starter battery)
-DC fuse box: 100a mega fuse
-Lynx positive output cable to battery: ???a ANL fuse with fuse holder

I've been working countless hours to learn all of this stuff on the internet from rock bottom/scratch with ZERO prior electrical experience. With the vast amount of information, seemingly infinite variations of design, conflicting viewpoints, my 'noobability', and the inability to discuss the issues face to face with a knowledgeable human, the whole process has been very challenging. I am proud of how far I've progressed in the past two months from the drooling idiot at the solar warehouse to someone who can actually read through a solar forum and understandstand the language and glean information; however I am not too proud to know that I still don't know sh*t and I need help!

When I dip my head into that huge barrel of questionable apples, these are a few that float to the surface:

1)Can the following devices (going into the Lynx Busbar/fuse block) all be wired with 6awg?
*Orion DC to DC 12v/18a
*50a scc
*DC fuse box (blue seas w/ blade fuses)
-100a, 150a max (I think)

2)Inverter to Lynx cable gauge? (Short run <2 feet)
*1/0, 2/0 or 4/0 awg?

3)Lynx to battery cable gauge?

*1/0, 2/0, or 4/0

4) I have some insulated 6 awg in two different types: one is like 50 strands or more, and the other is exactly 7 strands. Which is preferable to my application? Basically, coarse or fine strand cable? (I already learned that solid is not recommended for mobile applications)

5) Orion DC to DC 18a charger:
*Can it be wired to either the starter battery or alternator, or does it have to wire to both (I'm confused because none of the many, many install videos on 'the Tube' ever wire directly to the alternator.)
I'm assuming, based on extensive thread surfing, that connecting to the starter battery in effect connects to the alternator as well?

6) Is it advisable to put a dual pole DC breaker between the solar panels and the SCC? If yes, then what Amperage breaker)

7) Can the Inverter and SCC be grounded on the DC fuse box instead of the chassis? (Grounding to chasis is viable option if not)

8) What fuse (???a) between main positive of Lynx bus and battery bank? ANL, Mega?

9) Any recommendations or comments on my setup just based on the components listed?

Thank you in advance to everyone who contributes their time, money, and energy to make these sorts of 'far-flung' endeavors possible for a noob like myself.

Cheers,

Oak Sandalfoot

IG: Dumpstarsdivingbus
(Skoolie stuff & Dumpster Diving)
 
Last edited:
1)Can the following devices (going into the Lynx Busbar/fuse block) all be wired with 6awg? highly recommend the following sizes
*Orion DC to DC 12v/18a 12awg
*50a scc 6awg
*DC fuse box (blue seas w/ blade fuses)if feeding with 100a,use 2awg
-100a, 150a max (I think)

2)Inverter to Lynx cable gauge? (Short run <2 feet)
*1/0, 2/0 or 4/0 awg? recommend 2/0awg

3)Lynx to battery cable gauge?

*1/0, 2/0, or 4/0 recommend 2/0awg or 4/0awg if you plan to add more batteries.

4) I have some insulated 6 awg in two different types: one is like 50 strands or more, and the other is exactly 7 strands. Which is preferable to my application? Basically, coarse or fine strand cable? (I already learned that solid is not recommended for mobile applications)
fine strand

5) Orion DC to DC 18a charger:
*Can it be wired to either the starter battery or alternator, or does it have to wire to both (I'm confused because none of the many, many install videos on 'the Tube' ever wire directly to the alternator.) can go to either. Anywhere on the 12v system.
I'm assuming, based on extensive thread surfing, that connecting to the starter battery in effect connects to the alternator as well?

8) What fuse (???a) between main positive of Lynx bus and battery bank? ANL, Mega? It's a type CNN fuse like this: https://www.currentconnected.com/product/lynx-s-fuse/
 
Thank you, HTL, for your recommendations and for being the first responder!

My only question regarding your answers is about wiring the DC to DC charger to the Lynx: why do you recommend the smaller 12 awg wire over 6awg?

I'm very grateful for your input!
 
Really need to check the specs on max cables that will fit in a Victron device.

I believe the recommendations of 12 awg and 6 awg are correct, but the Victron SCCs i purchased did not allow wires bigger than the smallest cable rated to handle the amperage at 60 c. For example my 50 amp SCC does not take thicker than 6 awg, and my 15 amp SCC does not take thicker than 12 awg.

I had wanted to run thicker cable for voltage loss, but could not.
 
If you can't fit a big enough conductor in the controller, you can use your fuseblock right next to the controller as a point to upsize to the bigger wire for voltage drop. The shorter & smaller wire from the fuseblock to controller won't have much of a notable loss.
 
The DC-DC is only putting across 18 amps max. 12awg is good for over 20 amps.

Your #12 wire rating is from the NEC specifications that rate the wire's voltage drop to 3%/100 feet energized with 120VAC, a 3.6 V drop. One should not use this rule for lower voltages. For example, if the energized voltage is only 12V (AC or DC) @ 20 amperes the voltage drop over a 100 foot length would still be 3.6 V with #12 wire.

Now the percentage is NOT 3% but 100( 12-8.4)/12 = 30%! NOT insignificant! That is the reason to use larger gage wiring for lower voltages. And the best way to size the wire is to determine how much voltage loss you are willing to accept and then use ohm's law to calculate how much is lost in the selected wire. Wire resistance charts are easily found using a search engine. And do not forget that the wire length is the sum of both to the source AND return.
 
Your #12 wire rating is from the NEC specifications that rate the wire's voltage drop to 3%/100 feet energized with 120VAC, a 3.6 V drop. One should not use this rule for lower voltages. For example, if the energized voltage is only 12V (AC or DC) @ 20 amperes the voltage drop over a 100 foot length would still be 3.6 V with #12 wire.

Now the percentage is NOT 3% but 100( 12-8.4)/12 = 30%! NOT insignificant! That is the reason to use larger gage wiring for lower voltages. And the best way to size the wire is to determine how much voltage loss you are willing to accept and then use ohm's law to calculate how much is lost in the selected wire. Wire resistance charts are easily found using a search engine. And do not forget that the wire length is the sum of both to the source AND return.
He is not running 100 feet. I believe my recommendation is still correct. Do you have a different recommendation or just here to call me wrong rather than offer a better suggestion?
 
He is not running 100 feet. I believe my recommendation is still correct. Do you have a different recommendation or just here to call me wrong rather than offer a better suggestion?

I did not say nor imply he is running 100 feet. What I did explain is he should avoid so called rules of thumb that do not apply to his situation. He should determine what level of voltage loss between the source and the load is tolerable and calculate the PROPER wire size. Any other approach is pure guessing and yours is in the guessing category and that is sloppy engineering.
 
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