Length of Solar Cable run

[JetPowers]

I realize a vague question might get me in trouble but here goes:

Details of a solar installation aside, I'm at the buying cable stage for a 34ft pilothouse ketch. PV location is undecided and might be moved anyway but thinking atop the cabin roof just ahead of the wheelhouse (least obstrusive) or eventually a solar arch if I every take that plunge (canoe stern/no davits yet either).
As the crow flies...err, crawls, the cabin location to battery compartment is about 5 ft and the stern arch location about 12. However I realize there are vertical drops and potentially lots of snaking around obstacles such as bulkheads.
I'm thinking 5 ft direct can become 15' snaked and 12' direct can become 25+.

Anyone have "in my experience" to guide the purchase? I've found a good sale (8awg - 16ft red/16 black plus 50% off second additional purchase) and thinking 'perhaps' I can always make extensions. Maybe thru experience folks will say...just buy a 25 or 50' reel and cut what you need? Even there I may not really know till I've already made the cuts though I'm hoping to use a fish tape first.

As details. I will be starting with 2 x 100W Sunpower flex panels/2 controllers for house/starting separation and thinking 8 awg...or a 10awg/8awg for one another since one is only for a 12V starter battery. Most likely I'll go uniform 8 awg all the way simplifying ancillary parts. Fuses..undecided but thinking ANL if I can find in 20Amp size. I do have a Xantrex inverter with battery monitor and unsure if I need to shunt the negative battery wire into the monitor. I was told to go direct to battery though, but these are details as an fyi and not my main question currently.
Thank you

[tkeithlu]

General principle - the thicker the stranded and the finer the strands (that's important) cable, the less the loss. Invest in the heavy stuff. Electrons chug along the outside of wire, so the more surface area the better.

In that regard, I've occasionally found that the cable I needed to move electrons was cheaper by my sacrificing a jumper cable or an extension cord than by buying the stuff by the foot. Outdoor extension cords usually have the various insulation ratings needed.

[Reeve21]

Originally Posted by JetPowers

I do have a Xantrex inverter with battery monitor and unsure if I need to shunt the negative battery wire into the monitor. I was told to go direct to battery though, but these are details as an fyi and not my main question currently.
Thank you

I'm following along and interested in what folks think about this question.

[JBP]

Some things to consider

For a 25 ft run, the 3% voltage drop rule gives 10ga for 10A, 8ga for 15A

If you wire those two panels in series, you get twice the power for the same current. Then a single controller plus a DC-DC charger could handle both batteries and give you more flexibility in charging.

[SV Confianza]

Need to know what voltage the panels are at and figure out max amperage. The size cable is determined by the max amps going through (possibly adjusted by long lengths).

Then you need to make sure the voltage drop is acceptable for that size and length.

[SV Confianza]

Originally Posted by JBP

Some things to consider

For a 25 ft run, the 3% voltage drop rule gives 10ga for 10A, 8ga for 15A

If you wire those two panels in series, you get twice the power for the same current. Then a single controller plus a DC-DC charger could handle both batteries and give you more flexibility in charging.

Wired in series will kill your output with any kind of shading. Not good for sailboats (unless you need to boost voltage for some reason).

There are lots of good YouTube videos on series vs parallel shading performance.

[JetPowers]

My apologies as I was obviously unclear or confused the issue with the details which do not matter for my question. My boat is tightly covered and temps already 30 degrees/snowing so estimating is tough. All I want to know is how much cable length to buy. If you see say.... a 5 ft direct run do you end up needing 3x that amount to snake it all. If you have 12 ft from a stern rail to battery do you end up needing 20 or 25 or whatever. Down holes, around or through a couple bulkheads I'm expecting the needed length to escalate fast. I realize it's a loaded question full of "it depends" but just asking your experience. Stuff is expensive and I have a habit of overbuying then hoarding the excess so trying to avoid that. I can buy 16ft extensions, 20 ft...40 feet and cut, 50' reels., etc. I'd like to catch a decent buy of 8 awg x 16ft on @mazon but if too short perhaps I can then add extensions.
I added a few details only because I know people ask but it won't affect the basic question - how much cable length you've ended up needing for your install? Thanks.

[sailorboy1]

I have 640w solar going 25 feet to mppt controller at 31V through 8awg cable with no problems. If using a mppt controller don't forget to adjust current for higher voltage and lower current.

[JetPowers]

Originally Posted by sailorboy1

I have 640w solar going 25 feet to mppt controller at 31V through 8awg cable with no problems. If using a mppt controller don't forget to adjust current for higher voltage and lower current.

Of that 25' run, roughly how much would have been a direct measurement if there were no obstacles to snake - 5ft? 10? 20?

My immediate goal is just to maintain my batteries topped off till March and I will be hanging my panels atop the cover with hanging wires/direct run of about 15'. But when I permanently mount them atop the cabin, drill holes and snake that 15' will not be the same even from that location. I may need to buy 20' or 25' or maybe just 10' being closer to the battery. So your direct run vs snaked run might help me visualize my need. Again, I realize your layout will be different than mine.
Thanks.

[Jammer]

There's no way around actually measuring unless you're prepared to waste a lot of expensive material. Splices add a source of future problems, avoid them.

Originally Posted by tkeithlu

the finer the strands (that's important) cable, the less the loss.

Only in high frequency AC circuits (e.g. radio). See https://en.wikipedia.org/wiki/Skin_effect for a thorough treatment of the subject.

[sailorboy1]

Originally Posted by JetPowers

Of that 25' run, roughly how much would have been a direct measurement if there were no obstacles to snake - 5ft? 10? 20?

straight line is probably around 15'

Are you using a mppt controller????

If not 25' for 200w system is too much for a 8awg as at max (it never does max) power at 12V that is a 5.2% voltage drop round trip.

But a mmpt holding a 30V panel voltage is only 7 amps and a 0.91% and just fine

[sailorboy1]

I like to use the following for this and note that 3% loss is max for a non critical system

https://www.calculator.net/voltage-d...late&ctype=nec

[NorthCoastJoe]

If you have the time run a thin extension cord or any cordage the run you need to follow, then measure it off that distance.

Otherwise just buy the best deal on a spool. I have a collection of partial spools all gauges that come in handy. Get just one color and color the last 6" of the ends with colored tape.

[JetPowers]

I haven't got it all thought out as timing was tight. New to me boat, many systems to learn and winterize, just managing to cover before the nighttime freezings. After getting 2 of the 5 heavy batteries out the bilge and down the ladder I gave up, reinstalled the batteries and decided to maintain with solar and caught some cyberweek deals. I've yet to really decide location so please excuse that it's not thought out. I'm awaiting 2 x 100W with one dedicated to the start battery. I will toss them right over the tarp for winter and think about permanent mounting. The other will either go into a closet over summer to be used next winterization over the tarp or be paralleled into a 200W - for 300W total into the house bank permament. At $100 is was cheap enough as a charging spare and not have to worry about it being covered over in winter. I could use more Watts but space is limited unless I get an arch or go over the side rails. Sales team recommended 2 controllers. I researched a combiner but was confused so went with advice and yes they are MPPT. Complicating my thoughts is a fear of drilling holes in perfectly good fiberglass so really need to think out location
I appreciate the advice to avoid splices and to buy by the reel. And a package of connectors, probably 8 AWG. I'll arbitrarily add ~50-60% to length and just bite the bullet. Pretty sure runs will be under 25 ft. and if atop the cabin less than 15ft. single color was in my mind too. Any extra at 8AWG I can probably make controller-battery cables. Thank you

[sailorboy1]

I am in the camp that a properly done connector is nothing to worry about.