RV: DC Power Distribution

[Kingfish]

Lil’ conundrum problem for the graybeards. We have 5 acres in the forest far removed from The Grid and we create our own power via Generator and trickle via Solar. We have two RVs with permanent snow roofs that have solar on top, plus two out-buildings (utility & storage) with more solar.

The two RVs are about 200 feet apart. There are three distinct charging systems: The primary RV is tied into the local solar and the Utility building. The Secondary RV to its’ solar, and the Storage Shed is about 100 feet from the Primary RV and has its’ own solar. The layout is close to an obtuse triangle with the RVs at the long base, and shed slightly closer to the Primary RV.

I believe the batteries used are 12V Deep Cycle, with two in series to make 24V. We have four generators: Each RV has its’ own propane, plus two portables that run on gasoline (2kW and 7.5kW) that output both AC and DC.

I would like to unify these systems using 2-conductor that we can safely bury into the ground maybe a foot deep. We get about 3 feet of snow in the winter and runoff can be a bitch in the low areas, but the ground is pretty hard and I think a mobile trencher could get the job done fine in one day.

The question that I cannot workout is the wire gauge; I don’t know enough about RVs to figure out what is reasonable. I can tell you that we run the generator whenever we do laundry, or pump water into the holding tank (via the Utility Bldg), and I think the RV generator kicks on if we run the microwave AND the coffee pot – which I think is the highest load on the land.

I know that there’s not enough solar to keep the batteries charged; we have to run the generator for an hour minimum to keep the Primary RV up to snuff (traditionally done when we do laundry). The Storage Shed overproduces power, and the Secondary RV is only used when guests are there, so my thinking is to tie the systems together and share the load. Now we’re back to the size of wire for the cable.

We also have a little stream that runs through the property but the drop is not very much as is the flow. I’ve toyed with trying to create a lil’ hydro but I don’t think it’s worth the cost. Best drop we can get is 2 feet; I could get 3 or 4 upstream but my Mom would really have a hissy fit and probably take out a contract to erase my birthday if I messed with that purdy section filled with wildflowers. However that has always been a tantalizing source of 24/7 low-output power flowing at least 1 gal/s.

Life is tough when you have to reach for a beer Sidebar related thread here.

Anyways, thanks for listening. Look forward to ideas.
Best, KF

 

[Kingfish]

ADDENDUM:
with what distance of wires can 12v battery be used?. Eye-opening. I can tell right away this can get very expensive.

This link was quite useful: Wire Loss Tables for Solar Electric Systems. Guess I need to figure out the minimum capacity and over-current protection.

~KF

 

[inh]

At such a low voltage, you're amperage will be quite high if you are trying to move any decent amount of power. That's going to take some large cable to pull off if you try to do it at your DC voltages.

If possible, tieing everything together with 120v AC would be much cheaper for cable, but it doesn't sound like that's possible. I don't think it'd be cheap to up the voltage of your DC storage systems and then drop it back down to 12-24v with a DC-DC converter in each RV...

If you're just looking to use some of that solar on the shed and guest RV, figure out how many amps you would need to pull from those to your other RV and size your cable for that. You shouldn't need a large cable for that I don't think. Then just protect the cable with an appropriately sized breaker and you'll be good to go. The two RV systems should equalize and share some of the load nicely.

 

[KMB]

Thinking here.... I've had RV's most of my adult life....tent trailers to 40' diesel pushers...they have all been 12v...passing throught invertors...and 120v through convertors. Most rv refridgerators etc. are 120v/12v/propane. Sure it's 24v??? Not trying to be a know it all ....just thinking..I know your smarter than I.
Kent

 

[edcastrovalley]

Here are some charts from my charge controller manual. They're for 12vdc but you double the lengths for 24vdc (see "Notes") and a couple sizes in there would reach 200 feet.

View attachment 2

 

[Hwy89]

The ideal solution would be to consolidate all of the solar into one location as close as possible to the battery bank. get a quality charge controller and an inverter that will accept generator input when the battery bank gets low. You can then run 110V AC through #12 direct burial cable which will be much less expensive than the cable you would need to move DC that distance. The two RV's would still need their house batteries but would be kept charged through their converters.

 

[Kingfish]

Consolidate Solar: In concept – good, in practice – not as. There are tall trees, so we get our solar where we can. We also have a “mobile” array which is repositioned by younglings to optimum ad hoc… but I digress.

Ideal Solution: I don’t know why I didn’t think of this before – though it appears to me that the best solution is to create charging arrays in series, razing the voltage so that the negligent impedance is overcome. Relatively speaking, who cares what the charging voltage is so long as we sample the battery frequent enough to know when we’ve hit our target, and then regulate the top-off. Geez, this appears dead-simple now; just need a comparator circuit and a VR.

Energized, KF

 

[dnmun]

need to cut down those trees that get in the way of the sunlight. burn the wood for the heat in the winter or rip it for lumber if you can, then burn the slash.

then go solar, add a passive solar porch on the south side of the RVs and insulate it so you can go out and be in the sun in the winter. getting early morning light to the optic nerve is very important in maintaining the circadian rhythm and serotonin for mood enhancement and protection during the shorter winter days.

cut big thermopane windows into the side of the RV and park it for solar gain in the winter.

 

[wineboyrider]

Run 36v or 48v dc and smaller gauge wires?

 

[Kingfish]

need to cut down those trees that get in the way of the sunlight. burn the wood for the heat in the winter or rip it for lumber if you can, then burn the slash.

:lol:

I just got back from HKG yesterday. The smog was really bad there; I have never seen a Blood-Orange-colored full moon before. They are planting trees like no tomorrow trying to reverse 3,000 years of past incompetence. If they keep at it -> burning coal, Solar will be of no help.

Grateful to be back home in a true rain forest, KF

 

[dnmun]

they will not burn coal much longer as the economy improves and they convert more to burning natural gas. as soon as they can start shipping LNG from the shale gas into japan and singapore their price will drop by 30-40%. the CCP is making it a current goal to convert and electrify the fleets.