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Small Cabin Forum / Off-Grid Living / Electrical planning - advice on 12v vs 110
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# Posted: 9 Feb 2023 20:00

Hey guys, I’m getting ready to start my 10x15 bunkie build this summer up on our island. I’ve pretty much mapped out the construction plans but I’m a little hung up on the electrical plans. Let me elaborate and maybe some of you with more experience can provide some feedback:

Dilemma: Dropping a line across the river to be on the grid is too expensive for us (AT THIS TIME). However, it could be an option later and also knowing that we will re-sell this property down the road (20-30 years or so) we’d like to keep that window open for future buyers. I also wouldn’t balk at the idea of wiring up a generator for occasional glamping sessions. However, for now I’m planning on a solar panel and battery setup. Most likely the solar power setup will be the long term solution. So my issue is, how should I wire the cottage to run off a battery bank now, but possibly a generator later and also leave the option open for possibly being hooked into the grid one day down the road?

Bunkie plans: Nothing fancy, minimal needs. The plan is for lighting (indoor and outdoor), ceiling fan, maybe a small tv one day, and some device charging ports so we can work from the island if we want (there is cell coverage). Appliances: 2 burner propane table top, a propane heater and a small wood stove for heat, compostable toilet.

Bunkie construction: 10x15 with loft. Walls out of 2x4 and insulated with Roxull for winter use. Everything being built from scratch so easy for me to install myself.

So I was thinking that the easiest way would be to just wire it up with standard 14-2 electrical like I would the house. I’d put in a mini panel for a couple of circuits and run it to a plug that would allow me to switch between input from the solar inverter or to the generator. This would also serve as the source if we ever wired to the grid down the road.

This way I could also run some designated 12v lines for LEDs off the charge converter if I really want to. Or just use LEDs bulbs and other low energy appliances in the standard household outlets.

So what do you guys think? Is it as simple as I’m thinking or is there a better way to do this that I’ve missed?

Panels → charge controller → battery → inverter → circuit panel → outlets

# Posted: 9 Feb 2023 20:47 - Edited by: darz5150

I ran wiring for both 12 volt dc and grid power when I first built. We have have grid/solar/and generator capability. Its worked well for us. If there is a power outage, we still have lights running water and some power from the solar. If it is a major outage, then I do the transfer switch and fire up the genny.

# Posted: 9 Feb 2023 22:16 - Edited by: gcrank1

Ive done 12vdc, mixed 12vdc/120vac and finalized at 120vac.
16x24 off-grid, dry rough built sawmill lumber cabin.
Your expressed elec wants are modest, much like ours.
12vdc would do it, and 12v stuff for truckers and rv's are common; the downside of 12d is the need for heavy gauge wire and fuses and holders (typically not circuit breakers), switches, etc. and line losses over distance.
Do you have excellent solar exposure at or close to the cabin? All day? Your best exposure is due solar south and you really only get good charging from 9-3or 4pm for 3 seasons, winter, um, inhales greatly.
Does this location get below freezing? That will be important regarding the battery chemistry used; ie, LFP, unless it is a 'heated battery' cant be charged below freezing (though they can be stored below freezing). That locks you into old Lead Acid batteries. That would be too bad as LFP was a Huge game-changer for me.
Inverters: Do yourself a favor and do not consider anything other than Pure Sine Wave. Beyond that there are High Frequency, Low Frequency, Pass Though, Inverter/Charger.....
So, the quick & dirty is you run a heavy duty ext. cord from genny into the cabin with a multi plug inside to power stuff. That gets you going.
The better way:
Wire an RV type inlet plug on the outside of the cabin (a hatch with a male plug beneath). You safely plug the genny into it with a std heavy-duty extension cord.
The wire from that inside should, imo, ideally go into a 2 fuse/cb 'accessory box' with disconnect. Wire 2 circuits from that with 14/2 c/w grd like house circuits.
Btw, our genny is a 1700/2000W peak inv/gen, gas. Were I buying a new one Id get the upgrade 2000?/2500W peak dual fuel so Id have the option of running on propane.
Now, to run on battery (regardless of how the battery gets charged) you have it in a box outside by the RV plug along with the psw inverter. The inverter plugs into the RV plug when you dont need to run the genny for high draw loads. Everything inside is 120vac but it is quiet. Cheap fixtures and switches, LED lights, usb charger and tool chargers if you want, tv/dvd player, fan, etc. IF you want/need to have a Small microwave, toaster, coffee machine you start the genny, switch off and unplug the inverter from the rv plug and plug the genny in. Everything inside runs like before only you can run 'big stuff' too.
If you have a battery charger in with the battery and inverter it can be charging the battery any time the genny is running.
After/during using it like this you can work on solar if you still want to, but this works great for us as is.
Fwiw, I have solar too and never reconfigured it last year at all. Still can, just not a priority.

# Posted: 10 Feb 2023 09:36

Theres a million ways to wire these systems and everyone has there own ways. Il tell you how I did ours.
Basicly everything runs through the inverter. I have 120v LED lights, 120v microwave and 120v mini fridge. Why 120v everything? Because 120v appliances are cheap and solar is fairly cheap. We do have a 120v to 12v charger ran by a generator for low sun exposure weekends.

Alot of a solar setup depends on sun exposure and load so you really need to do the calculations your self.

We dont even have a breaker pannel in our 10x14 shed. All the 120v power comes into a surge protector behind the fridge and microwave. How ever they do make small 6 spot breaker pannels. We have no way for generator power to get into our building as it's really not needed. Our 1200w inverter can run everything (not at once) even the shop vac. So when we need to use a high load device and the batteries are low we run that device off the inverter and start the generator to charge the batteries.

Honestly for our area (central NY) the lowest solar gain is in the summer as we have alot of tree cover.

# Posted: 10 Feb 2023 09:53 - Edited by: Nobadays

Quoting: Fenny
Panels → charge controller → battery → inverter → circuit panel → outlets

Yes... Buy an inverter/charger (more costly than cheap Asian inverters but do you want to enjoy your place or fiddle with solar when you visit? ) in this way your solar -or- generator can both charge your battery bank.

Wire the cabin for standard 120vac, use a 6 slot breaker panel for circuits. If your inverter/charger outputs only 120v, a jumper between the two power inputs will energize both sides. Most tier 1 inverter/chargers will output 240vac so a jumper is not needed.

Your power system in my mind is not a place to skimp on. Do it right with adequate size to power your expected loads.... and a little extra...(an energy audit is needed to gauge this) and good, name brand equipment. Buy once, cry once!

THIS is a good energy calculator.

# Posted: 10 Feb 2023 11:02

For my toolshed/workshop pre-built shed we put in last summer I hooked up a 'micro system'.
A small 20ah agm 12v battery and a 9W? maintenance solar panel to charge it. A 'spare' (one of my 1st purchase mistakes) msw 400W inverter runs to an overhead led light and the inv has a built-in usb charger. I can flip the inverter On switch and the light is on, also can keep my phone charged, run a little usb corded fan, etc.
Msw may not be the best for led lights but I havent blown any out yet, and I buy a pack cheap at the ReStore. The usb is just a redirect from the 12v battery, a 'passthrough' even with the inv Off so no worries on the msw thing.

# Posted: 10 Feb 2023 12:48 - Edited by: redwolfguild

Wire it like a house, and feed it with an inverter/solar or generator. If you pull power across the river, you are set. Because you are going small, you only need 120v but do yourself a favor, and put in a standard 100-150 AMP 240volt panel with room to grow. Get an exterior panel so it is easy to expand, not as sexy but put it on the side you don't see.

I have done it both ways, 12 volts only, just to tear it out. Panel inside, was great until I wanted to expand or add a circuit. The exterior surface mount panel was the last and easy to expand when needed.

I power my cabin with a 200 AMP Lith. battery and 800w inverter wired to the panel. I also have a power plug for my generator when I want more power or charge the battery. With 410 watts of solar with an mppt charger controller, I run a small fridge, a few lights, and StarLink - Never used the generator unless I was running power tools.

On the Inverter and charger controller, I tried all the chineese / cheaper models, they worked but I finally upgraded to Victron - kept the old stuff as back up but wish I went with Victron first.

My generator choice, Honda EU2000IC - runs everything I need and always runs.

# Posted: 10 Feb 2023 13:13

I would go all 120v in the cabin, with a good quality inverter / charger and solar. If the solar isn't sufficient and you need to charge the batteries, run the generator which will provide power to the house while it charges the batteries. If you ever run grid power it will be a super easy changeover where a mixed or 12v system would not be.

This is what we ended up doing and I've been very happy with the results. The wiring is straightforward, everything is relatively inexpensive household stuff, easy to find (as opposed to the more expensive and harder to find RV 12v stuff). Don't discount the "normalcy" factor too, it's nice if you have people visiting or even for yourself you're not fiddling around with mixed systems, oh don't plug that in there etc. Just watch out if it gets too routine people forget and start running hair dryers etc But on nice sunny days I can run anything 120v I want off the system (vacuum, electric weed wacker, electric lawn mower etc), I've actually been able to move away from gas powered things because my 120v is so robust.

Here's the power schematic I worked off of:

-- Bass

# Posted: 10 Feb 2023 14:56

Thanks so much guys, way more info here than I was immediately looking for. I think I agree with most of you that spending extra on a good electrical setup will be worth it in the long run.

I think I'm going to go all 120v for the wiring system for now. Just to make life simple. Sounds like the safe route to go.

# Posted: 10 Feb 2023 15:07

This is just a 10x15, though, easy to go overboard for 150sf.

# Posted: 10 Feb 2023 15:25

Wire it for 110VAC, run an inverter for your power form your battery. Charge battery with a small solar array or run system with generator or both. One system, can work either way.

# Posted: 10 Feb 2023 15:30

in my mind if 120 is a future possibility, either run both or just 120.
I will never have 120, so a simple 12v system is more than enough for me and I don't regret it one bit, been going strong for 10 years now with no issues.

I do have an inverter and one 120v outlet, just for charging the laptop, but everything else is 12v.

As Brettny said, there are a million ways to go here, so thinking it through up front as you are is a good way to realize what you need and what makes sense to do now during the build, with an eye for the future. Even where I am, if I was building new, I would have at least ran 120v lines, but since I was only adding to an existing structure and see no future need I just pulled in 12v lines. Would be easy enough to upgrad if I ever really need to.

# Posted: 11 Feb 2023 07:48

One thing to keep in mind is if you ever have this hooked to the grid in the future you may need to bring it up to code and get it inspected. That means you will need to pass an inspection at that time. Codes may change between now and then.

Keep it simple but safe. I would not go putting a huge 100a pannel in a 150sqft building.

# Posted: 12 Feb 2023 06:25

Just some quick numbers to consider:

Using an Inverter to convert from Battery to 120VAC is a very simple thing in reality and a small system can do quite a bit if well thought out and does not have to cost a lot of money nor be inconvenient & complicated.

Rough numbers:
1000W÷120V = 120V/8.3A pulls 83A from 12V
2000W÷120V = 120V/16.6A pulls 166A from 12V
3000W÷120V = 120V/25A pulls 250A from 12V *
4000W÷120V = 120V/33.3A pulls 333A from 12V
* 250A is the recommended Max Draw from batteries
Figures not corrected for inefficiencies.

A typical 120V Circuit is 120V/15A allowing for 10 devices per circuit where a device is a plug, switch or light fixture and is wired with 14/2 AWG to a 15A Breaker. 120V/20A requires 12/2 AWG wire.

You can simply use Square-D 4 Slot Breaker Box like a Square-D QO4L100S to run TWO 15A Circuits within the cabin. Inverter Output would be tied in to this box. If you require all 4 slots useable you can simply bridge lines A & B with 8AWG making that box 120V for the 4 breaker slots. * You are limited to whatever watts output the Inverter is rated at.

Looking at it from "outside" at the generator.
1x Inverter Generator sized to support Inverter/Charger - charging via L5:30 plug on genset. To Plug on Cabin Wall, then to input Breaker/Switch then to Inverter/Charger. Inverter/Charger then ties to Square-D Sub-Panel for 120V circuits.

Inverter/Charger DC: Battery leads from Inverter to Battery Pack ON/OFF Switch then to FUSE then to Battery Pack.

Solar can be tapped into this nicely with a respectable Solar Charge Controller and a few panels BUT be aware that components & capabilities vary a LOT and there is a heap of misinformation out there. Take a Midnite Classic 150 SCC which takes a maximum of 150VDC to output 94A Charging Power for a 12V Battery Pack. This translates into 6 Solar Panels using 6 QCell 395W Panels configured, 2 panels in Series Strings with 3 strings in Parallel.

Batteries are tricky due to the ongoing transition from Lead Acid to Lithium Based batteries. I abandoned the Lead Acids and now run only LFP (LiFePo4 - Lithium Iron Phosphate) batteries. Note that you can use 100% of the battery capacity with LFP but only 50% of a Lead Acid Battery or you're damaging it.

A 12V/100AH LFP battery has 1280 Watt Hours / 1.2kWh storage and weighs on average 9kg/19.8 Lbs each.

Batteries in Parallel increase Storage (AH) so if you add a 2nd battery in parallel your doubling stored capacity while also dividing the Load & Charge between the two batteries reducing stress on them and having fail over fault tolerance should one pack shutdown for any reason.

FYI: A 12V/100AH Battery can take a MAX of 50A Charge for 2 hours to charge from 0% to 100%.

Last Notes
AIO's (All In One) Inverter/Charger/Solar Controller units are NOT suggested for Part Time small systems as they have a higher running overhead and most do not allow you to turn off the inverter/charger side leaving only the SCC to maintain the batteries while away. These are quite attractive because they can simplify many things with regards to installation and management but there are serious trade-offs and must be evaluated for your particular use case.

A Component based system with independent Inverter/Charger and separate SCC (Solar Charge Controller) are better for P-T Residences/cabins as everything except the SCC can be shutoff so that batteries are maintained and no other power is wasted while away.

Hope it helps, Good Luck

# Posted: 12 Feb 2023 08:55 - Edited by: Grizzlyman

I wouldn't overcomplicate it for something that small.

I did my entire cabin w/ 12v.

Solar panel on the roof > Charge Controller (which came with the panel) > Battery > Boat-type Fuse panel>fixtures

You can buy 12v LED bulbs for a normal fixture.
I have an RV fan as well.

Wire is THNN- cheaper than romex. I had to use a bigger gauge since I had longer runs w/ 12v. Your small bunkie can use relatively small gauge.

A marine battery by itself will run your few LEDs and fan for probably several days without a charge. All you have to do is use the solar to charge the battery.

My panel was less than $200 on Amazon.

I actually did wire a separate two outlets for 120v and hooked them to a plug if I want 120v I can fire up the generator, plug it into the circuit and have it in the cabin... but in 2 years I have yet to use it for anything other than power tools.

# Posted: 13 Feb 2023 09:41

I had considered 12v for my 10x16 toolshed, but once I had the panel up and wired to the bat and looked at the farm lamp reflector c/w clamp and 120vac cord it was a simple thing to hook up the small extra cheap inverter's two wires and just plug the lamp in.
It makes no draw afaik turned off and is effectively my on/off switch for the shed electrics. Too easy.

# Posted: 13 Feb 2023 15:14

Quoting: toyota_mdt_tech
Wire it for 110VAC, run an inverter for your power form your battery. Charge battery with a small solar array or run system with generator or both. One system, can work either way.

Winner, winner, chicken dinner. Do it this way.

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