Blue Skies Cabin – Tiny Home Electrical Upgrades

Now that the insulation is done and the work has begun on enclosing the walls, it is time to install the electrical wiring in the cabin. Our wiring will be primarily solar-driven 110V from an inverter. In our case we are starting with a 2KW inverter that lives out in our “solar shed” and is connected to our cabin with a standard heavy-gauge outdoor extension cable using a “shore line” style 110V weather-proof receptacle. We may upgrade this in the future to use an RV-standard TT30 receptacle, and upgrade our inverter to something that can support a 30-amp circuit which will likely be hard-wired with a 110V LNG to a traditional TT30 outlet. For now, 110V it is.

With that in mind, our next upgrade focuses solely on the interior of the cabin. We want to have standard comfort items in the cabin via a few 110 outlets. We will also provide some support for our typical USB-based personal devices like phones, tables, and even some of our favorite portable LED table lamps via a small solar/battery-brick style setup.

Our “Tiny Home” 110V AC Setup

For our 110 connection, we will put in a junction box where the “short line” connection comes into the cabin. We will put in a distribution or breaker box that will distribute that power to 4 separate 110 outlet lines. We will label these as well for easy reference. Most wiring with be 3-wire interior wiring. Gauge will be based on use, 14 gauge will suffice for the 15a circuits that will power our coffee maker or a small LED TV. 12 gauge on a 20a circuit for the mini-split.

110R for the right side of the cabin near the distribution box. A short 2′ run of 14 gauge mostly for the coffee maker and maybe a small 3/4 fridge pulling 3A.

110L for the left side of the cabin for the TV or small electronics. A longer 40′ over-the-ceiling run of 14 gauge. This will also have a ceiling receptacle box where we can later mount a ceiling LED light fixture if desired.

110B for the back of the cabin near the bed for small electronics or a table lamp. A 30′ run up to the ceiling joist, along the wall, and back down the back wall.

110AC for the minisplit. Another 30′ run of 12 gauge for a 20a circuit for the minisplit.

AC Wiring Basics

For the new breaker box setup to run a minisplit AC.

The USB DC Setup

We already have a 12V 15A terminal included in the charge controller that is mounted in the cabin. This allows us to monitor the solar array and battery performance. This gives us an easy way to directly tie into the 12V circuit driven directly from the battery bank with no inverters. The charge controller provides a simple on/off switch to power the entire circuit.

We have a rudimentary battery terminal block that allows us to connect this to both an old-school cigarette lighter outlet that allows our 12V cooler to run (drawing 2 -3A when the compressor runs) as well as the 0.07A vent fan for our composting toilet. We will upgrade this at some point to provide a proper DC “breaker and distribution box” to power other 12V devices and likely include various connectors as there is no solid 12V connector standard — with the fallback favorite apparently these large and somewhat less safe cigarette lighter receptacles.

However, our main use of DC power will be based on older USB-A “flat blade style” connectors or newer USB-C connectors. We will likely keep these systems separate from the main solar and instead use a simpler off-the-shell small solar panel + USB brick configuration to power our devices.

Photovoltaic (PV) Solar Expansion

To drive all these updates we need to continue to expand the solar array. The main focus will be on battery expansion as a typical use will be 11 days generation + storage then 3 days of use (with generation). That means we want more batteries to hold the energy we generate over those 11 days and enough solar to help refill them before depletion over the 3 day weekends we are on site.

The RVR-40 Electrical Specification

Current Solar Panel Configuration

Currently we have 400W of PV generation in place with another 200W ready to go online. The current configuration is 4x100W panels with ~20V output each , so we are just below the 90V input limit of the charge controller. On a cloudy day the real0-world readings were just over 80V and up to about 10A. In theory these panels should push 20.4v at 4.91A each x4 should be around 81V and 5A, no idea where the extra 5A is coming from but likely a phantom reading from the charge controller with the system under load.

The In Series Solar Panel Math

Let’s recap the solar properties of panels wired in series with some help from ChatGPT:

When solar panels are wired in series, the voltage of each panel adds up, while the current (Amps) remains the same as that of a single panel. The specifications you’ve provided for each panel are as follows:

  • Maximum Power (Pmax): 100W
  • Optimum Operating Voltage (Vmp): 20.4V
  • Optimum Operating Current (Imp): 4.91A
  • Open Circuit Voltage (Voc): 24.3V
  • Short Circuit Current (Isc): 5.21A

Given that you have 4 solar panels wired in series, let’s calculate the total output characteristics of the array:

  1. Total Optimum Operating Voltage (Vmp_total): This is the sum of the Optimum Operating Voltages of all panels. Vmptotal=Vmp×Number of PanelsVmptotal​=Vmp×Number of Panels. This is the normal output of the system when under load and considered the “normal output” under perfect conditions (sunny day, right angle, etc.) — same with optimum current below.
    81.6V
  2. Total Optimum Operating Current (Imp_total): When wired in series, the current remains the same as a single panel. Imptotal=ImpImptotal​=Imp
    4.91A
  3. Total Open Circuit Voltage (Voc_total): This is the sum of the Open Circuit Voltages of all panels. Voctotal=Voc×Number of PanelsVoctotal​=Voc×Number of Panels. This is the theoretical maximum if there is no load that this system can put out. This is what should be used to size the charge controller — we are taking our chances at the moment by using the RVR-40 controller with a max input of 90V, though they don’t say if that is optimum or Voc maximum. Also it is winter and our solar output will not be this high, and we are going to step down to a 3-series configuration soon.
    97.2V
  4. Total Short Circuit Current (Isc_total): The current remains the same as that of a single panel in a series configuration. Isctotal=IscIsctotal​=Isc
    5.21A
  5. Total Maximum Power (Pmax_total): This can be calculated by adding the power of all panels, but it’s also equal to the product of the total optimum operating voltage and current. Pmaxtotal=Vmptotal×ImptotalPmaxtotal​=Vmptotal​×Imptotal
    400W

Upgrading The PV Array

Next trip we will get the other 2 panels online and configure them in sets of 3 panels series pushing around 60v , then wire each 3-panel series together in parallel. When connecting in parallel the voltage stays the same, but the amperage goes up.

One series of 3 100W panels like those above:

  • Total Optimum Operating Voltage (Vmp_total): 61.2V
  • Total Optimum Operating Current (Imp_total): 4.91A
  • Total Open Circuit Voltage (Voc_total): 72.9V
  • Total Short Circuit Current (Isc_total): 5.21A
  • Total Maximum Power (Pmax_total): 400W

Now when we attach these two series in parallel we boost current while voltage remains the same meaning the final output would be:

  • Total Optimum Operating Voltage (Vmp_total): 61.2V
  • Total Optimum Operating Current (Imp_total): 9.82 A
  • Total Open Circuit Voltage (Voc_total): 72.9V
  • Total Short Circuit Current (Isc_total): 10.42 A
  • Total Maximum Power (Pmax_total): 800W

With the upgrade 2 parallel configuration of x 300W series-connected arrays we are producing 800W via 61.2V at 9.82A. Into a 12V battery being managed by the charge controller that should generate about 5 x 9.82A = 49A on a perfect day. Real world is showing 50 – 60% of that, so we should be pushing about 29A * 8h this time of year = 232Ah per day, enough to fill two 100Ah batteries each day.

Blue Skies Cabin Electrical Loads

Here are the electrical loads at Blue Skies Cabin.

January 2024

Compost toilet + cooler + charge controller: 22.68Ah / day.

200Ah battery array is installed.
50% preferred lowest draw = 100Ah available.
70% maximum draw = 140Ah max available.

ItemPowerHours/DayAh/Day
Nature’s Head Compost Toilet Fan0.07 A 12 VDC = 0.84 W241.68
Alpicool CF55 Cooler (fridge/freezer)5.5 A (incl. +10%) 115VAC to 12VDC = 66 W
3.1A 12 VDC direct = 37 W
15m / hour
6
33 converted
18.6 direct
Renogy RVR40 Charge Controller.1 A 12 V242.4
Renogy 2000W Pure Sine Wave Inverter90% efficiency : + 10% in above AC/DC conversions
Total:22.68

Current setup should provide 4 days of run time on preferred draw with NO solar generation.

Homework & Shopping Lists

Time to do some homework and create a shopping list.

Tools and Supporting Items

“Killawatt” Real World Consumption Monitoring

ProductFeaturesPrice
P3 International P4400-VP Kill-A-Watt (original)15 A max, 0.02% accuracy, 8 measurements$36 at Amazon
P3 International P4456 Kill-A-Watt Flex (2nd gen)15 A max, CO2 forecasting$44 at Amazon
P3 International P4460 Kill-A-Watt EZ (3rd gen)15 A max, 0.02% accuracy, forecasts costs and usage$30 at Amazon

P3 International – founded in 1987, HQ in North Carolina, makes consumer electronic “gadgets”. Rating: B

Solar System Expansion

(2) 100W Solar Panels

Renogy 2pc 100W 12V Panels : $161 at Amazon

(2) 100AH Gel Batteries

Adding two more 100Ah batteries to the parallel array brings the system up 800Ah at 12V.

Weize 12V 100Ah Deep Cycle Gel Battery : $149 at Amazon
So far this has been our choice based on the 30% lower price compared to the Renogy equivalent. We will see how they hold up.

(2) Pairs Of Battery Lug Cables

Need 3/8 inch (M8) lugs on each end, red/black pairs only, 2ft length.

iGreely 8 8AWG 2ft: $10 at Amazon
We went with these for our battery interconnect.

Voltworks 4AWG 2ft : $19 at Amazon

Voltworks 2AWG 2ft: $19 at Amazon

AC Wiring

Wiring order: black, then red, then white/neutral, then earth ground.

Grounding

TT30 RV Outlet Block for Inverter

This will be our primary connection to the inverter via the LNG terminal. We will upgrade the connection to the Blue Skies Cabin to use a standard TT30 cord and inlet.

RVGuard Outdoor Power Panel With Breaker $130 at Amazon
14-50 , TT30, 110 outlets

Connecticut Electric CESMPSC74GRHR Power Panel $210 at Amazon
14-50 , TT30, 110 outlets

TT30 RV Inlet For Cabin

RVGuard TT30 Inlet $20 at Amazon

TT30 RV Twist Lock 15′ Power Cable

Liesure Cords 90-degree 15′ TT30 Twist Lock RV Cable $40 at Amazon

Indoor Main Breaker Box

Indoor Wiring

14-Gauge 3 Wire 110V Interior Wiring for 15A circuits (need 70′ min)

12-Gauge 3 Wire 110V Interior Wiring for 20A circuits (need 30′ min)

Southwire 63946828 Romex Simpull Solid 14/3 W/G NMB 100′ $84 at Amazon

Southwire 63947628 Romex Simpull Solid 12/3 W/G NMB Yellow 100′ $125 at Amazon

Southwire 13058323 Underground Feeder 12/3 Grey 100′ $88 at Amazon
* can be use indoors, also UV protected, flame retardant, and can be used in wet locations

(4) 110V AC Outlets

(1) Ceiling fixture box

DC Wiring

DC Distribution/Breaker Box

12V USB Battery / Power Brick

Minisplit AC Unit

Requirement: a high efficiency 110V mini split air conditioner for a 12′ x 16′ x 8′ room (1500cf, 200sf) = a 3/4 ton or 9,000 BTU unit.

ProductSEER2Power (Cool / Heat)Cost
Senville LETO SENL-09CD-1621.5 720W 6.26A$750 at Amazon
Klimaire ‎KSIV009-H119-S(W)21.5780W 6.8A / 925W 8A$720 at Amazon 10 day delivery
Della 048-TL-9k1V-19S19840W 7.4A
Pioneer WTY-00920.5770W

Wall cuff for protecting wall with piping pass-through.

Table-top Stove , 2 Burner

Some AI Art, Just For Fun

Playing with AI has been interesting including having it generate art for some of our articles. Here is what Open AI’s ChatGPT came up with versus Google’s Gemini. Here is the prompt to both – clearly ChatGPT and Dall-E have a lot more training on this sort of thing. Both, however managed to not get the concept of off grid or solar as they both include some kind of power line in the back.

Please ingest the following article and generate a new image based on the content: https://www.rallycreek.us/2024/02/19/blue-skies-cabin-tiny-home-electrical-upgrades/ The image should include some element of electricity and connected components. If possible add blue skies and sunshine the image.

ChatGPT : Interesting – but AI still cannot draw hands or solar panels worth a damn.

And Google Gemini…


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