Sunday, April 10, 2011

Electrical Diagram

Awhile back, we promised to publish a diagram of our electrical system here at the tent. Well, we finally got the laptop it was on fixed so I can post it for you :)

This is how we have our tent wired with only two AC circuits, one for lights and one for receptacles. It's usually a good idea not to have your lights and sockets on the same run, or at least not all of them, so that if an appliance blows the circuit breaker you aren't left scrambling in the dark. All the AC wiring starting from the service panel is standard, so you can refer to any wiring manual available at your local library or home improvement center. The only part that is tricky is the wiring between power sources... you just have to be careful that the wires aren't live when you're doing it (hook up the ground FIRST, and hots to the power sources LAST), but otherwise it's really not that complicated.

Our tent frame is aluminum conduit, so all our receptacles and light fixtures are grounded to the frame as well as the common ground in the 3-12 Romex... and both the wiring and the frame are grounded together with 00 braided copper cable to a 4' length of 1/2" Rebar embedded in the earth. This offers protection from electrical shorts as well as lightening strikes. Caution: do not store fuel canisters or firewood on/near your ground cable & spike, as fire and explosion can occur!
We're planning to wire the cabin the same way, except that we're replacing the SLA batteries with AGM batteries, and adding more circuits to the panel so some special equipment (like kitchen appliances and the home office) are on their own dedicated run. We've also added a 3kw generator as a backup and to provide additional juice for heavy draw items (like the log splitter) when we need them. We will also have a dedicated GFCI circuit for the exterior porch receptacle and light beside each door.

Because the battery bank is located in the loft (keeping them warm in the winter, and well vented/cool in the summer), we are wiring 30amp MALE power inlet boxes on the porch and in the loft with 3-10 Romex between them... using the male connectors rather than female connectors, with a specialized prong arrangement, ensures that someone can't accidentally plug a standard appliance into that receptacle. The heavy-duty arctic cable from the generator to the outside wall will have a standard 3-prong male plug into the  generator (2kw is only 20a, so only has a 3-prong), and a 30a female socket into the house; and the cable from the inside wall into the inverter will only have a 30a female connector on the wall side because the leads are directly wired to the inverter terminals.

We may add some additional components such as a larger freezer (AC or DC), well pumps and electric fencing that may or may not have their own dedicated power source (PV panel with battery/generator backup) depending on the draw, run distance, and electric current type. At the very least, we'll be adding a 75w PV panel dedicated to the current DC freezer and utilizing the remaining good SLA batteries as it's own dedicated back up rather than drawing from the house batteries (we only need the freezer in the summer, so power availability is not an issue).

Since the cabin isn't made of metal like the tent frame, we will be wiring all the receptacles and light fixtures to the common ground in the 3-12 Romex, installing lightning rods on the roof peak, and connecting the house wiring and rods with 00 braided copper cable to 4'  of 1/2" Rebar embedded in the earth (once the ground thaws enough!).

Both battery banks are designed to provide 800+ amp-hours at 24v, this provides us an average of 5 days between charges for normal use and up to 10 days with conservative use. A full recharge normally takes less than 8 hours running the 2kw generator, and our generator runs 8-14 hours on a gallon of gasoline depending on load and whether the eco-throttle is on. We intend to add 5 PV panels rated at 225w each (1+ kw total) which should be more than adequate to keep the batteries trickle charged AND provide us with all the power we can use during the long summer days. The addition of a 2kw wind turbine will take up the slack on cloudy days, so we don't expect to need the generator at all during the summer unless we're running some seriously heavy-draw equipment for long periods. The wind turbine and PV combo should provide ample charging of the system during early spring and late fall with rare need for the generator; and the wind turbine should reduce the frequency and duration of running the generator during our long winter nights. PV output from moonlight and snow reflection in the winter is documented up here, but we are not counting it in our plans.

So that's all things electrical for now, hope this was helpful information. Thanks for your patience.


Kris Watson said...

WAAAAY over my head, but incredibly impressive.

Plickety Cat said...

Kris, I hope the diagram was at least simple enough to grasp even if my description and explanations went into the ether a bit :)

Gungnir said...

Thanks for the compliment.

It's actually really simple, everything connects to the batteries. The Inverter stands between the batteries and the service panel, which is wired just like anyone else's normal electrical panel.

The Genset also connects to the inverter (since it's an inverter/charger), it's grounded through it's grounded via the ground pin on the connection into the generator.

The freezer sits directly across the 24 volt bus bars, as do the charge controllers (there's more than one one for the wind, one for the solar, but for simplicity we just condensed it into one). The only additional thing between the 24V bus bar and the charge controller is the diode, to prevent any power flow into the positive terminal of the charge controller(s) (i.e. when the solar or wind isn't generating a whole hell of a lot of juice and we're running the generator) which would be bad. This may be internal to the controller, or may be an additional extra, it depends on the solar charge controller.

Then the generators/panels themselves just hook up to the input terminals of the their respective controllers. The Overflow comes only from the Solar panel charge controller, since it's a shame to waste that extra juice.

Anonymous said...

The combination of the simplicity of the diagram and the written explanation of the parts makes it come to life, at least for me. We really CAN do this!! I especially appreciate the grounding info. Did you write technical stuff before moving to AK? I found it easy to follow. Jennifer

Gungnir said...

Plickety used to write Requirements specs (human readable) for a living, I used to write architecture/design/test docs (geek readable) as part of my job (along with actually developing some of those into software.

Anonymous said...

please use a copper grd rod for your safty. Go as deep or as meany as you can.

Gungnir said...

Most "Copper" ground rods, are 8-10 mil 0.008 to 0.01 inches copper electroplated steel. (This is effectively the same cross section as an 11 gauge wire on a 1/2" steel bar stock)

Steel has a conductivity of 3 to 15% the conductivity of copper (higher carbon steel has lower conductivity) . Rebar (iron) has a conductivity of 17% of copper.

For comparison most common solders (lead/tin or phosphor bronze) have a conductivity of 15% copper.

There isn't a lot of difference between them electrically. Both require a solid connection to ground water to be an effective ground. There's a significant price difference though. Both will more than adequately provide a safe ground return in the event that the hot wiring insulation breaks down, and shorts to the case of any of our equipment.

Ultimately of course since we're providing ground via a 2/0 stranded copper cable, we've got a max carry current of a little under 283 amps before that begins to fail, this is 4 times the maximum possible current from the battery bank (24V) and 15.5 times the maximum possible current from the inverter (110V).

I think we'll be ok.