backup generators

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Something that I have wanted to do for years was to install a backup emergency generator at our house, along with solar. 20 years ago when we had a large house on 10 acres, I simply could not afford to do the generator, and the cost of solar was out of our reach too. 10 years ago, we bought a house in an HOA that would have made it difficult to install a generator, but I was able to solar. Solar City was all the rage at the time, and we were able to have an 8500 watt grid-tied system installed with monthly payments. Looking back over our historical electricity bills, we were able to save a huge amount of money on our electric bills with the solar system. But, without a battery bank, we still weren't able to use the system in the event of a power failure.

After I divorced and bought my current house in a very small rural town, some of my goals for backup power included a large enough generator to run the whole house (minus the A/C), and 12VDC lighting throughout the house that could be used whether I have grid power or not. We have frequent power outages here, ranging from lines being snapped during wet and heavy winter snow events, to lines being broke from high winds, to lightning strikes taking out transformers. I am fortunate that I have a gas cook stove that still works when the power is out.

I have partially accomplished the 12v lighting goal simply by snipping the AC outlet off a couple cheap table lamps, and installing Anderson Powerpoles onto the end of the cords. A few 12v 60 Watt equivalent bulbs off Amazon and I was in business. These bulbs draw about 6 Watts, or .5 amps. And with an inline watt meter, I can confirm that they do indeed draw about 0.55A. The lamp beside my recliner in the living room is on a battery, and is usually the only light I have turned on in the evening while watching TV. The battery is one of my DIY LiFePO4 batteries, a 100Ah prismatic pack that I put together but never really had a dedicated use for it. Even with using this lamp every night, it lasts about 3 months!

The next step to having 12v lighting available to most every room in the house will involve using the existing telephone wires throughout the house to provide power to LED light strips that draw about 0.25 amps each. The POTS lines in the house are 24 gauge. Four twisted pairs, eight conductors total. Just two conductors twisted together is the equivalent of one 21 gauge wire, and 21 gauge wire will handle 1.2A at 12VDC. More than enough for the LED strip lights. I currently have several of them hooked up to small 3S Li-Ion battery packs throughout the house. More on this project in a later article......

The generator I selected is the Wen DF451I dual fuel inverter generator (Wen DF451i Super Quiet Dual Fuel Generator). Having already owned a smaller Wen inverter generator (2350 watt super quiet inverter generator, perfect for field day!!) made getting another Wen an easy choice. They are quality units, priced right, and readily available. The generator I picked for this project is a dual fuel model (gas and propane). This was important because I did not want to have to stock large amounts of gasoline that would need to be treated so it would not go bad. All of my lawn equipment like the lawn mower, trimmer, leaf blower, etc. are all battery powered, so a generator would be the only thing I would need the gas for anyhow. Also, there would be the need to drain the carburetor after each run, as well as cycling the fuel in the gas tank to keep it fresh. Running the generator on propane solves all these problems. I have a 100# tank always connected to the generator which holds about 23 gallons of propane. I don't have to worry about it going bad, gumming up the carb, or refueling the generator every so often while running for long periods of time. I do have a second tank full and ready to be swapped out in the event of a looong power out scenario.

It is also an inverter generator, so it will supply clean, pure sine wave power to the house. While I would most likely run the radios and TV on batteries, I feel comfortable knowing the other items in the house like the refrigerator, freezer, furnace, and my daughter's electronics are going to get clean power.

At the house, I installed an interlock kit in the sub-panel outside the house. The interlock kit is a mechanical interference device that will not allow the generator breaker to be turned on until the main breaker is turned off. This eliminates any possibility of feeding power from the generator back into the power grid and potentially hurting or killing those working to restore power. It also prevents power from the grid damaging the generator once grid power is restored.   

For the time being, I run a very large 50' drop cord from the generator to an outlet on the corner of the house. Soon, I will bury a cable underground that will be permanently wired into the sub-panel. That way, it will always be connected to the generator, and I won't have to drag out this cord each time. 

The end result is a generator that his hidden in plain sight, VERY quiet (48-50dBa under load from 25 feet away), and able to run for several days continuously. It is capable of running the furnace, refrigerator, small chest freezer, lights in all rooms, and the TV all at the same time. Running the microwave will necessitate turning off a few things though while it is running as to not overload the generator. But if that's the only complaint I have, I just as well not have any complaints at all. :) 

In the beginning, I had planned to build this as a portable generator on wheels. As with a lot of things in my head, the idea took off in a different direction during the planning stages. So instead of a portable generator, it has become a 3277 Watt backup power supply for the house. The power supply consists of eight (8) 32Ah LiFePO4 batteries wired in parallel, resulting in a 12.8V 256Ah (3277Wh) battery. Power from the batteries feed an Edecoa 3500W pure sine wave inverter. When in use as an emergency power supply, the batteries will be charged via a Victron BlueSolar MPPT 100V 30A solar charge controller connected to 400 watts of monocrystalline solar panels. I also have the option to recharge the batteries from grid power (or the Wen generator) by using my Victron Blue Smart IP22 12V 30A charger.  

The idea for the solar/battery generator is to give me options that will allow me to power the house during outages, depending on whether it's day or night, and what I might need or want to use in the house at that time. 

I can say without hesitation this is probably the ugliest project I have built! But winning a beauty contest is not high on the list. It is, however, functional, safe, and sort of hidden away, so away we go!

The eight batteries are wired in parallel using bus bars made from hammering 1/2" M-type copper pipe flat. The two battery sections are tied together with short sections of 4 AWG cables. The completed 12.8V 256Ah battery is wired to the inverter using 2 AWG cables. The + is connected to one end of the battery, and the - is connected to the other end. Hopefully this will insure even charging and power distribution from all batteries. 

There is a 150A fuse on the + end of the battery, which runs through a 250A circuit breaker that also acts as a battery disconnect switch. I used 2 AWG equal length cables from the batteries to the inverter. In other words, both sections of the red positive cable is the same length as the single black negative cable.

To get power from the inverter to the manual transfer switch I used a 2' section of 12/3 600V portable power cord to a 15A connector. I then have a 25' 10/3 extension cord that will plug in there and run to the manual transfer switch.

The transfer switch is a 4 circuit unit from Goal Zero/Reliance Controls. It allows four 15A circuits to be quickly selected between line power and the generator. I selected the following four circuits to run off the battery:

     - Furnace (includes the furnace fan, and electronics needed to run the tankless water heater)

     - Freezer (a small 7 cu/ft chest freezer)

     - Kitchen (includes the fridge, lights, and microwave)

     - Master bath (lights, fan) 

With all the lights turned on in the kitchen, both sets of lights turned on in the bathroom, the bathroom fan, and the furnace fan running, there was 7.8A (936W) being drawn off the system. With all the lights and fan turned off, and no furnace fan running, the idle fridge and freezer drew between 0.9A and 1.6A (108W to 192W).

The idea to build this into a backup power supply for the house instead of making it a portable power supply came about after deciding to find a way to keep the furnace, refrigerator, and freezer running while sleeping without needing to leave the propane generator running all night. Then once the sun comes up, allow it to recharge from the solar panels. Or, if there's not enough sun to fully power the panels, to use the Victron 30A charger while the generator is running.

Once everything was assembled I decided to test the system to see just how long it would power the furnace fan, fridge, and freezer during an outage. I flipped all 4 circuits over to the battery at roughly 6PM on Saturday night. My daughter and I each showered, which meant having the bathroom lights and fan running. Plus, whatever electronics it takes to run the tankless water heater (about 240W to light the burner). Keep in mind this was assembled and tested in mid-July, so the AC was running all night. Although the AC unit itself was powered by the grid (240VAC), the forced air fan was running off the battery. 

I received a text from my (very sleepy and confused) daughter a little after 5AM Sunday morning, saying "your battery is beeping and going crazy and it's really loud!". Sorry it woke you up dear daughter, but thank you for letting me know when it ran out of juice!

Now I know..... during a prolonged power outage, I can shut down the generator around 9PM, switch to the battery, and power the furnace (or just the fan), fridge, and freezer all night (around 11 hours. And if I don't need to run the furnace fan, probably up to 30-some hours!) Then I can shut down the battery around 6 or 7AM and go back to the generator while letting the battery recharge from either solar or the Victron charger.

This has been a very successful test using items I mostly had already. But I would be remiss if I didn't say that in my head, I am already planning a 48V 9000Wh system to include a  hybrid inverter/solar charger!

Up to this point, I have been using a 25' long 10/3 extension cord that stays plugged into the manual transfer switch in the basement. To use the battery, I would need to unroll the cord, run it up the stairs, then plug it into the battery. I found a flush-mount shore power inlet plug on Amazon a couple nights ago, and promptly ordered it!  

I was able to feed the extension cord from the basement, through the crawl space, and right to the bottom of the wall right next to the battery. I cut the end off the extension cord and wired it directly into the back of the shore inlet plug. The short 2' long 10/3 cord that comes from the inverter is now plugged into that inlet. 

Now all that needs done is to close the breaker (what I'm using as the battery shut-off switch), press the power button for the inverter, then go downstairs and flip the four switches from LINE to GEN. This will especially make it very easy for my daughter to use in the event she needs to fire up the battery when I am not at home.

We received a little rain on Friday evening, so I knew the back yard would be easy to dig in order to bury the PV wire from the panels to the house. I was able to dig and bury the wire with ease, get an entry gland installed to run the wire into the crawl space, then run the wire a short 3 feet and into the mud room where the battery and inverter lives. It enters the mud room through the wall and goes straight into a 15A breaker/panel disconnect switch. From there it runs to the Victron Blue Solar 100/30 MPPT charge controller. The wire then runs to the battery through a 40A auto reset circuit breaker (not shown in pic).  

It was pretty exciting to flip the breaker and watch the app for the MPPT on my phone, and see it all come to life! Soon I will be adding two more 200 watt panels to the shed.