120VAC Lighting Via an Inverter


A spin-off from my emergency power setup is having free energy available.  My solar panels easily keep my battery bank topped up, and the unused power is going to waste.  Until now.  I am slowly taking portions of my home off the grid.  This is an example of how easy this is, and a good starter project for those wanting to get their feet wet.

From here, I'll take selected lighting throughout the house off the grid.  It will be an ongoing project, so check back occasionally.


The solar controller I'm using is a MorningStar Sunlight-10.  Regulates up to 10 Amps  (120 Watts).  Fine for my initial setup.  I can parallel a larger charge controller later. 

A slick feature about this controller is that it has the ability to control lighting.  When the sun sets, it starts a 10 minute timer to verify the array hasn't been briefly shielded from the sun.  The internal relay then supplies up to 10 Amps of 12VDC to external lights.  The amount of time they are on is adjustable by turning a small switch.   I'm using this to turn on my LED garden lights, and a 400 Watt inverter, which is connected to a couple of Compact Fluorescent (CF) bulbs. 

Northern Tool has these popular Vector brand inverters on sale for the bargain price you see above.  I bought another one to keep in my SUV.  My original one was purchased in 2002.  The new one includes a carrying case, cigarette lighter adapter, and battery cables.

My old original Vector inverter has seen a lot of use.  It now lives in the garage, and runs my exterior lighting for 6 hours per night.

Some might question whether CFL bulbs can run from a MSW inverter.  Mine do, with no flickering, or noise.  As an example of how useful these cheap inverters are, net folklore says you can't run a computer from a MSW inverter.  Rubbish!  The switching power supply used in computers is not very sensitive to power fluctuations.  I've used my personal laptop with a MSW inverter for the past 4 years.  Even longer with the computers at work.

Here's how a MSW emulates a sine wave.  Some of the newer, non sine wave inverters, actually have many more steps.  But this is the most common waveform you'll see with an inexpensive inverter.

This is the actual waveform from this inverter.

This is a common Bosch type automotive relay.  The coil is rated at 12V, and the contacts are rated for 40 Amps continuous, or 30 Amps switching.  These can be purchased in bulk (10+) at places like EBay for about $2 each.  I bought some there, they work great, but the wiring diagram is wrong.  The Normally Open (NO) contact is reversed with the Normally Closed (NC) contact.  Not a big deal, but causes the relay to work opposite of what is expected!  The fix was to move one wire over to the other contact.  You can also find these relays at any automotive store, Radio Shack, etc. 

The MorningStar solar controller will handle up to a 10 Amp load (such as garden lights), but I added a couple of 30 Amp relays to the lighting control on the charge controller,  increasing the current handling capability.  So the controller turns on these relays at night.  The first relay operates my LED garden lights, the second relay turns on a 400 Watt inverter.  I have two standard 120VAC CFL lights on the outside of my house connected to this inverter.  The exterior carriage lights, and the garden lights, go on/off simultaneously, everyday.  Never need to adjust for the ever changing sunset all year.  The controller measures the output of the panels.  No Voltage, sun has set.  10 minutes later, lights turn on.

This picture was taken shortly after the lights turned on.  In another hour, it's much darker outside, and the lighting does an even better job.  6 hours every night, grid free power.  I can easily adjust the run time by turning a small dial on the solar controller.  Can even make it dusk to dawn.  Power cost is still the same, nada!

One last thing I added to this setup is an automatic blackout switch.  When the power goes out in the neighborhood, I don't want my house lit up.  This invites people to knock and ask why I have power, and would I mind them plugging their refrigerators (etc) into my house!

I added a relay that is powered by a small 12V (wall wart) transformer. As long as grid power is available, the relay stays engaged, allowing the Morningstar controller to turn on my outdoor lighting every night. When the grid goes offline, the relay drops out, turning off my outdoor lighting. Simple. The only extras I've added was an LED to indicate the grid status, and a bypass switch which allows me to turn on the outdoor lighting even when the grid is down.  I submitted an article, with pictures and a schematic, to the Rubicon website.  You can read it here.


The CFL bulbs I'm using are rated at 10 Watts.  Once they are up to temperature, they consume closer to 7 Watts each (measured).  I run them for 6 hours every night, so 20 Watts x 6 hours = 120 Watt/Hrs.  My small solar array is currently 225 Watts, so in a little over 1/2 hour (during peak sunlight), I will have replenished the energy used.  I was able to run this same setup with only a 45 Watt solar panel kit from Harbor Freight.  The panels produced enough energy to replenish the energy used the night before, providing I had good weather.  Now with the larger array, I can replenish the power if there's any hint of sunlight.  And with a big battery bank, it can rain for day without being an issue.  The array is now big enough that when the sun does finally show his face, the array will replenish the energy used from almost a weeks worth of use in a single day.  I have 5 (+) peak sun hours in my location.  5 x 225 Watts = 1125 Watts per day (ideal).  There is a derating factor on solar panels, so expect to get about 70% of the rating.  1125 x 70% = 788 Watts (actual).

CFL bulbs are the way to go.  They use so little energy, yet produce plenty of light.  20 Watts of CFL bulbs is the equivalent of 80 Watts of incandescent lighting.

One nice part about this setup is energy isn't wasted having the inverter running when not needed.  My Prosine 1800 Watt inverter uses 20 Watts per hour, or 480 Watts per day, when left on with no load.  That's 4 times what this cheap setup uses for useful power.  Unless you have a large solar array, leaving an inverter running is a waste of energy, especially in this application.  Other than checking the water levels in my batteries once a month, this system takes care of itself.  No need to adjust the time as sunset changes, or worrying about the house being lit up during an outage.  This is completely autonomous.




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Last updated 10/19/08    All rights reserved.