Off-grid Christmas lights?

MushCreek · December 21, 2010, 05:26:15 PM

Wasn't sure where to put this.....

Our place in SC won't be off-grid, but considering how far away things are on a big lot, I'm thinking about clever ways to put some lights on Christmas trees in various places away from the house. With the new LED lights, I wouldn't think they would draw much juice. How about if I put up a solar panel, hooked it up to a deep cycle battery, and ran the lights of a power inverter? I wonder how many strings of lights I could run off of a single battery? I'd probably make the whole thing portable, so I could move it at will when I didn't need it, and put it away so someone doesn't run off with it. I know some of you folks are pretty good at this stuff- any thoughts?

muldoon · December 21, 2010, 05:47:34 PM

We did that as a geocache two years ago with this idea. few strands of LED lights, solar panel, battery, inverter. In our case, a decent marine battery with plenty of AH for the task. The solar panel was the weak spot, it was a simple 12"x12" or so panel, it was around 25 bucks. As for lights, we only lit up one side (so it wouold not be too visible from the street side of the woods), and only used 2 strings. Basically it died about 3am each night. A larger solar panel probably would have made it last longer. A photocell switch to keep it from running during the day would have worked as well.

December 23, 2010, 03:56:26 PM

We bought several strings this year and put them up on the cabin. One colored Christmas set and the rest white for area lighting. 50 LED C6 lights per string. Lighted length about 16 feet IIRC. 4.8 watts per string. Running 6 strings for about 6 hours a night I can see no real difference in power used by the entire PV system.

So no reason, other than $$, that a small panel, charge controller, battery, inverter could not be used to light individual trees in remote areas. One possible iffy thing could be cloudy weather. Several cloudy days in a row would likely mean not enough recharging for the battery.

MushCreek · December 23, 2010, 04:35:50 PM

Wow- they don't draw much, do they? Sounds like it would work OK. In SC, you don't get long spells of cloudy weather, and even if you do, it's just Christmas lights. Half to add this to my future to-do list!

MountainDon · December 23, 2010, 05:40:44 PM

Interesting side note: At the cabin we use an Outback inverter. There are may programmable features. One I use is the search function. This allows the inverter to run in a standby mode when no power is being used. When a load is sensed the inverter turns on. It is adjustable for sensitivity. I have it set down to where a small LED night light will activate the inverter. However, a single string of the LED Christmas lights or the single LED night light, must be plugged into the receptacle the "proper way". Reversing the plug the light?string will not trip the inverter on. Rather the light(s) pulse on-off in sync with the search signal. Changing the orientation of the plug resolves the issue.

December 25, 2010, 09:46:37 PM

I'm going shopping for LED lights on clearance tomorrow and will be rewiring the strings to run on 12V. Not hard to do, measure the voltage drop across 1 LED and figure out how many need to be in each series string to get 12V

MountainDon · December 25, 2010, 09:54:47 PM

Is it that simple? What happens when one string is plugged into another?

I think I read that different colors have different voltages

Not sure and not an expert.

Rob_O · December 25, 2010, 10:24:00 PM

Quote from: MountainDon on December 25, 2010, 09:54:47 PM
Is it that simple?

Pretty much, this will help

http://www.kpsec.freeuk.com/components/led.htm

edit: More info

http://www.otherpower.com/otherpower_lighting_leds.html

MountainDon · December 25, 2010, 11:09:50 PM

Thanks Rob_O!

December 25, 2010, 11:23:02 PM

You're welcome, Don.

I have some ideas about what's causing your lights to flash when the plug is "backwards" but I need to cut up a string to verify. I'll let you know what I figure out

Rob_O · December 26, 2010, 07:32:01 PM

Update: Went to the orange store and got 6 strings of 100 lights for $5 each. They were available ready to go with a small solar panel ready to go for $12 each but the wallet said "no way, Jose, that's 3 floor joists"

Each string has 4 parallel sets of 25 lights in series with a resistor at the end. 30V drop across the resistor leaves 90/25=3.6V (now where have I seen that number before

)

For a quick proof of concept, I slit back the insulation on either end of 4 lights of one string and put it to 12.8V... "Let there be light"! Did the same thing with 3 lights and they got real bright

Plugged a few numbers into Watts law and determined I want about 20mA across each LED. Got out the meter, 3 is not enough bulbs and 4 is too many so I need to build a voltage regulator

About that time, the phone rang and my buddy offered to buy me brunch. We ate like pigs going to slaughter then decided to go out to the camp and finish the trail I started a few months ago. Good times were had, trail is finished but my voltage regulator did not get built today.

Rob_O · December 28, 2010, 11:36:49 PM

It Works!

I'm not a bit surprised. The links I posted had most of the info I needed, my meter told me the rest.

Also bought a couple of the pre-fab solar light sets. The light output is pathetic compared to my "hacked" set but they will do for the intended use

MushCreek · December 29, 2010, 07:46:31 AM

The old-school little white lights come in different voltages, depending upon the length of the string. The 100 light sets are around 1.2 V, IIRC. I used to rig them up on a wreath mounted to the grille of my old truck. 10 of those lights works out to 12 V, so they worked fine in short strings.