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Help with solar post light build, please

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Posted by rich on November 4, 2007, 4:50 pm
We have a standard incandescent post light. We like the shape, height etc.
of it as it stands now.  It was wired to 110 v a/c and the power line was
cut between the house and the post.
Rather than replacing it...( it was constantly blowing bulbs and not working
well anyhow)...

I'd like to convert post light to a solar powered one.  I can buy some
ready-made units ranging from $0.00 up to $70.00 or so.  In most cases, we
really don't like the shape and appearance of the new lights.  I wonder if
anyone here could point me to what items I would have to buy ...i.e.  some
small solar panels, and a light; batteries and a daylight on-off switch.  I
went to my local Radio shack store  ( ha ha ha .. what a total waste of time
that was).

I am comfortable soldering. I have some NiCad 4.8 and 7.2 volts; NiMh 7.2
and 8.4 bolts. and even Lipo batteries ( 7.2 volts ) around that I use for
some r/c planes.

Is there a site or a schematic that I could follow to get this done? I don't
need an overly bright light, nor do I need it to last all night long.  I
live in Hot and sunny Houston, TX so daylight probably isn't a problem.

Any and all help or direction/sites etc. appreciated.

thanks very much  RichG

Posted by Anthony Matonak on November 4, 2007, 7:31 pm
rich wrote:

It would help if you told us what wattage bulb you are using now.

Say you had a 60W bulb in there. You could replace it with a 15W
12V compact fluorescent light, 50W panel and a 20 amp-hour battery.

If you're willing to go with a little less light you can downsize
the bulb, panels and batteries accordingly.

I've heard reports that the Harbor Freight system is a cheap
source of panels but you'll need a proper charge/light controller.

I did a google search and found these guys sell 12V CFL lights and
the appropriate controller.


Posted by rich on November 5, 2007, 1:42 am
 Hmmm ....I have a 40 watt bulb in there.Thanks for LINKs..but each of the
LINKs far exceed --size-- and price limitations.    Hope someone else has a
smaller, cheaper solution...if not..thanks for your assistance, anyhow.

Posted by Anthony Matonak on November 5, 2007, 7:35 am
 rich wrote:

Solar PV is expensive. You can go smaller and cheaper but you'll also
have less light so it's all a question of what you're willing to pay.
You might want to buy some regular CFLs in the 5 to 15W range and see
if they provide enough light and then go from there.

Another option to going solar is to repair/replace the wiring going
to the light and switch it to 12V using a power supply in the house
and a 12V CFL in the post. Laws and regulations are a lot more lax
for 12V DC wiring.


Posted by Eric Sears on November 5, 2007, 8:12 pm

Solar lighting will inevitably be much more expensive in that
situation (ie - compared with grid power). If you could get a flouro
of about 5 watts, with a correspondingly smaller solar panel (say
about 10 watts) and a 6amp-hr gell battery - cost may be not too bad.

But a different solution :  you mentioned that the wires to the house
had been cut. Are they still in place?
While you may not want to get an electrician in the rejoin or replace
them - you could do it yourself if you stuck to low voltage.
Simplest suggestion - replace the bulb with a 15 watt, 12v flouro;
join the wires (add a bit if needed) then run a dc power pack (dc
plug-pack) at the house, preferably with about 15v to overcome the
slight voltage drop in the wires. (You will need to disconnect the
wires at the house and connect them to the low volts!) You don't say
how far it would be to the post but probably up to 50 meters will be
ok at 1 amp.
There are other possible solutions if the distance is greater - eg 24v
system - or even a battery system (without solar panel) charged via
the wire.
Personally I would rejoin the cable and make use of it!

Eric Sears.

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