# How to convert 120v AC to 1.5V DC?

Discussion in 'Electronic Basics' started by [email protected], Sep 17, 2008.

1. ### Guest

I have an outdoor solar light with automatic photo sensor which
operates with single 1.5v AAA battery. I want to connect the solar
light to 120v outlet so it can stay on all the time at dark. Can
anyone tell me what kind of options I might have to do this
conversion? Thank you in advance for your help.

2. ### Ted PavlicGuest

There are several canned products that can do exactly what you need. A
quick Google search for "1.5V DC transformer" leads me to this
"battery eliminator:"

http://www.testpath.com/Items/DC-Power-Supply-Battery-Eliminator-15V-or-3V-3A-122-014.htm

All of these products will use a transformer internally to step-down
the 120V to some lower level. They'll then use a rectifier to keep the
voltage positive, and then they'll use some signal conditioning
circuit (often a linear regulator IC) and some large output buffering
capacitors to hold the output constant. Here's a more do-it-yourself
example:

http://www.awrr.com/1point5voltPS.html

That example is nice because it uses an LM317, which in that package
can give you 1A of output current --- plenty for your use.

3. ### JamieGuest

they make universal types that will select down to
that low of voltage.

http://webpages.charter.net/jamie_5"

4. ### Dave, I can't do thatGuest

Shine a light on the solar cell and put black tape over the sensor.
<grin> OK, just sorta kidding.

Go here...
http://www.allelectronics.com/make-a-store/category/815200/Wall-Transformers/D.C.-Wall/1.html

Get one of the 3v ones and use a resistor in series. The "light" will
be an LED which will almost certainly have a resistor already in
series to limit current. Someone here smarter than me can tell you
what value for the resistor.

Dave

5. ### ehsjrGuest

Get cat # DCTX-5200 from Allelectronics
http://www.allelectronics.com/make-a-store/item/DCTX-5200/5-VDC-2000-MA-WALL-TRANSFORMER/-/1.html
(watch for line wrap in the above)

Put 6 1N4001 diodes in series with the 5 volt DC output
and the solar light. That will drop the voltage delivered
to the light down to about 1.4 volts.

Ed

6. ### Jasen BettsGuest

easist is to merely replace the battery:
you need a way to get 1.5v from 120V
and, if you want it lit during the day, some black paint over the photo sensor
except it's probably not a 1.5V battery (more likely 1.25V or 1.2V)

it may be simpler to disconnect the LED from the rest of the circuit and power that
from a higer voltage with an apropriate dropping resistor. (eg use a 5v wall wart
and a 68 ohm resistor)

Bye.
Jasen

7. ### neon

1,325
0
Oct 21, 2006
LOOK you just forget about running 120v ac on your yard that is very dangerous. so now what? well get a cheap phone transformer battery charger. WHAT VOLTS? it has to be be 1.25v. there is some circuits inside there that must charge the battery correctly and make the whole thing work.
But since you are going to put wires in the ground do it right remove all the electronics just leave the LED and then any small transformers will work and not only that no more costly yearly battery replacement . what you need is the LED (OR MAYBE ADD MORE) and put a resistor in series with it what value? measure the voltage out of the transformer subtract 2-3v and allow 10ma per lamp. and you may leave it on constantly since the power will be into less the 3-5w total. Don't fall for all the crazy add on sugested LEDS are diodes with a very low voltage breakdown so a in4001 will work fine no need for capacitors no need for regulator not unless you can see 60hz turning on-off the leds like a bulb in yuor /mine house.

Last edited: Sep 18, 2008