eliminating wall warts (ac to dc transformers)

[bobhenry]

Eliminating wall warts has been high on my list as I would like to directly DC power almost all of the lighting in the caboose build. I have successfully ganged together the 4.5 volt arrays to run off of 12 volt without incident but I have a failure I need imput on.......

I found seven 9 volt led desk lamps at Goodwill and will be using them in the kitchen (galley) area as task lighting. The reason there is 7 is that I need six and bought an extra to experiment with. Well last night was the night to experiment. I dragged out the ac to dc converter and cut off the wall wart from the lamp and simply connected the wiring to the 12 volt source. All went well and the light shown bright and beautiful so I left it on to check long term. Well, about 30 minutes later the light output was somewhat diminished. Another 1/2 hour and it looked like a real tired flashlight. Well so much for that lamp. I attempted to reconnect the wall wart to the original feed wires with no improvement so I have fried a resistor or something else delicate with the additional 3 volts.

The harbor freight solar panels I have purchased have a 3,6,9 and 12 volt tap so I have some investigating to do and choices to make. I can utilize an inverter and continue to rely on the inverter and wall wart combo to power the lamp heads ( which will be mounted into the ceiling). Can I set up a seperate 9 volt battery and re charging system ? OR perhaps drop the voltage to accomidate the 9 volt lamps with the 12 volt DC feed. I have a real problem with resistors and inverters due to the ineffeciency but I really want to use my $7.00 lamps. I also fail to see the logic of creating DC converting it to AC to reconverting it to a different voltage DC to feed the lamp heads. I really am in over my head here and am looking to the electronics crowd for a bit of guidance.

HELP !

[pohukai]

For me, I kept everything 12V for simplicity. AC power can come in from the outside to power the computer power supply which outputs 12V. During the time I don't have hookup, I can swap out my the power supply with my 12V drill batteries. I don't plan to run anything other than lights and fans if I'm not hooked up and if I am, perhaps a microwave oven; a drill battery charger or maybe a space heater....that's it for me. The last thing I want to do while camping is too much thinking.

Regards

[Wobbly Wheels]

Bob, it sounds like all you need is a dropping resistor in the lamp's power lead. That way you can wire it into 12v but the lamp will only see9. The math is online and resistors are dirt cheap.

[Dale M.]

How about a little circuit board and a couple of DC voltage regulators ( DC in at 12 volts DC out at 5 or 7 or 12 or ---)...

http://www.digikey.com/us/en/techzone/p ... ators.html

http://www.digikey.com/scripts/DkSearch ... 5w&cur=USD

Running 7 or 9 volt devices (leds) at 12 volts may not blow them out immediately, but you simply wear them out with over voltage..... You have forever decreased its efficiency and there is no way to recover them.....

As you have learned, you may just have to put up with load limiting resistors or voltage regulation devices on LEDS if you expect to keep them functioning... It's a fact of nature (electronics) ....

Dale

[H.A.]

Nw

[Bogo]

But also has a current limiting feature.

X1,000,000,000

For the most part that is the most important thing, but most devices will also need voltage limiting too not go over a maximum voltage.

The puck lights that work fine at 12VDC but die a youthful death at auto battery voltages have a resistor to current limit in them. At 12VDC the resistor is sized just right. At 14VDC or 15VDC like when a battery is charging, the resistor lets through to much current and it slowly kills the LED. https://www.sparkfun.com/tutorials/219

There are current limited power supplies available. Many will run off of 12VDC, but others are made to run off 110VAC. For the most part these are designed to drive the high current LEDs: (http://www.ledsupply.com/led-drivers.php) If you look at the specifications and wiring diagrams for them you can see that they can drive multiple LEDs, but requirements like the total LED voltage must be X voltage higher or lower than the supply voltage must be followed. Also the maximum input and output voltages must be followed. Also most of these units are fixed for their output current, ie 25ma, 350ma, 700ma, etc.. If you want a different output current, then you may have to make your own. There are driver chips available, but they do require a few external parts to operate properly. You may even find a PCB to build one up on at one of the Maker electronics sites.

If your lamps need 350mA, 500mA, or 700mA then a device like the A011 FlexBlock power supply could power 3 to 5 of them at one time. http://www.ledsupply.com/flexblock.php

[hankaye]

Howdy All;

Comming in late and feeling truly thick ... (normal for me).

What are these "wall warts" you are talking about. Have never
heard the term till I came on this Forum.

Thanks
hank

[Shadow Catcher]

Wall warts are the transformers that plug into the wall 120AC and transform it to the power required for something like a printer or...

[Bogo]

If they show up in the middle of a cord they are often called bricks. Some bricks and wall warts provide multiple voltages to the device, but that is getting rare these days. You can usually tell by it listing multiple voltages on the label on the wall wart or brick. Another clue can be multiple pins, but sometimes that is just for more power. A wall wart will have on it a label, and on that label it will tell the output voltage, and how many watts, Amps, or mA it supplies. It will tell the type of power it provides. AC will show a squiggly line like: "~". Rectified AC has a solid line with a 3 dashed line under it. DC has a "=" sign like symbol.
Here is a good page on wall warts: http://wiki.diyfaq.org.uk/index.php?title=Wallwart#How_to_choose It's British, but still mostly applicable.

[Socal Tom]

http://www.radioshack.com/product/index ... d=13133351

These only work on low power applications ( this on is only rated at 1 amp), dunno what your LEDs pull. I ran the 5v equivalenat to regulate the dash guages on an old bronco I had. Its a pretty simple setup, I think its more efficient than a resistor. I would hook it to a heat sink ( I used aluminum angle), cause they can get warm.
At the very least its cheap enough to experiment with.
Tom

[hankaye]

Howdy All;

Thanks for the responces... Reckon I'm starting to
learn another 'language' . Like when I started learning
to tye flies ...whole 'nuther can of worms there ...

hank

[Richard A.]

One thing you could try is ... get an even number of those lamps and connect them in a series/parallel configuration (what did he say?)

Example: for two 9 vdc lamps you would connect the lamps in series ... Lamp A would be one wire to the battery and one wire to Lamp B. Lamp B would be one wire to Lamp A and one wire to the battery. This will give you two lamps that want 18 volts ... you will be running them on 12 volts so they won't be as bright, but should be fairly bright.

To add more lamps .. do it in pairs with the same configuration as above.

NOTE: you will need to connect the plus polarity wire of Lamp A to the negative polarity wire of Lamp B ... just be sure not to connect plus to plus or neg to neg.