Efficient low-wattage DC power supplies?

[arcas]

I know there's a "Power Supplies" sub category but since that forum focuses on PC power supplies, I figured ATOT is probably the better place for this...

I've been toying with the idea of making some LED-based lights for in and around the house...in the garage, the stairways, etc. Night-light type stuff so they don't need to be very bright. A single LED or three would be enough per fixture. Problem is once I account for the power wasted by wall wart style power supplies, I might as well use an incandescent light.

(The smallest CFL I've found is 5W and 210 lumens which is way brighter than I'm looking for. Does anyone make a 1W CFL?)

Has anybody done this efficiently?


edit:

I'm not an EE but I understand switch-mode PSUs are more efficient than linear (75+% vs 50%) although the two switch mode wall warts that I have appear to be a lot worse than the linear wall warts that I have. For example, my cell phone power supply is a 5W switching supply (outputs 5VDC at 1000ma) but the label claims 36W input (120V @ 300ma). Perhaps small switch mode power supplies simply aren't very efficient?

 

[Oscar1613]

in a/c to d/c applications, there are other things that can cause inefficiencies, such as the transformer design

 

[Aluvus]

You cannot simply multiply voltage by current to get real power used by an AC system, unless you know the load is entirely resistive. Switching supplies are not resistive loads.

If you want to know the efficiency of the switching supplies that you have, you will need to measure it.

Categorically yes, switching supplies are substantially more efficient than linear supplies.

 

[DangerAardvark]

Originally posted by: Aluvus
You cannot simply multiply voltage by current to get real power used by an AC system, unless you know the load is entirely resistive. Switching supplies are not resistive loads.

If you want to know the efficiency of the switching supplies that you have, you will need to measure it.

Categorically yes, switching supplies are substantially more efficient than linear supplies.

This post just made my head assplode. Which might explain why I failed Physics 151...

 

[Googer]

Originally posted by: Oscar1613
in a/c to d/c applications, there are other things that can cause inefficiencies, such as the transformer design

I think the opening post means he is looking for an DC/DC PSU.

 

[Oscar1613]

Originally posted by: Googer

Originally posted by: Oscar1613
in a/c to d/c applications, there are other things that can cause inefficiencies, such as the transformer design

I think the opening post means he is looking for an DC/DC PSU.

he mentioned wall warts and his cell phone charger that does 36W@120V -> 5W@5V so i assumed he's looking for an AC to DC PSU... unless he's got 120V DC in his house :Q

 

[Googer]

Originally posted by: Oscar1613

Originally posted by: Googer

Originally posted by: Oscar1613
in a/c to d/c applications, there are other things that can cause inefficiencies, such as the transformer design

I think the opening post means he is looking for an DC/DC PSU.

he mentioned wall warts and his cell phone charger that does 36W@120V -> 5W@5V so i assumed he's looking for an AC to DC PSU... unless he's got 120V DC in his house :Q

I overlooked that.

Radio Shack has some high wattage AC-DC PSU's for hobby applications. Some go up to a few hundred watts. But if you really want to get fancy, a variable voltage PSU with LCD read-out can be found for several hundred to a few thousand dollars.

Concerning Waste. Use one high wattage PSU will minimize waste by run special DC only power lines through the house to the places where DC power is desired. For safety, be sure to use separate circuits using standard 12-14GA power cable with fuses on each line.


Or you can simply buy pre-made LED lights from dozens of online vendors. You will pay a nice dime for them, but they are highly durable and last a long time.
http://www.ccrane.com/lights/index.aspx

 

[Eli]

LOL, neat.

Minimum order is 5,000 though. Wonder where you could find one at a B&M...

 

[edro]

You should definitely stick with a pre-made assembly.
By the time you buy a power supply of any type, you will be above the price of a night light assembly.

Also, no power supply you get will be small enough to be used around the house for decoration.

I get cheap power supplies from here: AllElectronics
They are like Big Lots for electronics.

 

[Jeff7]

Wee-little 2 watt CFLs
LED night lights

Various lights

 

[Googer]

Originally posted by: edro
You should definitely stick with a pre-made assembly.
By the time you buy a power supply of any type, you will be above the price of a night light assembly.

Also, no power supply you get will be small enough to be used around the house for decoration.

I get cheap power supplies from here: AllElectronics
They are like Big Lots for electronics.

But cheap does not necessarily mean efficient.

 

[Modelworks]

If you want an efficient supply simply don't regulate it.
Use a transformer to step down the voltage, couple diodes to convert it to dc and a capacitor to filter out the ripple.
Efficiency is near 98%


Or since your using LED, use them for the diodes and power them off AC.

 

[Googer]

Originally posted by: Modelworks
If you want an efficient supply simply don't regulate it.
Use a transformer to step down the voltage, couple diodes to convert it to dc and a capacitor to filter out the ripple.
Efficiency is near 98%


Or since your using LED, use them for the diodes and power them off AC.

Schematic diagrams?

 

[Modelworks]

http://www.turbokeu.com/myprojects/acled.htm

Thats the transformerless method.
Be careful. 120vac can and will cause death/fires.

more led driven from ac
http://ourworld.compuserve.com...Bill_Bowden/page10.htm


I think most people forget that led are diodes and not little "lights"

 

[Googer]

Take note, the colour temperature emitted by white LEDs is not the most comfortable thing to live with. compact florescent bulbs will emit a light that is easier on the eyes and is more comfortable to live with.