Propper 12 VDC reduction to 4.5 VDC

[coldspot]

I would like to reduce the volts off a 12 VDC system to power

a few LED Flashlights at cabin.

Just figuring out the values for the resisters good enough?

(thinking that they would heat up and shorten life)

I got a 9 LED F/L that uses 3 AAA's

So thats 4.5 VDC

I'd like to hook this up to show better light for the watt.

If any electronic experts have a better plan that

a guy with some but limited electronic's could do

PLEASE share.....



I could get some old cell phone car chargers from

thrift store if need be, (they tend to be 4.5 to 5 VDC)

Thanks

[coldspot]

I

will probebly end up using the C/P

charger on this one.

I've used they on a lot of little stuff

when I'm building new from junk stuff.lol



Anyway

reading things like this is why I asked,

"Addition of a resistor is quite illogical for such purpose, home "projects" have the tendency of NOT installing the proper arrangement BUT what is easy and cheap, as well as, to "heat" the environment."

So, if I'm just being crazy again

let me know.



The FlashLight cost

$3.99

Has great amount of light

so it has to be better on the watt useage

compaired to 12 VDC incandesant 40 watt bulbs being used now.

[dinges]

Depending on just how electronically challenged you are, I'd go with either cell phone chargers (though measure them first, if they really put out 4.5-5V) or build your own, with a 7805 voltage regulator IC. Pretty easy stuff, and a good introduction into electronics; check out this website, for example:

http://electronics.howstuffworks.com/digital-electronics3.htm

http://electronics.howstuffworks.com/digital-electronics4.htm

Or search for '7805' (that's the actual voltage regulator IC that you should use). Or find a friendly electronics expert in your area and have him solder it, while you look over his shoulder. HAMs tend to be friendly & easy going guys (did I mention I was one? :0 )

[AbyssUnderground]

You should forget LED's and go for CCFL's as they get the best light per watt. They are very cheap too. You can find one for around $6 if you are lucky. Most PC CCFL's come rated at 12v so it will work straight out the box.

[dinges]

Oops, your reply of using cell phone chargers showed up while I was still typing...

Anyway, if you intend to light up a cabin, I agree with the other poster: use 12V CFLs (not CCFLs). They're 2-3 times as energy efficient as LEDs (measured in umen/Watt).

Besides, when you build a voltage regulator based on a 7805, resistors or (many!) cell phone chargers, you'll lose the power as heat! Yes, that's right, if you convert from 12V to 5V, the excess power is lost as heat, so you're NOT saving energy by going to the lower voltage... (Unless you use a switchmode power converter, then you would actually save energy. Not a DIY project, but some car cell-phone chargers use a switchmode PSU. Hard to tell from the outside though)

If you could wire three of those LED-lamps in series (3 * 4.5=13.5V) you could make them work straight off a 12V battery...

Personally I'd go for 12V CFL lamps, but those LEDs should work fine too (but, less efficient than CFL).

Succes!

[coldspot]

Yea I know

cold cath's are better

I have a about 6 UV ones in this surfer system

But I had forgot about them.lol  

"electronics expert in your area"

The problem with this is-

Everybody thinks thats me. LOL

I know better and have followed a few of the stuff you guys do.

I'm limited but do know some stuff

I'm an expert solderer, have patched a couple of ethernet

cables together, (to cheap to buy longer one) with each wire

shrink wrapped and patch was only a bit over 1/2" long.

have built about 20+ kit stuff.

But need advice sometimes

So the C/P chargers are ok then?

Yes I volt test them, (Haul in stuff to do "instore" before buying) LOL

Thanks

[dinges]

Cell phone chargers should work, provided that they can deliver the required current.

You have to know how much current your LED lights use. Let's assume it's 50mA @ 4.5V.

Then, you have to decide how many LED lights you need in your cabin; say, 5 pces. That would give a total current requirement of 5*50mA = 250 mA.

Your cellphone charger should be able to supply 4.5-5V at those 250mA. This kind of data is normally printed on the charger or its box.

Won't comment on you being an expert. Guess that in the land of the blind, a one-eyed man is king

Now, if you were really cheap (like me), you wouldn't buy those cellphone chargers, but tear open an old piece of computer equipment, find the 7805 and a few caps in there, take them out and wire them together.

PS: I wonder why there are so many proverbs in English that combine 'Dutch' with 'cheap'. It's a lie! We're not cheap, we're frugal!

[Nando]

Oh Boy, what a bunch of MASOCHISTS !

The question was general in nature without any data or technical information to be able to supply a logical response.

The lamp has 9 LEDs with 3 AAA = 4.5 Volts battery bank.

There are an internal resistor that is in series with all the LEDs that are parallel connected.

There are several LEDs manufacturing processes that give different Forward Voltage for the LEDs, I presume that these type may be the 2.4 or so volts, I may be wrong, since the LEDs are 9, then I do not expect the Series parallel scheme.

If each LED receives 40 milli amps then the overall current would be 360 milli amps -- which I expect to be less, just for battery life considerations, I would say around 250 milli amps.

I fusing some of those battery charges, make sure that the LED circuitry has the necessary resistance to protect the LEDs.

Even those CFLS that run with 6 volts, will give much more light than the above mentioned 9 LEDs flash lamp, or torch.

Home Depot in Dallas have some of 6 and 12 volts lamps for AA batteries or external power.

I use 2600 mah NiMH batteries in them, which I buy sometimes at less than 50 cents each ( Fry's sales), then I adapt the external power plug to charge the batteries or use the power directly.

Nando

[ghurd]

Tell me about the flashlight.

Is it cheap, metal, about 1" dia and 3" long?  Brand name of 2 letters?  'SE' or so?

Some have been showing up like that. They are overdriving the LEDs very hard, and they are going to fail soon.  Can't recall about that one, but others from the brand I'm thinking about don't even use resistors.  Other China brands do it too.

Look at the LED circuit board.  If there are nothing but LEDs on it, I'd suggest going with about 3.2V.  Not as bright... but it could last through the 1st weekend!

A similar one (I figure) lost the 1st LED before 1 hour, another before 3 hours, 1 or 2 more before the 8 hour mark, then testing stopped.

CFLs don't always win. LEDs will win for small amounts of light.  

Like a decent LED nightlight with 3 series LEDs, 12V, 1ma.

Maybe a LED light for the stairs and porch for trips between the campfire and catsup, 3 or 6 LEDs at 3 or 5ma.

If they have no resistor (or even if they do), you could try to series 3 flashlight heads and a 2W, 22 or 25 ohm resistor (or 2, 1W, 12 ohm resistors, etc) for '12V' direct.  Try to keep it below 180ma.  Not a great idea, just an idea.

G-

[wooferhound]

Here is a Very Useful

LED Resister Calculator

http://ourworld.compuserve.com/homepages/Bill_Bowden/led.htm

Super informative page about using LED Lighting

[coldspot]

Thanks people

NOT trying to light up a cabin!(Has full 12 VDC and 120 VAC systems)

Would like to add a reading light from this Flashlight, (will pass now)

PC cold cath's have about a 10th the light of this flashlight.

ghurd-

1. " dia
   
3. 5/8" length
   
   

Dousn't look like any thing but LED's

On the 2nd one, first failed about two days,

(switch only problem, would still work if beat hard enough, LOL)

This one on first battery set about 4 days,(maybe one hour on time)

No name or marks on light, came with belt sheath and thumb size strap.

Has a battery holder pack type side in/out

Has rear rubber covered switch.

O-well on to new plan

[terry5732]

LED resistors

For 3.4V typ LEDs

5. V    82-100ohm
   
7. 2V    220ohm
   
9. V    330ohm
   
12. V    470ohm
    
13. 2V    560ohm
    
    

For 2V typ LEDs

5. V    180ohm
   
7. 2V    270ohm
   
9. V    390ohm
   
12. V    560ohm
    
13. 2V    680ohm
    
    

Diodes don't work in series.

[dinges]

"Diodes don't work in series."

Incorrect. They do work in series. As long as they're wired in the correct direction (as is shown in the picture on that resistor website), just like any single diodede should be, diodes in series can work. In fact, my LED light I've built with white LEDs in series.

[Norm]

   But you still wouldn't be able to drop the

voltage from 12 or 13.5  to 4.5 by putting them

in series ...even if you used 40 or 50 of them

...they would still need resistance wouldn't they?

            ( :>) Norm

[dinges]

Yep, but you could use less resistance. And you don't save any energy by using just one LED off 12V; all the excess energy is wasted in the resistor. If you put multiple LEDs in series, you get more light with the same energy. Your resistor can be both less ohms (less resistance), and in special cases even less power (lesser watt-rating).

If you play a bit with that resistance calculator it should become clear.

[coldspot]

LOL,

Life can be funny sometimes!

I was saying that the LED Flashlight was

a brighter and thinking would be cheaper also.

My limited cold cath experience from PC UV, (Black Lights)

For the Bling/Bling in my systems and the automotive

clearance ones I picked up a couple years back and have been

adding to PC repairs I've done for the Extra Touch/Bling

It brings, LOL, (these auto type arn't very bright and are

seldom/ never so far, white ones.

(The string lights are still pretty cool, lol)

BUT-

This morning while helping girlfriends daughter n husban move,

(LOL, the things we Do!)

I stopped at one of the better "Dollar Stores",

And they have for $1.00

"Lightning Bug"

Mini fluorescent lights

model FW77R

4 AA's (6 VDC)

A power in plug hole

6", 4 Watt bulb

Power on/off switch

YES Very Bright White !!!!!!

I picked up 4 of them thinking 6+6=12, for two light sets.

Later remember that bank is built from 6 VDC batteries, lol

Am headed back to get a lot more.

LOL



l8r

[Norm]

  For $18 you can get 6 super-brite solar lights

at some Family Dollar stores....they run on one

AA rechargable battery each...stick em out in the

sun and use them in the house at night for your

reading light and nite lites.

  They are quite brite...exceeded my expectations!

              ( :>) Norm.

[ZooT]

There's an LED array calculator at

http://led.linear1.org/led.wiz

I've been fiddling with it as of late for a project I'm working on and learned a bit about the way this stuff works.....

[Baz]

The 'proper' way is a switch mode regulator. Only a few components, an IC , few R and C and a coil which is the secret that makes them efficient. A radio ham or a bit of googling will provide a circuit.

[Errol]

after a little bit of looking i found that to run 2.5v leds like this 47 ohms per led that is 9 leds = 423 ohms i have used this and it works