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Propper 12 VDC reduction to 4.5 VDC
By coldspot, Section Light Posted on Fri Jul 28, 2006 at 09:34:04 AM MST
Thinking about using a LED Flashlight on 12 VDC system

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

Propper 12 VDC reduction to 4.5 VDC | 19 comments (19 topical)

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#1)
by coldspot on Fri Jul 28, 2006 at 03:49:40 AM MST

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.

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#3)
by AbyssUnderground on Fri Jul 28, 2006 at 03:56:10 AM MST

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.

http://www.repowered.co.uk - My Renewable Energy site.
msn[at]m3ezw.co.uk - my msn if you want a chat.
[ Parent ]

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#2)
by dinges on Fri Jul 28, 2006 at 03:54:57 AM MST

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 )

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#4)
by dinges on Fri Jul 28, 2006 at 04:09:28 AM MST

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!

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#5)
by coldspot on Fri Jul 28, 2006 at 04:15:47 AM MST

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

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#6)
by dinges on Fri Jul 28, 2006 at 04:30:40 AM MST

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! :)

[ Parent ]

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#7)
by Nando on Fri Jul 28, 2006 at 07:16:25 AM MST

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

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#8)
by ghurd on Fri Jul 28, 2006 at 08:13:11 AM MST

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-
Ghurd.info

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#9)
by wooferhound on Fri Jul 28, 2006 at 10:07:07 AM MST

Here is a Very Useful
LED Resister Calculator
http://ourworld.compuserve.com/homepages/Bill_Bowden/led.htm
Super informative page about using LED Lighting

W o o f -={(

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#11)
by terry5732 on Fri Jul 28, 2006 at 08:48:52 PM MST

LED resistors
For 3.4V typ LEDs

V 82-100ohm
2V 220ohm
V 330ohm
V 470ohm
2V 560ohm

For 2V typ LEDs

V 180ohm
2V 270ohm
V 390ohm
V 560ohm
2V 680ohm

Diodes don't work in series.

[ Parent ]

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#12)
by dinges on Sat Jul 29, 2006 at 03:10:58 AM MST

"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.

[ Parent ]

diodes work in series? (3.00 / 0) (#13)
by Norm on Sat Jul 29, 2006 at 06:08:42 AM MST

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
( :>) Norm
[ Parent ]

Re: diodes work in series? (3.00 / 0) (#14)
by dinges on Sat Jul 29, 2006 at 06:35:42 AM MST

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.

[ Parent ]

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#10)
by coldspot on Fri Jul 28, 2006 at 05:12:56 PM MST

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-

" dia
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

Re: Mini fluorescent lights (3.00 / 0) (#15)
by coldspot on Sat Jul 29, 2006 at 03:52:46 PM MST

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

solar lights..... (3.00 / 0) (#16)
by Norm on Sun Jul 30, 2006 at 07:04:37 AM MST

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.

( :>) Norm
[ Parent ]

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#17)
by ZooT on Fri Aug 25, 2006 at 03:26:37 AM MST

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.....

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#18)
by Baz on Sun Oct 22, 2006 at 01:24:07 PM MST

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.

Re: Propper 12 VDC reduction to 4.5 VDC (3.00 / 0) (#19)
by Errol on Thu Jul 24, 2008 at 09:30:04 PM MST

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

[ Parent ]

Propper 12 VDC reduction to 4.5 VDC | 19 comments (19 topical)

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