Using LEDs in a rectifier bridge in a suspended light?

A

Adam Funk

Guest
A kid's ceiling night-light, which shines planets, stars, &c., over
the walls & ceilings, has failed (after several years & changes of
tiny 12 V halogen lamps). I've been asked to see if it can be fixed.
The lamp-holder inside the globe has corroded & is no longer usable.
The whole thing consists of the following:

a wall-wart with a British plug & AC output, labelled

PRI 220-240V~ 50 Hz 0.1A
SEC 11.5V~ 10-20 W
SELV

a plug that fits into the wall-wart, cabled through an in-line
switch, to the lamp-holder, which clicks & twists into the globe

the globe, which is just a plastic sphere (more or less) with
colored disks to shine various shapes on the wall & ceiling


My first thought was to put a rectifier bridge on the SELV output &
then a few white LEDs with series resistors, but then I wondered ---
why not use either

1. a suitable resistor in series with a rectifier bridge arrangement
of LEDs,

or

2. a rectifier bridge arrangement of series resistors & LEDs

?


Thanks,
Adam


--
The internet is quite simply a glorious place. Where else can you find
bootlegged music and films, questionable women, deep seated xenophobia
and amusing cats all together in the same place? [Tom Belshaw]
 
On 11/8/2013 5:03 PM, Adam Funk wrote:
A kid's ceiling night-light, which shines planets, stars, &c., over
the walls & ceilings, has failed (after several years & changes of
tiny 12 V halogen lamps). I've been asked to see if it can be fixed.
The lamp-holder inside the globe has corroded & is no longer usable.
The whole thing consists of the following:

a wall-wart with a British plug & AC output, labelled

PRI 220-240V~ 50 Hz 0.1A
SEC 11.5V~ 10-20 W
SELV

a plug that fits into the wall-wart, cabled through an in-line
switch, to the lamp-holder, which clicks & twists into the globe

the globe, which is just a plastic sphere (more or less) with
colored disks to shine various shapes on the wall & ceiling


My first thought was to put a rectifier bridge on the SELV output &
then a few white LEDs with series resistors, but then I wondered ---
why not use either

1. a suitable resistor in series with a rectifier bridge arrangement
of LEDs,

or

2. a rectifier bridge arrangement of series resistors & LEDs

?


Thanks,
Adam
Click to expand...
You can get this done but you may also be able to buy an LED replacement
for your bulb.
 
On Fri, 08 Nov 2013 22:03:21 +0000, Adam Funk <a24061@ducksburg.com>
wrote:

A kid's ceiling night-light, which shines planets, stars, &c., over
the walls & ceilings, has failed (after several years & changes of
tiny 12 V halogen lamps). I've been asked to see if it can be fixed.
The lamp-holder inside the globe has corroded & is no longer usable.
The whole thing consists of the following:

a wall-wart with a British plug & AC output, labelled

PRI 220-240V~ 50 Hz 0.1A
SEC 11.5V~ 10-20 W
SELV

a plug that fits into the wall-wart, cabled through an in-line
switch, to the lamp-holder, which clicks & twists into the globe

the globe, which is just a plastic sphere (more or less) with
colored disks to shine various shapes on the wall & ceiling


My first thought was to put a rectifier bridge on the SELV output &
then a few white LEDs with series resistors, but then I wondered ---
why not use either

1. a suitable resistor in series with a rectifier bridge arrangement
of LEDs,

or

2. a rectifier bridge arrangement of series resistors & LEDs
Click to expand...

A LED is not a good rectifier, therefore you will always find
diodes in series to the LEDs.

w.
 
"Jasen Bleatts"


> the reason not to is it'll flicker at 50Hz if you do that,

** Not true.

There is normally no visible flicker from a LED operating with 50Hz pulses.

Try it and see.

In the OP's night light app, it will be a complete non-issue.

But getting an array of LEDs to act like a point source ( for projecting
stars etc) may be one.



.... Phil
 
"Helmut Wabnig"

A LED is not a good rectifier, therefore you will always find
diodes in series to the LEDs.
Click to expand...

** Are you for real ???

Rhetorical question alert.

FYI:

LEDs are run from AC supplies all the time, with no additional diodes.

White LEDs normally have reverse breakdowns that exceed 20V so there is no
issue with 12VAC even when using just one.


.... Phil
 
On 2013-11-08, Adam Funk <a24061@ducksburg.com> wrote:
A kid's ceiling night-light, which shines planets, stars, &c., over
the walls & ceilings, has failed (after several years & changes of
tiny 12 V halogen lamps). I've been asked to see if it can be fixed.
The lamp-holder inside the globe has corroded & is no longer usable.
The whole thing consists of the following:

a wall-wart with a British plug & AC output, labelled

PRI 220-240V~ 50 Hz 0.1A
SEC 11.5V~ 10-20 W
SELV

a plug that fits into the wall-wart, cabled through an in-line
switch, to the lamp-holder, which clicks & twists into the globe

the globe, which is just a plastic sphere (more or less) with
colored disks to shine various shapes on the wall & ceiling


My first thought was to put a rectifier bridge on the SELV output &
then a few white LEDs with series resistors, but then I wondered ---
why not use either

1. a suitable resistor in series with a rectifier bridge arrangement
of LEDs,

or

2. a rectifier bridge arrangement of series resistors & LEDs

?
Click to expand...

Or leds facing both ways,

the reason not to is it'll flicker at 50Hz if you do that, but at
100Hz (which is much less noticeable) if you use a real bridge
recitfier and keep all the LEDs pointing the same direction.



--
For a good time: install ntp

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
 
On Fri, 08 Nov 2013 22:03:21 +0000, Adam Funk wrote:

A kid's ceiling night-light, which shines planets, stars, &c., over the
walls & ceilings, has failed (after several years & changes of tiny 12 V
halogen lamps). I've been asked to see if it can be fixed.
The lamp-holder inside the globe has corroded & is no longer usable. The
whole thing consists of the following:

a wall-wart with a British plug & AC output, labelled

PRI 220-240V~ 50 Hz 0.1A SEC 11.5V~ 10-20 W SELV

a plug that fits into the wall-wart, cabled through an in-line switch,
to the lamp-holder, which clicks & twists into the globe

the globe, which is just a plastic sphere (more or less) with colored
disks to shine various shapes on the wall & ceiling


My first thought was to put a rectifier bridge on the SELV output & then
a few white LEDs with series resistors, but then I wondered --- why not
use either

1. a suitable resistor in series with a rectifier bridge arrangement
of LEDs,

or

2. a rectifier bridge arrangement of series resistors & LEDs
Click to expand...

Phil Allison touched on this, but didn't go into detail.

You need a light source that's pretty close to a point source.
Basically, the larger the light source the more blurred the images of the
stars, planets, naked dancing girls, or whatever will be. A tiny halogen
bulb is a pretty small source of light, an LED isn't.

I don't know what might be a good solution, other than to try to find
some other thing that uses the same or similar bulbs, and scavenge the
socket out of that.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
 
"Tim Wescott"

A tiny halogen
bulb is a pretty small source of light, an LED isn't.
Click to expand...


** You could have expressed that one better ...



.... Phil
 
On 2013-11-08, Tom Biasi wrote:

On 11/8/2013 5:03 PM, Adam Funk wrote:
A kid's ceiling night-light, which shines planets, stars, &c., over
the walls & ceilings, has failed (after several years & changes of
tiny 12 V halogen lamps). I've been asked to see if it can be fixed.
The lamp-holder inside the globe has corroded & is no longer usable.
....
You can get this done but you may also be able to buy an LED replacement
for your bulb.
Click to expand...

To clarify the "corroded" bit above: I'd only just replaced the lamp
again when it started going off intermittently. When I took it apart
& examined it closely, I found that the stranded copper wire connected
to the "squeezers" that the lamp legs get pushed into was falling
apart (with greenish bits), so I think I need to strip back to clean
wire & work from there.

I came up with this crazy idea as a more permanent solution --- if
used well (!), LEDs should last nearly forever. But maybe I could
splice a new lampholder in.


--
A recent study conducted by Harvard University found that the average
American walks about 900 miles a year. Another study by the AMA found
that Americans drink, on average, 22 gallons of alcohol a year. This
means, on average, Americans get about 41 miles to the gallon.
http://www.cartalk.com/content/average-americans-mpg
 
On 11/9/2013 4:20 PM, Adam Funk wrote:
On 2013-11-08, Tom Biasi wrote:

On 11/8/2013 5:03 PM, Adam Funk wrote:
A kid's ceiling night-light, which shines planets, stars, &c., over
the walls & ceilings, has failed (after several years & changes of
tiny 12 V halogen lamps). I've been asked to see if it can be fixed.
The lamp-holder inside the globe has corroded & is no longer usable.
...
You can get this done but you may also be able to buy an LED replacement
for your bulb.


To clarify the "corroded" bit above: I'd only just replaced the lamp
again when it started going off intermittently. When I took it apart
& examined it closely, I found that the stranded copper wire connected
to the "squeezers" that the lamp legs get pushed into was falling
apart (with greenish bits), so I think I need to strip back to clean
wire & work from there.

I came up with this crazy idea as a more permanent solution --- if
used well (!), LEDs should last nearly forever. But maybe I could
splice a new lampholder in.
Click to expand...
Well Adam you need to fix it. Maybe LEDs will do what you need and
maybe, as was mentioned, they won't give the same light characteristics.
Replace the socket and put in a new bulb, how long will the kid need
this thing? Play with the LEDs if that is fun to you. I might:)
Tom
 
On Sat, 09 Nov 2013 00:54:58 -0600, Tim Wescott <tim@seemywebsite.please> wrote:

On Fri, 08 Nov 2013 22:03:21 +0000, Adam Funk wrote:

A kid's ceiling night-light, which shines planets, stars, &c., over the
walls & ceilings, has failed (after several years & changes of tiny 12 V
halogen lamps). I've been asked to see if it can be fixed.
The lamp-holder inside the globe has corroded & is no longer usable. The
whole thing consists of the following:

a wall-wart with a British plug & AC output, labelled

PRI 220-240V~ 50 Hz 0.1A SEC 11.5V~ 10-20 W SELV

a plug that fits into the wall-wart, cabled through an in-line switch,
to the lamp-holder, which clicks & twists into the globe

the globe, which is just a plastic sphere (more or less) with colored
disks to shine various shapes on the wall & ceiling


My first thought was to put a rectifier bridge on the SELV output & then
a few white LEDs with series resistors, but then I wondered --- why not
use either

1. a suitable resistor in series with a rectifier bridge arrangement
of LEDs,

or

2. a rectifier bridge arrangement of series resistors & LEDs

Phil Allison touched on this, but didn't go into detail.

You need a light source that's pretty close to a point source.
Basically, the larger the light source the more blurred the images of the
stars, planets, naked dancing girls, or whatever will be. A tiny halogen
bulb is a pretty small source of light, an LED isn't.

I don't know what might be a good solution, other than to try to find
some other thing that uses the same or similar bulbs, and scavenge the
socket out of that.
Click to expand...

One of the bright white LEDs would work, the small wide-angle illumination
types.

Yesterday I poked a white Cree T1-3/4 LED up against a photodiode, 30 mA on the
LED. The photodiode current was just a bit above what I get in direct sunlight.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
 
On Fri, 08 Nov 2013 22:03:21 +0000, Adam Funk <a24061@ducksburg.com>
wrote:

A kid's ceiling night-light, which shines planets, stars, &c., over
the walls & ceilings, has failed (after several years & changes of
tiny 12 V halogen lamps). I've been asked to see if it can be fixed.
The lamp-holder inside the globe has corroded & is no longer usable.
The whole thing consists of the following:

a wall-wart with a British plug & AC output, labelled

PRI 220-240V~ 50 Hz 0.1A
SEC 11.5V~ 10-20 W
SELV

a plug that fits into the wall-wart, cabled through an in-line
switch, to the lamp-holder, which clicks & twists into the globe

the globe, which is just a plastic sphere (more or less) with
colored disks to shine various shapes on the wall & ceiling


My first thought was to put a rectifier bridge on the SELV output &
then a few white LEDs with series resistors, but then I wondered ---
why not use either

1. a suitable resistor in series with a rectifier bridge arrangement
of LEDs,

or

2. a rectifier bridge arrangement of series resistors & LEDs
Click to expand...
I think the part where you say it "projects" the planets etc. makes
the led idea a non-starter. Assuming they just have some holes in the
sphere to "project" light from, the light must be a point source to
work. Using a large light emitter or several would make the
projection fuzzy at best, or in the case of focused leds, multiple
iterations of the same planet.

Halogen lamps in a plastic globe sounds like a fire hazard to me.
 
On 2013-11-08, Adam Funk wrote:

A kid's ceiling night-light, which shines planets, stars, &c., over
the walls & ceilings, has failed (after several years & changes of
tiny 12 V halogen lamps). I've been asked to see if it can be fixed.
The lamp-holder inside the globe has corroded & is no longer usable.
....
My first thought was to put a rectifier bridge on the SELV output &
then a few white LEDs with series resistors, but then I wondered ---
why not use either
Click to expand...

Thanks for the interesting replies. I'll play with the LED rectifier
bridge idea sometime soon just for fun.

What I hadn't realized when I thought of it was the simple solution:
strip back to clean wires & splice in another G4 lampholder (leaving
intact the plastic fitting that locks into the top of the sphere). It
hadn't occurred to me at first that I'd be able to find the part, but
it exists & is not expensive.


--
It is probable that television drama of high caliber and produced by
first-rate artists will materially raise the level of dramatic taste
of the nation. (David Sarnoff, CEO of RCA, 1939; in Stoll 1995)
 
On 2013-11-09, Phil Allison wrote:

"Tim Wescott"

A tiny halogen
bulb is a pretty small source of light, an LED isn't.



** You could have expressed that one better ...
Click to expand...

Well, I understood his point!


--
The Nixon I remembered was absolutely humorless; I couldn't imagine
him laughing at anything except maybe a paraplegic who wanted to vote
Democratic but couldn't quite reach the lever on the voting machine.
--- Hunter S Thompson
 
On 2013-11-10, default wrote:

I think the part where you say it "projects" the planets etc. makes
the led idea a non-starter. Assuming they just have some holes in the
sphere to "project" light from, the light must be a point source to
work. Using a large light emitter or several would make the
projection fuzzy at best, or in the case of focused leds, multiple
iterations of the same planet.
Click to expand...

I'm going to splice in a new G4 lampholder instead.


> Halogen lamps in a plastic globe sounds like a fire hazard to me.

It's just a G4 in the middle of an empty globe about 15 cm across,
with some vent holes in the top.


--
The internet is quite simply a glorious place. Where else can you find
bootlegged music and films, questionable women, deep seated xenophobia
and amusing cats all together in the same place? [Tom Belshaw]
 
"Adam Funk"
Phil Allison wrote:
"Tim Wescott"

A tiny halogen
bulb is a pretty small source of light, an LED isn't.



** You could have expressed that one better ...


Well, I understood his point!
Click to expand...

** He did not make one - smartarse.

Clearly, a LED is a smaller light source than the 12v lamp filament.



.... Phil
 
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