Yes, another daft LED question. Sorry.

I have a set of small LED Christmas lights, to decorate a miniature
tree. Power is from 2 AA batteries. Were I to have four identical sets,
could I wire them in series and run using a 12v transformer? I am
thinking of an old (1960s) toy train transformer which provides 0-12v
DC. My first thought is 'yes, of course', but realise that not all
power sources are equal.
--
Graeme, WTF is switch mode anyway?

On Monday, 20 March 2017 10:06:14 UTC, Graeme wrote:
Yes, another daft LED question. Sorry.

I have a set of small LED Christmas lights, to decorate a miniature
tree. Power is from 2 AA batteries. Were I to have four identical sets,
could I wire them in series and run using a 12v transformer? I am
thinking of an old (1960s) toy train transformer which provides 0-12v
DC. My first thought is 'yes, of course', but realise that not all
power sources are equal.

If it really is 12v, yes. Odds are it's rather higher on light load.


NT

Graeme wrote:

Yes, another daft LED question. Sorry.

I have a set of small LED Christmas lights, to decorate a miniature
tree. Power is from 2 AA batteries. Were I to have four identical sets,
could I wire them in series and run using a 12v transformer? I am
thinking of an old (1960s) toy train transformer which provides 0-12v
DC. My first thought is 'yes, of course', but realise that not all
power sources are equal.
If any of the lights pulse on and off running in series will end in tears.
There are a number of wall-warts with adjustable output voltage.
Get one capable of 3 vdc and pit your lights in parallel.
I use several lloytron one switchable in 1.5v steps between 3 and 12 v
They seem very reliable and cool running.

In article ,
Graeme wrote:
Yes, another daft LED question. Sorry.

I have a set of small LED Christmas lights, to decorate a miniature
tree. Power is from 2 AA batteries. Were I to have four identical sets,
could I wire them in series and run using a 12v transformer? I am
thinking of an old (1960s) toy train transformer which provides 0-12v
DC. My first thought is 'yes, of course', but realise that not all
power sources are equal.

If you Google on how to drive LEDs, you'll find calculators to give a
suitable value series resistor to set the correct current from different
DC voltage sources and for series parallel connection of LEDs.

--
*If vegetable oil comes from vegetables, where does baby oil come from? *

Dave Plowman London SW
To e-mail, change noise into sound.

Bob Minchin wrote:
Graeme wrote:

Yes, another daft LED question. Sorry.

I have a set of small LED Christmas lights, to decorate a miniature
tree. Power is from 2 AA batteries. Were I to have four identical sets,
could I wire them in series and run using a 12v transformer? I am
thinking of an old (1960s) toy train transformer which provides 0-12v
DC. My first thought is 'yes, of course', but realise that not all
power sources are equal.
If any of the lights pulse on and off running in series will end in tears.
There are a number of wall-warts with adjustable output voltage.
Get one capable of 3 vdc and pit your lights in parallel.
I use several lloytron one switchable in 1.5v steps between 3 and 12 v
They seem very reliable and cool running.

Yes, I've done this with a led Xmas picture display.

In message , "Dave Plowman (News)"
writes
Graeme wrote:

I have a set of small LED Christmas lights, to decorate a miniature
tree. Power is from 2 AA batteries. Were I to have four identical sets,
could I wire them in series and run using a 12v transformer?

If you Google on how to drive LEDs, you'll find calculators to give a
suitable value series resistor to set the correct current from different
DC voltage sources and for series parallel connection of LEDs.

Thanks for all the replies. I confess that my eyes glazed over when
following Dave's advice, but at the end of the day, sets of lights are
pennies from China via eBay, so a little experimentation is in order.
--
Graeme

On 20/03/2017 10:27, wrote:
On Monday, 20 March 2017 10:06:14 UTC, Graeme wrote:
Yes, another daft LED question. Sorry.

I have a set of small LED Christmas lights, to decorate a miniature
tree. Power is from 2 AA batteries. Were I to have four identical sets,
could I wire them in series and run using a 12v transformer? I am
thinking of an old (1960s) toy train transformer which provides 0-12v
DC. My first thought is 'yes, of course', but realise that not all
power sources are equal.

If it really is 12v, yes. Odds are it's rather higher on light load.


NT

I would say no. The LEDs can doubtless flash, and so the current
consumption will vary. In a series connection, individual controller
voltages would be all over the place.

Cheers
--
Clive

In article ,
Graeme wrote:
In message , "Dave Plowman (News)"
writes
Graeme wrote:

I have a set of small LED Christmas lights, to decorate a miniature
tree. Power is from 2 AA batteries. Were I to have four identical sets,
could I wire them in series and run using a 12v transformer?

If you Google on how to drive LEDs, you'll find calculators to give a
suitable value series resistor to set the correct current from different
DC voltage sources and for series parallel connection of LEDs.

Thanks for all the replies. I confess that my eyes glazed over when
following Dave's advice, but at the end of the day, sets of lights are
pennies from China via eBay, so a little experimentation is in order.

Small LEDs can be driven from near any DC voltage source with just a
series resistor to set the current. With 12v, you could series say three
LEDs and use one resistor for those three. Likewise for others. Then just
parallel each of these units off the same supply. Suitable resistors only
cost a couple of pence each.

But it would probably be cheaper/easier to just buy a string of mains
fairy lights of the length you need. I've no doubt they'll be on sale
cheap on Ebay this time of year.

--
*If you can read this, thank a teecher

Dave Plowman London SW
To e-mail, change noise into sound.

Yes and the effects bit of modern lights present varying loads which is
also going to mess up the calculation. How about a voltage regulator chip?


Most train supplies have minimal smoothing as thraw chopped dc helps to get
th motors turning. Indeed later on may controllers wiwere duty cycle based
not voltage based.

If you are building a supply around one of the more crude ones, often only
half wave rectifiers were used and I've successfully used briidge rectifiers
to make them into 24 volt psus when I could see.

What is the current usage of these lights, I'd guess not a lot so you might
be able to use a simple series regulator and use the heat sink as a hand
warmer in winter...

Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
wrote in message
...
On Monday, 20 March 2017 10:06:14 UTC, Graeme wrote:
Yes, another daft LED question. Sorry.

I have a set of small LED Christmas lights, to decorate a miniature
tree. Power is from 2 AA batteries. Were I to have four identical sets,
could I wire them in series and run using a 12v transformer? I am
thinking of an old (1960s) toy train transformer which provides 0-12v
DC. My first thought is 'yes, of course', but realise that not all
power sources are equal.

If it really is 12v, yes. Odds are it's rather higher on light load.


NT

On Monday, 20 March 2017 17:49:03 UTC, Graeme wrote:
In message , "Dave Plowman (News)"
writes
Graeme wrote:

I have a set of small LED Christmas lights, to decorate a miniature
tree. Power is from 2 AA batteries. Were I to have four identical sets,
could I wire them in series and run using a 12v transformer?

If you Google on how to drive LEDs, you'll find calculators to give a
suitable value series resistor to set the correct current from different
DC voltage sources and for series parallel connection of LEDs.

Thanks for all the replies. I confess that my eyes glazed over when
following Dave's advice,

Yes I know the feeling ;-)

but at the end of the day, sets of lights are
pennies from China via eBay, so a little experimentation is in order.

The problem of those from ebay is that aren't alway in spec.
Sometime they can be seconds or ones that dontl come up to standard.
LED's idea should be current driver rather than volatge, but that isn't always easy to do.
If yuo look at the LED as a single entity it will have typically charcteristics
and figures given something like a RED LED will be 2V at 20ma.
SO if you are using 12V you need to 'lose' or drop 10V with the LED is series with your resistor.
So above you want 20ma and to drop 10V so R=V/I 10/.02 =500R so a 470 ohn or 560 resistor will be OK.
Some LEDs white or blue require more voltage ours are 3.3V
So 12-3.3= 8.7 so 8.7/.02 = 435R so a 390 or 470 should be OK.

In article ,
whisky-dave wrote:
Thanks for all the replies. I confess that my eyes glazed over when
following Dave's advice,

Yes I know the feeling ;-)

but at the end of the day, sets of lights are
pennies from China via eBay, so a little experimentation is in order.

The problem of those from ebay is that aren't alway in spec. Sometime
they can be seconds or ones that dontl come up to standard. LED's idea
should be current driver rather than volatge, but that isn't always easy
to do. If yuo look at the LED as a single entity it will have typically
charcteristics and figures given something like a RED LED will be 2V at
20ma. SO if you are using 12V you need to 'lose' or drop 10V with the
LED is series with your resistor. So above you want 20ma and to drop 10V
so R=V/I 10/.02 =500R so a 470 ohn or 560 resistor will be OK. Some
LEDs white or blue require more voltage ours are 3.3V So 12-3.3= 8.7
so 8.7/.02 = 435R so a 390 or 470 should be OK.

Which is why I said Google for an online calculator. Does all the maths
for you. ;-)

--
*The modem is the message *

Dave Plowman London SW
To e-mail, change noise into sound.

On Tuesday, 21 March 2017 13:15:02 UTC, Dave Plowman (News) wrote:
In article ,
whisky-dave wrote:
Thanks for all the replies. I confess that my eyes glazed over when
following Dave's advice,

Yes I know the feeling ;-)

but at the end of the day, sets of lights are
pennies from China via eBay, so a little experimentation is in order.

The problem of those from ebay is that aren't alway in spec. Sometime
they can be seconds or ones that dontl come up to standard. LED's idea
should be current driver rather than volatge, but that isn't always easy
to do. If yuo look at the LED as a single entity it will have typically
charcteristics and figures given something like a RED LED will be 2V at
20ma. SO if you are using 12V you need to 'lose' or drop 10V with the
LED is series with your resistor. So above you want 20ma and to drop 10V
so R=V/I 10/.02 =500R so a 470 ohn or 560 resistor will be OK. Some
LEDs white or blue require more voltage ours are 3.3V So 12-3.3= 8.7
so 8.7/.02 = 435R so a 390 or 470 should be OK.

Which is why I said Google for an online calculator. Does all the maths
for you. ;-)

don;t need one.
if you type into the google search area 12-3.3 as soon as you hit the "=" key the result is shown. works for quite a few functions even sin(x) no need to find a calcluator

whisky-dave wrote:
On Monday, 20 March 2017 17:49:03 UTC, Graeme wrote:
In message , "Dave Plowman (News)"
writes
Graeme wrote:

I have a set of small LED Christmas lights, to decorate a miniature
tree. Power is from 2 AA batteries. Were I to have four identical sets,
could I wire them in series and run using a 12v transformer?

If you Google on how to drive LEDs, you'll find calculators to give a
suitable value series resistor to set the correct current from different
DC voltage sources and for series parallel connection of LEDs.

Thanks for all the replies. I confess that my eyes glazed over when
following Dave's advice,

Yes I know the feeling ;-)

but at the end of the day, sets of lights are
pennies from China via eBay, so a little experimentation is in order.

The problem of those from ebay is that aren't alway in spec.
Sometime they can be seconds or ones that dontl come up to standard.
LED's idea should be current driver rather than volatge, but that isn't always easy to do.
If yuo look at the LED as a single entity it will have typically charcteristics
and figures given something like a RED LED will be 2V at 20ma.
SO if you are using 12V you need to 'lose' or drop 10V with the LED is series with your resistor.
So above you want 20ma and to drop 10V so R=V/I 10/.02 =500R so a 470 ohn or 560 resistor will be OK.
Some LEDs white or blue require more voltage ours are 3.3V
So 12-3.3= 8.7 so 8.7/.02 = 435R so a 390 or 470 should be OK.






Low power tranformer adjustable walwarts have crap regulation IME and
don't need a series resistor if driving multiple LEDs.

On Tuesday, 21 March 2017 14:11:55 UTC, Capitol wrote:
whisky-dave wrote:
On Monday, 20 March 2017 17:49:03 UTC, Graeme wrote:
In message , "Dave Plowman (News)"
writes
Graeme wrote:

I have a set of small LED Christmas lights, to decorate a miniature
tree. Power is from 2 AA batteries. Were I to have four identical sets,
could I wire them in series and run using a 12v transformer?

If you Google on how to drive LEDs, you'll find calculators to give a
suitable value series resistor to set the correct current from different
DC voltage sources and for series parallel connection of LEDs.

Thanks for all the replies. I confess that my eyes glazed over when
following Dave's advice,

Yes I know the feeling ;-)

but at the end of the day, sets of lights are
pennies from China via eBay, so a little experimentation is in order.

The problem of those from ebay is that aren't alway in spec.
Sometime they can be seconds or ones that dontl come up to standard.
LED's idea should be current driver rather than volatge, but that isn't always easy to do.
If yuo look at the LED as a single entity it will have typically charcteristics
and figures given something like a RED LED will be 2V at 20ma.
SO if you are using 12V you need to 'lose' or drop 10V with the LED is series with your resistor.
So above you want 20ma and to drop 10V so R=V/I 10/.02 =500R so a 470 ohn or 560 resistor will be OK.
Some LEDs white or blue require more voltage ours are 3.3V
So 12-3.3= 8.7 so 8.7/.02 = 435R so a 390 or 470 should be OK.






Low power tranformer adjustable walwarts have crap regulation IME and
don't need a series resistor if driving multiple LEDs.

So this multiple LEDs is any number from X to Y
you should try it with some cheap pound LED toches then put recharable batteries in them and watch them get hot and die. Why not because the voltage is too high when recharagables are less but because those torches uses the series resistance of the battery to current limit.

On Tuesday, 21 March 2017 14:11:55 UTC, Capitol wrote:

Low power tranformer adjustable walwarts have crap regulation IME and
don't need a series resistor if driving multiple LEDs.

only true in some circumstances.


NT

In message ,
writes
On Tuesday, 21 March 2017 14:11:55 UTC, Capitol wrote:

Low power tranformer adjustable walwarts have crap regulation IME and
don't need a series resistor if driving multiple LEDs.

only true in some circumstances.

The bottom line seems to be that I should be OK if wiring four sets of
these LEDS in series, together with a +/-435R.
--
Graeme

On Tuesday, 21 March 2017 17:30:31 UTC, Graeme wrote:
In message ,
tabbypurr writes
On Tuesday, 21 March 2017 14:11:55 UTC, Capitol wrote:

Low power tranformer adjustable walwarts have crap regulation IME and
don't need a series resistor if driving multiple LEDs.

only true in some circumstances.

The bottom line seems to be that I should be OK if wiring four sets of
these LEDS in series, together with a +/-435R.

depends entirely on the details.


NT