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Author Topic: Christmas battery operated LED's  (Read 543 times)

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Offline Digger1

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Christmas battery operated LED's
« on: January 06, 2017, 06:55:57 pm »


Here is a pack of battery operated xmas LED's I brought just before Christmas, there is 20 LEDs and run of 2 x AA batteries, they cost around 3.   Below is a close up of one of the bulbs, as you can see they are on two copper wires, and not being an electrician I don't know if they are wired in sequence or parallel.   I can't see any resistors(or should that be diodes??)  anywhere in the circuit. They are very tiny at around 2mm square with a small blob of plastic around them.



My question is this, can I cut them off into individual bulbs and wire them up for lighting buildings?? and if so what would I have to do to them and how would I power them, obviously I don't want to use any batteries...
"I hear the train a comin'.."  Folsum Prison Blues, Johnny Cash

Offline Digger1

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Re: Christmas battery operated LED's
« Reply #1 on: January 06, 2017, 07:02:10 pm »
What I should of said also is that they are 3.2V/0.064W.........well that's what the box says anyway, yep talking boxes too(just before any of you wags mention it!!) :D
"I hear the train a comin'.."  Folsum Prison Blues, Johnny Cash

Offline Sprintex

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Re: Christmas battery operated LED's
« Reply #2 on: January 06, 2017, 07:02:27 pm »
I can't see any resistors(or should that be diodes??)  anywhere in the circuit.

I can see diodes, 20 of them, light emitting ones ;)


Paul

Offline Digger1

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Re: Christmas battery operated LED's
« Reply #3 on: January 06, 2017, 07:04:21 pm »
 :doh: :doh: :doh: like I said Sprintex, I'm no electrician.... :-[ :-[
"I hear the train a comin'.."  Folsum Prison Blues, Johnny Cash

Offline keithbythe sea

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Re: Christmas battery operated LED's
« Reply #4 on: January 06, 2017, 07:50:56 pm »
Thanks for posting this Digger. Bought several packs of similar lights which I have just packed away for next year. Now if they could be put to good use for more than 4 weeks a year.... :hmmm:

Look forward to lots of informed information from the sparkies on the forum.

Offline themadhippy

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Re: Christmas battery operated LED's
« Reply #5 on: January 06, 2017, 07:59:24 pm »
looks like parralel,and being 3.2v sort of confirms that ,quick calc says they need 1ma each,if you leave them in parralel you could add a resitor and run them from a power supply.To calculate the resistor value  take 3 (or 3,2 if you want precision) from the supply voltage and divide by the number of leds,then multiply the answer by 1000.So for 6 leds and  a 12v supply ,youd need a 1.5K ohm resistor or ((12-3)/ 6)x 1000,
« Last Edit: January 06, 2017, 08:10:58 pm by themadhippy »

Offline Steve.T

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Re: Christmas battery operated LED's
« Reply #6 on: January 07, 2017, 11:00:39 am »
looks like parralel,and being 3.2v sort of confirms that ,quick calc says they need 1ma each,if you leave them in parralel you could add a resitor and run them from a power supply.To calculate the resistor value  take 3 (or 3,2 if you want precision) from the supply voltage and divide by the number of leds,then multiply the answer by 1000.So for 6 leds and  a 12v supply ,youd need a 1.5K ohm resistor or ((12-3)/ 6)x 1000,


I must be honest I thought this calculation was wrong to begin with, but it was me just being thick and misunderstanding it.
However, now i read it properly yes this is right. If you want to use 6 of the LEDs in parallel with a supply of 12V then a 1K5 resistor is needed, if you use 3 of them then use a 3K resistor and so on.
So to use a single led use a 9K resistor (9K not a common size so using 10K would be a little dimmer, 8K2 would be okay and give about the same brightness).

What would be interesting is how bright are these LEDs ?
Would one of them be enough to light the inside a small building, or do you need several of them ?
I ask because the OP in the thread below bought some 2 mA yellow leds to light a church but they were not bright enough.

http://www.ngaugeforum.co.uk/SMFN/index.php?topic=35830.0

I personally though that leds at 2 mA would not be bright enough to do this and suggested using ones at 10 to 20 mA but maybe I am wrong and white leds at these low currents will do and that maybe put a thin layer of yellowish paint on them to subdue the whiteness a bit.

So it would be interesting to know how you go on with these  :thumbsup:

Steve
« Last Edit: January 07, 2017, 11:02:35 am by Steve.T »
I don't suffer from insanity. I enjoy every minute of it.

Steve

Offline Digger1

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Re: Christmas battery operated LED's
« Reply #7 on: January 07, 2017, 01:09:59 pm »
Thank you for the replies, I do have another couple of questions though.

Firstly I had thought to use an old phone base station power adapter, I have 2, one rated as 6.5V - 300mA and the other one  is 9V - 150mA.   Could I use either of these to power a lighting bus? ( my layout is DCC ).  Obviously I realise I would have to take into account the difference in supply voltage when doing the calculation for the resistors.

Secondly where do I put the resistor in the system, would it be possible for someone to post an easy to understand laypersons diagram please.

Also Steve.T they seemed quite bright when they were strewn across the mantlepiece at Christmas, I don't want them to be too bright in the buildings so was going to experiment with them first using the battery pack and just putting the last LED in a building to see how bright they are.
"I hear the train a comin'.."  Folsum Prison Blues, Johnny Cash

Offline Digger1

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Re: Christmas battery operated LED's
« Reply #8 on: January 07, 2017, 04:58:09 pm »
What would be interesting is how bright are these LEDs ?
Would one of them be enough to light the inside a small building, or do you need several of them ?
I ask because the OP in the thread below bought some 2 mA yellow leds to light a church but they were not bright enough.
Steve

Well I just tried putting the end one inside a small cottage, I covered all the others in the line to eliminate light pollution, and it was fine I thought it looked right, this was running off the battery pack, so assuming they don't go dimmer /brighter when wired into the lighting bus I'm well happy.  :claphappy:
"I hear the train a comin'.."  Folsum Prison Blues, Johnny Cash

Offline keithbythe sea

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Re: Christmas battery operated LED's
« Reply #9 on: January 07, 2017, 05:21:00 pm »
Once again, thanks for this Digger. Very interesting. I see that you are thinking about using an old transformer as the power source. Have you thought about connecting your lighting bus to a battery? My 100 lights set lasted for at least 3 weeks (8 hours on a time). Therefore I think that a few building lights on a layout would run for months off of some AA batteries.

More help please skilled sparkies!!

Offline sprogman

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Re: Christmas battery operated LED's
« Reply #10 on: January 07, 2017, 07:11:58 pm »
If there is no resistor in circuit anywhere then they are relying on the internal resistance of the batteries to limit the current. This is cheap engineering and not to be recommended.

Always use a suitable resistor. Ideally, parallel LEDs should each have an individual resistor.

 

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