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Old 9th February 2013, 01:15 AM   #11
srinath is online now srinath  United States
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So as per the LED calculator wizard, with the 27v supply and 2 diodes in series setup, I can put a 10k resistor in it and limit the current to 2.5 milli amp.
Now will it light up worth anything ?

I guess I should try it, and if it fails to light, go to a 4.7K etc etc...
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Old 9th February 2013, 01:24 AM   #12
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Quote:
Originally Posted by srinath View Post
So as per the LED calculator wizard, with the 27v supply and 2 diodes in series setup, I can put a 10k resistor in it and limit the current to 2.5 milli amp.
Can not say until we know the LED specs: Vf, nominal current
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Old 9th February 2013, 01:29 AM   #13
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Vf varies from say 1.4 to 4V !!!

nomial current varies from 5mA to 50mA !!!
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Old 9th February 2013, 03:05 AM   #14
srinath is online now srinath  United States
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Sorry I had posted these in the first posts I made on this thread.

Its Vf = 3.4, If = 20 ma. To make it last forever I thought I should keep it low, like 2.5 ma.

I have a few other resistors, but the 10K will be my first try.

Cool.
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Old 9th February 2013, 04:11 AM   #15
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Quote:
Originally Posted by srinath View Post

1 - Sorry I had posted these in the first posts I made on this thread.

2 - ts Vf = 3.4, If = 20 ma.

3 - To make it last forever I thought I should keep it low, like 2.5 ma.
1 - can never be too sure. I must have 20 different LEDs on hand - all different specs

2 - is the If nominal? I assume so.

27v supply - [2 x 3.4] = 20V {close enough}

20V / 2.5mA = 8K or your 10K resistor will give 2mA

I would say the light would be very dim, you can safely use 5K or even 2K5


3 - forever is a long time. Do you want to use it as a night-light in your coffin?
at nominal current it ought to last 30,000 to 50,000 hours {you can do the arithmetic}
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Old 9th February 2013, 07:29 AM   #16
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normal leds if a few milliamps will not be able to replace bulbs that used to light the dial it can be replacement for stereo indication for example but this one works with DC any way .

Even if one uses high brightness leds to lit the faceplate this also will not work since leds focus -spot their lighting while bulbs flood all around

so what is the case here ?
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Old 9th February 2013, 08:09 AM   #17
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Originally Posted by sakis View Post
normal leds .... will not be able to replace bulbs that used to light the dial

Even if one uses high brightness leds to lit the faceplate this also will not work since leds focus -spot their lighting while bulbs flood all around
The problem with incandescent bulbs and FL lights is that the light emits from 'all directions. Some of it wasted, or must be re-directed - hence reflectors.

LEDS have rather narrow angled emission. If you have a broader angle you have to use either more LEDs or diffusers [either as part of the LED 'cap' itself, or a separate element]. This is done all the time.

One can also obtain broader coverage by using distance - the further the distance, the broader the 'foot-print'
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Old 10th February 2013, 02:51 AM   #18
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I put LED's in the yamaha CR840 - 27v with 2 bulbs circuit, used a 2.2K 1/2 watt resistor.
The blue lighting is awesome. The old green meter lights look ancient in comparison.
Now this one has a sort of acrylic fitting that the light travels through, like a fiberoptic conduit, it works great. Also the lights were facing the acrylic, so LED's that fire in front work fine. The original bulbs had a silicone sleeve, I left that out, dont think I need it, but yellow will mimic the original better IMHO.
The Meter lights are next, and I think the pointer - which needs to be red, and since I dont have red, I have to get those ...
Of course the blue lighting doesn't get the metal good and bright so we can see the black lettering under it ... so its nearly unreadable ... but see that cos these LED's were blue ... not the fact that they are LED's. White or yellow will have fixed that, but NO .... I had to have blue ...

Then I put em in the MCS. That one uses an acrylic fiber optic conduit types too, but that was a cup shaped holder ... the side of the bulb was lighting the acrylic up. That ended up needing LED's installed facing forward, and I got all 4 slightly off from each other, so one is really bright, the other 3 ... not so, and of course blue lights and black letters ... same issue as before.

Either way ... get the right color and 1/2 the battle is won. Get them installed right, and maybe put a little tin foil or a bit of tracing paper and your LED will light the dial and not blind you.

I have ordered several other sets ... I also believe somewhere I got a cache of clear and bright very low Vf - like 1.5v LED's lying around. I remember playing with those and a button cell ~10 years ago. I have to find it ...

Cool.
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Old 10th February 2013, 06:15 AM   #19
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Quote:
Originally Posted by srinath View Post
I put LED's in the yamaha CR840 - 27v with 2 bulbs circuit, used a 2.2K 1/2 watt resistor.
The blue lighting is awesome. The old green meter lights look ancient in comparison.
Now this one has a sort of acrylic fitting that the light travels through, like a fiberoptic conduit, it works great.
Great! Glad you enjoyed the effect and had success!

For the acrylic plate, what some people to do is;

1 - file off the top of the LED so it is flat, OR use a rectangular LED

2 - glue or mount the top of the LED to the side [or top] of the plate [the LED points into the plate]

Then it lights across the plate. Hope I made that clear.............

The effect is improved by using say 1 small LED every 1 or 1.5 cm along the top or side of the plate.
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Old 10th February 2013, 06:23 AM   #20
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Quote:
Originally Posted by srinath View Post
Of course the blue lighting doesn't get the metal good and bright so we can see the black lettering under it ... so its nearly unreadable ... but NO .... I had to have blue ...

yep, got to pick a color that will 'bring out' the lettering or scale or whatever

Keep in mind, that another color or brightness will have a different Vf - you might have to use a different resistor.

Did you know there are 'flashing' LEDs? They change color randomly. Vf is 3 to 3.2V The effect can be cool, depending how and where they are used.
You can get slow and fast [color changing rates].

Also - just to mention it - do not put LEDs in // as one will likely hog the current and burn out.
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