Castell Mawr - A joint GWR/LMS route

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Bufferstop
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Re: Castell Mawr - A joint GWR/LMS route

Postby Bufferstop » Thu Jun 20, 2019 2:56 pm

Geoff the light output of LEDs isn't proportional to the power consumed, choose the resistor value the limits them to bright but not brilliant and try putting an extra diode in series with them the volts dropped across the diode leaves them drawing the same current, at a lower voltage, or wire pairs of LEDs in series.
Yesterday I was testing a big bundle of red LEDs cannibalised from Christmas lights, changing the voltage I could get them to light up at a reasonable brightness at around 2 volts, but it was quite critical a touch too low and they flickered on and off like the ones in the fake candles. At 3 volts they were bright enough for indicator lamps and anything over was ridiculously bright, and I suspect they wouldn't have lasted too long. Putting a resistor in series didn't really dim them but the current went down. Among them I found half of one of the candle lights. It comprises a button cell a switch and an led, no other components. When I switch it on it comes on red, then fades to green, then to blue and back to red. There are 3 junctions visible through the clear plastic and what may be small resistors in the legs of two of them. The whole thing works on some carefully balanced voltages as I can cause the colours to switch by touching the exposed wires, I can see I'll have to Google the theory of colour LEDs.
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Dad-1
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Re: Castell Mawr - A joint GWR/LMS route

Postby Dad-1 » Thu Jun 20, 2019 5:10 pm

Hi John,

I'm beginning to wonder if there are inadequate soldered joints ?
I've always run at 4.5V and the 1K resistors worked .... until
they didn't !!
Here you see the middle light now with a 220R, the other two
are still happy with their original 1K. I prefer the lower light levels.
It's only modern station lights that can be bright - Sometimes ?

Image

I'm also going to look into buying a few (3) Frog Juicers. The replacement
PL13 on this board is working fine, but I know when I get the sidings
boards out there will be problems with polarity switching.

Geoff T.
Remember ... I know nothing about railways.
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Bufferstop
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Re: Castell Mawr - A joint GWR/LMS route

Postby Bufferstop » Thu Jun 20, 2019 11:40 pm

The old ways are often the best, I moved on to the next mystery box and found a string of 100 grain of wheat bulbs, at 3v they give out a soft yellowy gas light glow, and they are actually smaller than the LEDs just right for my platform lights. Have you thoroughly scraped the leads on your LEDs they often seam to have some sort of skin over them, you can solder to them ok but you'll do it a bit better if you've exposed the raw metal. It may be down to oxidation of the wire, whatever it is.
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Dad-1
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Re: Castell Mawr - A joint GWR/LMS route

Postby Dad-1 » Fri Jun 21, 2019 3:40 am

John,

If it was easy enough and I could afford to change to filament bulbs I would.
I do believe they are more easily adjusted for output than LED's that need that
trip voltage (Abt 2.7V?) before they work and are then already too bright !!

The one disadvantage is power consumption and heat. One melted the plastic shield
used in a building to disapate the light into a room glow.

Geoff T.
Remember ... I know nothing about railways.
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Bufferstop
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Re: Castell Mawr - A joint GWR/LMS route

Postby Bufferstop » Fri Jun 21, 2019 10:12 am

GoW.s run at well below maximum voltage don't produce that much heat, I think the wiring is proportionally that much thicker that it acts as a built in heat sink.
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TimberSurf
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Re: Castell Mawr - A joint GWR/LMS route

Postby TimberSurf » Fri Jun 21, 2019 5:37 pm

Matching a resistor to an LED as per the calc will give 100% brightness and long life.
For us modellers, modern LED's are too bright.
Increasing the resistance will dim the light, but only when using one resister per one LED, as soon as you string LED's together (Series) or group LED's with one resister (Parallel) then the troubles start!
LED's brightnes is dictated by current and can be controlled with a current limiting circuit for best results. Using a resister in series is actually a voltage divider and is a poor (electronic) method to limit brightness (supply voltage will still effect it).
Quite simply the best method, is to set the resister and brightness to manufacturers specs, then control the brightness by dimming with PWM (pulse width modulation)
This can be achieved relatively cheaply, maintains the long life and gives ultimate control of the brightness desired.
Dimming Guide

P.S. also works well on incandescent bulbs!
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Dad-1
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Re: Castell Mawr - A joint GWR/LMS route

Postby Dad-1 » Fri Jun 21, 2019 7:26 pm

Must read that later TimberSurf .........
Dimming Guide, for me that's lack of sleep, was up last night wandering around at a silly time.

Anyway the first board is 100% working even if 2 are brighter. Today before I went looking for a
club member in hospital I had a go at board No.2. Here you can see the dead light just above the
57XX cab roof. Did a couple of resistor changes, but still not getting steady light, must find another
220R as a final try.
Anyway a picture to lighten (Pun) my mood. Thought I'd swing the water bag to a tank filler.

Image

I believe these LED's are inconsistent in demand. Put my 4.5V power onto the negative. Then clipped
positive onto the resistor leg, up stream, result a steady bright LED. Clipped onto the resistor down
stream so light power came through the resistor, result a dull, but flickering LED. The flicker couldn't
have anything to do with my soldered joints, so my conclusion is that this LED is being starved of power
with the resistor being too high a value - I think this was a 470R to keep brightness down. How come
others work with 1K ??????

Geoff T.
Remember ... I know nothing about railways.
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heda
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Re: Castell Mawr - A joint GWR/LMS route

Postby heda » Sat Jun 22, 2019 6:22 am

I'm not able to give any advice regarding the rogue led but if it's any help you can use a emote dimmer to control led brightness.

https://www.ebay.co.uk/itm/Mini-12V-3-K ... 28E9i4-i5Q

At worse could you put a workman on a ladder replacing the bulb.
Dave

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End2end
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Re: Castell Mawr - A joint GWR/LMS route

Postby End2end » Sat Jun 22, 2019 10:41 am

heda wrote:I'm not able to give any advice regarding the rogue led but if it's any help you can use a emote dimmer to control led brightness.
https://www.ebay.co.uk/itm/Mini-12V-3-K ... 28E9i4-i5Q

I bought some of those. Good iem!
heda wrote:At worse could you put a workman on a ladder replacing the bulb.

Great idea for a cameo. :)
Thanks
End2end
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Dad-1
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Re: Castell Mawr - A joint GWR/LMS route

Postby Dad-1 » Sun Jun 23, 2019 7:03 pm

While both TimberSurf and E2E's suggestions are fine I'm working
on a 'holding' job here. I had already bought 3 identical lights to replace
the failed items.

Two responded to a change from a 1K resistor to a 220R the third light
didn't want to play so today I've removed and fitted a replacement.

The removed light works fine although a little bright with a 4.5V supply.
It will not work with ANY resistor in the circuit ????? How's that ??????
Yet it did and so does the replacement .......

Geoff T.
Remember ... I know nothing about railways.
viewtopic.php?f=22&t=32187 and Another on viewtopic.php?f=22&t=28436&start=60&st=0&sk=t&sd=a

Dad-1
Posts: 5848
Joined: Sun Aug 24, 2008 8:05 pm
Location: Dorset - A mile from West Bay.

Re: Castell Mawr - A joint GWR/LMS route

Postby Dad-1 » Tue Jul 02, 2019 3:54 pm

What a Nice Day !!

Had the last boards out today to clean tracks and check electrics.
Also replaced the Diesel tank that had fallen away from the council roads dept yard !!

Unashamedly bumped up the listings to easily tie in with my exhibition posting !!

Geoff T.
Remember ... I know nothing about railways.
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