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Harry

Dimming the Dapol Lighting Bar

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Hi,

 

I'm hoping someone can help with this...

 

I have recently got the Dapol 153 and have fitted it with a Lenz Silver mini and the Dapol lighting bar. Although it runs very well I find the lighting bar much too bright (especially considering it's N Gauge) and wondered if it's possible to control it with a decoder function to turn it on and off at will and also to dim the brightness?

 

Thanks in advance for any suggestions.

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I have a feeling that the light bar and decoder run off different circuits and as such the bar is not dimmable.

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I think the light bars are powered straight off the pickups, so the only way might be to put a resistor in somewhere, if at all possible?

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The light bars are powered off the pickups, but if prepared to modify them, then you could use a function output of a decoder.

 

But, in the standard guise of a N DMU with head/tail lamps, the two function outputs on a six-pin decoder have been used up. Some decoders offer more outputs, but to be six-pin, they would then require soldering onto pads on the decoder, eg. Zimo MX621's if they arrive in the shops in the new year.

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Thanks for the replies - sadly, that's as I thought! In which case IMO they don't seem such a good thing as they first appear. I would like to have the option of having the DMU on the track without the carriage lights on but that could never happen. I will investigate the resistor idea but it still wouldn't give the on/off option.

 

Thanks anyway!

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I rather suspect a simple resistor is not going to do the job either. If the lighting bar is seperate and powered from the pickups, then it will most likely incorporate a bridge rectifier and some sort of regulator to set the correct 3.3 volts for the LEDs. So putting a resistor in the circuit will not achieve anything.

 

A simple way of reducing the light output is to get some offcuts of car window tinting film. Cut these into small sections and glue over the LEDs. Most places that do window tinting will gladly give you offcuts.

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One cheat is to break the link between the track and the lighting decoder and the wire the lighting bar to the same output as the headlights. Most of the time either both sets are on or neither...

 

Alan

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I was thinking the same (too bright) when I put light bars in my settle carlisle 156. I then had an idea of turning the light bar upside down. The roof is thick enough not to leak any light and the interior of the coaches is vastly improved.

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I had a 156 with light bars fitted, at first my layout was poorly lit and they looked stupid. But after i got proper lighting they looked ok and fitted in nicely but turn the layout lights off and they looked like a light saber! But with my 156 the lights were the least of my troubles.

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what about painting the leds with black paint and leaving just a small opening for light to escape from in the paint?

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On a quick look the light bar (a white one in my case) has a bridge rectifer (MB6S) and another component which appears to be marked 8A638. Google can't match this exactly but I'm guessing a voltage regulator (possibly a clone of MAX638?). I presume it's outputting somewhere around 8 to 9 volts, as the LEDs are in series pairs each with a 180ohm resistor. I don't have a light bar operating at present so I can't measure any voltages or currents. There are also a couple of capacitors probably for smoothing purposes.

 

On DCC you could probably dim it by adding external resistance to bring the input voltage below the regulator voltage, but the result would be very sensitive to DCC track voltage and a solution of this type would not work on DC. You could also experiment with replacing the three 180ohm resistors by larger values, say around 500ohm or even 1k. They are surface mount but there looks to be space to bodge in a 0.125W leaded resistor.

 

I think I'd try the black paint or fitting it upside down first!

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Not convinced that black paint is suitable, but I've used a pale paint mix of cream with a dash of red, yellow or orange to reduce white LED intensity and blueness. I did this with a home made light bar when I found the dimmable function output from the decoder tended to flicker at low intensities. So, instead of using the full range of dimming provided by the decoder, I just painted thin layers over the LEDs until I was satisfied with the intensity. Colours can of course be varied to simulate different lighting types.

 

Nick

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I was thinking the same (too bright) when I put light bars in my settle carlisle 156. I then had an idea of turning the light bar upside down. The roof is thick enough not to leak any light and the interior of the coaches is vastly improved.

 

 

I've just tried doing this, but I couldn't get the roof on properly, I managed to get it in to a certain extent, but with a gap, and it did make a difference. Might have to try moving the bar, that's after I re-solder the connections which have just snapped, Dapols soldering doesn't seem to be a strongpoint :(

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