# How to Wire an LED Cab Light into older Analog/DC powered LGB Locomotives



## LGB333$$$$ (Oct 11, 2017)

Hi Folks - I want to install an LED Cab Light into an older analog/dc powered LGB Mogul locomotive. The Massoth LED Spot Light has a built-in resistor and can operated at 5 - 22 volts dc/dcc/ac 2 - 10mA. I could connect the LED to smoke unit terminals on the circuit board but these older circuit boards change the output polarity when the locomotive moves in reverse direction. The LED unit won't work when the polarity changes. How can I install an LED in an older LGB locomotive circuit board so the LED will stay lighted in both operating directions.....can it be done?


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## trainmanfw&sw (Nov 4, 2020)

I wouldn't consider using the smoke wiring under any circumstances, they require too much voltage to work. Since LED's come in many voltage ranges and most can be regulated by a resistor, I would go that way and yes LED's are directional and if it doesn't burn, reverse the wiring. Just a thought here, since you will be using the LED for a cab light, I usually want my light to be rather dim, then bright, soft white color is what I use. I buy 12v 3mm LED's on Anazon and they come with a resistor already installed which will rate them at 7-9 volts, one more resistor in line will burn just fine on 5 volts. Buy a package of 20 for about $11.00 and experiment with different voltages, you may burn one out, but they a cheap. 

trainman


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## Greg Elmassian (Jan 3, 2008)

use a small full wave bridge if you have changing polarity... easy...

why did you want to use the smoke output? To use an existing switch?


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## krs (Feb 29, 2008)

Greg Elmassian said:


> use a small full wave bridge if you have changing polarity... easy...


or you can also use two LED in parallel wired with opposite polarity, 
sometimes called "anti-parallel"
Image from net - R1 value probably needs to change or use LEDs with an integrate constant current source.


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## LGB333$$$$ (Oct 11, 2017)

There are only two voltage output pins on these old LGB 2018D/2028D circuit boards.......the directional headlight and the smoke unit. The circuit board's smoke unit output is about 6.5 volts and should be sufficient for both the smoke unit and the Massoth LED Spot Light which I want to use, not some other LED device














.


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## krs (Feb 29, 2008)

To use that Massoth spot light, just use a low current, low voltage integrated full-wave diode bridge as Greg suggested.
Connect the AC terminals of it (~) to the smoke unit pins and the LED to the + and - terminals.
I would test the Massoth unit first to see what the minimum voltage is it requires beause a typical diode bridge will add about a 1.4 volt drop to the smoke unit output pin voltage - if that is an issue you may have to go for a Schottky bridge or as an alternative consider wiring the bridge to track voltage.


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## LGB333$$$$ (Oct 11, 2017)

krs said:


> To use that Massoth spot light, just use a low current, low voltage integrated full-wave diode bridge as Greg suggested.
> Connect the AC terminals of it (~) to the smoke unit pins and the LED to the + and - terminals.
> I would test the Massoth unit first to see what the minimum voltage is it requires beause a typical diode bridge will add about a 1.4 volt drop to the smoke unit output pin voltage - if that is an issue you may have to go for a Schottky bridge or as an alternative consider wiring the bridge to track voltage.


See the photos below: The Massoth LED Spot Light is definitely brighter at 12 - 22 volts compared to the minimum 5 volts. I've installed many of these Massoth LED Spots in LGB locomotive dcc sound conversions and they're great. Here's my plan: Connect a LBP307 Flat Bridge Rectifier 3A 700V to the smoke unit, connect to it a DC-DC Boost Converter 2A Adjustable Step Up Regulator Board Input 2V-24V to 5V-28V Output to provide 22 volts output to the LEDs. Does that sound workable?


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## krs (Feb 29, 2008)

It's workable but more complex and more expensive than it needs to be.
Do you already have the bridge rectifier and boost converter-is that why you want to use them?


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## LGB333$$$$ (Oct 11, 2017)

I recently bought these items on Amazon cheap.


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## krs (Feb 29, 2008)

Tom -
I quickly read through the Massoth manual for these lights.
One thing I should mention is that one English translation under Technial Specifications is wrong and maybe that creates some confusion.
On page 12 it states that with an applied voltage of 5 volts the light provides "normal brightness" and with an applied voltage of 22 volts = "remote light"
In German 22 volts = Fernlicht
Although "remote light" is the literal translation of Fernlicht, the meaning is totally different - Fernlicht really means "High Beam".
I would try the Massoth light as is with just the diode bridge, without the boost converter. Especially with the Mogul loco - I don't think that loco would have had a bright cab light in its day.


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## LGB333$$$$ (Oct 11, 2017)

krs said:


> Tom -
> I quickly read through the Massoth manual for these lights.
> One thing I should mention is that one English translation under Technial Specifications is wrong and maybe that creates some confusion.
> On page 12 it states that with an applied voltage of 5 volts the light provides "normal brightness" and with an applied voltage of 22 volts = "remote light"
> ...


Thanks for the great advice. As I mentioned, I've used these Massoth Spot LEDs in the last three ESU 5XL conversions of LGB locomotives I did for a customer, e.g., LGB Uintah for the headlight, cab light and custom-installed rear light. I use them with the full 22 volts input. And for my cutomer's LGB 2028D repair project, he specifically requested I install a cab light so he can see the engineer when running it outside at night. So, that's why I decided to use a brighter-output LED rather than a standard 5 v. incandescent bulb. 

All the technical inputs from everyone have been great.........I've never had a need to install LEDs on an analog locomotive before, only done so on the LGB DCC conversions I've done for customers.


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