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Constant voltage headlights

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Posted by lionelsoni on Tuesday, December 22, 2015 8:02 AM

You're welcome!

Bob Nelson

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Posted by Frisco Brakeman on Tuesday, December 22, 2015 12:06 AM

as soon as I got  this info, I went and ordered this mag. I just got today and so far I've read about half of the article, it looks like what I'm wanting to know, Thank you so much.

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Posted by Sturgeon-Phish on Monday, December 21, 2015 8:54 AM

Neat idea Bob, good job!

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Posted by JTrains on Friday, December 18, 2015 7:55 AM

lionelsoni

Strictly speaking, they aren't both lit--at the same time.  They alternate on the successive half-cycles of the AC voltage, but too rapidly for our eyes to see that.

Ah ha - never thought of using LEDs that way.  Pretty clever!

IT consultant by day, 3rd generation Lionel guy (raising a 3YO 4th generation Lionel Lil' Man) by night in the suburbs of the greatest city in the world - Chicago. Home of the ever-changing Illinois Concretus Ry.

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Posted by lionelsoni on Friday, December 18, 2015 7:51 AM

Strictly speaking, they aren't both lit--at the same time.  They alternate on the successive half-cycles of the AC voltage, but too rapidly for our eyes to see that.

Here's an excerpt from the Wikipedia article on "antiparallel":

"In electronics, two anti-parallel or inverse-parallel devices are connected in parallel but with their polarities reversed....Two LEDs can be paired this way, so that each protects the other from reverse voltage. A series string of such pairs can be connected to AC or DC power, with an appropriate resistor. With AC, the LEDs in each pair take turns emitting light, on alternate half-cycles of supply power...."

Bob Nelson

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Posted by JTrains on Thursday, December 17, 2015 10:42 PM

lionelsoni

However, there is an even better way:  Wire two LEDs in antiparallel (each LED's cathode connected to the other's anode).  

"Anti-parallel" - that's a new one for me! I have a modest understanding of electricity, but how is it that both LEDs are lit and not just the one that's conceptually "facing forward"?

IT consultant by day, 3rd generation Lionel guy (raising a 3YO 4th generation Lionel Lil' Man) by night in the suburbs of the greatest city in the world - Chicago. Home of the ever-changing Illinois Concretus Ry.

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Posted by lionelsoni on Thursday, December 17, 2015 8:14 PM

Well, if I do say so myself, I recommend the article I wrote for the September, 2008, CTT.

Bob Nelson

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Posted by Frisco Brakeman on Thursday, December 17, 2015 7:53 PM

wonderful info but maybe a circut layout to see, I was thinking something in the line of LED's but thats new area for me  and don't understand all the extras you have to add to make it work. As a matter of fact I would like to convert all my incondesant light bulbs to LED's such as passenger cars and caboose's. Even some books or litature you can recomend would be helpful. I'll gladly track it down and buy for my library.

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Posted by Frisco Brakeman on Thursday, December 17, 2015 7:48 PM

JTrains
 
Frisco Brakeman

I have a several lionel mpc steamers and diesels and would like to know how to go about converting them to constant voltage headlights?

 

 

What specifically are you trying to achieve (i.e., the lamps staying on even when the train is stopped, the lamps remaining the same brightness regardless of how fast the train is going, etc.)?

 

Yes lamp bright from start to stop, no dim to bright to dim.

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Posted by lionelsoni on Thursday, December 17, 2015 7:27 PM

An incandescent lamp has the disadvantage that its light output varies approximately as the 3.5 power of voltage.  This means that when you double the voltage, the brightness goes up tenfold.  However, the brightness of an LED in series with a ballast resistor varies in nearly direct proportion to the voltage.  It also puts out the same color whatever the voltage, unlike an incandescent, which becomes distinctly yellowish at low levels.  So, simply replacing incandescents by LEDs goes a long way toward hiding the effect of varying voltage.

However, there is an even better way:  Wire two LEDs in antiparallel (each LED's cathode connected to the other's anode).  Then wire that combination in series with a couple of incandescent lamps.  (I recommend the number-53 lamp.)  This replaces the ballast resistor and has the advantage that the lamp resistance increases with voltage, thus reducing the variation of the current through the LEDs and therefore also reducing the light variation even further.

You will have to hide the incandescent lamps, and one of the LEDs if you don't have a need for two.  I just now hooked up this circuit and found that, except at low voltage before it shuts off, the brightness variation is practically imperceptible. 

Bob Nelson

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Posted by Firelock76 on Thursday, December 17, 2015 6:28 PM

I'm not sure it's even possible unless the engine's designed for it to begin with.  Williams constant voltage headlights operate off a circuit board separate from the main one.  I believe MTH's work the same way. Considering you're working with MPC era units bear in mind you'd have to convert in incoming AC to DC and THEN connect the DC current to a proper circuit board and then power the lamp from the board.

Personally I don't think it's worth the headaches.

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Posted by JTrains on Thursday, December 17, 2015 4:15 PM

Frisco Brakeman

I have a several lionel mpc steamers and diesels and would like to know how to go about converting them to constant voltage headlights?

What specifically are you trying to achieve (i.e., the lamps staying on even when the train is stopped, the lamps remaining the same brightness regardless of how fast the train is going, etc.)?

IT consultant by day, 3rd generation Lionel guy (raising a 3YO 4th generation Lionel Lil' Man) by night in the suburbs of the greatest city in the world - Chicago. Home of the ever-changing Illinois Concretus Ry.

  • Member since
    January 2014
  • From: Rogers,Ar
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Constant voltage headlights
Posted by Frisco Brakeman on Thursday, December 17, 2015 12:19 PM

I have a several lionel mpc steamers and diesels and would like to know how to go about converting them to constant voltage headlights?

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