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What is the J&C Studios O Gauge Archive?
(Guest)   JCS Archive   Dale H   Converting Marx towers to LED lighting
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Converting Marx towers to LED lighting
Dale H
Joined: Sep 25, 2010
Topics: 32 Replies: 39 Topics: 32
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posted Mar 30, 2013: 

Purchased a bunch of these at York for a layout I am building,some are in better condition than others but none of them light when power is applied,a few have dead shorts so rewiring is in order for some. There are replacement screw in LED lights but they do not offer a whole lot of light appropriate for Floodlight towers.

Instead I chose to hard wire using 26 gauge black wire with extra bright 5 chip LEDs. These are 8mm warm white 100ma, not the more common 20 ma LEDs 3.2 volts forward. LED view angle is 140 degrees. Shown here along with a 1 amp bridge rectifier. Two are insulated with shrink tubing for installation into the towers.

Here is a wiring diagram. Note it is for 12VAC input. Adjust resistor value accordingly. Since these are 100ma pay attention to wattage as well as ohm value. The resistor in this application uses .56 watts,thus 2, 120 ohm are used in parallel

First step is to remove the backs of the socket,not always easy,I drilled them out ,care must be taken not to spin the socket from the housing.Then they are bent a little to make room for the LED leads

Next the LEDs are pushed in from the front,a loose press fit. The leads protrude out the back.

Then wires wire run down and fished out of a lower hole,where the bridge rectifier is to be mounted.
Appropriate wires are soldered to the bridge and LED leads. Tin all connections and wires,then tack on. I used a Weller 100/140 gun but a 25 watt pencil tip one is fine. Solder quickly to minimize heat

The bridge is insulated with shrink tubing and pushed into the tower body. The 2 AC lead wires go through the bottom hole. One wire connects to the resistors,insulated with shrink tubing in series to the frame body. The other terminal goes to the screw insulated from the body.

Here is a tower stood up with LEDs inserted

Now we bench test applying 12VDC. Hard to show in a photograph and I have no scientific measuring,but the LEDs appear at least as bright as original bulbs. No bluish appearance at all with a spectrum a bit whiter than bulbs. Power consumption with 12 volt AC input is 1.2 watts, a bit over half used by the resistor,where as bulbs would use 5 to 8 watts.

Since the LEDs are press fit in the socket and loose,a bit of silicone is placed in the back to lock them in and keep them from moving. I used red here so it would photograph,but black or clear silicone is better looking and less noticeable

Here is conversion of the Marx single bulb spotlights

First it is disassembled,front lens and back come off by twisting and pulling

A little different then the double bulb flood towers,the leads are shortened and 2 wires are soldered on,then shrink tube is added to insulate. The green wire is minus.

I then wrap a bit of tape around to make sure leads do not touch socket body

After drilling out the back of the socket, I put a dab of clear Silicone in the socket then insert the LED with wires and let dry.

As with the other towers the wire is snaked through and soldered to the bridge rectifier.

As in the first tower,the rectifier is insulated then the wires inserted through the tower bottom. One wire goes to the insulated post,the other goes to the ground post connected in series with a resistor. The super bright 5 chip LED is 100ma,3.2 volts forward drop so,ignoring the voltage drop of the bridge rectifier, for 12VAC input, this calls for an 88 ohm 1 watt resistor. To make it I combined 2, 330 ohm and one 240 ohm half watt ones in parallel. This makes up about 95 ohms resistance,close enough.

Here is the tower assembled,then lighted. Seems as bright as the original with a bulb like appearance in spectrum to my eyes.

This makes 16 total towers converted for the layout I am building. At 1.2 watts per tower 16 of them will use about 18 watts and hopefully not need LED replacement. Light bulbs would use maybe 60-80 watts,depending on bulbs used. After you do a few the conversion is easy,perhaps as easy as dealing with the bad wiring,loosing ground through the rivet that swivels, loose or corroded sockets etc, to get them working.

When using LEDS in open application,one should not stare right into the LED. Be advised if children are present.

Dale H


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