Protecting Lionel No. 1121 and 1122 swtiches from smoking

[San Jose]

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 I have read many posts on the clever idea of using a resistive load in series with a capacitor to turn the voltage off on Lionel No. 1121 and 1122 switches even while a train is sitting on the switch.   I tried a GE53 lamp (35 ohms) in series with a 3300 microfarad capacitor and there is not enough power to switch; a variety of lamps with resistances from 2 ohms to 35 ohms gave the same result, as well as a 2.2K resistor.   I have tried double to capacitance in case the time constant was too short to activate the switch and there was no change.  

I must be missing something but am not sure since the circuit seems to be simple:  13.3 volts DC to the bulb, the other side of the bulb to the switch coils as well as to the positive side of the capacitor and the negative side of the capacitor to ground.   Without the resistive load, the switch works fine.   I do not have a controller hooked up.

A friend did concoct a relay-activated solution which works well but it’s more complicated than the lamp/capacitor idea.  Since I have five (5) No. 1121 and five (5) No. 1122 switches in my layout, that’s a lot of soldering etc. for this lazy railroader. 

Nino from San Jose

 

[lionelsoni]

The resistor or lamp affects the recharge time, but shouldn't have anything to do with whether the turnout throws.  There's no point in measuring the lamp's resistance, since that varies widely with the filament temperature.  The important thing is that the lamp's current at the DC supply voltage should be less than what the coils draw at that voltage.  The number 53 draws 120 milliamperes at 14.4 volts, which is ideal.

I use 5000 microfarads, which gives about a 50-millisecond time constant for discharge.  Since you tried two 3300-microfarad capacitors in parallel, the capacitance is probably not the problem.

The lamp should be completely dark most of the time.  When you throw the turnout, it should light up fully, then dim down to nothing in a second or two.  The lamp in the turnout should not be powered from the capacitor, but should remain connected to the center rail or, if you want, connected to an accessory  voltage supply.  To be sure you haven't included the turnout lamp in the circuit, just remove the lamp while testing.

Have you tried raising the voltage?  13.3 volts may be a little low.  I just measured mine, which I seem to have set at 19 volts; but I'm using several layers of diode logic, which eats up a few volts.  I would recommend 16 volts for a simple turnout.

[gunrunnerjohn]

To add to Bob's excellent suggestions, you need to make sure the switch moves mechanically very easily, if there's any binding or friction, you'll probably have issues with the capacitive discharge scheme.