Capacitive discharge turnout throwing

[lionelsoni]

In the past, I have described the capacitive-discharge scheme that I use for throwing O27 turnouts, to allow them to operate from an auxiliary (DC) supply without risking coil burnout from the anti-derailing feature.  I use a 5000-microfarad aluminum electrolytic capacitor, charged through a 100-ohm, 10-watt resistor.  The recharge time of this circuit, to 95 percent, is 1.5 seconds.

I recently started to replace the rather crude, unregulated DC supply that I have been using (just a half-wave rectifier running off one Z-transformer output) with a regulated, overcurrent-protected 16-volt supply.  Some of my turnout combinations can throw as many as 7 at one time, which would draw 1.12 amperes momentarily.  Unfortunately, the new supply puts out only about 2.5 amperes, most of which I wanted to reserve for future signal circuits.

So I discovered a better way to charge the capacitors, using number-53 lamps.  I group together any turnouts that can be thrown together in combination and power the entire group from the same capacitor, as large as needed for the maximum number thrown at a time.  Then I recharge the capacitor through the lamp(s) instead of a resistor.  The resistor charging time (to 95 percent) is 3RC, where R is the resistance and C is the capacitance.  The lamp charging time is 2.222CV/I, where V and I are the lamp's rated voltage and current, 14.4 volts and 120 milliamperes for the number 53.  The  charging time using the lamp is to a virtually complete charge, not just 95 percent.

For example, I am powering all 7 turnouts in my yard throat, 3 of which can throw at once, from 10000 microfarads (a little less per turnout than I used before) and recharging with a single lamp.  Although I am using a 14.4-volt lamp with a 16-volt supply, the lamp voltage is about right, since the coil resistance drops a little of the voltage.  So the peak recharge current is only 120 milliamperes; and the recharge time is 2.7 seconds, which is not as long as it takes me to realize I made a mistake and want to select a different track.

The lamp also lets me know when charging is complete, by going dark.

[USNRol]

Sounds neat. Got a schematic of that setup?  Your method requires the "MOD" to be done to the 1122 switches right?  So the theory is that when the train completes the non-derailing circuit the CAP charge throws the switch once but discharges and stays discharged while the train continues to keep the non-derail circuit closed; all the while keeping your light lit?  Then when the train moves off the switch the CAP charges back up through the light in a couple seconds.  Does the lamp current flow through the switch coils?  I guess .12 amps won't bother them?

I think it's been discussed before, but would you need to do anything special to get the 1122 switch to work with the DC power?

Neat way to get the best of both worlds...park trains on switches and retain non-derail feature without melting spools in the switch.

Roland

[lionelsoni]

It seems like you understand it perfectly.  It is necessary to disconnect the coil common from the center rail inside the switch, which can be a pain if you're not lucky enough to have some slack in the wires already.  The capacitor goes between the track common (outside rails) and the coil common.  You're right that the lamp current does flow through the coil but isn't enough to harm it.

What's new for me is using a single capacitor for a larger group of turnouts.  This requires more capacitance, since my diode logic can throw a bunch of turnouts at once.  This led me to using a lamp for a faster recharge without increasing the recharge current very much, to avoid loading my new power supply.

So far I have two groups of 7 converted.  In the first group, I used 10000 microfarads and a number 53 lamp, since no more than three can be thrown at once.  In the second group, I used 20000 microfarads and a number 432 (14 volts, 240 milliamperes) since all 7 can sometimes be thrown at once.

Now I'm working on a group of 4, with a maximum of 2 thrown at once.  This group has its controls split between two places on the layout; so I can't easily put a single lamp at the controls.  Instead, I have installed an old number 260 lighted bumper on a completely isolated little piece of track at the end of a nearby siding.  I'll use a number 53 amp in it to recharge the group's capacitor.