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Old 10-12-2018, 08:03 PM   #1 (permalink)
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Default Delay/Soft Start With Sound Enhancement for Instantaneous Starts

I have a Delton Doozy in which I installed a Phoenix 2K2 sound card. The sound card is programmed as a Galloping Goose with a klaxon horn and will do the sound of the operator opening and closing the cab door and starting the engine (takes three tries to catch) if you provide about 2 volts to sound card. The entire routine takes a bit over 20 seconds to completion.

My Doozy and AristoCraft railbus typically run point-to-point (P-T-P) during open houses. The railbus also has the Phoenix 2K2 card programmed as the Galloping Goose but with a standard horn. In the past I devised a method to make the railbus wait and go through the start routine when it receives an instantaneous voltage, such as when running P-T-P, but function as normal when the voltage is “ramped up.” The circuit involves a delay module that uses a 555 timing chip, assorted components, and relays to delay the engine, and a “low voltage” board to provide the start-up routine voltage (~2 volts) that is readily available through Banggoods in China. These are $3.21 (less in quantities).

The delay module can be used to either postpone the engine’s motion, or provide a “soft start” for that motion. In the past, I had constructed the delay module from its individual components. But Banggoods now offers a module that will do a delay, firing its relay, and is almost ready to go for just $2.04 (less in quantities). This is less than I was paying for just the relay when constructing the circuit from scratch.

In this case we only need to make a slight modification to the module replacing one capacitor to extend the timing, if desired. The delay only goes for up to ~11 seconds using the 100 mfd capacitor already mounted on the board. If one wanted to delay the engine for this period (e.g., a “soft start” or a “leap frog” situation and you don’t want the second train to leave as soon as the first arrives), the existing capacitor is fine. Longer delays can be had simply by changing this capacitor to a higher value. I used a 330 mfd, 25 volt cap to get up to ~36 seconds of delay.

The delay timing is easy to estimate. Just divide the value of the capacitor by 10 and multiply the resulting value by 1.1 to get the total time in seconds. For example; 330 mfd / 10 x 1.1 = 36.3 seconds. This is the maximum duration that the onboard relay will stay fired, but the onboard pot will allow you to reduce the timing to any lesser value.

These delay modules are rated for 12 volts. But we want to be able to run the trains up past 20 volts. And we only want the delay feature to kick in if the voltage is instantaneous, such as when used with a reversing unit or in a “leap frog” situation, etc. If we “throttle up” the voltage, we are driving the train, and don't want the delay. We also need to consider that the polarity of the voltage to the wheels will continually change and the delay module needs a “dedicated” plus and minus.

Polarity is handled with a bridge rectifier placed before the delay module and low voltage board, if used. The rectifier will properly route the plus and minus voltages to the boards regardless of the track polarity.

When running at more than 12 volts to the rails, the “overvoltage” to the delay module is handled using a 470 ohm resistor on its input. With the resistor in place, the voltage at the module will not exceed the 12 volt rating relay until the track is well over 20 volts.

Of course it is rare to run at these speeds and the Doozy will be run P-T-P at 12-14 volts. At these voltages the 470 ohm resistor will restrict the current to the delay module such that it has enough power to run the electronics, but not enough to make its relay “fire.” Therefore we need an instantaneous “blast of current” to fire the relay, and let hysteresis hold it closed.

This is accomplished by placing a 220 mfd (25 volts or more) capacitor in parallel with the resistor. The capacitor will pass a pulse of current around the resistor allowing the relay to fire then saturate itself so that the input voltage instantaneously drops to that allowed by the 470 ohm resistor. And while this voltage is not enough to fire the relay, it is plenty to hold the relay closed. When the voltage to the wheels is removed, the capacitor will discharge itself through the resistor and is ready for the next pulse.

The noted part values will actually activate the delay module when an instantaneous voltage of ~10.5 volts is applied to the rails. If a lower voltage is applied and ramped up, the capacitor will saturate and will not pass the necessary pulse of current to fire the relay so the Doozy will “drive” like any other engine.

If one simply wanted to delay the engine without including the low voltage board for sound enhancement, it is a matter of using the common and normally closed contacts of the onboard relay connected in series with one side of the motors’ terminals. When a pulse of track power is received, the delay module will open the circuit to the motors and the engine will wait for the set duration before moving on. If a resistor is placed between the relay’s normally open and normally closed contacts, a reduced current will pass to the motors slowing its speed until the delay ends. The value of the resistor will depend on the desired speed and the motor in the engine. Values of between 4 and 10 ohms provide a nice speed reduction for most G-scale requirements. A higher value may be used in some applications (e.g., pull the slack out of the coupler before the engine moves off). Use at least a 20 watt resistor in this application. The schematic is included below.

If we want to take advantage of the Phoenix sound card’s starting routine, we need to add a 4pdt relay to the circuit. This relay is activated by the relay on the delay module and simultaneously breaks the power to both sides of the motors and routes the low voltage board’s output to the sound card.

Again, we’ll use a 12 volt relay with a series resistor to reduce the voltage when running at higher speeds. I used a nonpolarized relay (Aromat NF4EB-12V) so the + and – are irrelevant to its operation and I connected it directly to the wheel pickups through the series resistor. If using a polarized relay, connect it at the + and – from the bridge rectifier, as appropriate. Also, I found with the Aromat relay that a 220 ohm resistor would fire the relay at about 8.5 volts to the rails. Because this is less than the 10.5 volts required to activate the delay module, it will not present a problem. Additionally, I noted that the voltage at the Aromat was about 12 volts when the track was at 20 volts so overvoltage should not be a problem burning out the relay. In this case, no additional capacitor was necessary to trigger the relay.

As noted, the Phoenix start routine takes a bit over 20 seconds, so to include the entire routine one would change the capacitor on the delay module to no less than 220 mfd (25 volts or more). A larger value (e.g., 330 mfd) will just let the rail bus sit at idle and warm up the engine a bit longer if desired. The schematic for the delay with sound enhancement is included below.

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Old 10-14-2018, 03:49 PM   #2 (permalink)
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I found that on the bench and running in the engine are a bit different because of the resistance imposed by the wheel contacts. I've reduced the value of the 470 ohm resistor to 39 ohms and the 220 ohm resistor to 100 ohms to get reliable starts. Again, the unit works as normal if the voltage is ramped up, but with the reduced resistance the unit will trigger the relay if the track voltage gets to about 18 volts even when ramped. This is fine for my purposes running down at 12-14 volts, and I can turn it off if I wanted to run faster. The Doozy is only designed to run up to 12 volts and I've added resistance to the motor and wired the three lights in series allowing this train to run with the Aristo Railbus and USA 44-tonner, which run too slow at <12 volts.

If one wanted to use this feature and run at higher voltages with it turned on, raise the resistor values a bit and just test it by ramping up the voltage to the wheels to be sure that it doesn't trigger before you reach the maximum operating voltage.
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Old 10-17-2018, 04:40 PM   #3 (permalink)
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Sounds like a nice set up.
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Old 10-21-2018, 07:59 PM   #4 (permalink)
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Real world testing revealed that the carbon pickups on the Doozy induce a voltage drop such that the use of the 470 ohm resistor and 220 mfd capacitor are unnecessary and actually a hindrance. Other engines with less voltage drop should be able to use the original circuit, perhaps reducing the value of the 470 ohm resistor.

The voltage drop across pickups on the Doozy is so great in fact that the bridge rectifier was replaced with a combination of a relay and diode. When 12 volts was applied to the rails, only about 8 volts was actually getting to the delay module without any resistor or capacitor in place at all. The replacement of the rectifier reduced the voltage drop by about 0.8 volt. This is not illustrated in the schematic. Most engines should be fine using the rectifier though.

Last edited by toddalin; 10-21-2018 at 08:19 PM.
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