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Snap-IT for Atlas, Peco, Bachmann EZ or other Twin Coil Switch Machines

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Dimensions: 1.80" x 1.50" (46 x 38 mm)
Control for one twin coil switch machine
Capacitive discharge for very low current draw of track power
Snap-It supports the full range of DCC accessory addresses (1-2044)
Easy address programming, no need to connect it to programming track
Simple hook up, 2 wires to the track, 3 wires to switch machine
Includes optional connections for "local" control push buttons
An external power supply can be connected for more power.


The NCE Snap-It stationary decoder is designed to operate a single snap action turnout motor. It measures 1.80 X 1.50 inches and is specifically designed for low current motors such as Atlas, Lifelike, Bachmann, etc., but it will operate high current machines such as the Nick & Jack International, Kemtron, or Rix with the addition of external capacitors or the use of an external power supply. The Snap-It uses a capacitive discharge technique to operate coil motor switch machines. In this technique, a capacitor is slowly (e.g. about 1.5 seconds) charge and used to store electrical energy. When a command is issued to operate the switch, this energy is released all at once through switch machine causing it to change position. The current pulse is large, but is present for only a short time (0.125 seconds) while the capacitor discharges so it will effectively operate the switch machine while preventing switch motor burnout and keeping the current drawn from the layout quite low.

The Snap-It supports address ranges from 1 to 2044 and is programmed directly on the main rather than by using the programming track. Pushbutton inputs are provided for manual switch operation. As delivered, one manual switch will open the points and the other will close them. A CV value change will cause the Snap-It to toggle the switch position with each push of either manual pushbutton. For those wanting to fine tune the Snap-It operation, the duration of the output pulse and the capacitor re-charge time are both programmable by changing the appropriate CV value.

Feedback

The Snap-It has no provision for cab bus feedback.

Programming

Programming is easy and does not require the use of the programming track. The Snap-It is designed for programming directly on the mainline. With power off, an included shorting plug is connected across the programming terminals. Track power is applied, and a switch command is issued to the desired address. The jumper is then removed. The Snap-It will now respond to the address issued when the jumper was present.

In addition to the address, the on time of the Snap-It can be programmed. This requires writing a value to CV 552 and requires that your system have a PROGRAM ACCESSORIES on the MAIN capability. The factory set pulse width is 125 milliseconds. It can be set from 1 to 255 milliseconds. I found the default value to work well with low current switch machines.

CV 550 can be set to vary the allowed recharge time of the storage capacitor. Acceptable limits are as high as 10 seconds. The default 1.5 seconds seemed to work well. Longer time will reduce the recharge current, but will also take more time before the Snap-It is ready to operate again.

Finally, CV 548 is set to enable the toggle option. In this mode, the point change position each time either manual control button is pushed. A 0 in CV 548 will disable the toggle option. In this mode, one manual switch will open the points and the other will close them.

Performance

On low current switch motors such as my Peco test load, the Snap-It work quite well right out of the box. However, I was unable to operate a Nick & Jack International twin coil machine using the Snap-It as I received it. I need to add 6,000 uF of extra capacitance in order to operate the NJI machine. The directions do cover this case, including Digikey part numbers for suitable capacitors, but 6,000 uF at 25 volts is a fairly large amount of capacitance. Two 3300 uF at 25 volts (parts recommended in the manual) will cost about $4.20. The manual also suggests that a separate power supply might be used. This would help if you are planning on using an array of Snap-Its with NJI machines to control your layout. One booster supply could operate all of the Snap-Its.

Recommendations

For low current switch machines, the Snap-It is a good choice. It operates the machines well, is easy to install and operate, and provides a very simple programming interface. The Snap-It may not be the best choice if you use high current switch machines such as the NJI twin coil machine. The required additional parts make the Snap-It less easy and more expensive to install. Other accessory decoders are more efficient at operating these high current switch machines (see Tony’s other accessory decoder reviews). If you like the Snap-It features and only have a couple of high current switch machines, then a couple of extra parts will have you up and running.

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