EZ DCC

EasyDCC AD4 Series Accessory Decoders

General: EasyDCC started as a series of how to articles in Model Railroader magazine. As a result of this heritage, there is a lot of documentation of their products in back issues of MR, and you can purchase their products as either completed units of a parts kit for self assembly. Clearly, the self-assembly approach results in significant cost savings if you don’t charge yourself by the hour on weekends and evenings. I was provided with two completed units, the AD4KA and the AD4HA.

These decoders are essentially the same unit, with the AD4KA optimized for stall motor switch machines and the AD4HA optimized for dual coil switch machines. The difference is that the AD4HA has its drivers jumpered directly to the output terminals, and can drive a maximum of 50 ma. This configuration is optimized to drive stall motor switch machines. The AD4KA has power transistors after the output drivers for increased current capability, and it has a built in capacitive discharge unit to ensure solid operation of dual coil switch machines. Both units use the same printed wiring board, and changes are made by selecting which parts are populated or not populated. Because of the way that the circuit is designed, a stall motor output will not work with a dual coil machine, and the unit configured for dual coil will not work with a stall motor switch machine. Since the same printed wiring board is used for both versions, all four outputs are configurable by changing hardware. If you start with an AD4HA and remove its output transistors and add two jumpers, you have a stall motor output. If you have an AD4KA and you remove two jumpers and add driver transistors you have a dual coil driver. In this case, you would also have to add some parts for the capacitive discharge unit, so if you are mixing outputs, it is probably better to start with the AD4HA.

When used for stall motor switch machines, the power to operate the switch machine comes from the track power or a dedicated DCC booster. For the dual coil switch machines, a separate AC power source is required to charge the capacitor in the capacitive discharge unit. The AC source can be the accessory output of an old power pack or a dedicated transformer such as the XFR4 from Tony's. The transformer does not require a large current output since it is only used to charge the capacitive discharge unit, it does not power the dual coil switch machine directly. You can customize the power source in terms of voltage and current to optimize switch machine response and recharge time. I used an XFR8 from Tony's to do my testing, although the 8 amp capacity is not required. Although the 2200uF capacitor supplied with the dual coil unit appears to be adequate, there is a provision for adding additional capacitance to increase the discharge capability.

The AD4 series provides four inputs for use with momentary push buttons. These inputs allow local manual operation of the decoder outputs. A unique feature of these inputs is that they can be locked out by writing the appropriate data to CV 514. The CV write can be done directly on the main. Thus, a dispatcher can lock out manual control of the decoders during a particular operation, and then restore manual capability once the operation is complete.

Connections: Connections to the AD4 series decoders are a little more difficult to do than with other decoders. The basic board has card edge fingers designed to mate with a card edge connector such as Mouser Electronics part number 15PC005. A second alternative is to solder in a screw terminal connector strip, also purchased separately. If you are really good, (and really lucky) holes are provided so that you can directly solder wiring to the printed wiring board.

Feedback: There is no provision for feedback to the cab bus. This must be provided by a separate unit.

Programming: Programming the AD4 series of decoders is very easy. I first used the programming track. My NCE system was able to read and write to all the required CV locations. I was also able to write to the units while connected to the main tracks. Using the Program Accessory mode of my NCE system, I could write (but not read) each CV while the unit was installed on the layout. This is handy if you need to modify the configuration after the unit is installed. The AD4 series also has a broadcast feature. By writing to a CV at address 511, the data are written to the specified CV of all AD4 series decoders. Thus, with a single write, all of the manual inputs to all decoders could be locked. Later, a single write to CV 514 of address 511 could re-enable all manual inputs.

I tried unsuccessfully to program the AD4 units with the PR1 programmer. The PR1 does have a programming module for the AD4 series, but I was unable to get it to either read or write address or configuration data.

Manual: The manual is not supplied with the units. It is available by download from the EasyDCC site at http://www.cvpusa.com/. The manual is well written and provides all the information necessary to get the decoders up and running. It has examples of mixed configurations, shows various wiring strategies, has an example of how to build a card cage for multiple units, and in general is an excellent resource for installing and operating the decoders.

Performance: I tested the AD4KA with the Tortoise™ stall motor switch machine and the grain-of-wheat bulbs without external power (power supplied by track DCC). The Tortoise™ ran very well. I measured 9.9 volts stall and 10.8 volts running. These values will provide top performance out of the Tortoise™.

The grain-of-wheat bulbs were tested in the flashing mode, such as would be used for a crossing guard. The flashing worked well with about 10.5 volts on the bulb, and could be programmed from 0.1 to 12.7 seconds per flash. One to two seconds actually looks best. One minor problem that turned up, the flashing turned ON when my NCE system said I was turning the accessory OFF, and turned OFF when the controller ordered it ON. Although backwards, this is a minor problem.

To test the dual coil machines, I switched to the AD4HA. This decoder is the only unit that I tested other than the Lenz that was able to operate the Nick & Jack International dual coil machine. It operated the NJI unit with AUTHORITY! Action was solid and repeatable in both directions with excellent force for moving mechanical systems. This performance is a result of incorporating a capacitive discharge unit directly into the decoder along with high current output transistors. The capacitor voltage measured 25.0 volts using my XFR8 18VAC supply. The short term current into the NJI switch machine would be in excess of 12 amps. This high current pulse ensures proper switch machine operation. The capacitor discharges quickly, so there is no chance of burning the switching coil from too long an operating pulse. Since the AD4HA was able to operate the NJI dual coil machine, it had no trouble at all operating the Peco dual coil unit. Again, the operation was solid and reliable with excellent throw force. Both of these tests were done with a 0.2 second pulse. Difficult loads could go to a wider pulse width. Remember that the energy comes from the capacitor, and once it is discharged, increasing the pulse width will not increase energy to the load.

I tried the AD4HA with the accessory motor. It really is not designed to run this type of motor. There is no way to connect the motor to reverse, so an external reversing switch is necessary if you need to run in more than one direction. I was able to run the motor in pulses of about one second. This was about the time it took the motor to discharge the capacitor and then coast to a stop. This might be useful in an accessory that only needed a short burst of rotation, such as a coal loader, to release the rest of the mechanism.

The AD4HA will drive a lamp that draws more current than the grain-of-wheat bulbs that I used. Be careful since the bulb will be subjected to the full charge voltage of the capacitive discharge unit.

Recommendation: I found the AD4 series of decoders to be well designed and to operate well with their designated loads. The AD4 decoders are a Best Choice for layouts with mixed stall motor and dual coil switches since the outputs can be customized switch by switch. It is also a serious contender for layouts that use bi-stable switch machines such as the Nick & Jack International unit. Its performance is equal to the Switch-It, and would be useful where four switches are in close proximity. If you are not put off by doing your own assembly, the AD4 series of decoders has the potential of providing the lowest cost per switch of all of the stationary decoders tested. The fully assembled units are also quite cost competitive.