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Decoder System Design

ACC Decoder Installation Specifications

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General

Cable layout and design is relatively simple for an ACC decoder system. The general rule is to run the two-wire paths in the pipe trenches, so that they pass near each valve location. In special circumstances, or if cable sizes need to be trimmed down to a minimum, the formulas in this document can be used. The second section of this document describes how to design the surge protection system.

Cable

It is important to always use a solid core, color-coded, twisted-pair cable. The twist of the cores protects the system from most types of noise and small surges. This is the same technology that has been used by telephone and data companies for many years (with smaller wires). Do not use 2 straight single cores, even though it works in most cases, as the surge resistance will be diminished. The size of cable can be selected depending on run distance and the number of passive and active decoders on the path.

As a general rule, IDWIRE1 (14 AWG/1.6 mm dia./2.08 mm2 area) is recommended for wire path length up to 10,000 ft (3,000 m) and IDWIRE2 (12 AWG/2 mm dia./3.31 mm2 area) for wire path length up to 15,000 ft/4,500 m (see unique wire run specifications for DUAL). These maximum wire path lengths are for activating 2 Hunter solenoids with up to 104 decoders idle in the system (97 station decoders, 2 P/MV decoders, and up to 5 sensor decoders). If the system is required to activate more than two solenoids at a time, the maximum wire length must be calculated. For a more exact maximum length, check the Cable Design Formulas section. Note that it is NOT the total system cable length, it is the length from the controller to the furthest away decoder on each path.

Avoid running power cables and decoder cable in parallel, especially if they are close. If a high voltage cable must be crossed, it is best to cross at right angles.

Layout

The maximum number of decoders on one ADM-99 output module is 99 stations, 2 pump/master valves, and up to 5 sensor decoders. Each of the station decoders can have a maximum 2 Hunter solenoids per decoder output.

A cable path can be branched off as many times as necessary. If the branches are long, use a decoder cable switch device to isolate the branches for troubleshooting purposes.

On normal installations, no calculation on wire path length is needed if the general design rule (two maximum stations active at once) are followed. 

Under special circumstances, the formulas below can be used. These formulas assume that the decoders are spread evenly over the wire path. A more exact calculation can be done, knowing:

  • Maximum allowed voltage drop is 14 V
  • Passive (standby) decoder current is approximately 3.5 mA
  • Active solenoid current is approximately 45 mA per solenoid

Using these values and Ohms law, the wire path can be sectioned up and calculated exactly. Do not design a system with a 6 station decoder and 2 solenoids per output (12 total solenoids) at the end of the wire path, unless the maximum wire length has been calculated. 

It is best practice to reduce the maximum wire length by 25% to compensate for wire connections, different types of solenoids, and aging of in-ground copper. 

Note that it is only the individual wire path lengths that matter, not the total length of all paths.

One controller can theoretically handle a 101-station system (including 99 stations and 2 Pump/Master Valves), but if large numbers of stations must be operated simultaneously, maximum length of the cable must be calculated.

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