Allen-Bradley 1785-L30B PLC-5/30 Controller | 32K Memory

Allen‑Bradley 1785‑L30B PLC‑5/30 Processor – Reliable Control for Medium‑Scale Automation

The Allen‑Bradley 1785‑L30B is a trusted member of the PLC‑5 controller family. This processor is designed for mid‑sized applications that demand balanced memory, I/O capacity, and communication flexibility. First, it provides 32K words of user memory, which is sufficient for moderate logic, arithmetic, and data‑handling tasks. Meanwhile, the battery‑backed static RAM preserves your program and data during power outages. For added security, you can install an optional EEPROM module (such as the 1785‑ME16, ‑ME32, ‑ME64, or ‑M100) to store a permanent copy of the user program.

I/O Capacity and Remote Rack Support

When it comes to I/O handling, the 1785‑L30B offers remarkable flexibility. It supports a total of 1024 I/O points in any mix of discrete and analog types. Alternatively, you can configure it for complementary operation with 1024 inputs and 1024 outputs simultaneously. Furthermore, this controller manages up to 29 I/O chassis in total. Specifically, 28 of those can be universal remote I/O chassis, while it does not support extended local chassis. This makes the 1785‑L30B an excellent choice for distributed control architectures.

Additionally, the I/O scan time depends on your baud rate: 10 ms per rack at 57.6 kbit/s, 7 ms at 115.2 kbit/s, and just 3 ms at 230.4 kbit/s. Therefore, you can optimize system speed by selecting the appropriate communication speed for your application.

Embedded Communication Ports

The 1785‑L30B comes with three built‑in communication interfaces. First, there are two combo ports (Channel 1A and Channel 1B) that can function as DH+ or Remote I/O (RIO) scanners or adapters. This dual‑role capability lets you build peer‑to‑peer networks or connect remote I/O racks without extra modules. Second, a dedicated 25‑pin serial port supports RS‑232, RS‑423, and RS‑422A standards. You can configure this port for ASCII, DF1 full‑duplex, DF1 half‑duplex master, or half‑duplex slave protocols. Moreover, an 8‑pin mini‑DIN connector on Channel 1A also facilitates DH+ connections. For Ethernet‑based architectures, you can add an optional Ethernet interface module to the system.

Front Panel Indicators and Mode Control

For easy diagnostics, the front panel includes several LEDs. The BATT indicator shows battery status, while PROC reflects the controller’s operating state. Moreover, the FORCE LED lights up when I/O forces are active, and the COMM indicator monitors serial port activity. Additionally, Channels 1A and 1B have their own status LEDs. A three‑position keyswitch lets you select between RUN, PROG, and REM modes. In RUN mode, the processor executes the logic and energizes outputs. PROG mode halts execution for programming and configuration. REM mode allows remote programming while the controller continues running. This design gives you clear visual feedback and flexible control over system operation.

Power Requirements and Environmental Specifications

The 1785‑L30B draws 2.3 A from the backplane at 5 V DC and dissipates approximately 12 W of power. It works with power supplies like the 1771‑P4S, ‑P6S, ‑P4S1, and ‑P6S1. For operating conditions, the controller functions reliably between 0 °C and 60 °C (32 °F to 140 °F). When not in operation, it can withstand temperatures from ‑40 °C to 85 °C (‑40 °F to 185 °F). This wide temperature range ensures durability in various industrial settings.

Battery Backup and Program Protection

The 1785‑L30B uses a 1770‑XYC battery to maintain memory when external power is off. At 60 °C, a fully charged battery lasts up to 84 days with the controller powered down. If the battery is at 50 % charge, it can last up to 150 days. When the BATT LED turns on, you still have approximately 5 days of operational battery life remaining. After the battery drains completely, the memory content remains intact only while power is applied. Once you remove power and the battery is dead, the user program will be lost. Therefore, we recommend replacing the battery promptly when the BATT LED illuminates.

Installation Considerations

Mount the 1785‑L30B in a suitable chassis with the correct power supply. Ensure proper ventilation and maintain the ambient temperature within the specified operating range. Use shielded cables for serial and communication connections to reduce electrical noise. Additionally, verify that the backplane current does not exceed the capacity of your selected power supply. The module fits standard PLC‑5 racks, and you can install or remove it without powering down the entire system.

Frequently Asked Questions

1. What is the maximum number of I/O points for the 1785‑L30B?
The 1785‑L30B supports up to 1024 I/O points in any mixed configuration. Alternatively, you can use 1024 inputs and 1024 outputs in complementary mode.

2. Can this controller communicate over Ethernet?
While the 1785‑L30B does not include a built‑in Ethernet port, you can add an optional Ethernet interface module to connect to an Ethernet network.

3. How long does the battery last on the 1785‑L30B?
At 60 °C, a fully charged battery lasts about 84 days with the controller off. At 50 % charge, it lasts up to 150 days.

4. What happens when the BATT LED turns on?
The BATT LED indicates low battery voltage. You still have roughly 5 days to replace the battery before data loss occurs.

5. Does the 1785‑L30B support remote I/O racks?
Yes, it supports up to 28 universal remote I/O chassis. It also works with a maximum of 29 total I/O chassis when combining local and remote racks.