Summary of common problems with RS485 converter

Question 1: What is an RS485 converter?

An RS485 converter, also known as a 485/232 converter, is a device that enables communication between a computer's RS232 serial port and an RS485 bus. It acts as a bridge, allowing data to be transmitted over longer distances and supporting multi-device communication, which the standard RS232 interface cannot handle on its own.

Question 2: What is the purpose of an RS485 converter?

The main purpose of an RS485 converter is to overcome the limitations of traditional RS232 communication:

• RS232 has a limited range—typically no more than 13 meters in real-world applications.
• RS232 only supports point-to-point communication, meaning one serial port can only connect to a single device.

With an RS485 converter, you can extend the communication distance up to 1200 meters (theoretical) or around 800 meters in practice. Additionally, it allows multiple devices to be connected on a single RS485 bus, making it ideal for networking systems. Depending on the chip used, a single bus can support up to 32, 64, 128, or even 256 devices, though it’s recommended to use only one-third of the maximum number for stability.

These converters are widely used in industrial automation, access control, surveillance, building intercoms, parking systems, and attendance management, where reliable long-distance communication is essential.

Question 3: How to choose an RS485 converter?

It’s best to go for a genuine, branded converter rather than a generic one. Although the price difference may be small, cheaper alternatives often use low-quality or recycled chips, which can lead to instability and performance issues.

Also, consider using an active converter instead of a passive one. Active converters come with their own power supply, while passive ones rely on the computer’s power, which can cause problems. Active models are usually compact, similar in size to a cigarette pack, while passive ones tend to be slightly larger.

Passive converters are generally less reliable. They often lack proper anti-interference and protection features, leading to unstable communication and potential damage from electrical surges or lightning strikes. Their performance tends to degrade when multiple devices are connected or when used over long distances.

Question 4: Is it necessary to use an opto-isolated RS485 converter?

Opto-isolated converters offer better noise immunity compared to standard models. However, their lightning protection is often based on a "self-destruct" principle, where the front end is sacrificed to protect the back end. While this can help prevent damage, it may increase maintenance efforts. When purchasing such a converter, always ask about its actual lightning protection capabilities before making a decision.

Question 5: What is the load capacity of an RS485 converter?

Load capacity refers to how many devices can be connected to the same bus and how far the furthest device can be located. This depends not only on the converter but also on the design of the connected RS485 devices. Both must be of high quality for optimal performance.

Some untrustworthy manufacturers may exaggerate the load capacity of their products. To verify this, it’s important to understand the chip specifications and perform real-world tests. There is often a significant gap between the advertised value and the actual stable performance in practice.