1606-XLSRED New In Box 1606XLSRED PLC Module Input Voltage 24-28V DC
PRODUCT DETAILS
1606-XLSRED — 24V DC Redundant Power Supply Module for 1606-XLS Series
The 1606-XLSRED is a redundancy module that connects two 1606-XLS power supplies in a true parallel redundant configuration. It provides an OR-diode function between two independent supply outputs, automatically feeding the load from whichever supply has the higher output voltage — typically the primary. If the primary fails, the secondary takes over within microseconds without any switching delay or output gap. The load experiences a continuous, uninterrupted 24V DC rail throughout a supply failure event.
By itself, two power supplies in parallel without a redundancy module will share current but won't provide true redundancy — the supplies fight over output voltage, and a failed supply can drag down the other through reverse current. The 1606-XLSRED's internal diodes prevent this: each supply sees only its own load side, not the other supply's output. One fails, the other takes the full load without backfeed or interaction.
Specifications
| Parameter | Value |
|---|---|
| Part Number | 1606-XLSRED |
| Function | OR-diode redundancy module for 1606-XLS power supplies |
| Compatible Supplies | 1606-XLS series (120W and 240W models) |
| Max Input Current per Channel | 10 A (per supply input) |
| Output Voltage Drop | ~0.5V (diode forward drop, compensated by supply trim) |
| Switchover Time | < 1 ms (passive diode, no active switching) |
| Status Output | Relay contact — signals loss of one supply input |
| Mounting | 35 mm DIN rail, clips directly to XLS supply |
| Operating Temperature | −25°C to 60°C |
| Standards | UL 508, CE, cUL |
How the Redundancy Module Works
Each supply connects to one input channel of the 1606-XLSRED. Inside, each channel passes through a Schottky diode before joining at the output bus. The supply with the higher output voltage naturally forward-biases its diode more than the other — it carries the full load. The second supply's diode is reverse-biased and carries no current as long as the primary is within normal output voltage range.
When the primary supply fails or drops below the secondary's voltage, the secondary's diode forward-biases and picks up the load immediately — no relay, no controller action, no switchover logic required. The diode voltage drop (~0.5V) means the output voltage is always 0.5V below the supply that's conducting. To maintain a nominal 24V at the load, each supply's output should be trimmed to approximately 24.5V using the front-panel adjustment — this compensates for the diode drop and keeps the load voltage within the 24V field devices' normal operating range.
The relay status contact opens when either supply input drops below an acceptable threshold, signaling the loss to a monitoring system or PLC digital input. This is the only active function — the power handoff itself is entirely passive.
Design Considerations
- Supply sizing: each supply must be rated for the full load independently. In a redundant pair, each supply carries the full load when the other fails. Sizing each supply at 50% of the load and expecting the pair to share defeats the redundancy — if one fails, the other is already overloaded.
- Output voltage trim: trim both supplies to the same output voltage (24.5V recommended to compensate for the diode drop). A voltage mismatch between supplies means only the higher-voltage supply carries the load — the other supply contributes nothing until the primary fails below the secondary's voltage, which may be a significant fault event rather than a gradual degradation.
- AC input diversity: for full redundancy benefit, the two supplies should be fed from independent AC circuits — ideally different distribution panels or even different utility feeds. Two supplies fed from the same breaker with a shared upstream fault provide no redundancy against that upstream fault.
FAQ
Q: Can any two 24V DC power supplies be used with this module, or only 1606-XLS?
The 1606-XLSRED is mechanically and electrically optimized for the 1606-XLS series. Non-XLS supplies can be connected to the input terminals electrically, but the physical DIN rail mounting and current rating must be verified. The key electrical requirement is that both supplies have adjustable output voltage so the diode drop can be compensated.
Q: Does the relay contact indicate which supply has failed, or just that a failure occurred?
The status relay indicates that one of the two inputs has dropped below threshold — it does not identify which supply failed. Additional monitoring (separate supply OK contacts from each supply) is needed to pinpoint which unit has failed.
Q: What is the maximum total load current the module can pass?
The module's output current is limited by whichever supply is conducting and the module's per-channel rating of 10A. Two 120W / 5A supplies produce a maximum output of 5A in redundant mode (not 10A) — the redundant pair capacity is limited to one supply's output, not the sum.
Q: How quickly does the switchover occur if the primary supply fails?
Switchover is passive — the Schottky diodes respond within microseconds of the primary voltage dropping below the secondary's. There is no active switching delay. The output voltage dips briefly by the diode forward voltage difference and recovers within the secondary supply's regulation time — typically sub-millisecond total interruption.