Relay Output Module | ABB DO821 3BSE013250R1 S800
Manufacturer: ABB
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Part Number: DO821 3BSE013250R1
Condition：New with Original Package
Product Type: Digital I/O Cards
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Country of Origin: Sweden
Payment:T/T, Western Union
Shipping port: Xiamen
Warranty: 12 months
ABB DO821 3BSE013250R1 Digital Output Module
The ABB DO821, also cataloged as the DO821 Digital Output Module, operates as a dedicated hardware component for relay-isolated actuator and contactor control within S800 I/O platforms. It provides direct physical switching of external AC and DC circuits while maintaining total electrical separation from the logical controller.
Hardware Specifications
| Parameter | Specification |
|---|---|
| Model | DO821 |
| Brand | ABB |
| Origin | Sweden |
| Weight | 0.32 kg |
| Dimensions | 119 x 45 x 102 mm |
| Operating Temp | 0 to +55 deg C |
| Power Consumption | 2.9 W typical (derived from backplane bus) |
| Output Channels | 8 individually isolated channels |
| Output Contact Type | Relay, normally closed (NC) |
| Output Voltage Range | 24 - 230 V AC/DC |
| Output Current Rating | Up to 3 A per channel |
| DC Load Capacity | 42 W per channel |
| Required MTUs | TU811, TU813, TU831, TU836, TU837, TU851 |
S800 Backplane Bus Communication and Output Mapping
The DO821 maps its 8 discrete output bits directly over the S800 I/O backplane bus to control internal relay coils. The module features localized I/O density scaling, enabling dense terminal grouping on a single rack without sacrificing heat dissipation margins. Power consumption on the backplane is monitored continuously, while onboard firmware controls the synchronization of relay transitions to reduce peak bus current draw during simultaneous block switching.
Frequently Asked Questions
Q: Are there diagnostic indicators on the face of the DO821 module?
A: Yes. The front panel features LED indicators for module status (Fault, Run, Warning) alongside eight dedicated yellow channel status LEDs that reflect the real-time physical state of each relay output contact.
Q: Can different voltage potentials be applied to adjacent output channels?
A: Yes. Each of the eight relay channels is individually galvanically isolated, allowing the mixing of diverse external control voltages (such as 24 VDC and 230 VAC) across different channels on the same module.
Q: How is backplane bus noise prevented during high-inductive switching?
A: Physical galvanic isolation barriers block any voltage spikes, flyback EMF, or surge transients from crossing back into the low-voltage logic side of the S800 backplane.
Field Installation Guidelines
- Confirm the S800 rack and associated Module Termination Unit (MTU) are securely mounted to the grounded DIN rail before sliding the DO821 module onto its mate.
- Verify the field supply breaker is switched off before terminating wiring on the MTU terminal blocks.
- Install external arc-suppression components (such as RC snubbers for AC loads or freewheeling diodes for DC loads) across highly inductive external actuator coils to protect the internal relay contacts from premature erosion.
- Route high-current field AC/DC output lines through separate cable trunking away from low-voltage communication buses to prevent capacitive signal coupling.