DS3800HDRA | GE Mark V 120V AC Relay Output Module

Description

Product Introduction

When you need to switch loads that exceed the current capacity of triac or MOSFET outputs—or when you need dry contact isolation—the DS3800HDRA is your solution. This board uses 16 electromechanical relays, each with Form C contacts (SPDT), allowing you to switch AC or DC loads up to 5A at 240V AC or 30V DC. The relays are socketed, so you can replace individual relays without desoldering. This board is used for applications like driving large contactors, motor starters, or interfacing with external logic circuits that require isolated contacts.

The HDRAs relays are rated for 100,000 operations at full load, which is typical for electromechanical relays. The 2.5kV isolation provides a high level of electrical separation between the logic side and the field side. The board’s status LEDs show the commanded state, but they don’t indicate the actual relay contact state. One downside is that the relays have a finite lifespan—we’ve seen relays on this board fail after about 50,000 cycles in high-cycle applications. If you’re switching loads frequently, the triac-based outputs (HDDB) are more durable.

Key Technical Specifications

Compatible Replacement Models

Frequently Asked Questions (FAQ)

Q: What’s the difference between Form C relays and other relay types?
A: Form C relays are SPDT (Single Pole Double Throw)—they have a common terminal, a normally open (NO) terminal, and a normally closed (NC) terminal. When the relay is de-energized, the common is connected to NC. When energized, the common connects to NO. This gives you both a normally open and normally closed contact per channel, which is useful for applications that need both types of signals (e.g., dual-path safety circuits).

Q: Can I switch 120V AC and 24V DC loads on the same board?
A: Yes, the relays are isolated and can switch mixed loads. Each relay is independent, so you can have some channels switching 120V AC and others switching 24V DC. Just make sure the load current and voltage are within the relay’s rating. The terminals are labeled C (common), NO, and NC, so you can wire different voltages to different contacts.

Q: How long do the relays last?
A: The relay contacts are rated for 100,000 operations at full load (5A resistive). If you’re switching a lower current, the electrical life increases—at 1A, you can expect 1 million operations. Mechanical life (without load) is 10 million cycles. In high-cycle applications (e.g., fast-cycling solenoids), we recommend using the triac-based output boards (HDDB) because they don’t have moving parts.

Q: How do I replace a failed relay on the HDRA?
A: The relays are socketed, so you don’t need to solder. With the board powered off, gently pull the faulty relay out of its socket. Insert the new relay, ensuring correct orientation (the relay has a polarity marking on its top). This makes the HDRA a field-repairable board—a big advantage over boards with soldered-on components. We’ve seen plants stock a few spare relays for quick replacements during outages.

Q: The status LEDs show the coil state. Does that indicate the actual contact state?
A: No. The LEDs show whether the coil is energized, which corresponds to the commanded state. However, they don’t show whether the contacts are actually making contact. If a relay is faulty, the LED could be on but the contacts may not be closed. Always verify the contact state with a multimeter. The LED is a logic indicator, not a contact verification.

Q: Can I use the HDRA in a safety-critical circuit?
A: The HDRA uses standard relays, which are not inherently safety-rated. They are not fail-safe in the way that force-guided relays are. If you need safety-certified outputs, use dedicated safety relay modules. The HDRA is suitable for general-purpose control, but not for SIL-rated safety functions. If you’re using the HDRA for emergency trip circuits, we recommend using a separate safety relay in series with the output.

Q: The HDRA has a 1.0A backplane current draw. Is that the same as other output boards?
A: Yes, the HDRA’s 1.0A draw is similar to other output boards like the HDDB (1.2A) and HDPA (1.2A). The relay coils are powered from the 24V logic supply, which is generated from the 5V backplane rail, so the current draw is moderate. The Mark V power supply typically provides 6A on the 5V rail, so the HDRA is well within the limit. However, if your rack has multiple HDRA boards, check your total backplane current.

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