The most critical power component of a scent machine is the pump: it is the actuator that atomizes the fragrance oil or pushes it into the HVAC duct. The job of the control board is to switch this pump safely and reliably from the 220–240 V AC mains. In this article we cover relay selection, the power supply, the difference between resistive and inductive loads, and mains safety.

Onboard AC-DC: why you don’t want an external adapter

Control boards run on low-voltage DC (typically 5 V / 3.3 V), but the pump is at mains voltage. There are two approaches:

  1. External adapter — an extra box, extra cabling, an extra point of failure.
  2. Onboard AC-DC module — the mains comes straight to the board and is converted to DC on the board itself.

A professional product favors an onboard AC-DC design: installation is a single cable (the mains input), no space is needed inside the enclosure for an adapter, and the EMI filter is managed on the board. The MARG SCENT board runs from the mains and requires no external adapter.

Switching an AC pump with a relay

The most common and durable way to turn the pump on and off is an electromechanical relay. The relay galvanically isolates the low-voltage control side (MCU) from the high-voltage power side (the pump) — providing both safety and noise immunity.

Two ratings are critical when choosing a relay:

  • Current capacity (e.g. 10 A) — must be comfortably larger than the current the pump draws
  • Voltage rating (e.g. 240 V AC) — must handle the mains voltage

MARG SCENT offers a single 10 A relay output (TIANBO HJR-3FF-S-Z; 10 A/120 VAC, 7 A/240 VAC resistive). One pump/motor is driven from the screw-terminal MOTOR connector. There are no multiple relays, SSRs or triacs — because a typical scent machine uses a single actuator, and one robust output is the most reliable solution.

Resistive vs inductive load — the point to watch

The current ratings on a relay label (such as 10 A/120 VAC) are for a resistive load. A pump, however, is an inductive load: it draws a high inrush current at start-up and produces an arc-generating voltage spike at switch-off. This can push the life of the relay contacts below the labeled value.

For this reason:

  • With inductive pumps, derating (operating below the labeled rating) is applied.
  • Protection elements such as a snubber/RC or MOV are considered to extend contact life.
  • Compatibility must be verified by testing for the specific pump model you will use — a “fits every pump” claim is not engineering-sound.

Mains connection and safety

The 220 V mains and the relay output are safety-critical. The basic rules:

  • Mains (L/N) and relay-output (NO/COM) connections must be made only by authorized technical personnel, according to the board’s connection diagram.
  • Appropriate fusing/protection and grounding must be provided.
  • The board must be mounted in a closed, suitable enclosure.

The connection diagram, terminal table and pin information are shared in the technical documentation according to the product version.

Beyond the pump: the board’s other power concerns

Beyond driving the pump, a good board should also consider:

  • RTC backup battery — preserving the clock during a power outage
  • Hardware watchdog — automatically resetting the board in the event of a software lock-up (important for field devices that run continuously)
  • EMI filter — limiting the propagation of mains noise both inward and outward

Do you need a scent machine control board that runs from the 220 V mains, with a single 10 A relay and a powerful onboard AC-DC? Review the technical specifications → or write to us for compatibility with your pump model.