HONGFA HF105F-4-024D-1HST=JQX105F-4-024D-1HS 24VDC Power Relay 4Pins 30A 240VAC

HONGFA · Power Relay · HF105F Series · 30A / 240VAC · 24VDC Coil · In stock

What Is the HONGFA HF105F-4-024D-1HST Power Relay?

The HONGFA HF105F-4-024D-1HST (also marked as JQX105F-4-024D-1HS) is a 4-pin SPST-NO (Single Pole Single Throw, Normally Open) power relay rated to switch up to 30 amps at 240VAC. The 24VDC coil draws modest current and is designed for PCB mounting — the four terminals solder directly into a printed circuit board. HONGFA is one of the world's largest relay manufacturers, and the HF105F family is their workhorse power relay line, appearing in appliances, HVAC control boards, industrial timers, smart home power switches, and automotive power distribution modules.

In short: A PCB-mount 30A relay from the world's largest relay brand — the component you design into a circuit board when a microcontroller needs to switch a heater, motor, compressor, or lighting load that draws serious current.

What Makes This Relay Different from Automotive Cube Relays

1. PCB Mount vs. Plug-In

Unlike the common automotive ISO relay that plugs into a socket, the HF105F solders directly to a circuit board. This eliminates the intermittent connection problems that plague socketed relays in high-vibration environments (the socket terminals relax over time, increasing contact resistance and generating heat). The trade-off is that replacing this relay requires desoldering — it is not field-swappable without tools. For production designs, the reliability gain from soldered connections outweighs the serviceability loss.

2. 30A Rating: Sustained vs. Inrush

The 30A rating is for resistive loads at 240VAC — heaters, incandescent lamps, resistive heating elements. For inductive loads (motors, compressors, contactor coils), derate to roughly 50-60% of resistive rating (15-18A) due to the arc that forms when interrupting an inductive circuit. The relay can handle brief inrush currents higher than 30A — typical tungsten lamp inrush can be 10-15x the steady-state current — but repeated inrush cycling at those levels erodes the contacts and shortens electrical life significantly.

3. Coil Polarity and Suppression

The 024D suffix indicates a 24VDC coil. Check the relay body or datasheet for polarity markings — if the relay has an internal flyback diode (some HF105F sub-models do), you must observe correct coil polarity or the diode will conduct and short your drive circuit. If no polarity marking exists, the coil is non-polarized. When driving this relay from a transistor or MOSFET on your PCB, always include a flyback diode on the board layout across the coil terminals — even if this particular variant has an internal diode, the PCB-level diode provides redundant protection and costs a fraction of a cent.

Key Specifications

Frequently Asked Questions

What is the difference between the HF105F and JQX105F model numbers?

These are the same relay. HONGFA uses HF105F as their internal model designation; JQX105F follows the Chinese GB/T standard relay naming convention where JQX designates a general-purpose power relay. The dual marking is for compliance — the HF105F number is used in HONGFA's catalog, while the JQX number appears on the relay body to satisfy domestic Chinese standards. Electrically and mechanically, they are identical parts.

How much PCB copper area do I need for the 30A traces?

For 30A continuous on a standard 1oz copper PCB, the general guideline is roughly 10-12mm trace width on outer layers, or substantially wider on inner layers. But at 30A the trace width is not the only concern — the relay pins themselves and the solder joints become the thermal bottleneck. Use large copper pours (planes) connected to the relay pads with thermal relief removed (direct connection) on both sides of the board. Add solder mask openings so the wave solder process deposits extra solder on the high-current pads. For production boards switching 30A regularly, consider 2oz copper and bus bars or reinforced traces. Browse our collections for PCB-mount terminal blocks suitable for high-current wiring.

Can this relay switch DC loads, and what is the DC rating?

The primary rating is for AC. The DC switching capacity is substantially lower — typically around 28VDC at a fraction of the AC current rating. Switching DC is harder on relay contacts than AC because DC current does not naturally cross zero to extinguish the arc. For 30VDC, expect a rating closer to 10-15A. For 110VDC, the relay may not be rated at all — DC arcs at high voltage are difficult to extinguish without magnetic blowout or vacuum contacts. If you are switching DC loads, check the datasheet for the specific DC rating and consider a DC-rated contactor or solid-state relay for high-voltage DC applications.

How do I suppress the arc to extend contact life?

For AC inductive loads: install an RC snubber (typically 100 ohms in series with 0.1uF, rated for the line voltage) across the load contacts, not across the load. The snubber absorbs the energy that would otherwise form an arc as the contacts separate. For DC loads: a reverse-biased flyback diode across an inductive load (not across the contacts) recirculates the inductive energy. For resistive loads, no suppression is needed — the arc is minimal. Do not install a capacitor alone across relay contacts — without a series resistor, the capacitor discharges through the contacts when they close, causing a high-current pulse that can weld the contacts.

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