Product Description

Maxwell MS-1DA4825 — Single Phase Solid State Relay | DC Control | 25A | 480VAC | Zero-Crossing | New Original In Stock

The electromechanical relay had a good run. For decades it was the default choice for switching AC loads from low-voltage control signals, and it still works fine where switching cycles are infrequent and the environment is clean. But in temperature control loops, PID controllers, and process automation panels where the relay switches hundreds or thousands of times per hour, the mechanical contact wears fast. The coil buzzes. The arc erodes the contact surface. Eventually something fails.

The MS-1DA4825 eliminates all of that. No moving parts, no contact bounce, no mechanical wear, no arc. The internal semiconductor switches silently at the zero-crossing point of the AC waveform, which means the load voltage is at its minimum at the moment switching occurs — the kindest possible moment for both the switching device and the connected load. Control input is a standard 3–32V DC signal, directly compatible with PLC discrete outputs, temperature controller relay outputs, microcontroller GPIO pins, and any other low-voltage logic source without interposing relays or signal conditioning.

For any application where a PID temperature controller is cycling a heating element, or where a PLC needs to switch an AC load cleanly and often, the MS-1DA4825 is a direct, practical upgrade over mechanical relays.

✅ Genuine Maxwell (Xiamen Maxwell Automation). New original. Ships worldwide via DHL / FedEx / UPS.

Technical Specifications

Parameter	Specification
Model Number	MS-1DA4825
Type	Single phase DC input / AC output SSR
Rated Load Voltage	480VAC (also rated 240V / 660V class available)
Rated Load Current	25A continuous
Control (Input) Voltage	3 to 32V DC
Control (Input) Current	3 to 25mA DC
Output Switching Mode	Zero-crossing trigger
On-State Voltage Drop	≤1.5V
Off-State Leakage Current	≤2mA
On / Off Response Time	≤10ms
Dielectric Strength	2500V AC (input to output)
Insulation Resistance	100MΩ / 500VDC
Ambient Temperature Range	–30°C to +75°C
Mounting	Chassis mount (panel mount)
Indicator	Red LED (operation status)
Built-in RC Snubber	Yes
Protective Cover	Included
Weight	0.135 kg
Certifications	CE
Compatible Heatsink	MW-I (60 × 50 × 50mm, for 10A and 25A)

Zero-Crossing Switching — Why It Matters

When a mechanical relay closes on an AC circuit, it does so at whatever point in the sine wave the coil happens to energize. If that moment happens to coincide with the voltage peak — which it frequently does, randomly — the full peak voltage appears across the contact gap as it closes. This creates an inrush condition and an arc, both of which stress the connected load and the switch itself.

The MS-1DA4825 waits. Its internal zero-crossing detection circuit monitors the AC waveform continuously and holds the output switch off until the AC voltage passes through zero — the point where instantaneous voltage is near nil. At that moment it fires the triac or back-to-back SCR output stage, and the load energizes from essentially zero voltage, rising smoothly through the normal AC waveform. There is no inrush spike, no arc, no EMI burst associated with switching.

On the deactivation side, when the control signal is removed, the output stage waits for the next zero crossing of the load current before switching off. Since AC current is naturally zero at each zero crossing, the turn-off occurs at a moment of minimum arc energy. The result is that the MS-1DA4825's internal switching device experiences vastly lower electrical stress per switching cycle than any mechanical relay — which is precisely why SSRs with zero-crossing control can execute tens of millions of switching cycles over their service life where mechanical equivalents wear out in the hundreds of thousands.

For temperature control applications where a PID controller is cycling a heating element continuously — outputting switching commands at rates anywhere from once every few seconds to several times per second — this noise-free, stress-free switching behavior translates directly to longer SSR life, cleaner electrical environment in the panel, and more consistent thermal performance from the controlled process.

The Built-In RC Snubber Circuit

The RC snubber is a small but important feature that distinguishes a properly designed SSR from a bare semiconductor switch. It consists of a resistor and capacitor wired in series, placed in parallel with the output switching device inside the relay.

Its function is to suppress voltage transients on the load circuit. Inductive loads — transformer primaries, motor windings, contactor coils, solenoid valves — generate voltage spikes when switched. When the load current is interrupted, the collapsing magnetic field produces a high-voltage transient (the inductive kickback) that appears across the switching device at the moment of turn-off. Without suppression, this spike can exceed the voltage rating of the output triac or SCR and cause a false triggering or, in severe cases, device failure.

The RC snubber absorbs this energy. The capacitor charges during the transient, limiting the rate of voltage rise across the semiconductor junction (the dV/dt), while the resistor limits the inrush current into the capacitor when the device next turns on. The MS-1DA4825's built-in snubber means this protection is always present regardless of what the load looks like — the user doesn't need to calculate, source, and wire an external snubber circuit, which is a meaningful simplification during panel build and commissioning.

One note: for purely resistive loads — heating elements, incandescent lamps, wire resistance heaters — the snubber is essentially passive and doesn't play a significant role. Its value is most apparent with any load that has inductance in the circuit.

Thermal Management and the Heatsink Requirement

Every solid state relay generates heat during operation because the output semiconductor has a finite on-state voltage drop — in the case of the MS-1DA4825, this is rated at ≤1.5V. At 25A continuous load current, the power dissipated inside the relay is up to 37.5W. That's not a trivial amount of heat to manage inside a sealed or semi-sealed enclosure.

The rated ambient operating temperature of –30°C to +75°C assumes adequate heat sinking. Running a 25A SSR at full load current without a heatsink will cause the internal junction temperature to rise well above safe limits within a short time, leading to thermal shutdown or permanent damage. Maxwell offers the MW-I heatsink (60 × 50 × 50mm) specifically rated for the 10A and 25A models in the MS-1DA range. The relay's aluminum base plate transfers heat through direct metal-to-metal contact with the heatsink, with thermal interface compound applied between the two mating surfaces to maximize thermal conductance.

In practice, three considerations determine whether additional heatsinking beyond the MW-I is necessary: the actual load current (continuous 25A is the worst case; lighter loads generate proportionally less heat), the ambient temperature inside the panel, and whether multiple SSRs are mounted close together and sharing heat. For most typical process heating applications running at partial load — a 3kW element on 240VAC drawing about 12.5A, for example — the MW-I heatsink is adequate with normal panel ventilation.

MS-1DA48 Series — Current Rating Selection

Choosing the right current rating matters for both reliability and cost. Undersizing leads to thermal stress and premature failure; oversizing wastes money and physical space.

Model	Rated Current	Typical Application
MS-1DA4810	10A	Small heating elements ≤2.4kW at 240V, signal circuits
MS-1DA4825	25A	Heating elements up to 6kW at 240V, process heating, kiln control
MS-1DA4840	40A	High-power heating up to 9.6kW at 240V, industrial ovens
MS-1DA4860	60A	Large industrial heating elements, furnaces, continuous heavy duty
MS-1DA4880	80A	Industrial furnaces, large resistance heating banks
MS-1DA48100	100A	High-capacity industrial thermal processes
MS-1DA48120	120A	Maximum single-phase capacity in the MS-1DA range

The general guideline when sizing an SSR is to select a unit rated for at least 1.5–2× the actual continuous load current. This derating accounts for ambient temperature effects on the semiconductor junction, momentary inrush currents at load energization (incandescent lamps and cold heating elements draw significantly more current at startup than when hot), and the reduction in heatsink effectiveness as panel temperature rises. For a 15A continuous load, the MS-1DA4825's 25A rating provides a comfortable derating margin.

MS-1DA vs MS-1AA — Choosing by Control Signal Type

The two most common single-phase SSR variants in the Maxwell range differ only at the input:

MS-1DA (this relay) — DC control input, 3–32V DC, 3–25mA. Use when the control source is a PLC discrete output, a temperature controller relay or logic output, a microcontroller, a function generator, or any low-voltage DC source. The 3V lower threshold means even 3.3V logic can drive it directly; the 32V upper threshold accommodates 24V DC industrial logic with full margin.

MS-1AA — AC control input, 70–280V AC, ≤12mA. Use when the control source is itself an AC signal — a transformer secondary, a mechanical relay contact switching AC, or a legacy control system with AC-level logic outputs. The MS-1AA accepts the same wide range of AC voltages (70–280V covers both 120V and 240V AC supplies) with no additional conditioning needed.

Everything else — load ratings, zero-crossing behavior, RC snubber, LED indicator, dimensions, heatsink compatibility, CE certification — is identical between the two series.

Common Applications

Process temperature control is the most widespread use case. A PID temperature controller measures a thermocouple or RTD signal, calculates the required heating power via time-proportioning or percentage output, and drives the MS-1DA4825's control terminals with a DC logic signal. The SSR switches the heating element on and off at the commanded duty cycle — quietly, quickly, without bouncing, and with far greater switching life than any mechanical relay at the same cycle rate.

Plastic and rubber processing equipment uses SSRs extensively because the combination of continuous high-cycle heating control and industrial ambient conditions demands the durability that solid state switching provides. Injection moulding machines, extruder barrel heaters, and mould temperature controllers all benefit from the MS-1DA4825's operating temperature range and cycle life.

Kilns and laboratory ovens with PID temperature control are natural applications for the 25A current rating — most single-phase kiln elements in the 2–5kW range draw comfortably within the MS-1DA4825's capacity.

Food processing and packaging machinery frequently specifies SSRs for sealing jaw heaters, conveyor heaters, and temperature-controlled forming dies where reliable, silent switching is required in environments where mechanical relay noise is unacceptable.

❓ FAQ — Maxwell MS-1DA4825

Q1: What control voltage does the MS-1DA4825 require, and is it directly compatible with a 24V PLC output?

The control input accepts 3 to 32V DC at 3 to 25mA. A standard 24V DC PLC discrete output sits well within this range — typically delivering 24V at 5–50mA per output, the SSR's 3–25mA control current draw is within normal PLC output source capability. The LED indicator will illuminate when the input is active, confirming that the control signal has been received. No interposing relay, no signal conditioning, and no current limiting resistor are required between a 24V PLC output and the MS-1DA4825 control terminals. The 3V lower threshold also makes it directly compatible with 3.3V and 5V microcontroller logic, making it equally useful in Arduino, Raspberry Pi, and similar embedded control applications for lower-voltage systems.

Q2: What is zero-crossing switching, and does the MS-1DA4825 always use it?

Zero-crossing switching means the output semiconductor delays turning on until the AC load voltage passes through zero volts, and turns off when load current reaches zero. The MS-1DA4825 uses zero-crossing switching as its standard output trigger mode — this is the default behavior for the MS-1DA series without any "-R" or random-fire suffix. Zero crossing eliminates the inrush voltage spike and EMI burst that occur when a switch closes at an arbitrary point on the AC waveform. For resistive heating loads, temperature control, and most general-purpose switching, zero crossing is the preferred mode. The only application where random-fire (phase-angle) triggering is preferred is phase-controlled power regulation for lamp dimming or motor speed control — that function requires a different product type (Maxwell's MS-1VD voltage regulator series).

Q3: Does the MS-1DA4825 need a heatsink, and what happens if it runs without one?

For any application where the relay will carry sustained current — meaning the load is on for significant time periods rather than brief pulses — a heatsink is necessary. At 25A continuous load current and the rated on-state voltage drop of ≤1.5V, the relay dissipates up to 37.5W. Without a heatsink, this heat accumulates in the relay body, the internal junction temperature rises, and the SSR will eventually reach its thermal protection threshold and switch off, or in the worst case sustain permanent damage. The MW-I heatsink (60 × 50 × 50mm) is specifically rated by Maxwell for the 10A and 25A models. Thermal interface paste should be applied between the relay's aluminum base and the heatsink surface. For sustained high-current applications in warm panels, forced-air cooling over the heatsink improves thermal performance further. Brief or low-duty-cycle loads with substantial off-time generate less average heat and may run adequately with minimal heatsinking, but the heatsink should still be used as standard practice.

Q4: Can the MS-1DA4825 control inductive loads such as small motors, transformers, or solenoid valves?

Yes, with the built-in RC snubber providing the primary protection. For small inductive loads — solenoid valves, small transformer primaries, contactor coils — the MS-1DA4825's built-in snubber handles the transient voltage suppression that the inductive kickback generates at switch-off. However, for larger or heavily inductive loads, or applications where the inductive load represents a significant fraction of the relay's rated current, an external metal oxide varistor (MOV) or additional RC snubber wired in parallel with the load provides an extra layer of protection. One important limitation: the MS-1DA4825 uses zero-crossing switching, so it cannot perform phase-angle control on inductive loads (such as speed control of a universal motor). It switches the full AC waveform on and off, which is suitable for on/off control of inductive loads but not for continuous variable power control.

Q5: What is the difference between the MS-1DA4825 and a standard mechanical relay for temperature control duty?

The functional difference is dramatic under high-cycle conditions. A mechanical relay switching a temperature control output at typical PID rates of 1–10 cycles per minute has a manufacturer-rated contact life typically in the range of 100,000–300,000 operations for relay loads in this current range. The MS-1DA4825 is rated for tens of millions of switching cycles over its service life because there are no contacts to erode. Additionally, the mechanical relay generates audible noise at each switching event, produces EMI at contact make and break, and has a response time limited by coil energization and armature movement — typically 5–15ms for a standard DIN rail relay. The MS-1DA4825's response time is ≤10ms and produces no audible noise or contact EMI. For temperature control applications running 8–24 hours per day with continuous PID cycling, the service life difference between a mechanical relay and the MS-1DA4825 is the difference between replacing the relay every few months versus running for years without intervention.

Q6: How is the MS-1DA4825 mounted, and what terminal connections does it have?

The relay uses chassis mount (also described as panel mount) installation — it is designed to bolt directly to a panel surface, DIN rail bracket, or heatsink using the two mounting holes in its base. The standard mounting footprint is the universal size common across the MS-1DA series from 10A through 60A, meaning heatsinks, brackets, and mounting hardware are interchangeable across these ratings. Electrical connections are made via screw terminals: terminals 3 and 4 on one side accept the DC control signal (observe polarity — terminal 3 is positive), and terminals 1 and 2 on the other side are the AC load connections (line in and load out). The protective cover snaps over the terminal area and should remain in place during operation, particularly important in panels where accidental contact with the load-side terminals is possible given that these carry mains voltage.

Q7: What is the significance of the 2500V dielectric strength rating?

The 2500V AC dielectric strength specification describes the isolation barrier between the control (input) side and the load (output) side of the relay. During a dielectric strength test, 2500V AC is applied between the input terminals and output terminals without breakdown — meaning no current flows through the insulation barrier at that voltage. This isolation is what makes the SSR safe to use in applications where the control signal is at a low voltage (3–32V DC) and the load circuit is at mains voltage (up to 480V AC) — the two circuits are electrically separated. In practical terms, a 2500V rating provides safety margin well above the 480V mains voltage on the load side, protecting connected control equipment (PLC outputs, temperature controller terminals, microcontrollers) from mains voltage even if the load circuit develops a fault. It also provides immunity to transient overvoltages on the load circuit from switching surges or lightning-induced spikes that might reach several hundred volts above nominal.

MS-1DA4825 New Original MS1DA4825 Maxwell Solid State Relay