MK3 ALU heated bed 235 × 235 mm, 24 V and 240 W — prepared connection

MK3 ALU 235 × 235 mm heated bed for 24 V systems, built on a 3 mm aluminium plate and rated at 240 W. It has four countersunk holes on a nominal 170 mm mounting pattern and includes an approximately 90 cm detachable connection harness.

This version reduces wiring preparation, but it remains a high-current component: its nominal draw is 10 A, so pinout, sensor, controller capacity and strain relief must all be verified before commissioning.

Specifications and supplied connection

Current and resistance are calculated from the stated 24 V and 240 W; they do not replace measurement of the supplied unit. Actual resistance may vary with tolerance and temperature.

Contents and required checks

The bed and an approximately 90 cm harness are supplied. The photographs show a multipole connector on the PCB, two insulated fork terminals and an auxiliary connector at the installation end. Connector series, conductor size and pinout are not documented.

An element secured near the thermal centre and an auxiliary branch are also visible, but the description does not explicitly identify the sensor type or curve. Do not configure firmware or connect the harness from wire colours or connector appearance alone: confirm the supplied revision or identify every circuit by measurement.

The power supply, power stage, print surface, insulation, screws and spacers are not included. For installations requiring a fully custom harness, choose the 235 × 235 mm MK3 ALU version without the prepared connection.

235 × 235 mm print surfaces

Borosilicate glass

The 235 × 235 × 5 mm tempered borosilicate glass matches the bed footprint and provides a rigid removable surface. Its 5 mm thickness adds height, mass and thermal inertia; check moving-axis capacity and recalibrate Z offset, levelling and the first layer.

It may be secured with spring clips for glass and heated beds when the combined thickness and accessible edge are suitable. Keep them outside nozzle and probe travel, and check underneath that they do not touch tracks, sensor or connector.

Flexible PEI sheets

The aluminium plate does not contain magnets. A compatible adhesive magnetic base is required for a flexible sheet. The current descriptions of these 235 × 235 mm options state that they include a soft magnetic base:

• 235 × 235 mm double-sided textured PEI sheet;
• 235 × 235 mm smooth/textured PEI sheet.

Confirm the current option contents and temperature rating. Fit the base only after bolting the bed down and checking flatness: its adhesive may cover the countersinks and make servicing difficult. Recalibrate the first layer whenever surface thickness changes.

Identifying the harness before connection

1. With the bed cold, disconnected and isolated from the controller, identify every contact by continuity; do not infer function from colour.
2. Locate the heater circuit: it should measure close to 2.4 Ω when cold after compensating for meter-lead resistance.
3. If the auxiliary branch is connected to a 100K NTC, it should read close to 100 kΩ at room temperature and change smoothly when warmed by hand. This test alone does not identify its Beta curve.
4. Verify that no conductor has continuity to the aluminium plate.
5. Confirm correspondence with the controller's sensor input, power output and terminals before applying voltage.

Do not rearrange contacts or substitute a visually similar connector without knowing its series, pitch, current rating and pinout. Fully seat the connector, never mate or disconnect it under load, and verify during the first cycle that it does not become abnormally warm.

Strain relief and travel

The supplied harness does not remove the need for strain relief. Secure it to the carriage with a solution that preserves its bend radius and permits full travel without pulling the connector, rubbing the frame or creating a repetitive sharp fold. Motion must not load the contacts or the auxiliary branch.

The visible fork terminals must only be used with terminals that accept their shape and size. If the controller uses a different clamp, fit a termination suitable for the wire's actual cross-section; avoid loose strands, splices in the moving region and tinned ends under pressure where the terminal manufacturer does not permit them.

Sensor and firmware setup

Identify the actual sensor before selecting a thermistor table. If a 100K Beta 3950 NTC is confirmed, the 100K B3950 NTC with Dupont connector or 100K B3950 NTC with XH connector may be considered as references, but only as replacements conditional on curve, mounting, connector and pinout; they are not universal substitutes.

Before enabling bed power, confirm a sensible room-temperature reading and check that it changes continuously. Keep failed-heating and thermal-runaway protection enabled. Perform the first test at a low target under continuous supervision with an independent temperature reference, then run the firmware's thermal calibration or autotune after fitting the final print surface and insulation.

24 V power supply and power stage

The bed draws a nominal 10 A. A 24 V, 10 A, 240 W supply would operate at its limit with the bed alone and is not suitable for powering the complete printer. Add the maximum demand of the bed, hotend, motors, fans, controller and accessories, then retain operating margin.

• The 24 V, 15 A, 360 W power supply may suit a dedicated branch or a printer whose verified total load remains within its capacity with margin.
• The 24 V, 25 A, 600 W power supply offers more capacity for higher-load systems, but is oversized for the bed alone and requires suitable protection on each branch.

The controller's bed output must handle 10 A continuously with margin across its MOSFET, PCB, terminal and cooling. Where its capacity is insufficient or undocumented, a 12/24 V external MOSFET module may be added after verifying its true continuous rating, cooling and terminals. Do not use an AC-only solid-state relay for this 24 V DC load.

Mounting, insulation and maintenance

Bolt the bed down without bending it; screw heads must sit flush and no spacer may touch the underside tracks. The three-layer heated-bed thermal insulation can reduce underside heat loss, but its metallised faces are conductive and must not touch tracks, connector, sensor or terminals.

Regularly inspect the multipole connector, terminals, cable, strain relief and mountings. Keep thermal protection enabled and never leave the bed unattended during testing. The surface remains hot after power is removed; wait at least 10 minutes before touching it.

Conditional compatibility

Sharing a 235 × 235 mm footprint does not guarantee a direct replacement. Hole pattern and diameter, carriage, travel, connector orientation, harness bend radius, permissible mass, Z height, 24 V supply, sensor, pinout and continuous 10 A capacity must also match. No automatic compatibility with any printer model is claimed without measuring and checking its exact revision.