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Power Expander (Mosfet Board)


Power Expander a versatile solid-state relay for heatbeds, hotends, fans etc.

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The Power Expander is a versatile electronics adapter for high current DC equipment. In 3D printing it is usually used for Heatbeds and Hot-ends, to offload the high current from the mainboards, which may not be equipped to handle the loads or be faulty.

The Power Expander makes use of a Mosfet to control the current. Mosfets are solid state and does not make noise when switching on and off and also does not produce EMC noise. This increases the lifetime of a mosfet, compared to relays for example. Mosfets have the added ability to switch on and off at a very high rate, allowing PWM control (which is what the PID Heater Management needs) to the other side

This Power Expander is designed to isolate the input signal from the power signal, allowing you to use 2 different power supplies (even different voltages) to operate it. This can allow you to use a small 12V power supply to power only the main electronics (mainboard, screen, logic, stepper motors) while offloading the heater management to a larger 24V power supply.

Multiple Power Expanders can also be connected to the same input signal, allowing multiple heaters from the same control; this is useful if you need to chain a few heatbeds together for the same printer.

Technical Specifications

  • Power handling designed for 12V to 24V DC (absolute Max of 30V DC)
  • Signal Input: 5-24V DC – this powers only an LED inside the Optocoupler Isolator.
  • Power Input and Signal Input are galvanically isolated.
  • Maximum Recommended DC current: 20A (Heatsink with cooling fan required).
  • Board Outline: 30x30mm
  • Mounting Holes: 22x22mm (diameter of 3.2mm)
  • Power Expander is not fused.
  • Datasheet for driving Mosfet: PSMN7R0-30YLC

Custom Configuration:

Solder pads are located on the rear side, these are intended for optional invertion of the operation mode.

By factory default the Pad designated NORMAL is shorted by a small trace between the solder pads. In this mode the output is turned off until voltage is applied to the Signal input terminal.

For inverse operation, first cut the small trace between the solder pads designated NORMAL. Then apply solder to the INVERTED pads. In this mode the output is switched on until voltage is applied to the Signal input terminal.

To restore normal operation reconnect the “NORMAL” solder jumper by applying some solder and remove the solder previously applied to the “INVERTED” solder jumper.

Avoid having both jumpers connected.


Q: What is the maximum amount of Watts that can be operated via a single Power Expander?

A: The maximum rating of the SMD Mosfet (the flat square black thing with four legs on one side, the thing that is actually doing the switching on and off) will tolerate up to 60 Ampere for a very brief moment, however under continuous load conditions we recommend that you do not exceed 20 Ampere. This amount largely depends on environment conditions and if you find the PCB is getting hot and the Mosfet is way too hot to touch please read on.

Please note that the Power ratings for the Power Expander output depend on the relationship of Ohm’s law: Voltage x Amperage = Wattage.
Therefore at a system voltage of 24 Volt the Power Expander can handle more power than on a 12 Volt system.


Q: What should I do if I need to draw more than 20 Ampere or  if my current Power Expander is running hot?

A: If your application needs more current we suggest you couple two or more Power Expanders in parallel so that they can share the load current.


Q: Could you please list some examples of operating conditions?

A: Sure, here is a list of  examples of operating conditions:

Example 1: a 12 Volt system operating a 1.2 Ohm heated bed will draw 10 Ampere and consume 120 Watts of power
12V / 1.2Ω = 10A and 10A x 12V = 120W

Example 2: a 24 Volt system operating a 1.2 Ohm heated bed will draw 20 Ampere and consume 480 Watts of power
24V / 1.2Ω = 20A and 20A x 24V = 480W

Example 3: a 24 Volt system operating a 2.4 Ohm heated bed will draw 10 Ampere and consume 240 Watts of power
24V / 2.4Ω = 10A and 10A x 24V = 240W

Example 4: a 24 Volt system operating a 4.8 Ohm heated bed will draw 5 Ampere and consume 120 Watts of power
24V / 4.8Ω = 5A and 5A x 24V = 120W

Power Input

12-24V DC

Signal Input

5-24V DC

Maximum Power

60A peak