Electro Permanent Magnet View larger

Electro Permanent Magnet V2.5


New product

Deprecated, replaced with V3R5C

The EPM688-V2.5 is an Electro Permanent Magnet, combining the advantages of electro and permanent magnets. With virtually no power during steady state operation (<1mW) and 800mA for 1.2s during a switch cycle. 

Holding force and consistency have been greatly improved (5kg under adverse conditions) and is more resistant to demagnetization during virbration. 

More details

More info

OpenGrab Electro Permanent Magnet

(Comes with one target square and 4x M3x0.5x5mm screws)


Git repository for Parts Drawing PCB Masks Pic12F source code


Schematics and PCB files 


OpenGrab Electro Permanent Magnet                                          


General Description

The EPM688-V2.5X is an Electro Permanent Magnet, combining the advantages of electro and permanent magnets.

The magnetic domains in the Alico magnets are aligned in a particular orientation as to form a magnetic circuit with a ferrous target plate. A short, 20us pulse current of 300A is generated by discharging the main capacitor through a Thyristor full bridge into the copper winding generating a field of 70kAm. This field is used to align Alico domains.

The key advantage is a very strong electromagnet that does not consume energy during steady state operation, only during cycling.

This device comes with integrated electronics that can be operated with a 50Hz 5V PWM signal common on RC electronics. The device is designed to hold 5kg of cargo under adverse conditions with a holding force of over 80N or 8kg.


  • Robot work holidng
  • Education demonstration of magnetic properties
  • Cargo holdong for UAV's


  • 5-6V Vcc
  • PWM signal
  • Minimal steady state power <1mW
  • Water resistant conformal coating
  • Short cycle time
  • On board Pic12F with source code and in-circuit programming header

Recommended Operational Conditions


Pin Functions


Ground pin


5V supply


RC PWM signal input


The Data pin puts out the current state of the EPM,TTL high for On and TTL low for Off.

Vpp, Vdd, Vss, ICSP Dat, ICSP CLK

These pins are broken out to provide the user with the ability to reprogram the on board PIC12F. Further information can be found in the documentation provided by Microchip


After connection VCC and GND the device will charge the capacitor.

When an On command is given, either by  toggling the push button or by a PWM signal, the device will discharge the capacitor 6 times into the coil. This takes 1750ms

When an Off command is given the device will alternately magnetize the Alnico magnets repeadly, while decreasing the amplitude of the voltage, thereby demagnetizing the Alnico magnets. This takes 1250ms.

Push Button Mode

Pressing the Push Button will toggle between an On and Off command

PWM Mode

A RC Pulse Width Modulated Signal can also be used. High times between 0.75 and 1.25ms are considered an Off command. 1.75-2.25ms are considered an On command. Moving the signal on time from neutral, 1.25-1.75ms to either On or Off range will command the EPM to go into the respected state.


The Led will blink once per second if the PWM signal is not present. An error is either a. signal is missing or b.out of the time range PWM, about every 2 seconds for a missing PWM.


Led goes on when the button is pressed. The Led will blink rapidly 4 times after a command has been executed, either going On or Off.




Principle of operation


U2 a boost converter creates 40V and charges the main capacitors, C1 and C2 storing 550mJ.





The full bridge Thyristor discharges this energy into a copper coil making up the magnetic assembly. This creates a 300A current