Overview
The P20/15 is a 12V DC holding electromagnet: energize its two leads and the flat 20 mm face grips ferrous metal with up to 3 kg (about 30 N) of force; cut the power and it lets go. That energize-to-hold behavior makes it a clean building block for cabinet locks, door latches, parts pick-and-place, robot end effectors, drop mechanisms, and magnetic fixtures.
It is a two-wire inductive load. You switch it with a relay, transistor, or logic-level MOSFET from an Arduino, ESP32, Pico, or Raspberry Pi — never directly from a GPIO pin — and you always give the coil a flyback diode so its stored energy has somewhere safe to go at turn-off. The wiring section covers both.
At a Glance
Voltage
12V DC
Holding Force
3 kg (~30 N)
Size
20 mm dia x 15 mm
Type
Energize to hold
Power
~2-3 W
Connection
2 wires + mounting thread
Specifications
| Parameter | Value |
| Model | P20/15 holding electromagnet (sucker type) |
| Rated Voltage | 12V DC |
| Holding Force | Up to 3 kg / ~30 N on flat, clean mild steel |
| Typical Power | ~2-3 W (~0.2-0.25 A at 12V) |
| Dimensions | 20 mm diameter x 15 mm tall |
| Mounting | Threaded hole/stud on rear face |
| Duty | Continuous operation supported; coil warms in normal use |
| Load Type | Inductive — flyback diode required with electronic switching |
| Polarity | Not polarity-sensitive for holding operation |
Wiring & Driving Guide
Two wires: one to switched +12V, one to ground. The microcontroller only ever drives the switch:
| Connection | Goes To |
|---|---|
| Magnet lead 1 | +12V supply |
| Magnet lead 2 | MOSFET drain (or relay COM/NO contact) |
| MOSFET source / relay coil GND | Supply GND, shared with microcontroller GND |
| MOSFET gate (via ~220R) | GPIO pin (logic-level MOSFET, e.g. IRLZ44N / 2N7000 for this small load) |
| Flyback diode (1N4007) | Across the magnet leads — cathode (stripe) to +12V side |
Warning: Never drive the coil straight from a GPIO pin — it needs 12V at ~250 mA, far beyond any microcontroller pin. And never omit the flyback diode: the voltage spike at turn-off can destroy your MOSFET or microcontroller.
Tip: Holding force is rated on flat, clean, thick steel with full face contact. Paint, rust, dust, air gaps, or thin sheet metal reduce it dramatically — design your mechanism so the armature seats flush against the magnet face.
Code Examples
Arduino: timed hold and release
electromagnet_control.ino
// P20/15 electromagnet via logic-level MOSFET on D5
// 12V supply for the magnet, grounds shared with the Arduino.
// Flyback diode across the magnet leads is mandatory.
const int MAGNET_PIN = 5;
void setup() {
pinMode(MAGNET_PIN, OUTPUT);
Serial.begin(9600);
}
void loop() {
Serial.println("Magnet ON - holding");
digitalWrite(MAGNET_PIN, HIGH);
delay(5000); // hold for 5 s
Serial.println("Magnet OFF - released");
digitalWrite(MAGNET_PIN, LOW);
delay(3000); // released for 3 s
}
Pico (MicroPython): button-controlled lock
electromagnet_lock.py
# Simple electromagnetic lock: hold while button is NOT pressed.
# MOSFET gate -> GP16, button between GP14 and GND.
from machine import Pin
import time
magnet = Pin(16, Pin.OUT)
button = Pin(14, Pin.IN, Pin.PULL_UP)
magnet.value(1) # locked at boot
print("Locked")
while True:
if button.value() == 0: # button pressed -> release
magnet.value(0)
print("Released")
time.sleep(3) # stay open 3 s
magnet.value(1)
print("Locked")
time.sleep(0.05)
Frequently Asked Questions
Does it stay magnetic when powered off?
No — it is an energize-to-hold magnet. A faint residual attraction can linger on very smooth steel, but any spring or gravity load breaks it. If you need hold-on-power-loss behavior, that's a permanent-magnet lock with reversed logic.
Why does it only hold 1 kg in my build instead of 3 kg?
The 3 kg rating assumes flat, clean, thick steel in full contact and a straight pull. Air gaps as thin as paper, paint, curved surfaces, or side-loading cut the force sharply. Add a flat steel strike plate to whatever you're gripping.
Can I run it continuously?
Yes — at ~2-3 W the coil runs warm, not hot, and continuous duty is normal for lock applications. Give it a little airflow in enclosed housings and it will last.
Can I power it from 5V instead of 12V?
It will hold weakly at 5V (force scales roughly with current), but for the rated 3 kg you need 12V. If you only have 5V logic, keep 12V for the magnet and let a MOSFET or relay bridge the two worlds.
Relay or MOSFET — which should I use?
Either works. A relay module is simplest and gives full isolation; a logic-level MOSFET is silent, faster, and has no contact wear — the better choice if you switch often. Both still need the flyback diode across the coil (relay modules usually include one for their own coil, not for your magnet).
Is polarity important?
Not for holding — either lead can go to +12V. Polarity only changes the magnetic pole orientation, which matters only in exotic setups pairing multiple magnets.