https://www.ebay.com/itm/312703154947?_trkparms=itmf%3D1%26aid%3D1110006%26rkt%3D5%26mech%3D1%26algv%3DDefaultOrganicWebV9BertRefreshRankerWithCassiniEmbRecall%26pmt%3D1%26amclksrc%3DITM%26sd%3D388044863232%26sid%3DAQAKAAAAECMbuyGDLwIZzwDl1LI5fic%3D%26itm%3D312703154947%26noa%3D0%26plcampt%3D0%3A150028188015%26algo%3DHOMESPLICE.SIM%26brand%3DPhoenix+Contact%26asc%3D20200818143230%26ao%3D1%26rk%3D4%26pid%3D101224%26b%3D1%26mehot%3Dnone%26lsid%3D0%26meid%3D7924c5d76be64b87ad115588b423f513%26pg%3D2332490&_trksid=p2332490.c101224.m-1&itmprp=cksum%3A3127031549477924c5d76be64b87ad115588b423f513%7Cenc%3AAQAKAAAA8FpV4T02GSLWmLmcYHS%252Bawhg9HB3NVAH8KQdy74hckvfm%252BTv7AoY9bWSvyrWMwnykYfzYbkMtous8borg3MTxgcKqFnGEe1BAjmNaEdIhfMDzORhJ1OoXVVkFJQfQeYPAVboDnwOps2R6MN1TGSjHrFTu2AK38LviJTMtgW8syu8fBcRXGQFMpb7%252BDlAUKH9ezGnmNQ%252FY7n1yVncV6mkIJEC55avRyQN%252B%252FAZ70KDjHWZjodn7JLMpW5E1oWOdqMDl%252BYivdNFdDdWMAJa%252FkHjeBhLDg%252FFQ9KzqNgumpMErElcK8MzG5B2sD8Icp9clWW76A%253D%253D%7Campid%3APL_CLK%7Cclp%3A2332490

https://www.unikeyic.com/media/datasheet/be/87/9686/be/76ba606d9cf1954e0516ce9771fd6c1a.pdf?srsltid=AfmBOoqzT5BeG2quRfQ1ypTPoe4BRH-rA8qVrOug0NFtN5_qK5DLUOK6

https://www.mouser.com/datasheet/2/324/2/905103-1469443.pdf?srsltid=AfmBOootqm0dqJqoOndpJvm0nsWhf7tYL7RuRkqnomV6czaWx9QkStLb

https://www.phoenixcontact.com/en-pc/products/solid-state-relays-st-ov2-12dc-60dc-1-2905022

ST-OV2- 12DC/ 60DC/1 – Solid-state relay
2905022
Product photo Solid-state relay ST-OV2- 12DC/ 60DC/1
The figure shows version ST-OV 2- 5 DC/ 60 DC/1
Plug-in power solid-state relay, with LED and protective circuit in input and output circuits, input: 12 V DC, output: 12 – 60 V DC/max. 1 A, can be plugged into basic terminal blocks

https://www.phoenixcontact.com/en-pc/products/solid-state-relays-st-ov2-12dc-60dc-1-2905022

OMRON Electronic Components Europe on esitellyt uudet G3VM-sarjan MOSFET-releet, jotka on suunnattu vaativiin testaus- ja mittaussovelluksiin. Uutuuksien keskeinen etu on erittäin nopea kytkentä ja pieni signaalikapasitanssi poikkeuksellisen kompaktissa kotelossa.

Releet on pakattu 2,0 × 1,45 millimetrin S-VSON(L)-koteloon, mikä mahdollistaa suuren kanavatiheyden laitteissa, joissa tila on kriittinen. Liitinnastojen välinen kapasitanssi (pin-to-pin) on vain 0,6 pikofaradia, ja kytkentäajat ovat parhaimmillaan 0,08 millisekuntia päälle ja 0,12 millisekuntia pois. Vuotovirta jää yhden nanoampeerin tasolle, mikä parantaa mittaustarkkuutta erityisesti herkillä mittausalueilla.

OMRON tuo markkinoille 20 voltin mallit G3VM-21QR ja G3VM-21QR1 sekä 40 voltin version G3VM-41QR4. Ne on suunniteltu erityisesti automaattisiin testausjärjestelmiin, suurinopeustestaajiin sekä sovelluksiin, joissa mitataan puolijohteita, 5G-ratkaisuja ja robotiikkaa.

Protection for the Microcontroller: Optocouplers use a light signal (an internal LED and phototransistor) to transfer the control signal instead of a direct electrical connection. This acts as a protective barrier, preventing dangerous voltage spikes, surges, or back EMF generated by the inductive relay coils from reaching and damaging the delicate low-voltage logic of the ESP32.
Noise Immunity: Relays, especially when switching high-current or AC loads, create significant electromagnetic interference (EMI) and noise on the power and ground lines. This noise can cause unpredictable behavior, such as the ESP32 freezing or resetting, which is likely what you experienced. Opto-isolation drastically reduces this interference.
Signal Integrity: By isolating the circuits, the optocoupler ensures that the low-level signal from the ESP32 results in a clean, unambiguous ON/OFF command for the relay driver, improving the system’s overall reliability and stability.
Safety Standards: In many applications, especially those involving mains voltage (AC power), safety regulations require galvanic isolation to protect both the devices and users.

For this isolation to work effectively on most hobbyist relay modules, you need to power the relay coil side (often marked as JD-VCC or having a jumper between VCC and JD-VCC) with a separate, independent 5V power supply, not from the ESP32′s 5V or 3.3V pin. The control pins (IN1, IN2, etc.) still connect to the ESP32 GPIOs.
Now that you know the importance of isolation, would you like to know how to properly connect the new relay module with a separate power supply?

Explained on automotive air conditioning relay for comprressor magnetic clutch

A relay is an electromechanical switch used to control a high-current circuit with a low-current signal. It acts as a bridge between a control circuit and the component it powers — like headlights, fans, fuel pumps, etc.

Relay Pin Types Explained
3-Pin Relay
4-Pin Relay (Most Common)
5-Pin Relay (SPDT – Single Pole Double Throw)
8-Pin Relay