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The questions:

  1. What should I look for when searching for a PCB relay to drive inductive loads?
  2. Any tips on how I could find relays like that (digikey, etc do not allow you to filter by snubber, peak-switching, etc)

The context:
I am driving DIN mounted latching relays with a custom build PCB. I usually switch on and off the PCB relays very quickly, around 100ms.

System diagram img

So far, I have been using PCN105D (datasheet)

The problem I have is that this relays creates very large spikes, that I tried to fix with capacitors and diodes on top of the relay driver (ULN2003A datasheet) but nothing seems to work. (link to another question describing the issue)

I have tried replacing the relay with an SSR and that seems to fix my problems. Reading as much as I could find, To drive inductive loads from my PCB, I need a peak-switching SSR relay with an internal RI Snubber.

The problem I have is that I could not find small&slim (under 25x5mm) PCB relay with internal snubber, and even less with peak-switching.

The questions again :)

  1. What should I look for when searching for a PCB relay to drive inductive loads?
  2. Any tips on how I could find relays like that (digikey, etc do not allow you to filter by snubber, peak-switching, etc)

Full schematics: link
Full PCB layour: link
Full project: link

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  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. \$\endgroup\$
    – Voltage Spike
    Aug 15, 2022 at 1:07

1 Answer 1

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Place a series resistor-capacitor (RC snubber) between the lines that control your latching relay. They can go on the board, next to the relay, or be built/spliced into the cable somewhere along the way.

The capacitor should be 220VAC rated and non-polarized, 10nF-100nF probably. The resistance should be on the lower end, 1-10Ohms maybe. The resistor wattage will vary depending on the size of the capacitor and it's resistance. You're not switching frequently so I imagine 1W should be okay.

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