Using HLK-PM01 safely

Other Hardware General Electronics
1

Hi

I'm about to build an Arduino circuit for switching 240v relays. I would also like to use 240v to power the Arduino circuit itself. I have ordered an AC-DC converter (HLK-PM01) for this purpose - the information I have read indicates this is a pretty good device. I only need 100-200mA in my circuit.

Because I am using 240v I am keen to ensure I take as many safety precautions as possible. With this in mind I have designed the board with a few extra safety features, namely:

  • included a slot in the board between the 240v pins of the HLK-PM01. The pins are only 5mm apart, and the pads themselves are more like 3mm.

  • included a 275v varistor in the circuit to effectively short circuit on the 240v in the event of a large power spike.

  • include a 300mA fuse on the 240v side. This will protect things in the event that the HLK-PM01 short-circuits (fails) or the varistor short circuits.

  • include slots around the common pin of the relay, to keep effective distance from the low voltage side.

  • keep the 240v circuit as far away as possible from the 5v circuit.

Keen to get some feed back on this design, or/and suggestions to make this circuit as safe as possible.

Thanks

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1 Like
2

Nothing jumps out at me (do you have the footprint for those relays right? With the common closer to the pins for the coil than the other contacts? Usually it's the other way around... Doublecheck that).

I've done similar things with el-cheapo AC adapters - though in may applications using a commercial phone charger makes more sense. Be sure to either ground the case, or use a non-conductive material for the case.

3

Thanks. Yes the pinout for the relay is as per the attached (from the data sheet). Common pin is between the 2 switching pins.

Relay_pin_out.png

4

I also don't see anything. Some people suggest adding a temperature fuse glued to the HLK case. There is a very long thread at the MySensors forum about integrating the HLK. They also do some output filtering.

Regarding the relay: I have seen exactly the same cutouts on commercial relays, so I am not surprised about that weird pinout.