16ch relay board and power supply

So I got two of the infamous 16ch relay boards which don't seem to have a proper isolation between the control part and the switching part (https://www.berrybase.ch/raspberry-pi-co/sensoren-module/relaiskarten/16-kanal-relais-modul). No schematics either, of course. They do have a 5V separate power connector for the coils but the resistance between the 5V/ground pins on the control pins and the power pins is about 1kOhm and current seems to flow through the control pins into the Arduino. At least the LEDs on the arduino are on even if it's not connected to a power supply otherwise.
Several questions:

  • Does anyone know a 16ch relay board with proper isolation? Ideally with 5V coil voltage.
  • Is it possible to power the Arduino and the relay with two different power supplies in order to reduce EMI going into Arduino's power supply network? I'm getting random USB errors on a Raspi connected to the same power supply as the Arduino and the relay board always correlated with a relay switch.
  • Which of the control pins do I actually need to connect with the Arduino. The individual relay pins for sure, but what about GND and 5V? Is it sufficient to only connect one of them? Otherwise the separate power supply for the relay board would still feed into the Arduino, wouldn't it?

Post a diagram showing how the relay board and it's power supply are wired to Arduino.

It appears it is not connected properly. You want to power the relay board with a power supply, A power supply an Arduino does NOT make. This same power supply can power the arduino. To help we need a schematic, not a frizzy thing we can only guess. I have several variations of the 16 Ch relay boards and all have the ability to power the relays independently of the Arduino. The inputs are opto isolated so grounds do not need to be connected but it is good practice to do so. It appears they are on your board. My boards are 5V, 12V, and 24V DC, they all work great. I generally use a 12V power supply and power the relay board and the arcuino via VIN. This gives me additional isolation and I have not had a problem. Your problem may be your inductive load causing EMI. It is hard to say as there is no drawing or definition of the loads etc. You can google for the schematics, you will find several and you get to determine which is the correct one.

sithmein:
No schematics either, of course.

Can’t see the board in your link.
Try the “Click to Download the Manual” link on this page.

sithmein:
Does anyone know a 16ch relay board with proper isolation? Ideally with 5V coil voltage.

No, I don’t. All common 16-channel relay boards have optos, but no user select-able opto isolation.

sithmein:
Is it possible to power the Arduino and the relay with two different power supplies…

Possible, but useless because you don’t have opto isolation.
Most (not all) common 16-channel boards have a buck converter fitted to also power the Arduino (if you also connect grounds)
Signal only needs VCC (5volt) and inputs, because opto LEDs are connected between in and VCC (not ground).

Just use two 8-channel relay boards if you want opto isolation.

Did you separate low voltage and mains wiring looms, and did you use snubber circuits on inductive loads.
Leo…

Hi,
OPs relay product description, translated.

Characteristics:
16-channel relay module
Relays are switched via low level.
Each relay needs 15-20mA to switch
Equipped with heavy-duty relays (switching capacity AC: max. 250V / 10A; DC: max. 30V / 10A DC)
Relay type: changeover switch
Can be controlled directly with a microcontroller (Raspberry Pi, Arduino, 8051, AVR, PIC, DSP, ARM, ARM, MSP430, TTL logic)
Contacts for controlling the relays are accessible via a pin strip (RM 2.54)
The relay card is supplied with power via a screw terminal
Input voltage: 5-12V
The relay contacts are accessible via screw terminals
LEDs for displaying the relay status
Dimensions: 180 x 90 x 18 mm
Ø mounting holes: approx. 3 mm

Relay.


Tom... :slight_smile:

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