How many amps can be drawn from the 5V output on sainsmart 16port 12v relay brd?

Hi,
I’m using a 16 port relay to power an arduino mega2560 from it’s 5v output line. It’s pretty steady at 5.01v I need 8 more relays and have a 8 port relay board available. (it is powering an ethernet shield as well)

I am powering the 16 port relay using 12v from an atx psu.

Should I power my extra 8 port relay board from the 5v power pins on the 16 port relay board ( which I use to power the arduino as well) or should I power the relay board straight from the 5v line on the atx psu?

To avoid having to run an extra cable I have it set up the first way for now. Things seem to be running fine. Relays have a strong click when I enable them individually & all of them together. This is my preferred setup, since I can choose to replace the 12v atx psu with any ole 12VDC psu if it ever dies.

Do any of you know from experience how much power can be drawn from that 5v output on the 16 port relay board? I can find more than enough videos an tutorials about how to use it but not an answer to this specific question. The “manual” is a pcb sketch.

If the relay coils are 5V, the current is about 75 mA each so 24 energized at the same time would be about 1.8 A, if 12V, current is about 30 mA each so 720 mA. Is the SainSmart regulator powering the coils or only the board logic?

First of all thank you for taking the time to reply.

outsider:
If the relay coils are 5V, the current is about 75 mA each so 24 energized at the same time would be about 1.8 A

I am not sure the 16 relays on the board relays are powered from the regulated 5V line, they might very well be powered from the 12 v line internally.
As for the 8 relays on the separate board, yes. 0.6 amps from those for sure.
Mega going full throttle about 500mW.
Ethernet shield about 150-200 mW I would think.

outsider:
Is the SainSmart regulator powering the coils or only the board logic?

I have connected both the arduino and the 8 port relay board to the 5V power on the 16 port relay board if that’s what you’re asking…
If you want to know if you can use a separate power source for the coils and for the board logic, on the 8 port relay board you can. That’s what I would do in option 2 ( the less desired option).
As for the 16 port board, I don’t know if the coils are powered form the 12v line or it’s regulated 5v internally.

I have drawn the 2 ways things could be connected. First one only uses the 12v from the atx psu and powers both the arduino and the 8 port relay from the 16 port board.

In the alternative you see the 8 port board gets powered directly from the atx psu.

Phoenixxl:
Mega going full throttle about 500mW.
Ethernet shield about 150-200 mW I would think.

Current draw of an Arduino is always the same. There is no 'throttle'.
A Mega draws about 70mA, and a W5100 ethernet shield about 180mA.
The relays on a 16-channel board with buck converter are AFAIK always 5volt (printed on the relays).

Not sure if you need opto isolation.
There is no opto isolation on a 16-channel relay board (optos are ornamental).
No opto isolation on the 8-channel board either if you share (ATX supply) ground.

I would try option#1 first, and see if parts of the buck converter are getting too hot (diode, etc.).
Leo..

Wawa:
Current draw of an Arduino is always the same. There is no 'throttle'.
A Mega draws about 70mA, and a W5100 ethernet shield about 180mA.
The relays on a 16-channel board with buck converter are AFAIK always 5volt (printed on the relays).

Not sure if you need opto isolation.
There is no opto isolation on a 16-channel relay board (optos are ornamental).
No opto isolation on the 8-channel board either if you share (ATX supply) ground.

I would try option#1 first, and see if parts of the buck converter are getting too hot (diode, etc.).
Leo..

Thank you for taking the time to reply.

I was going by this write-up where arduino power consumption is concerned , but if you say 70mA, sure.

Taking 80 for the arduino 200 for the shield and 640 for the relays that's under 1A . I'll keep it running and put my finger on the converter parts a few times to check during the day as you suggest. Maybe only enabling 4/8 relays on the 8 port board at first. Thank you.