I have remote setup of one ESP32 chip, with a couple of sensors on it and 3 relay boards (total 16 relays). I currently power them with two separate phone usb chargers. One charger for the ESP chip (which powers one 4-relay board through it 5v out) and one usb charger for the two other relay boards. All have common ground to a small breadboard for the ESP to be able to control the relays.

Although this set up seems to be working ok for a year now, i would like to upgrade the PSU as i have the feeling that sometimes (randomly - i can't place it) there's not enough power to switch all 16 relays on.

I was thinking of buying a dedicated PSU to power all of this stuff. Something like this, 5v 10A, or like this 5v 5a.

Unfortunately i have no clue how to go ahead and calculate my needs.

Could i have a small guidance as to how to select a PSU to power the following stuff adequately:

  • ESP32 Wroom something like this
  • Two (or perhaps three in the future) 4relay board. Sample
  • One 8relay board. Sample

Stuff plugged on the ESP chip:

The website I'm shopping from also has Meanwell PSUs for 2 or 3 times the price, is it worth going for a better brand? (safety wise i guess)

Is there an issue if I go for a larger UPS i.e. 5v 14A?

And lastly what about power consumption, will a larger UPS only draw the Watts I need or do they work at full consumption?

Looking forward to some help and sorry a very basic question.
Thank you

  • \$\begingroup\$ Without a data sheet, our guess is as good as yours. I'd recommend measuring the current through a relay, or all of the relays, needed to turn them on. As long as your supply has more current than this you should be ok. Maybe add an amp or two for the supporting equipment. Better power supplies arent just safer, they will maintain their output voltage at full load. \$\endgroup\$
    – user187594
    Nov 10, 2020 at 11:33

1 Answer 1


You will need to find the current draw of each device. Look up the part number and find the datasheet. Or look in the specs on the description on ebay and see if there's a current draw rating from the device.

The relay that you provided says it has a coil resistance of approx 70 ohm. Then you use ohms law to figure out the current draw (i = v/r). This gives you 71mA if you're driving the coil with 5V.

When I searched the ESP32 Wroom the datasheet recommended being able to supply a min of 0.5A.

I found that the IR sensor drew around 65mA

The buzzer you provided is 16 ohm. Assuming you're powering with 5v that would give you 0.313A. But since it's not going to be on 100% and more likely to be on 50% of the time because you pulse it on and off at a specific frequency. The rms current will be around 0.156A

The opperating current for the temp sensor said 2.5mA Max

16 relays * 71ma = 1.14amps. ESP32 = min 0.5A IR sensor = 0.065A Buzzer 0.156A temp sensor 0.0025A

total = 1.865A

I typically like to size my slightly bigger to give room for additional things in the future and so that the power supply also doesn't have to work as hard all the time. I think anything above a 2.5A 5v power supply should be sufficient for what you're doing. That 5A 5V supply you posted in the question should easily power everything you have.

  • \$\begingroup\$ Thanks for the precise explanation, I get the logic. So a good 5v3a rpi3 power supply should be able to power all these things up. Will I have to power the peripheral stuff directly from the psu or could i just connect them on the 5v out of the esp32? Where can i check the 5v out specs of the esp32 chip? Does it supply the same Amps as it's powered or does it limit them? \$\endgroup\$
    – krasatos
    Nov 11, 2020 at 7:13
  • \$\begingroup\$ I would just run everything off of the 5v power supply. The esp32 does not supply the same amount. \$\endgroup\$ Nov 11, 2020 at 13:44

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