rpi 5v rail max current


Postby tlfong01 » 2018-Jun-02 Sat 10:10 pm

5V Relay KY019 Specification

I bought a KY019 relay module some weeks ago. I could not find the specification (Errata – the shop does provide a spec, but placed below some irrelevant promotion ads, so I missed it) so I used an adjustable voltage regulator as input signal, and two multi-meters to measure the parameters.

I found the relay

1. activates at input Vin > 2.5V, driving current about Iin ~= 4mA, coil current Ic = 50 ~70mA, and

2. deactivates at Vin < 2.2V, coil current Ic < 40mA.

3. So I think the Rpi’s 3.3V logic GPIO signals can directly drive the module.

But Rpi’s 3.3V or 5V power with 50mA max (Errata – should be much more than that, see update below), from the 26/40 pin connector should not be used to power the relay, which takes 70mA+ to operate.

A separate 5V power supply should be used (Errata –

4. OK to use the 5V power pin of the 40-pin GPIO block connector

to power the module, and the grounds of the Rpi and Relay powers should be connected together.

My measurements are summarized below.

Update 1

My 3V3/5V rail current limit is out of date. I read recently that only early models of Rpi has the 50mA limit for 3V3.

For Rpi3, both 3V3 and 5V power current limit is up to 1A,
but I have not found any official Rpi documentation confirming this.

Update 2 – 2019jan14hkt2106

5. Hysteresis characteristic

Case 1. If relay is already activated by Vin > 2.5V, now decreasing Vin to just below 2.5V will not deactivate it. Only when Vin decreases to the lower threshold of 2.2V, then it will deactivate.

Case 2. Now if the relay is already deactivated by Vin < 2.2V, now increasing Vin to just above 2.2V will not activate it. Only when Vin increases to the upper threshold of 2.5V, then it wil activate.

This hysteresis thing is usually taught in the middle school physics subject of electricity and magnetism.

KY019 spec
ky019_spec_2018jun0201.jpg (228.32 KiB) Viewed 14647 times
Last edited by tlfong01 on 2019-Jan-16 Wed 9:27 pm, edited 10 times in total.

Categories: Uncategorized

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