Page 1 of 1

Safety of KY-019 relay

Posted: Sat Apr 20, 2019 4:49 pm
by ajocius
I intend to use KY-019 5V One 1 Channel Relay Module to switch on and off 2KW air heater. This is supposed to run during night, when sensors in my greenhouse would indicated that temp is below set threshold. It says it can handle up to 250V 10A, so seem to be not exceeding capabilities, but rather close. I would certainly do not want to start fire at night, not sure what safety measures I could take here...

Re: Safety of KY-019 relay

Posted: Sat Apr 20, 2019 4:58 pm
by dhylands
You probably want to make sure that you have multiple temperature sensors. If one of the sensors fails then you might keep the heater on indefinitely.

You probably also want a sensor to detect that the heater is being powered. That way if the relay fails in a mode where its powering the heater you can detect that the heater is still running when it shouldn't be and initiate an alarm.

I'm sure that there are other failure modes I haven't considered, but that should get you started.

It's really thinking about the various things that can fail and how to detect these failures.

You didn't mention how the relay was going to be connected to the MCU, but normally (unless the relay is specifically designed for a really low-current activation) you need to use a MOSFET or transistor to control the relay, and the MCU controls the MOSFET/transistor.

If the relay doesn't have one, having a flyback diode is a good idea. ... or-a-relay

Re: Safety of KY-019 relay

Posted: Sat Apr 20, 2019 6:31 pm
by ajocius
Thank you valuable response. I intend to use ESP32 with sensors and relay switch conected to it. Micropyhon as SW. Node Red to check temp every 10min and, if below threshold, Node Red sends mqtt to switch on heater for 5 min. Intend to test prior bringing plants, as I do have monitoring of temp already set up.

Re: Safety of KY-019 relay

Posted: Sun Apr 21, 2019 3:50 am
by cyberlab
Hi, in my experience I would not use a standard 10 amp relay for a load of an electric heater that consumes 10 amp, it will not last a long time and most likely the contacts are stuck and therefore your heater stay on indefinitely.
If you need to use that type of relay, use at least a 20 amp amp for that load and with RC snubber filters as you will also have to use a transistor diode and a pair of resistors as they tell you, I would recommend a relay solid state you usually already have all the aforementioned components included since most of them can be activated from 3 to 32 vdc in the same way I would recommend a 20 amp capacity so that it does not require a large heat sink or none

Re: Safety of KY-019 relay

Posted: Sun Apr 21, 2019 4:14 am
by chrismas9
All domestic room heaters have a tilt switch and thermal cutoff that is independent of the thermostat. I suggest an independent cutout that does not rely on software.

A suitable thermal cutoff is something like Digi-Key 317-1127-ND. These are available with different trip temperatures. It must be close enough to the heater to trip if it overheats. Try measuring the working temperature with the thermostat cycling, then pick a suitable trip temperature.

The relay module has a logic compatible transistor driver. I agree a solid state relay would be more reliable. In either case if there is any doubt whether the module is certified double insulated connect the logic (ESP32) ground to that mains ground.