relay controlled fermenter : what am I doing wrong?

[studioso]

Hello,
My name is Alex, I'm from Montreal and this is my first post!
I've converted a mini fridge into a fermentation chamber. I'm using a relay controlled by an Arduino, basically my intention was to replace the thermostat with the relay. however while testing i realized the fridge stayed on continuously, and after inspecting I realized that the relay is stuck in on, regardless of whether the controller energized it or not.
I'm using the following relay module, which is rated to 10A/125VAC 10A/250VAC:

https://abra-electronics.com/electromechanical/relays/relay-modules-shields/rm-2-two-channel-relay-module.html

if I move the energizing pin to the second relay it clicks nicely, so I know the issue is with the relay itself, and not the wiring or the programming. question is: was this just bad luck and the relay died prematurely or is it not compatible with the fridge? the fridge is only rated 1.5A, or 100W, here are the schematics:

Maybe the spike when the compressor kicks in killed it?
I would appreciate your input.
thank you!

 

[CU_tony]

I cant imagine that a compressor rated for 1.5a would spike high enough to kill at 10a relay.
If the 2nd relay works, why not hook it up to see if that will work. I probably would have just wired the relay inline with the AC input to the fridge so I wouldnt have to tamper with the inner wiring, though a light would be nice in my ferm chamber..

 

[laredo7mm]

I just recently had my relay stick. I am controlling a compressor rated at 8 amps. It ran fine for over two months. I tapped on the stuck relay and it would then work again. I did change it to the second relay on the board and ordered a 25A SSR to use instead.

I assumed mine stuck because I was pushing the 10A limit. I wouldn't think 1.5A would be an issue either. Maybe the quality on these relay boards are hit and miss.

 

[studioso]

Thank you for the advice. Would you think that it matters that im powering the relay module with an arduino pin, as opposed to using a separate 5v supply? In other words, im using the jumper so that the arduino both powers the optically isolated control as well as the coil power, as opposed to removing the jumper and using an independent source for the coil input...

 

[CU_tony]

Im not an expert in the matter, but I dont think you would want to use one of the I/O pins to drive the relay in the ON state.
It depends on what sort of current it takes to hold the relay ON and what sort of current the I/O pins can deliver.
I would likely tie the relay power to the power input of the arduino and let the I/O pins send the control signal.

Im not sure if this makes sense or if Im way off base here. How about a wiring diagram or picture for us to see?

 

[jsmsmk]

Why not use an SSR? They can be driven directly from the Arduino if you get one that operates at 3 + volts on the input. I'm using an extra one I had laying around and have no problems. Available for about 5 to 10 bucks.

 

[day_trippr]

Im not an expert in the matter, but I dont think you would want to use one of the I/O pins to drive the relay in the ON state.
It depends on what sort of current it takes to hold the relay ON and what sort of current the I/O pins can deliver.
I would likely tie the relay power to the power input of the arduino and let the I/O pins send the control signal.

Im not sure if this makes sense or if Im way off base here. How about a wiring diagram or picture for us to see?

I'm certain that he's using legitimate 5V to power the coils - his point I believe is just that: on that relay module there is a provision for separately powering the coil drivers through a header pin, with a jumper cap provided to instead use the same 5V that drives the "logic" side (basically, the optocoupler circuit).

In either configuration, the logic circuit to control the relay is amenable to an RPi or Uno or any other TTL-ish driver...

Cheers!

 

[studioso]

I'm certain that he's using legitimate 5V to power the coils - his point I believe is just that: on that relay module there is a provision for separately powering the coil drivers through a header pin, with a jumper cap provided to instead use the same 5V that drives the "logic" side (basically, the optocoupler circuit).

In either configuration, the logic circuit to control the relay is amenable to an RPi or Uno or any other TTL-ish driver...

Cheers!

that's correct.
thanks for everyone's advice, I'll try using the second relay on that module, if that fails I'll go for a SSR. which of course would not fit in that existing box...

 

[jsmsmk]

I put the SSR down by the compressor and just ran a 2 wire cable to control it. No room needed in the arduino box.

 

[ChuckO]

I just got 3 similar relay units, the first one I put in a circuit had 1 stuck relay right off the bat. The second one works fine, haven't tested the third yet. It isn't even worth it to contact the vendor for a replacement.

My application requires mechanical relays because an SSR has too much leakage current.