Need a little help converting brewpi set-up from switch relays to SSR

[jmrybak]

Hey all, I have been using the basic brewpi set-up commonly posted around here (ubiquitous schematic below). Overall, works fantastically well. I have no trouble holding fermentation temps within 0.1 or at worst 0.2F.

However, every few months one of the relays will stop working (sticks on or off), and cannot be revived. After figuring out why things stopped working, I just switch to the other relay on the board as I am only using cooling and continue on until that relay fails. But, now I have been through boards and I am getting tired of swapping these out. So I would like to switch to SSR as I am inclined to believe these may be more durable (double check me on this).

However, I can't seem to find a handy wiring schematic around here for SSR and don't really know how to wire these in place of the switch relay. If anyone could snap a photo or give guidance that would be much appreciated.

 

[jimmayhugh]

I'm not familiar with the arduino setup, but replacing the relay board with SSRs should be fairly simple providing the arduino outputs (pins 5 & 6 in your case) are capable of sourcing about 5 volts if the "ON" output is HIGH, or sinking about 20ma if the ON output is LOW.

If the ON output is HIGH, connect pins 5 & 6 to the + connector of the respective SSR and the - connector to ground.
If the ON output is LOW, connect pins 5 & 6 to the - connector of the respective SSR and the + connector to 5v.

The AC side of the SSR is connected the same as the Relays.

 

[day_trippr]

The Atmel 728p digital io pins are rated for a max of 40ma (short duration) and 20ma continuous, both at 5v.
So it would likely work, but I wager most designs stick a transistor or fet between the Atmel chip and an SSR or small relay coil input...

Cheers!

 

[jimmayhugh]

The Atmel 728p digital io pins are rated for a max of 40ma (short duration) and 20ma continuous, both at 5v.
So it would likely work, but I wager most designs stick a transistor or fet between the Atmel chip and an SSR or small relay coil input...

Cheers!

I use the Teensy board for all of my designs, and have used both transistors and FETs for more drive capability and level translation when necessary. I have directly run the SSRs with as little as 3.3v over short distances for hours with no problems. Like you said, it will most likely work, but YMMV.

 

[jmrybak]

I use the Teensy board for all of my designs, and have used both transistors and FETs for more drive capability and level translation when necessary. I have directly run the SSRs with as little as 3.3v over short distances for hours with no problems. Like you said, it will most likely work, but YMMV.

So is having switch relays crap out this frequently normal? It sounds like the use of an SSR is not as common as I thought. I could have sworn I saw several SSR BrewPi around here. But I certainly don’t know enough to develop anything new.

 

[jimmayhugh]

So is having switch relays crap out this frequently normal? It sounds like the use of an SSR is not as common as I thought. I could have sworn I saw several SSR BrewPi around here. But I certainly don’t know enough to develop anything new.

The main advantage with SSRs, IMHO, is that most of the SSRs are zero crossing function devices. This means that when you're running an inductive device such as a pump motor, there's not as large an in-rush current when turned on, nor is there a large inductive kickback when the device is turned off.

Relays are indiscriminate as to when they turn off and on, and the in-rush current or inductive kickback can temporarily exceed the current rating of the relay contacts, or cause sparking, which can fuse or pit the relay contacts.

 

[day_trippr]

I have been running four functional BrewPi Arduino sub-systems all using the same 2 channel Sainsmart relay modules and directed by a single RaspberryPi for a couple of years and have yet to suffer a relay failure. I expect that's simply because the start up loads across the fleet are below what the pissant relays can handle...

Cheers!

 

[jimmayhugh]

I have been running four functional BrewPi Arduino sub-systems all using the same 2 channel Sainsmart relay modules and directed by a single RaspberryPi for a couple of years and have yet to suffer a relay failure. I expect that's simply because the start up loads across the fleet are below what the pissant relays can handle...

Cheers!

It really depends on what you're controlling, and how frequently the relay is being turned on/off. I was controlling two large commercial freezers with one of my TeensyNet controllers and never had a problem, but I have always used SSRs. If I'm not mistaken, the max load on those little relays is 10 amps, and that could probably be exceeded temporarily with an older/large freezer/refrigerator.

 

[day_trippr]

Older/larger is likely key - my three fridges and keezer are all recent vintage/e-star appliances (a pair of 17cf top-freezers, a 23cf top-freezer and a 13cf keezer).

I will say I had a problem with a 10A lighted switched/fused bulkhead/ingress I used on all of my BrewPi minions - turned out the switch was only rated for 6A and it took only days in service for that switch to fail open...

Cheers!