SSR vs. Coil Relay

[Facinerous]

So I just have to know.

I have seen a few things that people are doing in the home brewing realm that seems unnecessary in my view. So I just have to ask.

Why is everyone using SSRs for their brewing setup opposed to regular old coil relays? For the life of me I can't figure it out. Is it just because they are solid state and cool, is it that those who come up with a good design used them and people are just copying the design? Is there a real practical purpose to this?

Just have to ask to see what others opinion are. For me personally I don't see a need for the use of SSRs. Due to the heat they throw off, and the potential need for a heat sink. Plus I don't think the package size makes a big difference between the two.

Help me understand. I don't get it.

 

[byrone]

The reason for choosing an ssr over an contact relay in a given application is because of speed. SSR's are able to operate at high speeds and contact relays operate at a slower switching speed. For example when using a pid controller with an electric element to maintain an exact temperature, a SSR is used because a very fast switching action is required where a contact relay reacts to slowly(it possibly could for a short time but would break). The best use of a contact relay is in a refrigeration setting because a fridge/freezer's compressor is turned on for a period of time then turned off again at a slower pace. They both have trade offs: SSR's require and heat sink and contact relays have a limited switching life. Hope this helps.

 

[Facinerous]

Oh cool. How many cycles do you think a relay would cycle through during a brewing session? I don't think most PID controllers use a PWM function. At least that I know of. So I couldn't see the speed of the relay really being a factor. Maybe it is though.

The standard 500K cycles for a coil relay seems like a good amount to me. Unless the temp controller is cycling a relay more than 1000 times during a brewing session.

What you are saying makes sense to me. If your PID is cycling that much though that seems a bit excessive though.

 

[byrone]

I'm honestly not sure how many times it would cycle during a brew session. It all depends on the type of application. It would be well under 1000. And you're right about not all pid controllers not having pwm but you want to know the type of output the controller has because some are ssr output and other are relay. Difference is that ssr output controllers output a DC voltage and the relay type pass voltage through when the on condition is met. What controller are you planning on using and what are you using it to control?

 

[iijakii]

Oh cool. How many cycles do you think a relay would cycle through during a brewing session? I don't think most PID controllers use a PWM function. At least that I know of. So I couldn't see the speed of the relay really being a factor. Maybe it is though.

The standard 500K cycles for a coil relay seems like a good amount to me. Unless the temp controller is cycling a relay more than 1000 times during a brewing session.

What you are saying makes sense to me. If your PID is cycling that much though that seems a bit excessive though.

Depends also how much temp maintenance you think your system will be doing. Are you going to just be mashing in a keg and having to run a herms setup? The PIDs are so accurate they'll turn on the elements for just a tad here and there, pretty quickly. Even then I'd be surprised if it cycled anywhere near that.


Edit: When I boiled on my last rig, I had to set the manual cycle at just ~25% to maintain a hearty boil. That's a lot of cycling.

 

[Brumateur]

Oh cool. How many cycles do you think a relay would cycle through during a brewing session?

The standard 500K cycles for a coil relay seems like a good amount to me. Unless the temp controller is cycling a relay more than 1000 times during a brewing session.

To control heating element you need high ampacity relay. And that type of relay has 50K-100K electrical cycles endurance.

Lets do some calculation. Pid cycle is about 4 seconds. So relay will fire 900 times per hour. It gives us about 90-110 hours of relay life.

Doesn't look very good

 

[Facinerous]

Ultimately I am setting up a RIMS mash recirculation system.

Have the pump and heat exchanger set up. I'm looking for a temp controller and appropriate thermocouple to moderate everything now.

I'm asking about relays because I have not been able to find a temp controller who's contacts can handle the heating element I am using. Its just a 1500 watt element, but that pulls roughly 13 amps. So alas I am stuck with a temp controller that cycles a relay for the heating element.

I wasn't really expecting the relay to cycle more than 100 times or so during a brewing session. I kind of created this thread to see if people could convince me to use an SSR though. Mostly to see if it was worth it. I do appreciate the advice you have all given.

I think my plan is to set the PID at a 1.5 degree f threshold to reduce the cycling. I don't think I need to maintain within the tenth of a degree. The temperature will be monitored on the output of the heat exchanger I am using. I expect a little overtemp after a full on/off cycle from the controller, (thinking .5 degree f) but that should all iron out in the wash.

Thanks for the help and input everyone.

 

[RadicalEd]

Definitely go SSR! As mentioned earlier, the PID's cycle rather frequently in operation. You'll hit the Mean Time Before Failure in no time at all with an electromechanical relay. A decent SSR and heatsink are like $20. Total. I've seen emag relays for about $5 less than that....totally not worth the savings!

Don't get me wrong, those old coil relays do a great job for applications that only have occasional switching. But this is not that application!

Credentials: Electrical engineer who designs relay systems at a power plant.

 

[Facinerous]

Nice. Thanks Ed. What plant do you work at?

I work at Diablo Canyon as a contractor.

 

[RadicalEd]

Cook Nuclear. I might actually be visiting Diablo in March to help with a self inspection .

 

[passedpawn]

SSRs are totally silent. Silence is golden.

SSRs are golden.

 

[The10mmKid]

Facinerous,
You can use relays if you'd like. Just keep their limitations in mind.

For a 13A draw, use a relay with contacts rated for 20A.

Make sure the controller you choose can be programmed for 'cycle time'. You'll want to place a minimum setting of 20-sec. Then let your controller tune itself with that limitation. If it wanders too much, go for 15-sec.

SSR's and relays share a common failure mode. The SSR will latch on, the relay contacts will weld closed.

Might consider replacing the relay after a couple years of use for good measure.

'da Kid