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PID Design Questions

Murray

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Sourcing out components for a PID build and have a few questions.

1) Can’t seem to get my head around solid state relays. Internet research suggests that a 40Amp is better than a 25 Amp relay although a 25 Amp will suffice for a 800Watt element drawing 6.7 Amps. Why would I consider a 40 Watt when 25 Amps is more than enough. House current is 15 Amps.

2) If I install a small fan is the enclosure do I still need a heat sink? I’m kind of thinking not but cooler electronics will last longer and perform better.
 

Steve H

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1) A 40 amp SSR is just beefier and should hold up better from all the on/off cycles a smoker is going to produce. And for the few extra dollars. It makes sense.
2) Yes, you should still use a heat sink. And use heat sink compound between the ssr and the heat sink. And add the cooling fan if you wish to ensure a long life from the ssr.
 

olaf

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These ssr's that you see for cheap online are not always what they claim. I had grand plans making a totally wifi controlled smoker all I need are parts and some borrowed code. The 15 amp ssr's six of them failed within 2 to 25 hours of use. Some only had 3 amp loads on them. I went back to my 25 year old digital temp controller with a built in (industrial) 10 amp ssr switching a 1500 watt heating element, it's been working for years.
 

JckDanls 07

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I will suggest that the heat sink be outside of the enclosure.. but I'm sure you knew that ...
 

Jonok

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In my experience, SSRs aren’t as robust as electromechanical contactors. I’ve used the internal ssr in $15 pids to power a $15 40a DPDT contactor and I haven’t had any failures. They make noise, but they just seem to work.
 

Murray

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I
I will suggest that the heat sink be outside of the enclosure.. but I'm sure you knew that ...
I thought of that, then the enclosure gets too “bulky”. I’ve decided to forego the fan for now, I’ll be able to add a fan later if needed. Figure I can stuff a TP-08 probe inside the enclosure to monitor temperatures and evaluate the need for a fan.
 

Murray

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These ssr's that you see for cheap online are not always what they claim. I had grand plans making a totally wifi controlled smoker all I need are parts and some borrowed code. The 15 amp ssr's six of them failed within 2 to 25 hours of use. Some only had 3 amp loads on them. I went back to my 25 year old digital temp controller with a built in (industrial) 10 amp ssr switching a 1500 watt heating element, it's been working for years.
I see quite a price difference, I’m going with an Inkbird PID and their 40A SSR. They are in my price range and it’s a recognizable respected name.
 

JckDanls 07

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If no fan then you would want the heatsink even more so outside of the controller box (enclosure) ...
 

Murray

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If no fan then you would want the heatsink even more so outside of the controller box (enclosure) ...
You figure there will be too much and a fan is a necessity? Other commercial PID don’t have fans that I can see so I figured I might be able to get away without a fan. That being said I have no idea what electronics the commercial ones use and how they mitigate heat. Thanks for your input.
 

JckDanls 07

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No... a fan is not necessary as I don't have one in mine... The heat sink gets really warm .. and heat and the PID controller aren't the best of friends...
 

olaf

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I see quite a price difference, I’m going with an Inkbird PID and their 40A SSR. They are in my price range and it’s a recognizable respected name.
I was looking at that one a month ago just not ready to do my major smoker rebuild. If you do have problems with ssr not handling the heat or current don't hesitate to go to an old school relay.
 

Murray

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1) A 40 amp SSR is just beefier and should hold up better from all the on/off cycles a smoker is going to produce. And for the few extra dollars. It makes sense.
2) Yes, you should still use a heat sink. And use heat sink compound between the ssr and the heat sink. And add the cooling fan if you wish to ensure a long life from the ssr.
Would dielectric grease work instead of thermal paste?
 

Murray

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All parts ordered the same time, so far only the Inkbird ITC-106VH has arrived so I set it up on the work bench to play with it. This unit is for an older MES at our summer home but in the mean time I’ll use it here at our winter home after I rewire the winter MES. A couple of questions.

1) No grounding terminal on the Inkbird or the SSR so I’m assuming I ground only the receptacle? If I install a switch(Question 4) should it be grounded? Plastic project box so no ground there.

2) Once the PID is tuned to say 225F for a hot smoke and I want to keep beer from freezing in sub freezing temperatures(cold smoke) will the PID parameters need changing since it was initially set at 225F and now I’m trying to keep the MES around 37F? I used keeping beer from freezing as an example since there is a big temperature difference from 225F to 37F?

3) I haven’t allowed for a fuse in the design. I probably should put a 15amp. fuse inline on the hot side?

4) I haven’t allowed for an off/on switch, figured pulling the plug would work. Do I need an off/on switch for safety or is a switch a nice to have?

Thanks for you time and suggestions.
 

olaf

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I'm reworking my smoker for an inkbird controller also got mine today.
1 grounding conductor any terminal that will accept this will require the connection to ground just assume its needed if there is a grounding terminal.
2 not sure but I wouldn't change anything
3 fuse may be a problem because there is no time delay if your drawing 16 amps it's gone whereas your circuit breaker won't trip for an hour.
4 I'm a fan of switches pulling a plug is sometimes fatal to electronics
5 switch the black conductor this also applies to the ssr the neutral and grounding wires go right on through.
6 black on brass white on silver green/bare on green.
 

Murray

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Thanks for the reply. I was thinking a fuse to potentially help with those power surges that sometimes blows up electronics and there’s a chance(small) that it might be run off a generator. The heating element is 800W and a small fan, less than 1 Watt so say 7Amps through the circuit. Found a on/off switch in the tickle trunk so that’s covered. If the box would arrive I can start assembly...
 

olaf

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Sounds like you'll have things covered well. Mine is more involved not sure why I'm doing it but I ordered 150 bucks worth of electric gizmos to put into the smoker. Good luck to ya or good luck to me I'll need it.
 

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