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4.5
Making a sous vide controller or almost anything else you want to heat or cool with a PID requires that you switch a bit of line voltage. The PID that many people use is the Dual Digital Display PID Temperature Controller. Ideal for FURNACE & KILN control and it has an internal relay which is capable of switching three amps at 110 volts. My presumption is that you want to use something like this at no more than 50% of its rated capacity for long life. If you were going to control an incubator where the heat would be generated by a 60 watt light bulb in a styrofoam box, I would definitely use the internal relay, but for a sous vide controller, switching a single 300 watt immersion heater like the NORPRO 559 Immersion Heater for Warming Liquids has the internal relay working at 91% of the rating at a nominal 110 volts, and more if you get a higher voltage like we do here, from our local power company.Now if you did burn out the internal relay, chances are that you could program the PID to use the SSR outputs, and then attach the SSR, but there is a chance that burning out the internal relay would break something else that would keep the PID from working, although I think that is small. I actually think that you want to use the SSR because the SSR/heat sink combo will be more reliable than the internal relay and any single failure could cause you to lose food that would be likely to cost more than the heat sink plus the SSR would cost.The SSR device that I believe most people use is the 25A SSR Solid State Relay DC:Input AC:Output for PID Temperature Controller since it is cheaper than others, reliable, and switches a lot more than the 15 amps that is the most that can be carried by the typical US wall plug. In order to work at or near its rated capacity and for the vendor to guarantee that it will work, that SSR requires a heat sink, and this heat sink is the one needed.Yep, this heat sink is designed specifically to work with that SSR.You should know that the heat sink is tapped for a metric screw which is available at ACE, Home Depot or Lowes. It is *not* an SAE thread. You might also want some heat sink paste or Permatex anti-seize lubricant. The heat sink paste is the best but the Permatex will work and help with the heat transfer from the SSR to the heat sink.The proper screws will go through holes in the heat sink and connect the SSR firmly, for good heat transfer. You don't need to crank them down, just tighten them firmly, probably 12 inch pounds. You want 4mm screws that are not longer than about 17mm. 10mm in length would still be fine, I think. Screws that are too long will hit the next fin and not tighten, you would have to cut them and it would be a mess. It is likely that you want the shortest 4mm screw carried by the hardware store, and you do not want a hex head, there may not be clearance to tighten it. Either get a screw that can be tightened with a screwdriver or one that can be tightened with an allen wrench.There are two slots that connect the heat sink to the enclosure. If your enclosure is plastic, I suggest nylon screws to hold the heat sink to the case, so that there is no chance of shock. You might decide not to mount the heat sink at all.I used my SSR with a countertop roaster and with a rice cooker. Maximum draw is probably 700 watts. In neither case did the SSR get more than the smallest bit warm. If I was using it closer to the rated capacity, it would probably get a lot warmer.I guess I believe in the use of these heat sinks - they are cheap insurance.
