In addition to my electronics hobby, I have a home brewing hobby. I have a fairly large system for a hobbyist, and do 20-25 gallon "batches". Regardless of scale, brewing requires a fair amount of heating water (and then cooling it back down, hehe). I started with Propane, but for various reasons have migrated to "All Electric".
The heating elements I use are 3kW-6kW @ 240Vac, so after more than a year of "flipping breakers" to control the power, I have decided to give SSR's a try. I just received some "Ruike SSR40DA" SSRs. This PDF http://www.google.com/url?sa=t&rct=...=MhYNiYC97YH9t6jSNR6DYQ&bvm=bv.57967247,d.cWc from Crydom absolutely confirms my low marks in thermodynamics, and it appears to be as "dummed down" as one can make Thermodynamics, lol.
While IN THEORY the fairly large heat sinks provided with the SSRs **should** handle the 45W of SSR heat gain, but I have little faith. My plan from the get-go was to mount the SSRs (five of them) to some 4" square aluminum tube stock (I happen to have on hand) with the SSRs on the "outside" of the tube stock and the heat sinks on the "inside" of the tube stock. I then planned on making water tight "end caps" for the tube stock and using a thermal sensor to regulate water flow through the tube (and over the heat sinks inside). With my ground water temp being ~58F (15C), I feel 100% confident I can keep these Chinese SSRs cool.
....but then the stupid side of me thought, "hrmm, 45W * 4 (most that should ever be on at one time) is almost 200W! That's a lot of heat...hrmmm how could I use that? (YES, the elephant in the room is the 24kW being switched!) As luck would have it, my brew room is located in a room below a built-in hot tub. The hot-tub is generally set < 104F ( 40C ), and it would be fairly trivial to "dump that heat" into the hot tub....1500L @ 104F + 200W for ~6 hours = 1.2kWh would only raise the hot tub temp ~1.24F (0.7C).......
...BB's @ Tanks, LMAO! But, it did lead me to my actual question, "Knowing I can keep these SSRs darn near cold, what is a good target temp? While I haven't seen a real data sheet on these specific SSRs, 125C seems to be the "max" on most NON-Chinese SSRs. I know I should assume these should be run less than 75% of rated current, and I assume "cooler is better", but how cool is cool enough?
A side-bar question, "If I wanted to implement PWM control for maintaining temperatures, should I go to the trouble of timing the PWM with zero-crossing?" My thought was to use a 4 second base frequency and have the "on time" go in 20 cycle steps (ie 4 seconds * 60Hz = 240 cycles per period, duty cycle would range between 1/12 to 1 or 500W to 6kW in 500W "steps". ) Maybe I am over-thinking this? I mean realistically I have been doing just fine flipping a breaker, lol (well, I have NEVER been happy with the breaker thing ;-) )
This is my FIRST adventure into SSRs, so any more salient suggestions would be VERY MUCH appreciated!
Fish
The heating elements I use are 3kW-6kW @ 240Vac, so after more than a year of "flipping breakers" to control the power, I have decided to give SSR's a try. I just received some "Ruike SSR40DA" SSRs. This PDF http://www.google.com/url?sa=t&rct=...=MhYNiYC97YH9t6jSNR6DYQ&bvm=bv.57967247,d.cWc from Crydom absolutely confirms my low marks in thermodynamics, and it appears to be as "dummed down" as one can make Thermodynamics, lol.
While IN THEORY the fairly large heat sinks provided with the SSRs **should** handle the 45W of SSR heat gain, but I have little faith. My plan from the get-go was to mount the SSRs (five of them) to some 4" square aluminum tube stock (I happen to have on hand) with the SSRs on the "outside" of the tube stock and the heat sinks on the "inside" of the tube stock. I then planned on making water tight "end caps" for the tube stock and using a thermal sensor to regulate water flow through the tube (and over the heat sinks inside). With my ground water temp being ~58F (15C), I feel 100% confident I can keep these Chinese SSRs cool.
....but then the stupid side of me thought, "hrmm, 45W * 4 (most that should ever be on at one time) is almost 200W! That's a lot of heat...hrmmm how could I use that? (YES, the elephant in the room is the 24kW being switched!) As luck would have it, my brew room is located in a room below a built-in hot tub. The hot-tub is generally set < 104F ( 40C ), and it would be fairly trivial to "dump that heat" into the hot tub....1500L @ 104F + 200W for ~6 hours = 1.2kWh would only raise the hot tub temp ~1.24F (0.7C).......
...BB's @ Tanks, LMAO! But, it did lead me to my actual question, "Knowing I can keep these SSRs darn near cold, what is a good target temp? While I haven't seen a real data sheet on these specific SSRs, 125C seems to be the "max" on most NON-Chinese SSRs. I know I should assume these should be run less than 75% of rated current, and I assume "cooler is better", but how cool is cool enough?
A side-bar question, "If I wanted to implement PWM control for maintaining temperatures, should I go to the trouble of timing the PWM with zero-crossing?" My thought was to use a 4 second base frequency and have the "on time" go in 20 cycle steps (ie 4 seconds * 60Hz = 240 cycles per period, duty cycle would range between 1/12 to 1 or 500W to 6kW in 500W "steps". ) Maybe I am over-thinking this? I mean realistically I have been doing just fine flipping a breaker, lol (well, I have NEVER been happy with the breaker thing ;-) )
This is my FIRST adventure into SSRs, so any more salient suggestions would be VERY MUCH appreciated!
Fish