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PID Temp Control for less than $50

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  • #16
    Re: PID Temp Control for less than $50

    Hi Wilki!

    i have just received the REX-C100FK02-M AN temp controller which i bought off ebay, and have now discovered it will not run my SSR... is there any chance you could put a picture up of the solder jump wire modifications you made? any help would be GREATLY appreciated!!!!

    Thanks!

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    • #17
      Re: PID Temp Control for less than $50

      Guys,
               When i did my Silvia PID, i got the small (din 32) XMT7100 unit that has 3A relay and SSR outputs. ($20)
      But, before installing the SSR, i ran the unit simply using the internal relay to switch the heater on/off.
      I only did that because i noticed that the relay was a Panasonic actually rated for 7 amps @ 250v. 
      This was a extremely simple install with only 3 wires to the PID..live, neutral, and one live feed back to the heater element. !
      I ran fine that way without the SSR for several days with the cycle timer set to 1 sec ( minimum)
      I only fitted the SSR to eliminate the "clicking" of the relay as it operated !  ;D

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      • #18
        Hey, liamjgough.
        Sorry it has taken me so long to see this. Hopefully I can still help.

        I have mine nice and boxed in my coffee machine, so I'd prefer not to dismantle it, but if you can post some pictures of your board I could draw a line in mspaint for you

        7A relay, nice blend52!

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        • #19
          So, the milion dollar question; how is the coffee?

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          • #20
            Bear in mind that the accuracy of a K-type thermocouple is +/- 2.5degC for the range we're interested in (though you can get higher accuracy, +/- 1.5degree units but I doubt a cheap evilBay purchase is likely to be one of those).

            Ideally you want a T-type thermocouple (and many cheaper PID controllers won't talk to these) which is +/- 1.0degC for the lowest accuracy class, +/- 0.5 for the highest.

            Oh and I wouldn't recommend running a 7A load through a PID rated for 3A regardless of what the relay rating is (especially if it's a cheap PID), the connections between the relay and the screw terminals would have been designed to handle 3A, so although it may have worked for a while, it is a potential fire hazard as whilst the tracks aren't likely to fail immediately, they will heat significantly more than they were designed to.

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            • #21
              I read it he brought out the ss control wires to the ssr mounted external to the control: unlikely the ssr would fit inside the pid. In which case no problem. But it's good practice to mount the ss on a metal base if it's a metal body.

              Originally posted by jbrewster View Post
              Bear in mind that the accuracy of a K-type thermocouple is +/- 2.5degC for the range we're interested in (though you can get higher accuracy, +/- 1.5degree units but I doubt a cheap evilBay purchase is likely to be one of those).

              Ideally you want a T-type thermocouple (and many cheaper PID controllers won't talk to these) which is +/- 1.0degC for the lowest accuracy class, +/- 0.5 for the highest.

              Oh and I wouldn't recommend running a 7A load through a PID rated for 3A regardless of what the relay rating is (especially if it's a cheap PID), the connections between the relay and the screw terminals would have been designed to handle 3A, so although it may have worked for a while, it is a potential fire hazard as whilst the tracks aren't likely to fail immediately, they will heat significantly more than they were designed to.

              Comment


              • #22
                Originally posted by jbrewster View Post
                Oh and I wouldn't recommend running a 7A load through a PID rated for 3A regardless of what the relay rating is .
                Fair comment,..but to be clear.....
                1) I was not running 7 A through it...the Silvia element pulls little over 4 A max
                2) I expect most elec designers build in a little safety margin ? ( maybe thats why they used a 7A relay !)
                3) the current draw is not continuous. 5 mins to initial heat from cold, then cycling for a few seconds at a time.
                4) It was a test..never intended to be permanent. ( Though i believe it is perfectly viable if you can tolerate the solenoid clicking !)

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                • #23
                  Originally posted by MrJack View Post
                  So, the milion dollar question; how is the coffee?
                  For me? Very hard to say. I have too many inconsistencies to be able to tell sadly.
                  I mostly just enjoy hacking things

                  Comment


                  • #24
                    Originally posted by brettchris View Post
                    I read it he brought out the ss control wires to the ssr mounted external to the control
                    No, he removed the internal relay and ran the lines which were driving that out to the SSR (I've done this myself on several PIDs) but initially he was running the element directly off the internal relay.

                    Originally posted by blend52 View Post
                    1) I was not running 7 A through it...the Silvia element pulls little over 4 A max
                    Whilst this is true, people with less experience in these matters might think "awesome I can run 7A through this" because they are not aware of the other considerations here. Also, good engineering practise dictates an 80% derating (5.6A in this case), i.e. you don't run things close to the rating on the spec sheet.

                    Originally posted by blend52 View Post
                    2) I expect most elec designers build in a little safety margin ? ( maybe thats why they used a 7A relay !)
                    On dirt-cheap chinese mass-production? Highly doubtful. I'd be surprised if the tracks are even appropriate for the rating on the box, copper is expensive and given the space constraints the way you'd get extra current handling is to use 2oz copper instead of 1oz, which means the whole board becomes more expensive.

                    A relevant anecdote, Jeri Ellsworth replicated the Commodore 64 in a joystick for some toy company or other, when the designs got shipped to the factory in China they couldn't get the prototypes to work, when she went over there to check it out she found that they'd removed a large number of essential components like bypass capacitors in order to reduce costs, high-speed digital systems don't work without proper bypassing.

                    The 7A relay would be because it fit and they could buy a few hundred thousand of them at a few cents a pop, the current rating has little bearing on the cost of such relay when you're buying in those sorts of quantities.

                    Originally posted by blend52 View Post
                    3) the current draw is not continuous. 5 mins to initial heat from cold, then cycling for a few seconds at a time.
                    Valid point, the main concern would be the initial warm up period.

                    Originally posted by blend52 View Post
                    4) It was a test..never intended to be permanent. ( Though i believe it is perfectly viable if you can tolerate the solenoid clicking !)
                    Barring the bit where the electromechanical relay dies after about 10,000 cycles (100,000 for better relays)

                    Comment


                    • #25
                      Originally posted by jbrewster View Post
                      No, he removed the internal relay and ran the lines which were driving that out to the SSR (I've done this myself on several PIDs) but initially he was running the element directly off the internal relay.



                      Whilst this is true, people with less experience in these matters might think "awesome I can run 7A through this" because they are not aware of the other considerations here. Also, good engineering practise dictates an 80% derating (5.6A in this case), i.e. you don't run things close to the rating on the spec sheet.



                      On dirt-cheap chinese mass-production? Highly doubtful. I'd be surprised if the tracks are even appropriate for the rating on the box, copper is expensive and given the space constraints the way you'd get extra current handling is to use 2oz copper instead of 1oz, which means the whole board becomes more expensive.

                      A relevant anecdote, Jeri Ellsworth replicated the Commodore 64 in a joystick for some toy company or other, when the designs got shipped to the factory in China they couldn't get the prototypes to work, when she went over there to check it out she found that they'd removed a large number of essential components like bypass capacitors in order to reduce costs, high-speed digital systems don't work without proper bypassing.

                      The 7A relay would be because it fit and they could buy a few hundred thousand of them at a few cents a pop, the current rating has little bearing on the cost of such relay when you're buying in those sorts of quantities.



                      Valid point, the main concern would be the initial warm up period.



                      Barring the bit where the electromechanical relay dies after about 10,000 cycles (100,000 for better relays)
                      If the tracks did burn out and you still wanted to use the relay, you could always open her up and solder wires directly to the relay

                      Comment


                      • #26
                        Originally posted by Wilki View Post
                        If the tracks did burn out and you still wanted to use the relay, you could always open her up and solder wires directly to the relay
                        Considering 25A SSRs (not that I'd trust them for more than ~10A) go for ~$7 on evilbay I wouldn't bother, bringing the drive out (or better yet getting a PID controller with SSR outputs to begin with) is a better option, to say nothing of the potential fire hazard if the tracks should burn out...

                        Comment


                        • #27
                          Originally posted by jbrewster View Post
                          No, he removed the internal relay and ran the lines which were driving that out to the SSR (I've done this myself on several PIDs) but initially he was running the element directly off the internal relay.
                          I think there is some confusion between posts here ..
                          To clarify further,..the PID, i used was the small (din 32) XMT7100 unit that has 3A ( 7A actual) relay, AND SSR outputs. (for $20)
                          So i didnt need remove the relay, run extra wires, or mess with anything internally on the PID.

                          FYI : there are simpler, cheaper electronic temp controllers available ( ebay..$10) with 30A internal relays .
                          They are not ideal, but they will hold a temp much closer than the stock bi-metal T'stats fitted as standard, and give a digital temp display.
                          The display itself is a huge help in getting consistent shot quality, and reducing a temp variation from 30 C,... to 5 C , is a bonus !

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                          • #28
                            Originally posted by jbrewster View Post
                            Barring the bit where the electromechanical relay dies after about 10,000 cycles (100,000 for better relays)
                            700,000 cycles or even more on the good non-Chinese ones: http://coffeesnobs.com.au/showthread...l=1#post279955


                            Java "You want to relay what?!?" phile
                            Toys! I must have new toys!!!

                            Comment


                            • #29
                              Originally posted by Javaphile View Post
                              700,000 cycles or even more on the good non-Chinese ones: http://coffeesnobs.com.au/showthread...l=1#post279955
                              Heh, at what percentage of maximum ratings? I generally divide MTBF/other reliability figures by 5-10 to get something more reflective of reality ;P

                              If it's worth engineering it's worth over-engineering ;D

                              Comment


                              • #30
                                Originally posted by blend52 View Post
                                To clarify further,..the PID, i used was the small (din 32) XMT7100 unit that has 3A ( 7A actual) relay, AND SSR outputs. (for $20)
                                So i didnt need remove the relay, run extra wires, or mess with anything internally on the PID.!
                                Ahh, must've been somebody else who commented about bypassing the relay.

                                the XMT7100 isn't a bad unit actually, I use two of them (one for boiler control the other is a group temperature display), I bypassed the alarm relay in the boiler control unit so I could direcly drive my steam control SSR.

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