I think we've turned a corner because it definitely seems like it's time to start on the other kind of plumbing!
Here's one I made earlier...
(Not sure how many here will get that reference).
For those who haven't come across them before, these are modular DIN rail industrial control components - aka Lego for electrical engineers. From left to right, AC distribution, 24v DC (blue) and 5V DC (black) power supplies, DC fuse blocks, DC distribution, 12V (white) power supply in the middle, unconnected terminal blocks and a magnetic contactor for switching large loads. The grey terminal blocks come in various flavours (1x1, 1x2, 2&2 etc) and can be jumpered together, converting them into bus bars for power or signal distribution. The metal DIN rail serves as a ground bar linking all the green terminal blocks together - the equivalent of chassis ground. I put this together a while ago for another project and kept it assembled as it often comes in handy.
The 12v supply wont be necessary and neither will the contactor, but the rest will be useful. The first order of business is the temperature control. I have this nice Watlow controller which I am borrowing from another project. It has a number of features that I want to take advantage of. The first is simply speed - this thing just works: five minutes of mandatory RTFM, specify the thermocouple type, change the set point and away you go. The other advantage is that it has a PID auto tune mode which should obviate the need to empirically determine the coefficients for the three terms of the control expression.
I ordered a few of these $2 thermocouples from China a few months ago (K type if I remember correctly). They are advertised as 6mm but are in fact 1/4-20 (but the nut is metric - what a world). They also don't seal, which is a pain as it means that they can be put directly inside the boiler.
A quick side-by-side test with the thermocouple that came with my multimeter shows that all is well in this particular tiny corner of the world.
The TC is hooked to the input of the Watlow and the output is sent to a solid state relay (SSR) that will control the heating element.
The setup so far, from left to right:
Arduino and protoboard (top left)
Unused contactor (bottom left)
Autofill probe connections
24V DC / 120V low amperage control relay (light blue)
Bidoowee brand 5V to 24V and 24V to 5V optoisolated signal convertor (green IC board)
DC distribution and fuseblocks
DC power supplies
AC distribution
SSR (top right)
GFCI outlet (to the left of and connected to the SSR) (powering the heating element)
A couple of words of warning here. The wire gauge used is technically not adequate for the amperage drawn by the heating element. Also, we are playing with 15amps and lots of water, thus the GFCI (Ground Fault Circuit Interrupter). Out of frame, the whole mess is plugged into another GFCI on a 12 gauge extension cable for belt and suspenders safety.
Here's one I made earlier...
(Not sure how many here will get that reference).
For those who haven't come across them before, these are modular DIN rail industrial control components - aka Lego for electrical engineers. From left to right, AC distribution, 24v DC (blue) and 5V DC (black) power supplies, DC fuse blocks, DC distribution, 12V (white) power supply in the middle, unconnected terminal blocks and a magnetic contactor for switching large loads. The grey terminal blocks come in various flavours (1x1, 1x2, 2&2 etc) and can be jumpered together, converting them into bus bars for power or signal distribution. The metal DIN rail serves as a ground bar linking all the green terminal blocks together - the equivalent of chassis ground. I put this together a while ago for another project and kept it assembled as it often comes in handy.
The 12v supply wont be necessary and neither will the contactor, but the rest will be useful. The first order of business is the temperature control. I have this nice Watlow controller which I am borrowing from another project. It has a number of features that I want to take advantage of. The first is simply speed - this thing just works: five minutes of mandatory RTFM, specify the thermocouple type, change the set point and away you go. The other advantage is that it has a PID auto tune mode which should obviate the need to empirically determine the coefficients for the three terms of the control expression.
I ordered a few of these $2 thermocouples from China a few months ago (K type if I remember correctly). They are advertised as 6mm but are in fact 1/4-20 (but the nut is metric - what a world). They also don't seal, which is a pain as it means that they can be put directly inside the boiler.
A quick side-by-side test with the thermocouple that came with my multimeter shows that all is well in this particular tiny corner of the world.
The TC is hooked to the input of the Watlow and the output is sent to a solid state relay (SSR) that will control the heating element.
The setup so far, from left to right:
Arduino and protoboard (top left)
Unused contactor (bottom left)
Autofill probe connections
24V DC / 120V low amperage control relay (light blue)
Bidoowee brand 5V to 24V and 24V to 5V optoisolated signal convertor (green IC board)
DC distribution and fuseblocks
DC power supplies
AC distribution
SSR (top right)
GFCI outlet (to the left of and connected to the SSR) (powering the heating element)
A couple of words of warning here. The wire gauge used is technically not adequate for the amperage drawn by the heating element. Also, we are playing with 15amps and lots of water, thus the GFCI (Ground Fault Circuit Interrupter). Out of frame, the whole mess is plugged into another GFCI on a 12 gauge extension cable for belt and suspenders safety.
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