New meets old... I've been pretty happy with how the microcimbali regulates the temperature, even with the two (1000 and 300 watt) switches and no thermostat. So why PID such a retro machine that seems to already have pretty good temp control? 'Cause it's kinda cool? 'Cause I got the PID unit cheap? To be really sure the temp is OK? Or just 'cause it can be done?

I found the REX C100 PID unit on Ebay for $22 from China complete with 40 amp SSR and thermocouple. It claimed to have SSR output, but it really came with relay only output, which is odd because it shipped with an SSR. In order to make it work without modifying it, you would have to add a power source to power the SSR through the relay, then you would still have a mechanical relay switching off and on a lot which would probably wear it out quickly. So I poked around and found a video on how to modify this PID for SSR (switched voltage) output. (http://www.youtube.com/watch?v=2NpcMycHDvk) It looked fairly straightforward so I modded it, tested and it powered the SSR just fine.

Then I found a plastic box, got out my dremel and started cutting holes for the PID, switches, and outlet. The microcimbali is a very simple unit, with only two switches to power two heating elements, so I thought it best to keep the PID unit standalone, and simply plug the microcimbali into an SSR switched outlet mounted on the side of the box. My plan was to keep both switches on (1300 watts of heating) and let the PID bring the microcimbali up to temp and hold it there using both heating elements. I ground a flat spot on the thermocouple and simply attached it to the side of the boiler with plastitak, near the cylinder. This was because of the temperature differential between the main boiler where the heating elements are and the area where the cylinder is located. When heating up, the boiler is around 10C hotter than the front of the machine. As the temp stabilizes, the temp is only 3-5C hotter. So I figured it would be better to measure the temperature near where the water enters the cylinder. I don't like the fact that the thermocouple is on the outside of the boiler, and I have yet to find a way to insert the probe into the water without irreversibly modifying the microcimbali.

I added two switches: one to turn on the PID/SSR/boiler, and another PID override switch will will send power to the microcimbali when I want to steam. For convenience, I wired the other plug in the box with constant power for my grinder.

I found this cheap PID unit works quite well in bringing the water up to temp. It gives full power to the boiler until it reaches 85C, then pulses the power until it reaches the target temp of 95C. It doesn't seem to overrun and keeps the temp fairly stable, if I can trust my alternate temp probe. I found that's it's pretty convenient to just turn on the PID and let it do its thing, whereas before I turned on both switches and had to wait until steam started spitting out the pressure regulator, at which point I would have to turn off the 1000 watt switch. Now I can keep both switches on. I find that steam spits around 2 or 3 minutes until the boiller wall temp near the cylinder reaches 95. Also, I could not set this PID unit to fahrenheit. Although I set it according to the documentation to display in fahrenheit, it seems stuck on Celsius.

The nice thing about this project is that it's very easily reversible. To remove the PID, I would simply unplug the microcimbali from the PID and back into the wall and remove the thermocouple. Or, I can keep it in place and just hit the override switch and mess with the two switches on the microcimbali.

Here are a couple of pics:

Nice work on the PID, I like the clear project box you but everything in, it gives a good contrast between the old and new. Regarding the thermocouple placement, if you don't want to modify the machine you may be able to correct the temperature acuraccy by setting a temperature offset on the PID controller. I believe the PID I use allows you to increase or decrease from the measured temperature to correct measurement errors.