Category: Electronics

On my visit to the ‘Acres I got my electric boiler hooked up. It worked really well at 140 deg F. I didn’t have a great load and next visit I’ll push it up to 180 deg where I’ll get a lot better heat transfer out of the radiators. No real hitches other than the TACO electronic low water cut off is a lot more sensitive that I’d like. On initial start-up I had to power cycle it to get it out of “service required” mode.. It’s also very sensitive to air pockets but it resets automatically.

I’ve consistently had inconsistent results from etching PCBs. My best luck has been with PCB developing using a laser printer and transparency sheets. I was whiping up a batch of PCBs for my 6 meter amplifier when I decided I was really getting annoyed with figuring  out how to keep the etchant hot, but not too hot. This PLC modulates the temperature at a predefined setpoint. It switches a relay on and off to a heating element I scrapped out of a 10$ coffee maker and I used a little fountain water pump that cost me $8. The rest of the materials I had laying around. I kept my etchant at 125 deg F. A probe within the 5 gallon bucket monitored the temperature. Because of the staged heating the temperature varied about 5 degrees total. The heat of the water pumping transferred through the plastic container and heated the etchant so I didn’t have to directly heat the etchant.

I still have the bones of this project though I haven’t etched a board in a solid two years so I re-purposed some of the items.

Warning: Boilers can explode and kill you. See:   http://youtu.be/fCej2OQSKnY Making/using your own boiler may cause issues with your homeowners insurance, etc. Have I talked you out of this enough?

I have build my own hydronic hot water heater for my “retreat”. In an attempt to have an option to run my farm house off grid I installed hot water radiators and ran them off an old propane hot water heater but the heater was past it’s end of life by a decade or two and so I removed it eventually for safety reasons. I have decided I’ll likely build or buy another propane boiler or even perhaps a wood burning boiler but for the near future I built an electric hot water boiler. I’m installing this in two weeks when I’m “vacationing” to complete some projects on the house.

I have the necessary basic safeties for this boiler including a low water cut out and a high pressure relief valve. My boiler stages two hot water heating elements on and off to modulate the hot water to a temperature set-point that is reset based off outside air temperature. (The colder it gets outside the warmer the water). I’ve also have a outside air temperature disable feature. My set-points are 140-180 deg F and 65 deg F lockout temp. I’m staying far away from 212 deg F as steam is a really really bad thing to generate in this kind of boiler.

During testing I jumpered across my water low limit because I was having an issue with it being too near metal. I have to insert of PVC part to fix that later on but you’ll notice in the photo on top of the grey controls cabinet I blew a hot water element apart. Not a fun time!

If you look under the pump you’ll notice the heat exchanger I plan to use for an open loop (unpressurized) wood burning boiler or perhaps just a purchased propane unit. (we’ll see how ambitious I am later on)

Although I used and programmed an industrial process controller for this; it could have easily been a Raspberry Pi or whatever you had laying around. For remote monitoring I purchased a GSM cellular interface that can text message reports and alarms as well as sensor inputs. You can also call/text it up to get data out of it. I purchased it off eBay out of Romania for $140. You just need to pop a SIM card into it. I don’t have a land line so I purchased a pre-paid AT&T phone for 30$ and used it’s SIM card. I did have to call AT&T to ask them to “unlock” the SIM card.

The rolling cart stand was a nice find I purchased for $2 from a HAM radio club that had gutted a weather radar controls system. They wanted to use the radar and had sunk a lot of money into getting it operational for Moon bounce it ended up being scrapped by the land owner so that the USAF could put in a local aircraft landing radar system. It came with about 40 10-tun 2W potentiometers in the 2k-10k range.. let me know if you need one! I’ll never use 40 of them 🙂

A thought came to mind that when I need a PID controlled process or something on the side of industrial automation I just take an old “recycled” controller that was bound for the garbage heap and I make whenever I need. That’s great for me; my blog readers, not so much. I recently replied to a posting on an electronics forum with a guy looking for a cheap and easy way to control is variable frequency drive (VFD). This is a device that varies voltage and frequency to vary the speed of a motor. You can buy these in single phase for fractional HP motors thought they’re more commonly used in three phase applications. The poster was looking for a way to vary the control voltage (0-10V). I bit my tongue through the comments from people misunderstanding that it was control voltage an in fact the guy didn’t need a 10V 300A power supply. In his case he wanted to manually adjust the speed, but if it was to be an automated process and if I was him; I’d used a stand alone PID controller. These controllers are great for a pool pumps, hot water solar panels, exhaust fan controls, or something along those lines. I would use the Johnson Controls System 350 series controller. http://www.johnsoncontrols.com/content/us/en/products/building_efficiency/commercial-refrigeration/system-modular-control/350controls/a350/sysa350p.html

You can get these to control off temperature, humidity, or pressure to vary your output. They also come in staged outputs. I’ve seen these for green house controls, water pump VFDs, etc etc. It’s pretty simple; have a control sensor, and command an output, adjust the set-point and proportional band/integration to “tune” the loop.

Full disclosure: I work for Johnson Controls, However! I do not/can not sell or install these. These are generally installed by electricians but trust me.. anyone could install one of these. I’ve played around with them from a condenser deck we were working on one time. You can pick them up at grainger or anywhere you can buy HVAC components, likely eBay as well?

.. also forgive the liberties I took with “PID”, I do realize it’s only a PI controller. It’s rare to find full PID implemented in an industrial or energy automation controller; we usually don’t need to use derivative.