There are numerous problems with our laser filtration system. Here’s a simple project that will help solve one of them.
Background
There is a furnace and ductwork that comes in at the back of VHS. The furnace has been disabled but the fan still runs, so we just use it as a fresh air intake system. It is controlled by a simple thermostat located near the metal lathe. Members turn it “on” by putting it all the way up, and “off” by putting it all the way down. The intake for this system is about 12 inches away from the laser exhaust, so running it while the laser is running brings the laser exhaust back in and disperses it around the space — not good. There is a note at the laser to remember to turn the furnace fan OFF before using the laser, but it’s easy to forget (I always forget).
Interlock idea
Plug a 12V wall wart into the power bar that runs the laser chiller and my telemetry controller box.
Find a small relay with a 12V coil that has NC (normally closed) contacts. There should be many MANY of these in the bin of relays at the space. Choose a different coil voltage if necessary.
The thermostat is a simple 2-wire variety. It’s basically just a switch. Cut one of its wires and put the NC relay contacts in series.
When the laser turns on, the wall wart gets power, and the relay’s NC contacts open, and the blower stops.
Implementation
I’m not in Vancouver much these days, so I’m not going to do this anytime soon. If you want to tackle this, post here! We can discuss the implementation. I am on the laser cutter committee, so we can work together to make this happen.
My thoughts are to mount the relay on a small base plate next to the thermostat. Will add LED to display ‘override’ status. Wiring would be Cat-5 to the wall-wart or telemetry controller box. If I can find a low current five volt relay, we could potentially skip the wall wart, and just tap power from the telemetry box ( fuse, small capacitor, and diode could be added for protection).
We have a RJ45 crimp tool at the space, but no ends last time I checked. I have a big bag at home and will try remember put a bunch somewhere near all the other connectors (to the right of the fasteners).
Override (interlock) relay tested and operational. Disables air conditioner when laser cutter interior cabinet lights come on. Delayed turn off (turns off when filter and chiller shut down), Currently powered by a 5V AC adaptor on the chiller power bar. Will power from telemetry box after a week or two, if no problems found.
Features:
Blue LED indicates override condition (Relay open, A/C disabled)
Dual voltage Jumper. On for 5V operation, allows for 12V use when removed.
Transistor to allow for logic level control (Pull up resistor may be needed for some driver boards)
Dual RF noise suppression capacitors.
Flyback diode to prevent back EMF voltage spikes.
Pre-existing wiring:
Black ‘hot’ (left) Thermostat power from wall (24-30 VAC via transformer.
White ‘neutral’ (hidden behind thermostat) Thermostat power from wall (24-30 VAC via transformer.
Red (hidden behind thermostat) Power from thermostat to air conditioner control.
Added wiring:
Black (right) — Power from override relay to Thermostat
Green/White-Green — Common
Orange/White-Orange— 5V power in (draws <100ma when relay on)
Blue/White-Blue— Logic level input 3.3-12V (draws <1ma, ok to drive from Arduino outputs)
@xquared@Gibbtall and I just tested it and it’s working great. Beautiful work, @DerrickA4mag! We stood around for the 5+ minutes while the laser went through its power-on and power-off sequences to observe it in all its glory.
To summarize the instructions for others:
As before, You use the thermostat to turn the HVAC blower on and off for the whole hackspace.
If someone turns the laser on, the blue light on this new unit will come on and force the HVAC blower to shut off. It won’t happen immediately. It will happen at some point in the middle of the laser’s power-on sequence.
When the laser shuts down, the blue light will turn off, allowing the HVAC blower to turn on. In fact if the thermostat is still up, the HVAC will turn on again immediately.
Improvements
I think the system is great right now. The only confusing thing is that we’re using a thermostat as a switch. It would be nicer if it was just an on-off switch.
That’s because we currently don’t use the heating functionality. I think @laftho mentioned something about this? Can we switch on the heating element in this?
The breakers for the heating elements are currently manually switched off
so only the fan works.
I suspect the system was originally designed to switch on both the fan and
the heating elements when the thermostat switched on.
I’ve suggested this before, but the best improvement to that system would
be to switch the direction of the HVAC fan to draw air out of the space
rather than pull it in.
That way it could also help cool the space, since we share the room with
both the electrical panel for the building and the boiler for the hot water
heater.
thanks