--
You received this message because you are subscribed to the Google Groups "Hive13 Makerspace" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cincihackerspa...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cincihackerspace/933ae2dc-343e-4cfa-9b45-6fbb2bbf6b16n%40googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cincihackerspace/fb56d4e6-f0fd-4d13-aba1-2f47ce724d47n%40googlegroups.com.
Hey Jim! Thanks for the thoughts! it sounds like your thoughts break down into one of four items, so let me break them down a response with my thoughts one by one:
1) Slack vs. Mailing List - Slack adoption definitely slowed our mailing list traffic, somewhat as-expected. I think we also saw another dip in activity when google recently re-vamped the web interface for the mailing list, and they made it so those of us who choose to not get the mailing list sent to our emails can no longer respond via mobile device web browsers. This all probably deserves it's own thread though...
2) Recommendation to add a forced convection fan for more uniform temperature - I absolutely agree that this could be a great improvement! though, without testing, its hard to say how much. the Thermocouple is installed in the top left rear corner of the oven, so it's likely to read a little hot compared to other parts of the oven. I personally do not have any specific need or use for this project myself, so I can't say what will or will not be sufficient. I just saw that people were excited to have a non-food oven available to use for making stuff, and figured an industrial temperature controller would offer a nice improvement on both the reliability and accuracy of the thing, but also the safety of the tool (after that autopsy of the OEM circuitry, I am VERY uncomfortable with the safety of home ovens, haha).
It would be VERY easy to add a blower/fan into the circuit. It could be wired up with it's own switch, or so that it was on whenever the temperature controller was on. A convection fan from another oven would work, or possibly a draft inducer blower from a furnace would be a good candidate.
Seeing as I don't have any immediate need for that additional temperature uniformity though, and I don't have one of those fan on hand, I'd say we punt this as a future improvement if the need or opportunity ever arises.
3) Recommendation to add ventilation - I am 100% on board with this thing having a vent hood over it's home, whenever it gets assigned one! That said, not all activities that involve heat require ventilation! In fact, kitchen OVENS do not require external ventilation per code, only cooktops do, due to a cooktop's increased likelihood of introducing aerosol greases into the air when cooking food.
Of the use cases I mentioned in my proposal however, I don't think any fall under the umbrella of requiring ventilation. To address them individually:
Wood drying - Wood drying is typically performed at low temperatures of around 120°-220°F. This process temperature is well below the flashpoint and smoke point, so there is little to no concern of combustion gases developing. I have found no references indicating significant VOCs are emitted from wood at that temperature range, and in fact, this document states the temperature range where small amounts of VOCs begin to escape due to vapor pressure starts at 356°F, again, well above the process temperature. Additionally, this manual for wood drying kiln operators mentions many safety precautions, but does not mention any special precautions to take due to VOCs, even when inside the hot kiln.
Wood Stabilization - the most common product I have heard people use for this is called ”cactus juice”. Their instructions recommend oven drying the wood to remove moisture prior to treatment, and then oven curing the resin after it’s been absorbed by the wood. They state that the product does not emit dangerous fumes, however, they do recommend using an oven dedicated to non-food use. There is note that for a short period (10-15 minutes) of the curing process, they say that some people find the smell to be mildly unpleasant, but that the smell does not bother most people and dissipates quickly.
Ink and dye heating - this is really a stovetop item, and doing it on this stove is identical to doing it on a hot plate or any other heat source. There are a million dyes in the world, but RIT is the dye I have most familiarity with, and they state that all their dyes are 100% non-toxic.
Plastic slump forming - this one is tricky! Some plastics DO emit bad vapors when heated! That said, we also have a vacuum former, and slump forming is identical to vacuum forming with this respect. If you stick with plastics suitable for vacuum forming, slump forming should be not more risky.
I would argue that yes, we should eventually build a vent hood that exhausts outside to go over the craft oven/range to help with odors and noxious fumes from some potential use cases. However, based on the list of activities above that do not require active ventilation, it still seems worth it to get the oven set up and usable now, so that it’s less work for the person who decides we need a vent hood!
I’ll also note that we had a stove and cooktop (and a gas one, which even more so needs exhaust) at the old building for 10 years without a vent hood, and the aerosol grease from cooking is far worse for people than most activities likely to be done on this craft stove.
4) Fire Safety - This one is a hard one to make generalizations about, and as I mentioned, I personally don’t have a specific use case in mind for this temperature controlled oven. However, I have done dye work, plastic slumping, and similar activities in other ovens in the past. Most of those, I absolutely would not leave unattended any more than I would the laser, plastic former, or a pot of a cooking stove.
My assumption is that the worry about un-attended, long-term use is related to Todd’s desire to use the oven as a wood drying kiln to prepare blanks for stabilization. I have never done this process myself, however, let me share what I have learned about it and my thoughts on it.
The cactus juice product does recommend 24 hours of drying in a non-food oven at 220°F prior to processing. While intuition does make leaving any flammable material in an oven seem unwise, I do think it’s worth evaluating the actual process, and that there is a strong argument to be made that it is safe. Fire requires three things to burn: fuel, heat, and oxygen. And at first glance, it seems like you are putting at least the fuel (wood) into the heat (oven), however, that neglects to consider how much heat is required. Wood’s flash point and smoke point are both at 570°F or higher, so a process temperature of 220°F is really quite safe, particularly with a reliable PID temperature controller controlling the process.
There may also be concern about the risk of flammable material contact with the surface of the heating element. This is also mitigated some by using a PID controller. In a thermostatic temperature controlled oven, you will end up with a longer element on times resulting in target temperature overshoot and high element surface temperatures, but a PID controller will limit the element on times, thus reducing peak element surface temperature as well. The risk of direct element contact ignition can also be further mitigated by simply placing the wood within a metal container, in the middle of the oven, so there is no risk of it falling down on the heating element.
If the wood is placed in a metal container in the oven, that additionally addresses the third requirement for combustion: oxygen. Placing the wood in something like a roasting pan or buffet tray with a lid will prevent oxygen getting into the mix. The moisture being driven out of the wood will displace oxygen already in the container as well, resulting in an atmosphere around the wood that is too low in oxygen to support combustion.
Between the low process temperature, fuel confinement, and low oxygen atmosphere, the risk of fire is very low for the process of drying wood turning blanks.
That’s all I’ve got for now, I’m open to further debate, but I think regardless of the outcome, it’s clear that a non-food stove top and a non-food oven will be valuable tools in our maker arsenal.
Thanks,
Kevin.
To view this discussion on the web visit https://groups.google.com/d/msgid/cincihackerspace/12119135-2fb7-4a22-b0ec-c0219dae498bn%40googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cincihackerspace/CANsTJ7ZGn5NysTM2FHoTzZD%3D0pBN%3D9e1rgPowRMz69AdvhLyYg%40mail.gmail.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cincihackerspace/CACHG8dg91SqTB0dw9Af9mO7WF9NNKfALA-aRVop%2BhNXvtrnM7A%40mail.gmail.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cincihackerspace/CANsTJ7azEV343diwanUcFDCw%3D%2BzAnjSgA_XyoEsLbUu7-87ugg%40mail.gmail.com.
The temperature controller we are using is an ITC-100HV, it’s manual can be found here. I also posted the intended circuit diagram both earlier in this thread and in the #electronics channel on slack. Several of these questions heavily suggest that those things were not reviewed before posting these questions/concerns. Please do your homework on your questions before asking me to spend time addressing each and every thing that pops to mind (the responses below took me several hours to put together, time I’d really prefer to put on more productive tasks).
What kind of temperature ranges do you expect this to be used at and is there something to limit going beyond that?
Kitchen Ranges are typically limited to a maximum setpoint temperature of 500-550°F (260-288°C). The self-cleaning function of most kitchen ovens operates at 900-950°F (482-510°C) (sufficient to burn away organic compounds).
Ovens without self-cleaning function typically have insulation rated for 1000°F (538°C). Ovens with the self cleaning function typically have insulation rated for a few hundred degrees higher.
The controller is configurable for many applications, read it’s manual if you want to know more. The parameters diP and diL let you set the minimum and maximum setpoints a user can enter, I was planning to set them to 50°C (122°F) and 285°C (545°F) respectively. HiAl is used to set the high temperature alarm setpoint, which I was planning to set to 350°C (662°F). That alarm point is high enough that it will prevent trips on overshoot during tuning, but is well below the insulation rating.
One big concern is someone at the Hive doing something crazy stupid with it and I don't know how we can prevent that. Ideas would be welcome. Seems like some degree of supervision may be needed.
I am not willing to design a tool around the possibility of someone doing something idiotic. We are all adults, and can be responsible for what we do. Nearly every single tool we have at Hive13 can be misused in a way that is dangerous, but with very few exceptions, we all collectively agree that it’s still worth having them.
Again, we are adults, we do not need “supervision”. notes/signs that state a device’s limitations as a reminder may be appropriate, but please have faith in your fellow makers.
How hot will the electronics get when this is in operation? Should there be a fan or something to keep it cool? My thoughts for my toaster oven project was to keep the electronics in a physically separate enclosure.
I plan to borrow Dave B.’s thermal camera during testing of this thing, both to check surface temperatures, and to check component temps and look for poor connections in the power circuits.
I have seen many toaster oven projects done that the electronics are mounted within the original control console without issue (including Hive13's own solder reflow toaster oven). I also modeled this circuit on ones used for controlling electric glass furnaces and kilns, which operate at vastly higher power and temperature, and they all had the electronics mounted in enclosures right on the side of the kiln wall without fans.
We will check with the thermal camera, and adjust the design as needed, but the power components are all mounted on a panel behind the oven and the back panel has lots of vents, they will get good airflow.
SSRs, like a lot of semiconductors, typically fail in short circuit mode. A frightening thing in an oven that is capable of self-cleaning temperatures. A simple thermal cutoff is worth considering.
It is a myth that SSRs tend to fail shorted, in reality it depends on the specific product, but it’s about a 50/50 split on how they fail.
That said, take a look at the circuit diagram. The two SSRs act as redundant safeties, current cannot flow through the coils unless BOTH are on. The only way the temperature controller would lose control is if both SSRs failed on.
I do not currently have it drawn this way, but we could also wire the NC terminal of the controller’s alarm relay to the main power relay’s coil, so that power is cut before the SSRs if the temperature controller enters an alarm state (such as over temperature)
An actual cutoff switch that disconnects the unit from the power would be a really good idea. Both to truly disconnect it for the power in case of a problem but also to be able to shut it off and disconnect the electronics from power line transients.
Take a look at the posted circuit diagram, the circuit does this for the oven circuit. The controller is isolated when the power switch/breaker is in the off position. The power switch does not directly cut power to the SSRs, but turning it off cuts power to the relay coil, which has the same effect without requiring a massive 40 amp switch on the user interface.
This configuration is also VASTLY safer than the OEM configuration, in which a single SPST relay controlled the oven elements, leaving them energized at 120VAC even when the oven was switched off.
The other circuits (surface burners, keep warm burner, and oven light) are all essentially unchanged from the stock configuration, if they are safe enough for a kitchen, they are safe enough for us.
What happens if the power cycles? Does the system shut down/reset/go crazy?
I will test this, but I believe the controller either resumes at the last programmed setpoint temperature after power is restored, or the controller enters an idle state.
What if sawdust or wood particles fall onto the lower burner? Will they ignite?
A reminder: I am not doing this modification with any specific purpose in mind, but to make something useful available to our members. I’d prefer to leave defense of any specific usage to the person interested in that usage.
However, I addressed this concern in my reply to Jim’s questions/concerns, please re-read that.
Note that this scenario is virtually indistinguishable from the oven’s self-clean cycle, because the oven’s chamber is oxygen deprived, no sustained open flame is able to develop.
If a small fire does start, will the oven just happily keep working?
I don’t know how happy it’d be with a small fire inside it, but yes, it would keep working. Again, this is virtually indistinguishable from the oven’s self-clean function, and no sustained flame would be possible due to oxygen deprivation.
If the fire was large enough to raise the temperature inside the oven above the alarm temperature setpoint, the controller would enter an alarm state and shut off the heating elements.
If a larger fire does start, what do we do? What could happen? What if no one is there? Fire propagation and smoke generation.
This question could be asked of literally everything at Hive13 that we leave energized. In fact, those “air filter” blowers that have been built have been found in the space left on, with the bearings clearly failed and overheating to the point they were scorching hot to the touch.
Please read my response to Jim above for more for my thoughts on the unattended use and associated fire risk (and mitigating factors).
What if someone puts improper stuff inside (treated wood, sappy wood, etc)?
See my responses to question 2 above.
Could some accidentally set crazy temps? Either by mistake or hitting the wrong buttons?
See my responses to question 1 above.
The biggest risk I see here is that the controller only functions in Celsius, so if someone didn’t notice that, and entered 220, assuming °F, they would actually be setting it to 220°C (428°F), nearly double the intended temperature (but still well below the flashpoint of wood). I believe the best mitigation to this possible error is labeling and signage.
Even if that did happen, all of the logic and safeties discussed above are still in place. The oven would still be well below the “self clean” temperature it’s designed for. The material placed in the oven would be ruined, but the oven is designed to withstand and contain burn off of organic compounds at 900-950°F (482-510°C), much more severe than our controller configuration will allow a user to run it at.
To view this discussion on the web visit https://groups.google.com/d/msgid/cincihackerspace/c5676247-5eb0-47c4-bd8d-0aa41a2e903an%40googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cincihackerspace/e1a09551-0f9b-4e8b-b08e-9041e3ce3217n%40googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cincihackerspace/CACHG8dh6akj4R4x-xxbcVpH%2Bnhw0UFZ9YM4314acA4A9EGmAZw%40mail.gmail.com.