Household oven?

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Household oven?

Author	Message
Dravis	Dravis posted 8 Years Ago HOT Post Details
Group: Forum Members Posts: 592, Visits: 1.9K	there are two types of ordinary household ovens.. the "Hot Air" oven, and the traditional type with no fan- For your purpose, a "hot Air type" would be most convenient .. they almost always have a circular fan at the back of the oven. If there is no fan ibn the oven, you will probably need to install one to circulate the air to maintain an even temperature. "Sapere Aude"... Dare to KNOW! The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind... 103% of all people do not understand statistics... Do not adjust our mind, theres a fault in reality :-)
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Motorious	Motorious posted 8 Years Ago HOT Post Details
Group: Forum Members Posts: 11, Visits: 99	morepower (01/07/2016) You also need to think about how fast it would heat up.. You do need a controlled ramp rate if you only have a simple PID controller. Some may not agree but I have seen a massive difference in finish with a higher ramp rate than the 1 degree every 90 seconds I currently run. I have also seen issues with a temp difference as little as 5 degrees too.. So make sure you check the oven has even heat in multiple locations through the oven and no hot or cold spots. A higher rate of flow from the fan would help if the air flow is not great. My oven recirculates the air once every 12 seconds according to the claimed airflow on the fan. This creates enough turbulence to make the oven have a more even temp throughout. On the subject of controlled ramp rate... I got the SSR and TA4-SNR PID wired and I was messing around with the settings and have realized that I cant control ramp rate with this setup. I can adjust the proportional band which does cause the output to the ssr to cycle on/off but only when it gets reasonably close to the setpoint. if it is say 50 degrees away from the setpoint or more, I haven't figured out a way to change the duty cycle (I dont have an oscilloscope, im just looking at an LED). I am guessing I should have bought a different PID but I'm cheap and went with the $25 one. To get around this and still use the cheapo PID, I was thinking of adding an external circuit inside the box that would intercept the on/off voltage coming from the PID. Then, when the PID is trying to go full blast with a constant 12V out, the auxiliary circuit would turn the signal into a PWM signal that I could control with say a simple potentiometer. Being a non-electrical engineer, I am not sure what would happen to the PID's ability to autotune or what the effect would be when the oven gets close to the setpoint and the pid starts cycling. I was thinking of trying it using a 555 timer based circuit like this one: DIY PWM I have also seen SSR's that are made to have a potentiometer attached and that sounds like it might also work...
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Motorious	Motorious posted 8 Years Ago HOT Post Details
Group: Forum Members Posts: 11, Visits: 99	Just to avoid the headache, I went ahead and snatched a killer deal on an RKC FB400. No time to mess around with controllers, I got carbon fiber parts to make! With this controller i can do ramp/soak as needed so with it and a constant recirculating fan (have not sourced yet), I should be able to get good finishes.
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ChrisR	ChrisR posted 8 Years Ago Post Details
Group: Forum Members Posts: 363, Visits: 3K	Good choice with getting a proper industrial PID controller, now you might as well junk the idea of bodging a home oven and just build the rest of it too
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Hanaldo	Hanaldo posted 8 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	Haha yeh I concur. The PID is the most expensive bit, the rest of my oven including element and fan/motor was only around AUD$100-150.
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Motorious	Motorious posted 8 Years Ago HOT Post Details
Group: Forum Members Posts: 11, Visits: 99	ChrisR (20/07/2016) Good choice with getting a proper industrial PID controller, now you might as well junk the idea of bodging a home oven and just build the rest of it too Funny you say that because after I unloaded it last night and opened it up I realized how small it is. There may be an MDF oven in the near future.
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