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Heater Protection via Arduino
I?ve been trying to integrate the use of an ACS712 current sensor in conjunction with a 5v relay on a new build for a while now. It?s part of a heater fail-safe during manual or automatic roasting? if the blower stops the heater will stop also. (I?m using IO3 fast PWM for a DD SSR for a DC blower, from the CONFIG_PAC2 setup)

I've discovered it is possible to add code to aArtisanQ_PID_6_7 to be able to run these devices with the safety in place even on manual mode. (Thanks Greencardigan for your feedback on my idea) I?m using two of the analog inputs on the TC4; OT1 for a heater and OT2 for a mixer motor for manual operation. Air supply comes from a DC blower triggered from IO3 to the DD SSR.

What I wanted to do is have heater protection by taking the analog input of about 2.5v (0 amps from the ACS712) or less to write LOW to a digital pinout, and conversely with an analog input of say 2.6v or more to write HIGH to the same digital pinout. That way a person could use IO3 functions to activate an SSR for a blower circuit in automatic/TC4 mode, or in manual mode using a separate switch to activate your blower for manual operation, both modes protected.

With this feature an Arduino based electrical heater protection circuit is in place to protect your heaters if the blower fails in either operation mode? (no fan, no current is detected from the ACS712, no 5v relay closing, no activation of your heater SSR)

My system is a little different as I'm using a secondary heater SSR in series with my primary heater SSR and a 24v power supply, but I?m quite sure the OT1 heater signal from the TC4 could be routed to the 5v relay with the normally open connection used, and then out to the heater SSR as the failsafe.

These (or similar) products we?re used for the control mod?



This mod is possible and easily done. I'm not an Arduino coder by any means, but with Youtube and some trial and error I managed to figure it out.

I added these 2 lines to the sketch at the end of the .ino after line 1302

const int output = A3;
const int input = A2;

added these 3 lines at the start of the void setup after the amb.init line

pinMode(A3, OUTPUT);
pinMode(A2, INPUT);
digitalWrite(A2, LOW);

and these lines at the start of the void loop before the Phase angle control lines this code

if( analogRead(A2) > 522)

This setup uses a 20A version of the ACS712 and a 5v relay both powered from the Arduino 5v power. The signal comes from the ACS712 into Arduino A2 and out A3 (if conditions met) to the 5v relay, which closes a low voltage circuit for a secondary SSR (in series with the primary heat SSR). Power will only go to the heater now if the blower is detected as pulling amps.

Pretty happy with this mod...
Thanks for posting this. Those Robotshop modules look good.
Good safety since some of those powerful heaters can vaporize when the fan goes.

Do you run a heater cool down procedure after the roast?

KKTO Roaster.


JackH wrote:

Do you run a heater cool down procedure after the roast?

On the transparent roaster build, the heater is off at drop and the fan keeps blowing ambient for 1-3 minutes while cooling the beans in the chamber. In 2 years and a couple of hundred roasts, there have been no failures, but I still like the safety concept and the ability to limit repair costs if it does happen.

On my new build, I have a 3-way valve to allow for air to be diverted from the blower to cool the beans out of the chamber while still allowing some airflow over the powered-off heat coil.
This protection only works with a DC setup as mentioned in the post. I'm trying to code for an AC fan now, but am having issues integrating the feature. The code above doesn't work for an AC blower on an intantaneous SSR.
With the help of Renatoa's professional programming, the code for heater protection when using an AC fan is now implemented in the Transparent roaster. It's using aArtisanQ_PID_ 6_7.

Thank you for your help and correspondence.

The original roaster is working as usual with a slightly modified look. The video shows the roaster's base with manual control features. It uses a Heater Cutoff Value of 30% in user.h (as normal), in addition to the 5v relay if no amperage is detected going to the fan (in case of fan failure). The 2 lamps(heaters) are on separate heating circuits to show the reaction time of the system)

The heaters have never felt so safe! Grin

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