Triac weird behavior on Building Automation card

T

txrocks

Member
I have my building automation card on a water well controller where one of the triacs controls a relay that controls the pump relay. Control power to the relay is 24VAC, I have had this happen twice now where the RPI has done something weird and the triac goes closed and stays there. The first time it ocurred, I turned off the RPI on accident. It happened again overnight last night, the power may have blinked causing the RPI to restart ( I am ordering the UPS for it now) . Hopefully it did not kill the pump. I have a second set of contacts on the pressure switch and am going to run the relay control power through there as a failsafe.

Do you have any ideas ?

thanks!
 
alexburcea

alexburcea

Administrator
Staff member
Hi,

The Building automation card has no power backup, so if the power glitches, all the outputs return to the default state (off for triacs and 0V for 0-10V outputs). It is recommended that the software on the Raspberry to detect power losses and restore the outputs to the appropriate state.

Alex.
 
T

txrocks

Member
I'm going to do more investigation on this today. I think it's doing this in the time when the raspberry pi is not in a operational state, once the RPI boots up and open PLC is up and running it goes back to normal. I am using open PLC.
 
T

txrocks

Member
I tried to get it to repeat the problem today and could not get it to repeat. Unplugged the power suppy that feeds the RPI and the Sequent boards, waited 30 seconds and plugged back in. System restarted just like it should. Tried pushing the power button on the RPI, tried holding it down to see if I could make it angry. I tried all the above while it was in the middle of a run cycle, it just shut down and restarted once the RPI booted back up and OPLC started back up. It is weird that this has happened twice now where it freaks out and makes all the triac outputs true. I am powered from an official RPI 5 power supply. I could not get any other power supply to work without getting a low power alert on the RPI. The first time this happened I remember opening the cabinet and seeing all the output LED indicators on. The last time it did it overnight, I am just glad it did not kill the pump or break something. The 100PSI gauge was wrapped all the way around to the back side of the needle at 0.
 
T

txrocks

Member
It finally repeated and figured it out.

My circuit went from the control transformer 24vac to Triac1 first terminal, then from the second terminal to the relay, then to the other side of the transformer. I guess the traic was still partially on and flowing enough current to keep the control relay pulled in. There was about 8vac drop across the triac during this. I swapped the wires and it acted like it should. Then I went and looked at the schematic for the board which confirmed that I had it wired incorrectly. Well hope this will help someone else in the future!
 
T

txrocks

Member
No worries! Its not like you have a truckload of other questions coming in all day! It was so weird when it would randomly do it, and only seemed to occur after a loss of power and restoration. I put the pressure switch contact in the circuit with the relay to eliminate the possibility of the over pressurization, along with adding an alarm to monitor for pump current when there was not supposed to be pump current. I had a different failure mode which led me to this, the system went into pump protection as we drew too hard on the well, and the pressure switch contact was closed but the triac did not clear. I found it very odd that it would only randomly do this, it did it twice in 6 months.
 
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