Hey everybody, I'm just looking for thoughts and opinions on how bad the mains would have to be to cause false triggering on TRIACS. We've got a machine that had been working fine for a customer in Saudi Arabia, but when they moved it to a new location, it blew its MOV and fuse, and then, after those problems were resolved, every TRIAC-based control in the machine is misbehaving.
Throughout the machine, there are multiple locations where we have a little subcircuit for controlling 200-250VAC with a 5V signal (essentially a proprietary, compact SSR.) Every one of these is "leaking" some amount of power such that the solenoid valves they control are humming, buzzing, and leaking just a little water when they should be off. If you provide the 5V signal, they turn on properly, but they never turn all the way off. Simple DMM measurement across the solenoid coil reads around 110-120V when "off" (should read zero) and the expected 230V when on.
Our first assumption was that they had accidentally wired the machine to 400V instead of 230V (people constantly ignore our specs and just hook up whatever two wires are closest to the machine) and that they had damaged most, or all, of the internal circuitry. We had them replace one of these mini-SSR circuits to see if that resolved the problem on the one circuit, but that one also buzzes immediately, so that rules out the idea that it was an accidental 400V connection causing the problem, because they're definitely on 230V now, and the brand new mini-SSR is misbehaving in the same way as the other ones. We've had them disconnect the signal wire entirely, so it's definitely not being triggered by erroneous signals on the 5V line.
Obviously a DMM will just read average and/or RMS voltage, but not tell you anything about the "quality" of the power, so I'm wondering if their mains could really be noisy enough to cause this behavior. I know TRIACs can be false-triggered by high dV/dt conditions, and I know some voltage sources are far worse than others (cheap power inverters putting out essentially square waves instead of sine waves, etc.) Do you think it's possible that their mains power is the right voltage, as read with a DMM, but noisy enough to perpetually trigger TRIACs?
The TRIAC in question is the T405-600B-TR (links to DigiKey and datasheet.)
Oddly enough, even though we paid for this design, we never got a schematic for it, just the Gerbers, so I've reverse engineered it myself. The circuit is as shown below (except that a few part numbers are wrong because I just used available standard symbols in LTSpice.)
I think it's particularly interesting that C2 is not being installed. If it were there it would act as a snubber for the TRIAC gate, right? Anyway, regardless of anything that could be improved in the circuit, my real question here is about the mains power. We've got tens of thousands of these mini-SSR circuits in the field and their failure rate is exceptionally low, so I'm quite confident that something strange has happened in Saudi Arabia, I'm just not sure what.
Throughout the machine, there are multiple locations where we have a little subcircuit for controlling 200-250VAC with a 5V signal (essentially a proprietary, compact SSR.) Every one of these is "leaking" some amount of power such that the solenoid valves they control are humming, buzzing, and leaking just a little water when they should be off. If you provide the 5V signal, they turn on properly, but they never turn all the way off. Simple DMM measurement across the solenoid coil reads around 110-120V when "off" (should read zero) and the expected 230V when on.
Our first assumption was that they had accidentally wired the machine to 400V instead of 230V (people constantly ignore our specs and just hook up whatever two wires are closest to the machine) and that they had damaged most, or all, of the internal circuitry. We had them replace one of these mini-SSR circuits to see if that resolved the problem on the one circuit, but that one also buzzes immediately, so that rules out the idea that it was an accidental 400V connection causing the problem, because they're definitely on 230V now, and the brand new mini-SSR is misbehaving in the same way as the other ones. We've had them disconnect the signal wire entirely, so it's definitely not being triggered by erroneous signals on the 5V line.
Obviously a DMM will just read average and/or RMS voltage, but not tell you anything about the "quality" of the power, so I'm wondering if their mains could really be noisy enough to cause this behavior. I know TRIACs can be false-triggered by high dV/dt conditions, and I know some voltage sources are far worse than others (cheap power inverters putting out essentially square waves instead of sine waves, etc.) Do you think it's possible that their mains power is the right voltage, as read with a DMM, but noisy enough to perpetually trigger TRIACs?
The TRIAC in question is the T405-600B-TR (links to DigiKey and datasheet.)
Oddly enough, even though we paid for this design, we never got a schematic for it, just the Gerbers, so I've reverse engineered it myself. The circuit is as shown below (except that a few part numbers are wrong because I just used available standard symbols in LTSpice.)
I think it's particularly interesting that C2 is not being installed. If it were there it would act as a snubber for the TRIAC gate, right? Anyway, regardless of anything that could be improved in the circuit, my real question here is about the mains power. We've got tens of thousands of these mini-SSR circuits in the field and their failure rate is exceptionally low, so I'm quite confident that something strange has happened in Saudi Arabia, I'm just not sure what.
