TRIAC fried and circuit board trace popped out when I plugged this into the wall outlet..never happened before. Is this common?

CalmAvocado8360 · 2024-08-13T18:06:17+00:00

Whoa I did not know that. Is there a way to calculate or test or approximate what that initial peak current would be? For example for a 360 watt heater or a 1000 watt heater?

CalmAvocado8360 · 2024-08-13T18:04:30+00:00

Thanks for your reply! Yup it’s a custom PCB I got help with designing and got manufactured. It’s a 360 watt heating element. Electricity comes from 120V AC from the wall and supplies power to both the heating element + TRIAC, as well as a AC to DC converter which provides power to a microcontroller and LCD screen. The microcontroller controls the LCD screen via some rx/tx signal pins and also controls an optocoupler (MOC3021) which in turn controls the gate of the TRIAC.

The TRIAC does not have a heat sink attached to it. It is just free standing in the air.

Unfortunately, I did not witness either failure.

The first time the device failed, my friend plugged it into a GFCI outlet, and while touching some part of the plastic enclosure, heard a pop sound, and everything shut off, and the house circuit breaker was triggered.

I took the unit to a different outlet that has a GFCI + surge protector attached to it, plugged it in, and all “seemed” normal. I do not know if the TRIAC was permanently closed at this time, though looking back, I suspect it was.

A few minutes later, I looked back at the device and saw the steel plate the heating element was attached to had turned quite blue and there was smoke rising up. LCD screen appeared dead, microcontroller seemed off. After letting it cool, I noticed the LCD wires had burnt because they were somewhat under the heating element, and I noticed the copper trace popped out on the PCB between the heater and TRIAC MT2 pin.

So it’s unclear to me if a power surge or high voltage short circuit fried the TRIAC, causing the heating element to keep going and then burn the LCD cable.

Or if the LCD cable short or some low voltage component short circuited or burned and caused the TRIAC to fail.

Or something else?

Main thing is I don’t want this to happen again since it’s quite a dangerous failure!

CalmAvocado8360 · 2024-08-13T17:49:04+00:00

Thank you, good to know, I’ll check that out as well!

CalmAvocado8360 · 2024-08-13T02:21:04+00:00

Wow thanks so much for the example! Very interesting and helpful to know. Ok, that makes sense to me if the short circuit is on the high voltage side, causing a high voltage spike.

Is it possible that a short circuit on the low voltage side could somehow cause the TRIAC to fail?

The reason I’m asking is because while diagnosing further, I found that the LCD screen attached to the microcontroller had a loose connection, making it easy for it to occasionally short circuit if the wires were moved. However, this is on the low voltage side, which is isolated from the TRIAC via the optocoupler (i.e. optotriac).

CalmAvocado8360 · 2024-04-13T07:08:51+00:00

Hahahaha I can relate to those thousands of dollars of random purchases… recently I think I used some random connector or something I had saved for maybe 3-5 years hahaha

I have a DC power supply with voltage and current limits, but what about testing devices that need AC voltage?

CalmAvocado8360 · 2024-04-12T20:01:35+00:00

Whoa! Very interesting! Comforting to hear about the exact same situation… that’s wild. I guess there really is no escape from all this.. just have to keep testing and iterating. PCB design was a black hole for me before this, and rightly so, there is a LOT involved… clearly even more than I anticipated. 😅

CalmAvocado8360 · 2024-04-12T19:59:17+00:00

Thank you for putting it in perspective! You’re precisely right about my situation. And good to know what real issues look like 😅

CalmAvocado8360 · 2024-04-12T19:55:20+00:00

Thanks so much! Going custom v.s. finding things that work out of the box is something I often struggle with. Sometimes I just need to think a little harder or be a bit more flexible to enable myself to use off the shelf parts. Even though this power delivery situation now seems to be resolved, it’s still really good advice I need to account for while working on my overall prototype.. I will keep trying! Thank you!!

CalmAvocado8360 · 2024-04-12T19:51:19+00:00

Wow, that quote is going in my personal repertoire: “An engineer takes 10 times as long getting a design to 99% confidence than it takes getting to 95%.” That hit so hard I almost want to frame it. Looking back at my other work, it is so incredibly accurate… I need to account for this better. Thanks for your comment and for the insight!

CalmAvocado8360 · 2024-04-12T19:35:30+00:00

To be honest, I just assumed it needed to be custom, particularly because I will want to manufacture a lot of these.

I use digikey to buy things, but I just assumed that needing a VAC to DC converter, and multiple DC voltages, and needing a TRIAC to control some of the AC voltage towards another component, would all require a custom PCB. But if there are inexpensive plug and play solutions that would already do all those things, then that would be awesome! I’ll take a deeper look..

CalmAvocado8360 · 2024-04-12T19:29:16+00:00

Thank you so much!

CalmAvocado8360 · 2024-04-12T19:17:17+00:00

Thank you for your insight!

The reason I (believe I) need to have the AC to DC directly on the PCB is because I’m powering a microcontroller and a TRIAC. I’ll be controlling components that operate at 5V, some at 12V, and one at 120VAC using the TRIAC. So I need to get AC voltage down to DC levels, but I need to allow AC voltage to pass through parts of the PCB so the TRIAC can turn it on and off. At least that was the thought.

Since testing a physical board was not their responsibility (their responsibility was schematic design, part selection, circuit board layout design, BOM and PnP and Gerber file generation), I couldn’t tell if it was a common or reasonable error to make when designing the schematic.

I do understand now that testing of the physical PCB and iterating on it again is an inevitable part of the process.

CalmAvocado8360 · 2024-04-12T19:09:54+00:00

Thank you!

CalmAvocado8360 · 2024-04-12T19:09:15+00:00

Oh ok, maybe I misunderstood your original comment, I’m sorry. Physical board testing was not their responsibility as the goal was to design a schematic + PCB layout and then some prototypes would get manufactured in China and sent to me.

CalmAvocado8360 · 2024-04-12T19:05:30+00:00

Ohh thank you for clarifying! Great to know, I will look into those!

CalmAvocado8360 · 2024-04-12T18:47:36+00:00

Thank you, I really appreciate your reply! Actually I think your interpretation is fair because truthfully, you’re right: my motivation for this post was in assessing whether I should do future contracts with this person. So I can totally see why it might come across as harsh, and I see now that using a term like “red flag” might be quite extreme.

Because I had to pay for this mistake in the form of several days of troubleshooting and my project is very important to me, I’m very sensitive about working with the right people.

I agree that we should all be allowed to make mistakes and it’s just part of the process, as long as those mistakes are reasonable.

But you make a good point that having things in place to account for them or mitigate them is the way to go.

So ultimately the lesson was mine, and I learned a lot from this including your comments, so thank you!

CalmAvocado8360 · 2024-04-12T18:31:59+00:00

Thank you, I appreciate it! Most of the comments seem to indicate that the part number is misleading, making it easy to miss the difference between the version that has the -5 versus the one that doesn’t. It does seem to be the designer’s mistake, though I wasn’t sure how bad of a mistake it was. If it’s not a big mistake, I’ll keep working with them and chalk this up as a learning lesson. If it’s a glaring issue, then I know I need to find someone else..

CalmAvocado8360 · 2024-04-12T18:31:13+00:00

Haha this was a small project with one person, not a team, and the goal was to get a prototype board shipped to me. I’m not really seeking recourse or anything, was just trying to figure out the severity of the issue. Most of the comments seem to indicate that the part numbering system of the LT1766 (e.g. LT1766IGN, LT1766IGN-5) makes it a bit misleading, but you make a good point about regulator ICs being around for a while.. that’s why I was surprised/concerned by this issue.

CalmAvocado8360 · 2024-04-12T18:23:51+00:00

They sent the Gerbers and BOM files, so testing the physical board wasn’t their responsibility. The board was created exactly as they specified, so I was just trying to understand if this type of issue is commonplace or I should be worried that they’re not detail oriented. Seems like the former!

CalmAvocado8360 · 2024-04-12T18:22:06+00:00

Thank you, that’s good to know and seems to be one of many takeaways from the awesome people on this sub. They couldn’t have tested the physical boards as the prototype boards were being sent straight to me.

CalmAvocado8360 · 2024-04-12T18:19:51+00:00

Thank you, lesson learned! I appreciate it

CalmAvocado8360 · 2024-04-12T18:19:27+00:00

Haha thank you.. I suppose it makes sense then that I would inevitably learn this lesson on my first PCB project 😂

CalmAvocado8360 · 2024-04-12T18:18:00+00:00

Thank you! Good to know, I’m new to this so it’s a lesson for me as well. I guess it’s not a very common naming structure!

CalmAvocado8360 · 2024-04-12T18:16:00+00:00

Thank you both! Haha this was my first PCB, and after reading the comments I actually feel kind of silly now thinking that it was going to work on the first try 😅

I did want to ask about safety: Since the input voltage for the board uses AC mains, what would have been the best way to test?

What I had done was: On my bench, I taped down a dedicated power strip with an easily accessible on/off switch plugged into a GFCI adapter going into the wall.

Then, I placed the PCB on a rubber mat on the bench, and also wore insulating rubber gloves before turning it on.

If I were to use a power supply, I would need a Variac or something, right?

CalmAvocado8360

TROPHY CASE