Hi folks, in wiring up a circuit I'm not sure exactly why, but I managed to cook what I think is an inductor.

I have a display from stone-hmi.com model STI070WT-01, which is a tft lcd with touch screen and a uart interface. Datasheet is attached.

I attempted to reach out to the mfg but have yet to get a response. also attached are a pic of the board, and two close ups of the component.

as far as what caused this, my best guess is that voltage fed back through the solid state relay I was attempting to add. which, if anybody could confirm that as being likely, I guess I would need to add a diode in line to prevent that from happening.

I have a 2s1p lipo with the + going to pin 5 of a vishay VO14642AT, then pins 4&6 are tied together and go to the Vin on the display, as well as feeding a dc/dc converter which outputs 5v for an arduino. The arduino has a pin going to pin 1 on the relay, and pin2 goes to ground on the arduino.
It should go without saying but the dc/dc converter has it's ground going to both the display and the arduino.

I connected the battery and as expected nothing happened. however when I shorted the battery + with the Vin on the display, I expected both the arduino and display to power up, and the arduino to activate the relay and thus keep the circuit up until the pin was pulled low. Instead, I got a puff of magic smoke....

Might anybody be able to clue me in as to what happened, and what I *should* have done here? In the meantime I'm going to start scouring my parts bin to try and find anything with similar componants...

Thanks in advance,
Nathan

 

Hello Raw, welcome to the forums.

Got schematic?

 

Hello Raw, welcome to the forums.

Got schematic?

LOL! if I had that, this would probably be a no brainer, On top of not having one, even if I am able to get one(very unlikely) it would almost certainly be unreadable to me as I don't read chinese, though the numbers would offer up some clues... I will say that unlike most of the sheets I've come across, this one does have a table of the current draw at several standard voltages...
VIN=5V 530mA VIN=12V 220mA VIN=20V 130mA
wiith the permissable range being 4.5v-20v.
hopefully that will offer some suggestions at acceptable replacements?

 

That is simply a common mode choke, used to prevent RFI from entering/exiting the board. From your pictures, it doesn't look burned, and you may be able to just solder it back in. Otherwise, just take a good look at it and rewind it with fresh magnet wire.

Or you could just add two short jumpers from the top to the bottom pads on each side.

 

That is simply a common mode choke, used to prevent RFI from entering/exiting the board. From your pictures, it doesn't look burned, and you may be able to just solder it back in. Otherwise, just take a good look at it and rewind it with fresh magnet wire.

Or you could just add two short jumpers from the top to the bottom pads on each side.

Oh boy.... now you've done it...
I got wrapped up in dealing with contractors all day that had to come back and redo work because they assumed that the building code didnt apply to them, BUT, I had been looking at that little bugger and an image in the datasheet of probably an older version which doesnt seem to have it, and the whole time I was thinking to myself hmmm... that looks alot like magnet wire.... i wonder if i have any that small....or i wonder if i could just bridge the gap where the stuff melted away....

In my very short time i had to take the pic its possible i got the wrong angle, but there is a quite obvious piece of one of the wires that melted into little beads on either side...

So I will see if i can locate my magnet wire, and attempt to rewrap it, and if that fails will likely bridge the pads. should I bridge both sides? or only the side showing no continuity?
and finally, are there any suggestions as to why this might have happened? I did think perhaps I had mis-interpreted the data sheet on how to connect the relay, but i found a post on here of somebody that fried a voltage regulator doing just what i am, and the last reply on that matched up exactly with how i wired it up...
It is rather daunting when you are so sure of the results of hours of reading and testing things along the way, all working just fine then poof out comes the magic smoke....

 

LOL! if I had that, this would probably be a no brainer, On top of not having one, even if I am able to get one(very unlikely) it would almost certainly be unreadable to me as I don't read chinese, though the numbers would offer up some clues... I will say that unlike most of the sheets I've come across, this one does have a table of the current draw at several standard voltages...
VIN=5V 530mA VIN=12V 220mA VIN=20V 130mA
wiith the permissable range being 4.5v-20v.
hopefully that will offer some suggestions at acceptable replacements?

You somehow connected a pile of stuff and failed.

Asking how you connected this stuff, ie, the schematic, should result in a schematic. Not laughter.

 

You somehow connected a pile of stuff and failed.

Asking how you connected this stuff, ie, the schematic, should result in a schematic. Not laughter.

Please accept my sincere appology, I incorrectly assumed you were referring to a schematic for the chinese display that I was focused on trying to get back to a working state... I will do my best to whip one up now, hopefully without getting lost down a rabbit hole of finding particular parts...

 

You somehow connected a pile of stuff and failed.

Asking how you connected this stuff, ie, the schematic, should result in a schematic. Not laughter.

It's a little rough, but it hopefully will lay it out well enough.

 

It's a little rough, but it hopefully will lay it out well enough.

The red wire here shows what caused the smoke.

 

[ If you rewind or bypass the inductor, use the same size or smaller wire - you want it to act as a fuse and not smoke any runs on the board. ]

Double check the polarity of the battery - be sure (-) is on the ground and the (+) is on the vcc input.

Then you will need to troubleshoot the STI070WT-01 independent of the rest. For some reason, the display is drawing much more current that it should.

After repairing/replacing/bypassing the common mode inductor, hook up the power pins of the display to a power supply that has some form of current limiting - that LiPo has too much punch for troubleshooting You need something that will supply the rated voltage and current to the display, but that you can short without melting wires.

Apply power and see if the display works. If not, then more in-depth troubleshooting will be required. If it does work, then connect it back into your circuit, using that current limited supply instead of the LiPo. When all is working, then you can go back to the LiPo. I would suggest a fuse be incorporated, as lithium cells can deliver fire starting amounts of current.

 

[ If you rewind or bypass the inductor, use the same size or smaller wire - you want it to act as a fuse and not smoke any runs on the board. ]

Double check the polarity of the battery - be sure (-) is on the ground and the (+) is on the vcc input.

Then you will need to troubleshoot the STI070WT-01 independent of the rest. For some reason, the display is drawing much more current that it should.

After repairing/replacing/bypassing the common mode inductor, hook up the power pins of the display to a power supply that has some form of current limiting - that LiPo has too much punch for troubleshooting You need something that will supply the rated voltage and current to the display, but that you can short without melting wires.

Apply power and see if the display works. If not, then more in-depth troubleshooting will be required. If it does work, then connect it back into your circuit, using that current limited supply instead of the LiPo. When all is working, then you can go back to the LiPo. I would suggest a fuse be incorporated, as lithium cells can deliver fire starting amounts of current.

Your timing is impecable, I was literally doing the first part of what you said as you were typing, and just tested the display on it's own with success... the wire on the part, well half of it anyways, matched the red magnet wire I got from radioshack so long ago, I did notice a marked difference in the wire I removed, one was as expected and held it's shape easily, the other had 2 fewer windings, and was very brittle, noticeably thinner, and falling apart...the slightest touch from my diag cutters and it would split, while the other side I could manipulate with the cutters. I counted 5 pieces of 'good' wire, and 3 thin ones, so made the assumption it should be 5 and 5, which just barely fit with a little manipulation.

I will proceed as advised, using my adjustable supply and hopefully can locate the problem. I know that the issue must be with something in what I did, as the display alone on the lipo works just fine, checking that was made much easier by the display having a connector and pigtail for the circuit along with solder pads off to the side, making disconnecting what I added quite simple.

I'm looking at the datasheet again for the relay and I wonder if I understood it correctly, as it seems strange that a pin would reverse it's purpose between ac and dc connection, would you mind taking a peek and see if that's what the issue is?

 

You know, please disregard the issue, since I'm having an issue with this part, and others before me have also had some troubles, I am going to be smart about it and use a different part...I know I already have a CPC1002N around someplace, just have to locate it. It has a current limit of 700mA vs 2A, but with the display running at 8v from the lipo, I should easily remain below that number by at least 100mA.

I thank you folks for taking the time to share your knowledge and time, I do appreciate how difficult it is to be vigilant with anything, particularly online on a forum. I need to get some things done for now but I will be lurking around a bit and if I find anything I can help on, will do so, even if it's only to try and help a newbie get their ducks in a row for someone else to more easily assist them.
I know I like to see how things turn out, so here is a picture after I rewound it, I checked the images from before and there was just enough blur to cover up the problem... the bright spot on the right side of the second photo is actually a blob of copper from the wire that melted, and all of the enamel is gone from the wire. I did find a few red flakes left behind, but for the most part it was all copper colored.

 

Just as a final follow up, I pulled off that relay and replaced it with a cpc1002n, leaving all wiring the same except for the short bridge that tied the two pins together, and it worked perfectly.

I didn't go dumb and use the lipo right away, testing first with the adjustable supply, and found all in It's using around 330mA so I'm well within budget for power. Thanks again guys for saving me from having to rush order a new screen and pay tooth and nail to get it quickly.