STC-1000 went bang

[Pataka]

Are all STC-1000s created equal?

I ordered one from Ali Express, which took an absolute age to arrive here. Finally it arrives, so I go and buy the parts I need, wire it up, and get an abysmal failure.

At first, I thought all was going well, because the LEDs lit up, then they went to EE and it began one long beep. I decided this must be because the temperature probe wasn't connected. So I unplugged it at the wall, wired the probe in, powered it back up... LEDs lit up again briefly, followed by a shotgun bang, then smoke.

I can't be totally sure because there's not much left of it now, but I think the culprit was a small ceramic resistor at the far side of the PCB, immediately in front of the main power input.

Our voltage here is 220v, and my unit was rated for 110-220v.

Any thoughts? Incorrect input voltage or shoddy choice of components on cheap hardware? Or, shoddy wiring on my part?

 

[Pataka]

Sorry that mightn't have been clear. The ceramic resistor (I think it was) is the part there is hardly anything left of now. It's literally just wires and a small bit of coating at each end.

 

[peteru]

I have never, ever purchased anything from Ali Express that wasn't total and utter rubbish. Had about 5 purchases and in 4 instances received a refund after contacting them. Most items were very low cost and either not as described or so poorly manufactured that they were not fit for purpose. The one item where I didn't even bother getting a refund was again rubbish, but it was rubbish by design and I should have known better than to order it!

I suspect that Ali Express is basically a way for Chinese manufacturers to offload products that did not pass QA and could have not been included in bulk shipments to their trading partners. This allows them to bulk export slightly better quality products and offload the defective lots at a bigger profit by selling at a price point somewhere in between wholesale and retail price.

Ask for refund, and don't buy from them again. Inkbird seems to be trying to build a good reputation here and there should be a few people that have used Inkbird controllers for a while. Perhaps you might want to consider those as an alternative.

 

[Pataka]

Thanks for the reply. I'm quite amused as the seller has just offered me a refund of about 20% of what I paid for the whole thing (which wasn't much, to be fair) and the proceeded to tell me it was important they got a four star rating!?!?

I told him a refund of anything less than what I paid was an insult, as the product died on first use. I said I am lucky it didn't start a fire, and even if I got the full refunded amount, I wasn't sure what would compel me to give a 4 star rating.

 

[sp0rk]

Still got it wired up?
Can tell you pretty quickly if you've wired it wrong

 

[Pataka]

Sadly, no. I don't know why, but as soon as it burnt the resistor, my instinctive reaction was to remove it from the wall outlet then unscrew all the wires I had added. I wish I'd at least taken a photo just to be certain.

The more comments I get along the lines of AliExpress' products being subpar tend to make me think it wasn't anything I did wrong.

 

[SBOB]

conversely ive ordered plenty of aliexpress items without issue

It's all the same chinese stuff coming from chinese sellers that sell via ebay etc... luck of the draw comes into it more than buying from aliexpress v elsewhere

 

[nosco]

Ive bought a few things off Ali with no troubles including stainless bits and 2 stc'. I ordered one to build an stc1000+. They sent me the wrong one and so gave me a refund no questions. Then i reordered and got the correct one. Scored 2 for 1. Both work perfectly.

Edit: "no problems"

 

[Pataka]

I think for my next one, I'll order one from a local supplier, then will wire it up and upload a pic of it all connected up before turning anything on.

 

[stilvia]

I suspect that Ali Express is basically a way for Chinese manufacturers to offload products that did not pass QA and could have not been included in bulk shipments to their trading partners. This allows them to bulk export slightly better quality products and offload the defective lots at a bigger profit by selling at a price point somewhere in between wholesale and retail price.

If that was the case, I doubt Ali Express would still be operating today. I have purchased two STC-1000's and three 80a DPDT relays from Ali with no issues. Quality of the units was great.

 

[TwoCrows]

Play it safe and get one of these........ Inkbird is a forum sponsor and I have one and have just plug it in this week and put the stc1000 aside for a different task. So far so good.
http://www.ebay.com.au/itm/AU-PLUG-240V-Dual-Stage-ITC-308S-Temperature-Controller-Pre-wired-Probe-sensor-/322087465021?hash=item4afde8b03d:g:NX8AAOSwaZdXHzbH



Good luck, stay safe.

 

[Camo6]

Never had a problem with Ali-express. Have bought plenty of cheap items from them and have received plenty of cheap items. Said the scorpion to the maiden, as she lay dying, "You knew I was poison when you picked me up." ( Any DT fans out there?) Admittedly, while some of the items bought from Ali were rubbish, a lot of them are still in use today. Heck, my Kaixin's were sent straight from Jackie Wu and haven't missed a beat for several years.

There are cheap STC's getting around but I have three or four of the Elitech variety and these still work flawlessly. One has controlled a ferment freezer for 5 years and two ran 10amp loads without hassle on my old brew setup.

There's not too many reasons a resistor goes bang. By all means, request a refund but if your wiring diagram wasn't proven, double check before you wire the next one.

 

[megabyte]

Are all STC-1000s created equal?
...
Our voltage here is 220v, and my unit was rated for 110-220v.

Nope, unfortunately all STC1000's are not all equal. There are a few models circulating and some of them have design flaws that I don't think would meet safety regulations if put to scrutiny. Here are pics inside 2 models I've photographed recently:


I've bought 6 STC1000's on various occasions from Aliexpress so far and while they have all worked, you don't always get what you ask for. E.g. when I asked a recommended seller to express courier two A400-P models to me (that I could upgrade with STC1000+ firmware), they still sent me the wrong model. When I showed them photos of the internals of what they sent me they apologised and said if I wanted to buy again they'd send me the right model next time. No offer of discount whatsoever, but what can you expect when they make about 50c on each sale?

Once thing that confuses me is you say it was rated 110v to 220v, but the way they're wired I think it depends on the transformer they use. You either get a 110 OR a 220v version. If you got the 110v model it's NOT gonna be happy running on Aussie mains voltages.

Also these things are built to a price and while mine have all worked, I do believe it's possible that you gat a faulty unit.

I'd love to see piccies of the internals, even if it's all unwired. It would be cool to see if its a different model and which parts actually went bang!

Play it safe and get one of these........ Inkbird is a forum sponsor and I have one and have just plug it in this week and put the stc1000 aside for a different task. So far so good.
http://www.ebay.com.au/itm/AU-PLUG-240V-Dual-Stage-ITC-308S-Temperature-Controller-Pre-wired-Probe-sensor-/322087465021?hash=item4afde8b03d:g:NX8AAOSwaZdXHzbH

Nice linky! Man now I want one of these to pull one apart and see if it can be hacked. You guys are keeping me poor

 

[Pataka]

Righto then.. Here's the pics taken by the investigation team shortly after the incident. The resistor that exploded is the one at the edge of the PCB.




Here's a recent one, sans resistor (which has all fallen off now) but otherwise showing the layout of the board


And here's the label that says 110-220v


I've already ordered an Inkbird now. I thought I'd play it safe.


It does annoy me, however, since it has to ship from overseas and is estimated to be here some time between 17 June and some point in July. It's only annoying, as my STC took forever to get here. I ordered it in early May. I spent all summer not brewing, because I had no way of getting the fermenter cool enough. "Never mind... at least winter's coming" I thought.

I'll be making the most of the remaining cool days once it does finally arrive, I'll say that much.

 

[nosco]

I read on here that the Elitech version is the original. I have one that has worked fine for 2 years. But who knows if they just stamp a Elitech logo on any old version.

 

[megabyte]

Righto then.. Here's the pics taken by the investigation team shortly after the incident. The resistor that exploded is the one at the edge of the PCB.

IMG_3661.JPG

IMG_3662.JPG

Well I'll be... That's a switch mode regulator in there (using that small yellow transformer to step down the voltage). You can see mine use an old fashioned iron core transformer (the big brown square) but your switch mode supply explains why it can run from 110-220v so mystery solved there.

As for the resistor, I think that's a fusible resistor with 2 purposes, first it limits inrush current when the power is first connected, but also it's designed to blow if things go wrong so the whole unit doesn't burst into flames. Looks like it did its job. Alas even if you replaced it the underlying problem would still cause it to blow again

Thanks for posting the pics. The only way I can imagine you getting that to blow is if live wires were connected to the low-voltage circuitry somehow. e.g. to the probe terminals? Otherwise I'd say it blew for the same reason about 10% of the shitty switch mode adapters I've bought from Aliexpress blow. They cut too many corners/costs to be 1c cheaper than the competition to get more sales when we sort by price.

 

[Pataka]

I think I've put the biggest 'what if?' to rest just now. Ever since the event, there's been a nagging thought in the back of my mind of "what if I connected the phase to the probe terminals by mistake?" but because I removed them all immediately after it failed, I thought I'd never know. But I just found a clue.

The screw terminals themselves need to be opened wider to allow the high gauge mains cable in, while the probe terminals of course can be quite narrow. I can see that terminals 1,2, 5,6, 7 and 8 are open much wider than 3 and 4. This proves that the narrowest wire (the temperature probe) was indeed connected to the correct terminals, while the phase was definitely not connected up to it. The labeling is consistent with that, as is the componentry, so it's not even that the terminals are mislabeled.

Your theory about an underlying problem further down the chain (as opposed to the resistor itself) may also be supported by the fact that the problem wasn't observed until the temp probe was connected up. Perhaps, with the probe disconnected, the faulty electronics weren't being touched, but once it was.... bang.

I guess I'll never really know, unless I suddenly get the urge to 1) remove the components , 2) learn a lot more about electronics than I currently know and 3) test them.

 

[megabyte]

Good investigating! I can't imagine how you could have botched it then. Perhaps when the probe was connected it tried to energise one of the relays, drawing more current and causing the power supply to fail. Honestly it could be any number of things.

Don't sweat it, your new controller should work well out of the box, and if you ever do buy another STC1000 you'll probably find that it works just fine. I would get a second opinion on your wiring though, just so you don't send yourself insane with self doubt if it blows up too!

 

[sp0rk]

Nice linky! Man now I want one of these to pull one apart and see if it can be hacked. You guys are keeping me poor

Rip apart one of their SSRs and investigate if you're going to do some investigation
Spog sent me a counterfeit Fotek SSR and upon investigation it's definitely dodgy, not upto the 20A they claim it to be
I'd probably trust it at 10A, but not at 20A
Will probably stick it in a voltage controller setup for a boiler and run it until it goes bang

 

[megabyte]

At that price point ($55) I doubt it will use SSRs.

I did a lot of design work on temperature controllers a few years back, but when it came to getting (expensive) certifications and going into production the $20 STC1000's were becoming really popular and there's no way I could have competed on price, even using mechanical relays. SSRs would have increased the BOM and also necessitated heatsinks, a larger enclosure, increased shipping costs etc.etc..

Here's a pic of the Prototype (sans enclosure)


The inkbird controller says it's rated to 10A and I can't see any beefy heatsinks in the pictures so my guess is it runs with mechanical relays. Not that that's a bad thing at all.