Stc 1000 warning!

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benbradford

benbradford

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It seems like it would be common sense, but after a while things can be taken for granted and items can be used in different ways than originally intended.

I built my stc 1000 a couple of years ago and originally controlled a dorm fridge and paint can heater with it. Now, 2 years later I used it to control a much larger fridge and decided a couple of days ago to do a diacetyl rest and finish a couple of kegs of beer using a space heater in the general area of these beers.

The stc 1000 that I had originally built had too small of a gauge wire I now realize and coupled with that I was pushing a space heater pulling 1500w.

This is the outcome that I discovered this morning.

USE THE CORRECT GAUGE WIRES AND DO NOT OPERATE SPACE HEATERS THAT ARE TOO BIG!!!

controller3.jpg
 
Wow. 1500W is gonna pull a lot of amps at 120V. I'm not surprised that you overloaded wiring that was otherwise up to the task.

That much heat in a chamber is huge overkill. I use one of the DIY paint can heaters inside a full-size fridge and found that a 40W bulb is perfect for the kind of gentle gradual heating needed.
 
it was actually heating a spare room that had 2 carboys and 4 kegs. The room stays around 65 and this was just helping get it to 72
 
I posted this because looking around hbtalk, it seems that there are many people using space heaters controlled by these controllers.
 
Thanks for sharing. Glad it wasn't worse.

Anyone thinking of building one of these: Make sure you use the proper AWG wire (should be 90deg 18AWG or lower), and a 10A fuse, to prevent these kinds of things.
 
benbradford said:
I posted this because looking around hbtalk, it seems that there are many people using space heaters controlled by these controllers.
Click to expand...

True dat, although the most common one I see discussed is that little 200W Lasko "My Heat" model since it comes on by itself when powered up.
 
At 1500 watts the circuit for the space heater would have drawn 12 amps. I'm not sure what size wire you had used, but I'm willing to bet it wasn't the wire that caused the problem.

The problem was generated from the STC-1000 itself. They are only rated for a 10 amp load, or 1200 watts. So the most unfortunate part of this problem is your load pulled pulled enough amperage for the STC to work at first. You probably didn't even think about it, and walked away thinking there was no problem. Over time the amperage pulled heats up the wires/contacts, and the failure happened. It probably took a couple hours though. Those are the worst problems to have. The sneaky ones.

From the picture it looks like its the STC that totally burned up, and the further away from the STC the better the actual wire looks.

This is still a very good thread and thanks for creating it. I hope it shows people what really can happen with electricity when it is done wrong. (in your case the wiring was good but your load was to much for the STC) I'm glad that the problem didn't make it out of the box for you. Electrical fires are no joke.
 
BeerGrylls said:
Thanks for sharing. Glad it wasn't worse.

Anyone thinking of building one of these: Make sure you use the proper AWG wire (should be 90deg 18AWG or lower), and a 10A fuse, to prevent these kinds of things.
Click to expand...

I second using a 10A fuse. I was worried about this when I built mine and feel much better knowing that it will trip before burning the house down. If anyone is interested retrofitting theirs with a fuse, here is what I used (available from radio shack):

http://www.radioshack.com/product/i...06&gclid=CPjXu96T5b0CFQcCKwodjQsAAA&gclsrc=ds
 
I read here on HBT somewhere (wish I had a link for you) that although the relays say 10A, that is technically the 240V rating. This person said at 120V, they are good for 15A. I've never tested this, but would love to know for sure.

It's hard to tell, but that looks like at least 16, maybe 14 gauge wire. 16 might technically work, but in an enclosure with no ventilation, I'd want 14.

A loose screw terminal could definitely cause that as well.
 
BeerGrylls said:
Thanks for sharing. Glad it wasn't worse.

Anyone thinking of building one of these: Make sure you use the proper AWG wire (should be 90deg 18AWG or lower), and a 10A fuse, to prevent these kinds of things.
Click to expand...

Just to be sure, *WHERE* should the 10A fuse be used? The power to the STC? Each of the controlled lines (heat & cool)? All 3?
 
balrog said:
Just to be sure, *WHERE* should the 10A fuse be used? The power to the STC? Each of the controlled lines (heat & cool)? All 3?
Click to expand...

The fuse should be in front of the controller and both relay feeds. You have a common hot line breaking out to all three loads, that's where to put a fuse...

Cheers!
 
Seems like an opportunity here for an enterprising electrician. I'm sure there are many here who would pay to have a properly built unit, myself included. The peace of mind would be worth the extra cost.
 
Facinerous said:
The problem was generated from the STC-1000 itself. They are only rated for a 10 amp load, or 1200 watts. So the most unfortunate part of this problem is your load pulled pulled enough amperage for the STC to work at first. You probably didn't even think about it, and walked away thinking there was no problem. Over time the amperage pulled heats up the wires/contacts, and the failure happened. It probably took a couple hours though. Those are the worst problems to have. The sneaky ones.
Click to expand...

GotPushrods said:
I read here on HBT somewhere (wish I had a link for you) that although the relays say 10A, that is technically the 240V rating. This person said at 120V, they are good for 15A. I've never tested this, but would love to know for sure.
Click to expand...

I'd love to know this for sure, from someone more electrically inclined than myself. I believe my freezer pulls something like 11-12A (manual just says it needs a 15 or 20A circuit). It only seems to run for 10-15 minutes at a time though, once every few hours or so. So if it really takes a few hours to run into an overheating issue like this, I'm nervous I'll be flirting with danger for a long time.
 
day_trippr said:
The fuse should be in front of the controller and both relay feeds. You have a common hot line breaking out to all three loads, that's where to put a fuse...

Cheers!
Click to expand...

And make sure you use a "slow-blow" fuse, as the electrical load (i.e., freezer compressor) creates a brief current surge on startup. Otherwise, you'll pop faster fuses every time the freezer powers up.
 
Here's an image of the internal relays of my STC1000:

wp_0000101-55781.jpg




IMHO, the failure of the OP's unit may be associated with the actual wire connections to the controller and not necessarily the relay. Although, the photo is not adequate for a decent analysis.

The terminal/wire connection may have been loose or poorly made. Loose connections generate heat and it sure looks like the heat was generated at the terminals. Dissecting the unit would shed additional light on whether the relay was directly involved in the overheat condition.

I can't tell from the posted photo, but using solid conductor wire on the type of terminals on the STC1000 could easily create a bad connection. I would recommend to always use stranded wire at those connections.

All that being said, there is a possibility that the relay had a catastrophic failure that created the damage seen by blowing out its side nearest the connectors.
 
Yes, at 120V these are rated at 15A as you can see from the picture above. I used a 15A circuit breaker in my enclosure....because if I ever blow a fuse I know I won't be able to find a spare handy when I need it :)
 
helibrewer said:
Yes, at 120V these are rated at 15A as you can see from the picture above. I used a 15A circuit breaker in my enclosure....because if I ever blow a fuse I know I won't be able to find a spare handy when I need it :)
Click to expand...

Why didn't I think of that...
 
This is not the first time the rating of these controllers has come into question on this forum.
The UNIT has a capacity rating of 10 amps regardless of the relay's higher rating. The copper traces on the PCB and the wire connectors are more likely to be rated lower than the relay.

Read your manual and abide by the posted rating. As noted adding a fuse to the power feed hot wire (generally black in power cords, and the smaller pin of a polarized plug/receptacle) will keep you and your controller safe.
 
helibrewer said:
Yes, at 120V these are rated at 15A as you can see from the picture above. I used a 15A circuit breaker in my enclosure....because if I ever blow a fuse I know I won't be able to find a spare handy when I need it :)
Click to expand...

Oooo! I really like that idea! Very nice. Just standard breaker wired to the hot incoming line?
 
jleiii said:
This is not the first time the rating of these controllers has come into question on this forum.
The UNIT has a capacity rating of 10 amps regardless of the relay's higher rating. The copper traces on the PCB and the wire connectors are more likely to be rated lower than the relay.

Read your manual and abide by the posted rating. As noted adding a fuse to the power feed hot wire (generally black in power cords, and the smaller pin of a polarized plug/receptacle) will keep you and your controller safe.
Click to expand...

I was about to make a comment about the traces but you're absolutely right since you're not connecting to (for instance) an SSR relay terminals, you're connecting to the cute little screw terminals, which are connected by traces to the relays on the PCB.
 
DrunkleJon said:
That truly is the best wiring diagram I have seen for the STC-1000, well done.
Click to expand...

One thing to consider on that drawing is that the additional receptacle is also drawing on the same 10a fuse, limiting TOTAL current to 10 amps. Feeding the extra receptacle directly from the incoming hot lead would leave the full 10 amps for the hot/cold controlled circuits, and the 15a (or 20 as applicable) breaker in your house panel would provide the overall limit.
 
jleiii said:
One thing to consider on that drawing is that the additional receptacle is also drawing on the same 10a fuse, limiting TOTAL current to 10 amps. Feeding the extra receptacle directly from the incoming hot lead would leave the full 10 amps for the hot/cold controlled circuits, and the 15a (or 20 as applicable) breaker in your house panel would provide the overall limit.
Click to expand...

Absolutely right, thanks for pointing that out! My primary use for it is a stir plate. Keep the total draw low.
 
balrog said:
I was about to make a comment about the traces but you're absolutely right since you're not connecting to (for instance) an SSR relay terminals, you're connecting to the cute little screw terminals, which are connected by traces to the relays on the PCB.
Click to expand...

Also because they are mechanical relays not solid state relays there is probably a higher chance of failure during switching I would think. Granted most are rated for thousands of switching cycles but there are always outliers from the norm, especially when it comes to Chinese parts.
 

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