Basic wiring question about DIY projects and the STC-1000

[Blue-Frog]

When wiring up the STC-1000 to a power cord and the hot and cold plugs, several lead wires are required.
When I went shopping, I needed to choose between 5A, 7A, 12A, and 17A lead wire.
What do I want to choose?
I am connecting the thermostat to a freezer that mentions 15A;
thought the STC-1000 was rated for 12A,
I have no idea what any future heating option would be rated....

How does one choose the appropriate wire rating?
Will the power voltage 100/220 impact the choice?
Is there a downside of using higher rated leads than necessary?

Ray

 

[tracer bullet]

Get wire for as much or more than you think you will pull. In this case the 17A wire would be best.
120 / 240 is voltage, you care about amperage, and should be good knowing the above.
Can't go too heavy a wire, within reason.

What exactly are you working on? Some more context could give better answers.

 

[day_trippr]

fwiw, the STC-1000 "manual" claims 10A relay contact rating.
Running a freezer with a build plate current rating of 15A on a controller sporting 10A relays is rolling the dice wrt longevity of the latter...

Cheers!

 

[IslandLizard]

I am connecting the thermostat to a freezer that mentions 15A;
thought the STC-1000 was rated for 12A,

15A sounds like a lot for a freezer, unless it's a huge commercial type, like you'd find in Supermarkets, but those are 220-240V usually.
A chest or upright freezer for use in homes would be more in the 150-300W (1.5-3A) range.

Maybe 15A is a misprint?

The STC-1000 has 10A miniature relays, AFAIK, for either the 220V or 110V versions.
16 gauge wire should suffice for a 10A load.

 

[RocketBrewer]

If my memory serves me correctly, I believe the relay in the STC-1000 (at least the version I have) is rated for 10A @ 220V and 15A @110V. I'm guessing that the freezer reference may have been to the recommended size of the circuit breaker. There are power monitors like this that can be had fairly inexpensively that will tell you what the unit draws if you're interested. A google search on the freezer model might find you the specs on power draw. The startup power is what you want to know, the run power is surly well within the limits of the STC

 

[day_trippr]

I have not found any purported spec for the STC-1000 that indicates the relays are rated above 10A for any AC voltage.
They all say "10A".
One example of the multitude...

https://images-na.ssl-images-amazon.com/images/I/71VSFdFfszL.pdf
Cheers!

 

[Blue-Frog]

Ok Everyone is correct about the "relay contact capacity" being 10A and not 12A...
(I was speaking from a 1 or2 year old memory which is why I wrote "thought" in the OP;
I suspected I might be off a bit)

The Freezer docs say to use a dedicated outlet rated at 15A or above.
It is not a particularly large unit... 145 L (max cooling = minus 20 C.)
[see: Haier JF-NC145F]

If "15A sounds like a lot for a freezer..." could it just be an extra wide safety margin?

Re: "Running a freezer with a build plate current rating of 15A on a controller sporting 10A relays is rolling the dice wrt longevity of the latter..."

So the danger is to the STC-1000 not the Freezer?

I would like to know what everyone elses Freezer specs say...
am I the only one who needs an STC-1000 rated for 15A rather than 10A?

 

[IslandLizard]

You're in Japan, right?

No, a freezer like that doesn't pull 15A continuously, I doubt even at startup. It's most likely a general direction to be compliant with the electrical code to plug it into a 15A circuit. But its continuous draw is way, way less.
For example, 15A at 100V (Japan) = 15A * 100V = 1500W; that would be like a space heater. Fridges and freezers are much, much leaner, thank goodness, or we probably couldn't afford running them as we do.

At startup it draws a quick pulse for a split second to get the compressor going (there's a large starting capacitor that sucks most of the energy for that short time). Once it runs, it's in Running Mode.

Your freezer is 145 liter = 38 gallons = 5.1 cubic feet.
It's indeed not that large.

From: Haier - Refrigeration Power Consumption (Amps and Watts) | Haier Appliances

"Refrigeration products use a higher amperage (wattage) momentarily at the time of compressor start-up than while they are running.​

The chart lists the Start Up and Running amps and watts of different models."​

For illustration, I copied a few rows from that table that apply to 5.0 cu.ft models, probably very similar to yours, for comparison:

Model

Door Swing

Start Up Amps/Watts

Running Amps/Watts

IF50CM23MW

6.6 / 759

1.7 / 195.5

F50CW10W		6.6 / 759	1.7 / 195.5
HF50CW33NW		6.6 / 759	1.7 / 195.5

Even the similar 7.1 models listed there draw the same as the 5.0 model. IOW, those use the same compressor.

So your 5.0 model draws around 6.6A (~760W) for a second or so at startup. Then runs at 1.7A (~200W) at regular duty, actively cooling.

Make sure to set the compressor delay function on the STC to the max time interval, which is 10 minutes, IIRC. That will prevent burning out the compressor prematurely. Double check, make sure it works.

 

[Blue-Frog]

yes.

I have a theory that humans rarely really understand each other...
most of our interactions are based solely on "just sufficient" understanding.

For example, when you wrote
"... a general direction to be compliant with the electrical code to plug it into a 15A circuit."

I think I understand and I think that sounds exactly like what the instructions said, but,
uh, what is it that is being implied, yet not clearly stated?
I mean,
What other choices are there?
I can't plug it "out of" a 15A circuit"

Is there some other interpretation ?
Are you saying the the instructions might pertain to the outlet itself and not Freezer nor the STC-1000 ?
That is the way it looks, but thats not the way I interpreted its' meaning.

Anyway thanks for the explan. I will use the largest rated wire that will fit the STC-1000 & the other connecters I'm using. Thanks to everyone who shared.

I am sure it is premature, but I feel better already.

 

[IslandLizard]

I can't plug it "out of" a 15A circuit"

Sorry, the emphasis I put on into was misplaced, it would have been better on the 15A(mp) circuit.

Since the freezer draws 6.6A for a second or so, a 10A circuit would even suffice. But given that most general circuits have more than one outlet that could be powered at the same time, a safety margin is built in per electric code.

We typically use dedicated circuits (only used by one single appliance, or a combination of such appliances) for larger draws, say for an electric clothes dryer, an electric range/HOB, baseboard heaters, etc. Their maximum (running time) draw is known, so those circuits (wires, fuses/breakers, the way the wires are routed, etc.) are designed to sustain those draws indefinitely, without causing overloading (overheating). The breaker/fuse then limits the maximum current (power) drawn as a safety guard by interrupting the circuit.

 

[IslandLizard]

Anyway thanks for the explan. I will use the largest rated wire that will fit the STC-1000 & the other connecters I'm using.

Using thicker, stiffer, less flexible wire can actually cause more problems while solving none.

16 gauge stranded copper is plenty for this application, and it should be flexible enough to do the job and make it easy to handle. Some (cheap) wire can be really stiff due to the harder plastics used in the insulation/mantle, making it more difficult to work with or route.

 

[Blue-Frog]

Yea, don't know about its gauge, but I went with the 17A lead wire.
(I wasn't sure in store, so I bought 3 different versions (7A, 12A & 17A) to choose from later!)

I did notice a strange behavior in the STC-1000 F-3 program... At first, the delay was not applied at all, later it began being applied, (although still being way below spec.), and got better the more I repeated the testing.
Seemed like it was rusty... or sleepy.

Maybe these things need occasional "exercise" when being stored for long tmes?

At last testing
1 min delay setting got me 37" delay
2 min delay setting got me 1'38" delay
3 min delay setting got me 2'44" delay
5 min delay setting got me 4'37" delay
8 min delay setting got me 6'41" delay
10 min delay setting got me 9'24" delay

 

[IslandLizard]

I did notice a strange behavior in the STC-1000 F-3 program...

That's weird...
Make sure you're using a 110V unit not a 220V one. Its source voltage is marked in a check box on the top label. That's the only way you can tell from the outside which voltage unit you got.

Now your mains supplies 100V in Japan, not 110V. I would think the 10% lower voltage compared with say, the US (110-115V) should not make a big enough difference, but maybe your lower input voltage does play tricks with the logic circuitry...

I'm not sure if there's a voltage regulator incorporated. There's a (3-prong) TO-92 component behind the transformer and rectifier bridge, but I can't see the label and don't have a schematic. I would almost assume there should be a voltage regulator to supply the logic board/chip, which does need a steady input voltage to work properly.

There's at least one big thread here on the STC-1000, and a few smaller ones. Some deal with hacks, modifications, and reprogramming, but information may be mixed, that's how life on these forums happens. Maybe they contain the needed info to shine a light on your case.

Leave the unit on for a day and see if it stabilizes.

 

[Blue-Frog]

Interesting.

While I did not do a careful test, it looks like the STC-1000 is smarter than I thought it was.
I had assumed the program delayed onset of cooling according to the interval set, from the point in time, cooling is set to begin.
NO,
the program delays onset of cooling according to the interval set, from the time the cooling previously turned off.

If the cooler has already been off longer than the specified interval, cooling will begin immediately.
If it has just turned off, you will get the full interval before it will start cooling again.

Not positive about this but it appears so. And makes perfect sense !

 

[day_trippr]

I believe you are experiencing the benefit of the "short cycle delay" which is specifically intended to avoid stressing compressors...

Cheers!

 

[Blue-Frog]

Yea, I just thought it was timed from when the cool cycle next engages, not from when it last ended.

Do you know if there is also a delay system on the heat side? On my current unit there does not appear to be.
I know this is supposed to protect cooling units, but am wondering if there is anything comparable on the hot side... ?

 

[IslandLizard]

Do you know if there is also a delay system on the heat side? On my current unit there does not appear to be.
I know this is supposed to protect cooling units, but am wondering if there is anything comparable on the hot side... ?

There isn't. Would there be a need for one?

While we're on topic...
Have you looked at (best) probe placement yet? That's important too.

 

[Blue-Frog]

haha, I was meaning to ask about that! Are there any??

As far as a reason for delay on the hot side, don't know but imagine some heating devices might be sensitive? Isn't it generally more stressful at start up for any device? Depending on the setup those devices could be cycling many many many times a day.
Not sure if lights or heat lamps or other devices could benefit, but maybe?

I have seen some models with a metal tipped sensor, mine is black plastic (or rubber?)
I was wondering if I could get replacement sensors. Are there choices? Have you heard of any?

 

[day_trippr]

fwiw, in my fermentation fridges I pin the temperature sensors to the side of the carboys under a ~4x4" piece of inch-thick closed cell foam, held in place by nifty velcro straps I found at a local big box diy store (Lowes, iirc). In my keezer I do the same thing with one of the kegs...

Cheers!

 

[bruce_the_loon]

The delay on the cooling circuit is to allow the compressor to physically relax. If you listen to a fridge as the compressor stops, you might hear some gurgling as the coolant finishes recondensing and the pressures normalizing. It also needs a couple of minutes to cool down.