STC-1000 on a 1.7A/12A Freezer

[dandavis]

My freezer runs at 1.7A but has a startup rating of 12A. I know that the STC-1000 is rated at 10A but I've read elsewhere that the internal relays are rated to 15A.

So, do I cross my fingers and try the controller? Or do I go ahead and design in a relay? Here's the one I'm looking at: http://www.amazon.com/dp/B0071NB12K/?tag=skimlinks_replacement-20

Thoughts?

If I go the relay route, anyone with experience with the STC-1000 care to assist with a wiring plan? Or can someone point me at some schematics? I'm comfortable with it on my own, but always on the lookout for lessons learned and best practices information.

Thanks!

 

[LoloMT7]

Did you check out this thread by chance,? it might be helpful but won't help on the relay issue. https://www.homebrewtalk.com/f51/ebay-fish-tank-controller-build-using-wal-mart-parts-261506/

 

[BrewCityBaller]

Generally, electronic components are rated for "peak" and "continuous" current, and for the peak value, the duration which the component can withstand that value is also given. I am certain that the listed 10A current is the maximum continuous current, with the peak value being quite a bit higher.

I would venture a guess that the 12A peak current is lasting <1 second, and well with in the margin of safety for this device.

It is totally up to you, but if it were my setup, I wouldn't think twice about using it.

 

[ramgeva]

I heard of someone that the relay failed with his freezer and ruined a batch that was fermenting inside (got too hot), the relay melted!! He replaced it with a 40A SSR (5$ on eBay) , I followed his steps and replaced it in advance.
He published an article with schematics how to replace (unfortunately it is not in English) but if you want I can give you a link, maybe you can use google translate and probably the schematics will help.

 

[dandavis]

OK, so BrewCityBaller echoed my own assumptions... I'm going to give the STC-1000 a go without using an external relay.

So, I had thought about a few options for wiring this controller in...

1. Standalone install built into a project box
2. Wire it inline with the existing power cord and a new cord
3. Replace the control panel and thermostat with the STC-1000

I like option 3. I've ordered a new control panel (plastic mounting panel) so that I can preserve the original. I'll use some quick connect fittings to interface the STC-1000 with the factory wiring using this schematic:

If I have issues or when I want to get rid of the freezer to upgrade, I can swap the original hardware back in and I'm ready to rock and roll.

 

[dandavis]

Did a bit more research and confirmed yet another suspicion...

The internal relays are rated 10A @ 250V which means at 120V, they should be rated closer to 20A... They are stamped 15A, so plenty for a 12A startup spike.

 

[BrewCityBaller]

OK, so BrewCityBaller echoed my own assumptions... I'm going to give the STC-1000 a go without using an external relay.

So, I had thought about a few options for wiring this controller in...

1. Standalone install built into a project box
2. Wire it inline with the existing power cord and a new cord
3. Replace the control panel and thermostat with the STC-1000

I like option 3. I've ordered a new control panel (plastic mounting panel) so that I can preserve the original. I'll use some quick connect fittings to interface the STC-1000 with the factory wiring using this schematic:

If I have issues or when I want to get rid of the freezer to upgrade, I can swap the original hardware back in and I'm ready to rock and roll.

Looks like a good plan. I literally did the exact same thing this weekend to a mini fridge. I put my controller in the door though. If you want any pictures or have any other questions, let me know! I think you will have no issues and be very satisfied.

 

[ramgeva]

Did a bit more research and confirmed yet another suspicion...

The internal relays are rated 10A @ 250V which means at 120V, they should be rated closer to 20A... They are stamped 15A, so plenty for a 12A startup spike.

Hi
Not sure you are correct here.
If they are rated 10A so they can Tolerate 10A in any voltage, you need to look at you're freezer wattage, that will tell you the amperage and if the relay can handle it.
For example if the freezer is about 2000W that means in 240V it will be about 8A and in 110V it will be about 20A.
not sure the relay can handle more than 10A.
I recommend to ask some Electricity Engineer or just replace it, the 40A SSR cost 5$ including shipping.

 

[BrewCityBaller]

Hi
Not sure you are correct here.
If they are rated 10A so they can Tolerate 10A in any voltage, you need to look at you're freezer wattage, that will tell you the amperage and if the relay can handle it.
For example if the freezer is about 2000W that means in 240V it will be about 8A and in 110V it will be about 20A.
not sure the relay can handle more than 10A.
I recommend to ask some Electricity Engineer or just replace it, the 40A SSR cost 5$ including shipping.

Electrical Engineer here! I missed this part in your earlier post. I believe he is correct. That would be 10A at either AC voltage. The current rating is probably different if it were a DC source, but your don't have to worry about that. I do know that for AC though, the P=IV for power is only an approximation. Please don't ask me for the AC version... I don't remember.

I guess I should have asked, where did you get the current ratings for the freezer? If you found 12A starting and it's a 120VAC freezer, you are fine.

 

[reynolds5520]

The internal relays are rated 10A @ 250V which means at 120V, they should be rated closer to 20A... They are stamped 15A, so plenty for a 12A startup spike.

I'm not disputing your conclusion that an STC-1000 can handle the startup current requirements of your compressor, I think it can because the time is short. (A 10 amp time delay fuse in the circuit would be a good precaution though.) But for the benefit of those that read this later, what you've said about 250 V versus 120 V isn't correct.

The controller claims a rating of 10 amps at up to 250 volts. That would still mean a rating of 10 amps at 120 volts. The amp rating quantifies how much current can safely flow through a circuit. (The relay itself may be rated for 15 amps but the size of the traces on the circuit board and the rating of the screw connector and the ability of the components to dissipate heat in this enclosure are all part of the overall rating of the controller.)

Edit: I see others were typing while I was...

 

[Misplaced_Canuck]

The problem you may have from high start current, IF it manifests itself, is that the relay switch will become "stuck" - I doubt it would ever get hot enough to burn up. Unless, of course, you are continuously drawing above the posted Amps.

I'm using an STC-1000 with a Beverage Air under-counter fridge, which runs at 8.2 Amps without any issues. I'm sure the startup amps is quite a bit higher.

MC

 

[raouliii]

Offering up a couple of data points on the current rating issue. Both sources indicate a 15A rating @125VAC & 10A rating @277VAC

Inside my STC1000:

Datasheet on the above relay:
Hongfa HF3FF Datasheet

Of course, we can only assume that the circuit board traces are capable of handling the current. I did not inspect them when I had it open.