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Old 04-03-2013, 04:17 PM   #1
crajax
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Default Q: Window AC Compressor cycling

Hi everyone, long time lurker here, who has gotten some good ideas from this forum.

I have a 15G conical, so its too big for a converted freezer. So, I built a fermentation chamber out of scrap particle board shelving and styrofoam packaging. heat source is a 25W coffee can lamp, and the cooling source is a small 5000BTU window AC unit that I picked up cheap. it's all tied together with the STC1000 controller, and my contraption is ugly as sin, but it is working very well holding my temp at 64.

my ferm chamber is sat in the basement right next to the water heater and furnace - which can be good or bad, depending...

I do have a question/ concern though that maybe someone can answer - the AC cycles a lot, no doubt its oversized for a small cabinet. its approx 45 seconds on, and 12 minutes off. so it runs maybe 5 minutes per hour.

But, I'm worried the short "on" cycle will cause significant harm to the compressor ?

What do you think ?

I tried googling but wasnt able to find anything. maybe this would be better in a HVAC forum, but I figure there are probably other homebrewers who have done something similar.

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Old 04-03-2013, 04:27 PM   #2
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Change the Compressor Delay and/or the Temp Set variances. Let your temp wander up/down half a degree F and see if that helps. I can't remember exactly what value they are in that controller but if you need them I can look it up when I get home.

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Old 04-03-2013, 05:39 PM   #3
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Normally the main concern for quickly cycling an AC is that the compressor motor can be over-strained if it turns on while the compressor is still holding a high pressure. Given a few minutes of the compressor being off and the pressure will normalize.

I can't think of any mechanical reason anything would be strained by it turning off quickly.

I have a similar set up with an AC and have wondered if it maybe doesn't reach peak efficiency when only running for a minute or two.

I do have my STC set to fluctuate 6-degrees Celsius and notice very little fluctuations in my beer.

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Old 04-03-2013, 08:26 PM   #4
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Thanks for the replies.
I checked the temp variance - it was set for .5 celsius, which I think was the default. and the compressor delay is set for 5 minutes. It's cycle - whilst in the active part of fermentation - was (approx) 45 seconds on/12 minutes off. This is my first "A/C temp controlled" brew - previously my method was frozen 2L bottles and a small fan, which worked OK, but required vigilence.

anyways, I've just bumped up the temp variance to .6 celsius, maybe that will help. I'm not too worried about efficiency (as in running costs), as its just 5 minutes an hour that its running, so shouldn't cost much in terms of electricity. but I was worried about stress on the compressor with such a short "on cycle"

"Normally the main concern for quickly cycling an AC is that the compressor motor can be over-strained if it turns on while the compressor is still holding a high pressure"

I didnt know this was the reason - I just knew cycling compressor = bad. But if this is the case, I think I should be OK with my 12 minutes off time.

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Old 04-10-2013, 02:31 PM   #5
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OK, so I thought I'd report back.
I increased the temp variance to .6C - that helped somewhat, I also did a better job of insulating the probe that's attached to my fermenter, previously I had a small single layer piece of bubble wrap (roughly) taped over it.

I've now made a small insulating block from styrofoam which is strapped to my fermenter with a rubber band, I now get a cycle of about 3 - 4 minutes on / 40 minutes off on my AC unit. (although the furnace that my fermention chamber is sat next to hasn't run as much lately due to milder weather) but still, this is an improvement, and I'm happy with it now - I didnt think the isulation around the probe would make such a difference, but it seems it does.

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Old 04-11-2013, 03:17 AM   #6
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Sounds like it's running nice!
How about a photo of your, "ugly beast"?

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Old 04-12-2013, 01:33 AM   #7
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just checked my camera, batteries are dead, charging them now.
I'll post some pics this weekend, when I have some time. I've been inspired by many projects I've read on this site and similar sites.

I've built a conical, conical stand, ferm chamber, and kegerator.

Can't imagine my projects will inspire much, but who knows - some of it does have the advantage of being very cheap, being built partly out of scrap.

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Old 04-13-2013, 05:21 PM   #8
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Pictures of my franken-contraptions:
My fermentation chamber is ugly junk, but it works, and the price was right. all built from scrap wood and styrofoam that I already had - cost: $0;
My ferm chamber stand - again, built from scrap - same goes for my fermenter stand; only cost was the AC unit ($40) and the stc1000 (about $20 IIRC) for heat, the old light fixture and coffee can are surplus that I already had around.

My kegerator looks a little nicer - nicer than this picture in fact. not that it needs to look nice in the utility room of my basement, but it does.

I got the wine fridge (barely) used, bought a beer tower, trimmed the shelving rack to accomodate my kegs, replaced the stock thermostat with a temp controller (similar to stc1000, but a 1 stage unit) ...and its been serving cold beer ever since

dcfn0001a.jpg   dcfn0002a.jpg   dcfn0003a.jpg  
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Old 04-14-2013, 11:40 PM   #9
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Great value, love it!

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