Short Cyce Compressor problem?

[BigNastyBrew]

Ok, so I ordered a couple digital JC controllers and NOW someone says to me "hey, you're gonna burn up your compressor if it short cycles like that on a 1° variance."

WTF!

What truth is behind this?

[cmanley542]

Well, if you set your controller to kick on the compressor every time it rises one degree above your target temp, that's a hell of a lot of off-on, off-on for your compressor and so a much shorter life.

Set the controller with a 4-6 degree swing (ie-cool to 2 degrees below target and don't turn on until 2 degrees above target) and you'll save the compressor some work.

[Mylo]

'Tis true. You will definitely shorten the lifespan of your compressor. Even if you insulate the probe from the ambient - the compressor will kick on A LOT to keep it within on degree of your setpoint. I recommend at least a 2 degree setpoint - but even that is a lot in the AZ summertime.

The mother uses fans to cool the upper, fermentation chamber - so I keep that within 1 degree - but my serving temp down below is on a 2 degree diff.


Mylo

[BigNastyBrew]

DAMMIT!!!

I'm fermenting in chest freezers. Should I just stick with the analog controllers then with the 3° diff? Or set the digital to 3°?

[BeerPal]

DAMMIT!!!

I'm fermenting in chest freezers. Should I just stick with the analog controllers then with the 3° diff? Or set the digital to 3°?

For this very reason I run my chest freezer with an anaolg controller. No advantage to using digital in this application, IMHO. I use those for my carboy heaters and the mini fridge my conical lives in. But even that I set at 3°.

[Mylo]

DAMMIT!!!

I'm fermenting in chest freezers. Should I just stick with the analog controllers then with the 3° diff? Or set the digital to 3°?

You can use a 2 degree diff. 3 is kinda pushing it for the yeast. To help out your freezer, you can 1) keep it full (ie., maybe store some extra beer in there for conditioning - or maybe just a few jugs of water), and 2) keep a small fan blowing on it - especially in the summer - that's how it sheds the heat. The hot side coils are right up against the metal skin.


Mylo

[andy77]

Ambient air temp swings back and forth very quickly, but If you're using a thermowell or insulating the probe on the side of the fermenter I don't think that it would cycle all that much. Then you're measuring the fermenting beer temp and not the ambient temp. I think that it takes a lot of time for 5 gallons of liquid to change temperature, even 1 degree. I keep my fermenting chamber w/thermowell on a 1 degree dif, I haven't noticed a really short cycle, but I haven't really sat there and observed for an hour either so I can't be sure. I do know that when it does go 1 degree hot, the fridge stays on for a long time to bring it back down, hinting at a pattern of frewer long cycles rather than many short ones.

My fridge is pushing 2 years as a full time fermentation chamber, so I'll let you know if it burns out any time soon.

[BadRock]

This is true. Are you using a JC A419? If so then open up your differential and set the adjustable anti-short cycle delay to 12 min.

The problem with rapid start/short cycles is that when a motor starts it draws up to 13 times (per NFPA 70) or more the rated full load amps for around 500-2000 milliseconds.

1/4HP = 3.1FLA = up to 40.3 amps
1/3HP = 4.1 FLA = up to 53.3 amps
1/2HP = 5.4FLA = up to 70.2 amps

Thus a 1/2HP can draw 70.2 amps inrush current which translates to 8424 watts or 28,742 BTU's.

The bottom line is that you create a shit load of heat with rapid starts. This can quickly breakdown motor windings causing the windings to short and the motor to stop working. Compressor motor are not designed to cool them selfs very efficiently either so you best protection is leaving the motor off for a prolonged period of time. Puling 70 amps momentarily 10+ times an hour will also kill your energy bill.