Ranco dual stage controller

[jstringer1983]

Hey everyone
Just wanting some feedback from those of you who is the ranco dual stage. I recently started using my ferm chamber, its a pretty standard setup-40 watt bulb in a paint can, mini fridge, im sure youve seen it done before lol. Anyways, until recently i only needed the heat to keep her at 65f. With temps climbing ive needed the fridge. I was always told to make your setpoint (65 in my case) and create a differential of say, 2 or 3 to keep the compressor from short cycling. This means youll get cooling above 65, down to however many degrees your diff is set. What im experiencing is it also goes that many points above my setpoint. So in my case, i have a differential of 3 and it keeps the fridge from kicking on until it hits 69f. Is this normal?

 

[jstringer1983]

Anyone?

 

[iijakii]

Yes, unfortunately that's how it works. Is there a compressor delay option? I'm not too familiar with the Rancos. You might be able to set it for a lower differential but set a 5 or 10min delay instead.

 

[brewfarmDan]

edit

 

[jstringer1983]

Not that im aware of, the instructions dont give you a whole lot of info, but ive seen it explained on here and other forums as the differential only affecting the below setpoint temp. That hasnt been the case for me and i kind of figured that was just how it works. I dont like the idea of my beers getting up to 69 then cooling back down to 62 so i made a differential of 1 this morning, compressor be damned lol guess ill se what its limits are this summer

 

[day_trippr]

The OP's description of Set Point and Differential would apply to a Johnson A419 set to cut-in mode (iirc), but it does not apply to the Ranco single or dual stage.

- Set point + differential is where the compressor turns on
- Set point is where the compressor shuts off

If you used a four degree differential with the Set Point two degrees below your ideal beer temperature, the beer should stay within 2 degrees of that while providing plenty of "off time". Doesn't seem unreasonable.

Unlike the A419 and most of the "STC style" controllers, there is no provision for anti-short-cycling on either Ranco model, so you do have to depend on the differential and not push it too small. Significant thermal mass coupled to the temperature probe helps...

Cheers!

 

[jstringer1983]

If i set the differential to 4 and my setpoint to 63 (2 degrees below my ideal temp) wont it hit 67 before it turns the fridge on and cool down to 59?

 

[day_trippr]

No. It doesn't work that way, read what I wrote:

o Set point + differential is the turn-on point for the compressor
o Set point is the turn-off point for the compressor

Differential is only added to Set point - not subtracted. With Differential set to 4, there is a net 4 degree difference between the turn-on and turn-off points above...

Cheers!

 

[jstringer1983]

Got it lol. Setpoint is at 63 with a diff of 3 so it wont get over 66 and will keep my beer close to my ideal temp. Thanks