Ranco Temperature Overshoot?

[Khirsah17]

Hey guys,

About two months ago I bought a Ranco temperature controller because of the good reviews I got from people on this site. I wired it up and off it went, keeping my freezer in whatever temperature range I set it for. However, lately I've been noticing that the indicated temperature often reads between 4-5 degrees lower than my minimum temperature. Right now I have it set to be between 65-69, but this morning I found it to be reading 59!

Do you guys think this is a new problem due to a defective unit? Or has it always been this way and I've only noticed it because I use it more. Has anyone encountered this and how should I correct for it?

 

[olllllo]

Do you have the probe in a container of liquid or is it dangling?

The air temp inside a fridge will vary by a few degrees- colder at the bottom and warmer at the top when the compresser is not blowing.

Some people find that putting the probe in a thermowell in the carboy or in some liquid will help get a better (less variable) reading.

Ultimately the air temp doesn't matter and what you want to target is the wort temp.

That said, I dangle. Not worth the effort IMO.

 

[FlyGuy]

Test the temperature probe by putting it in ice water. It should read pretty close to zero. If it is really 4-5 degrees off, it is going to be falsely reading a negative temperature, and you will know there is something wrong with the unit.

If it is reading fine, then look at where the probe is placed in the freezer. Maybe it is getting warmed somehow?

 

[Khirsah17]

Good suggestions. For the most part, the probe was dangling near the top of the freezer. So I thought I'd try to lower it near the bottom and check it, and still the same problem. I'll give it the ice water bath a shot and see what happens.

Is the probe fully submersible?

The only other thought I had (which I thought was a sure winner) was maybe the power setting of the freezer was really high and overcooling, so I turned it down to just above minimum. That way the chilling rate would be much slower, thus solving the problem. However, life isnt that simple and still the same readings.

 

[olllllo]

The freezer sttings should be set to max. You want that thermo controller essentially out of the equation.

 

[FlyGuy]

I suspect you have a temperature gradient from top to bottom, as Ollllo suggests. The top could really be a few degrees above the bottom.

And yes, the probes are submersible, providing that there are no cracks in the sheath. Especially check where the dark sheath around the probe meets the lighter gray sheath around the cable. If it is all sealed, it is fine to submerse.

 

[Khirsah17]

Yea, I believe that there is a gradient, although I expect it to be pretty small. I tested the probe both at the bottom and top, and for the most part the same results. Maybe 1-2 degrees of variance, which is what I would expect.

Im not really sure how turning the freezer to max would make any difference.. much less help?

 

[Drunkensatyr]

You set it to max so that the thermocon in the fridge never turns off, that way the ranco is actually controlling the temp.....won't help your specific problem, but it is how it should be done. The thermocon makes NO diffrence on the amount of cooling produced, just when it turns off.

 

[olllllo]

That way the chilling rate would be much slower, thus solving the problem. However, life isnt that simple and still the same readings.

Both thermo controllers are either on or off. The min/max sets the temperature where it turns on or off. Turn the Fridge control to Max.

You only want one brain working this.

Again: Don't focus on the air temp. It's your wort temp that you care about and it will vary way less that the air temp.

 

[evanmars]

Test the temperature probe by putting it in ice water. It should read pretty close to zero...

Hmm, mine reads right around 32. :cross:

 

[olllllo]

Those Canadians are always trying to impose their culture on us.

 

[Drunk Monkey]

There is a setting on mine where you can adjust the range. I have mine set at one degree so that it turns on/off within one degree of the target temperature. Maybe yours is set to a higher number.

 

[Gedvondur]

There is a setting on mine where you can adjust the range. I have mine set at one degree so that it turns on/off within one degree of the target temperature. Maybe yours is set to a higher number.

Drunk Monkey has it right here. Most temperature controllers have a "range" above and below the target temperature. Otherwise it will cycle your fridge in a mechanically and energy-unfriendly way.

That is probably what you are seeing. I am not sure it is adjustable on your particular controller.



Gedvondur

 

[malkore]

I think the one poster meant putting the probe in water should show zero degrees....of difference in temperature, rather than the 5 degrees the OP sees now.

and yes, those controllers have a range to prevent the compressor from running too often. My johnson controls temp controller has a +/- 4 degree range.

 

[Sea]

The "range" that has been referred to is called a setpoint differential. It is in place so that you can prevent the compressor of whatever piece of equipment you are controllong from running for too short of a period, or short cycling. Short cylcling is bad for compressor life span, and should be avoided when possible. That being said, if you want the maximim control over your ferm. temp., the differential should be set as low as possible. Refrigerator/freezer compressors aren't as suceptible to short cycling as larger HVAC ones are anyways.

Depending on your controller, the differential should iether be adjusted digitaly, or sometimes there is a mechanical adjustment under the lid. Read the instructions that came with it, they should tell you.

Gotta love monday!

 

[Monster Mash]

DO NOT put the probe directly in water. They are water resistant, not water proof. To me it is not worth the risk of ruining the probe so it is best to use a thermowell.

I have heard of a few people ruining thier probes like this so don't take the chance.

 

[david_42]

I agree that is is probably the setpoint differential. I believe in the cooling setting, the set temperature is where the control turns on and the differential determines how much lower it goes before shutting off. I use mine for heating, so I'm not certain. Your's is probably around 5F.

Whether or not the temperature is accurate is a completely separate question. There is only one probe and one temperature resolution circuit, so it is unlikely that the error is between what is being displayed and what is set.

The final consideration is buried in the way freezers work. Just because you shut the compress off, doesn't mean it stops cooling. There is some refrigerant in the lines that will evaporate and continue cooling the system. In a good freezer, this can be several degrees. Most refrigerators today use a fan to circulate the air over cooling coils, so they stop cooling when the power goes off and you don't get the over/under shoot.

 

[FlyGuy]

I think you guys have it backwards. For the Ranco controllers in cooling mode, you establish the setpoint first, which is the minimum temperature that you want to cool to. Then, you set your differential -- this is the amount you are willing to go above the setpoint before the fridge/freezer cuts in. For example, if your setpoint is 65F and your differential is 4 degrees, then the range of temp on the fridge should be 65-69F. As the OP says, his problem is that the freezer is dropping below the setpoint, so the differential cannot be the problem.

(reference: http://www.rancoetc.com/pdf/ranco_etc_instructions.pdf)

David_42: You have described the system correctly right for heating with a Ranco -- the setpoint and differential are reversed in this case. I also think you are correct about the freezer 'run-on' being the cause of the overshoot. But that should be easy to compensate for.

My suggestion to the OP is get a reliable thermometer (preferably a digital one with a probe) and put it right beside your Ranco probe to make sure it is accurate. Then begin ruling out the temperature gradient and freezer run-on problems one at a time until you find the source of your discrepancy. Please let us know once you have it figured out -- I am sure it will save someone else some frustration down the road!

 

[Khirsah17]

Alright, I'm back with more information. Thanks for all the replies, there was a lot to digest there.

So after reading everyone's ideas, I decided to put the temperature probe in a cup full of water at the bottom of the fridge. I had the setpoint set at 65 with a 4 degree differential, so the temperature range of the fridge was 65-69F. The Ranco controller still overshooted the setpoint temperature a bit. The freezer turned off at 65F, but the probe would still measure down to 63F, before going back up again. I decided that I could live with it, so I focused my attention to brewing again.

Then the other day, I decided to brew a lager using white labs san francisco yeast, which has an ideal range between 58-65 degrees. So I set my setpoint at 61 with a 3 degree differential, hoping for a range of 61-64F. Again, the ranco temperature probe was in a cup of water. I let the freezer do its thing for the day, and i hung around to see the whole temperature cycle, and the Ranco turned the freezer on at 64, and off at 61. However, watching the measured temperature, it eventually hit 49F! WTF? A second thermometer confirmed this temperature. Now I was really fed up.

I put the Ranco to the test. I have two different model True Temp thermometers. I put a pot of water on the stove and slowly brought the temperature up to boiling. All three thermometers were as submersed as possible. The two True Temp thermometers were usually within 1-2 degrees reading with each other, while the Ranco was about 10 degrees under. So when the True Temps read 150, the Ranco read 140. When the water got to a rapid boil, one true temp was reading 211, the other fluctuated between 208 and 210, and the Ranco, when it finally got there, held steady at 208. What I really learned from this test is that it seems that the Ranco is very slow to register temperature change. Anyone ever run a similar test? Can you verify the results?

I want to say that the Ranco temp probe is somewhat messed up. I plan on calling Ranco on Monday and talking to them about it. I hope they have helpful customer support. Oh, and i found out that their company is like 20 mins from my house. Maybe I can take it there and get it tested by the experts.. *crossing fingers*

So, just wanted to share some of my findings so far. Maybe you guys have some comments.

 

[Khirsah17]

Well, it seems like I'm going to be resurrecting a dead post. As far as the discussion above goes, I called Ranco and they gave me a sheet of voltages that the probe should correspond to based on the temperature it was sensing. They told me to measure the probe voltage and see how it compares with the manufacturer sheet. Well, I got lazy and never got around to doing it. I had put the probe in some water, and it seems to work ok as long as I don't change the temperature.

Fast forward a while to now, when I got a second Ranco for the kegerator I'm building. Excitedly wired it up yesterday, put the probe in a cup of water, and turned everything on. My setpoint was 43F with a 3F differential. Within about two hours, the cup with the probe had turned to ice, and the Ranco was reading 31F. AAAAARG! Thank god I was half expecting this and didnt put any beer in there. So I took the cup out, dethawed it and extracted the probe. Now I put it in the fridge and just let it dangle near the bottom of the freezer overnight. This morning the Ranco was reading -20F!

What is going on here? Im getting ready to throw these Ranco units out the window. I need to check on the freezer some more and see if I can determine some pattern, but right now it seems like the freezer is always on, no matter what the Ranco says. It's got a little light on the front that's on when the freezer is working, and it just never turns off. I have observed that the Ranco clicks when the sensed temperature is 43F, and I think it says S1 on the screen. As soon as the temp drops below 43, the S1 disappears. Not sure if that's normal or not.

I'm getting ready to give up in frustration about this. Who would have thought this would be so difficult?

 

[Beerthoven]

Well, it seems like I'm going to be resurrecting a dead post. As far as the discussion above goes, I called Ranco and they gave me a sheet of voltages that the probe should correspond to based on the temperature it was sensing. They told me to measure the probe voltage and see how it compares with the manufacturer sheet. Well, I got lazy and never got around to doing it. I had put the probe in some water, and it seems to work ok as long as I don't change the temperature.

Fast forward a while to now, when I got a second Ranco for the kegerator I'm building. Excitedly wired it up yesterday, put the probe in a cup of water, and turned everything on. My setpoint was 43F with a 3F differential. Within about two hours, the cup with the probe had turned to ice, and the Ranco was reading 31F. AAAAARG! Thank god I was half expecting this and didnt put any beer in there. So I took the cup out, dethawed it and extracted the probe. Now I put it in the fridge and just let it dangle near the bottom of the freezer overnight. This morning the Ranco was reading -20F!

What is going on here? Im getting ready to throw these Ranco units out the window. I need to check on the freezer some more and see if I can determine some pattern, but right now it seems like the freezer is always on, no matter what the Ranco says. It's got a little light on the front that's on when the freezer is working, and it just never turns off. I have observed that the Ranco clicks when the sensed temperature is 43F, and I think it says S1 on the screen. As soon as the temp drops below 43, the S1 disappears. Not sure if that's normal or not.

I'm getting ready to give up in frustration about this. Who would have thought this would be so difficult?

I have seen some overshoot of temps with my RANCO controlled freezer as well, but not as much as you report.

Right now my setpoint is 67 with a 2 degree differential, so I'm looking to maintain a pretty tight range of 67-69. The controller does what it is supposed to do: It turns the freezer on when the temp reads 69 and turns it off when the temp reads 67. I put a kitchen thermometer in there and it reads the same temp as the RANCO, so I think the RANCO is accurate.

The temp has dropped to as low as 64 after the controller turned off the freezer. But I think that is caused by the coolant in the coils that continues to cool down the freezer box after the compressor turns off. I've noticed that the more stuff I have in there, the less variable the temperature is.

Not sure this helps you much, but I thought I would share anyway.

 

[Bobby_M]

Maybe I can offer another perspective. If you have the probe in a small glass of water sitting on top of freezer shelves that have the cooling coils integrated or on the bottom of a chest freezer where the coils are right on the other side of the metal, you can imagine why those surfaces cool to near freezing before the water is affected. Once the temp of that water gets to your setpoint, the shelf/shell of the freezer will continue to cool it. This is an issue of thermal mass and you have a few options.

First, if you put the probe in a thermowell into your fermenter, you want to set your setpoint about 1F higher than you really want and set your differential to 1 degree. 5 gallons has a lot of thermal mass so the temp changes will be really gradual. Once it hits the set point, the additional cooling capacity of the freezer surfaces will probably only have enough to lower the full 5 gallons by a degree or two max (hence my recommendation to raise your setpoint to compensate).

The other option is to let the probe dangle in air but you'll want to set the differential to like 4-5F. The temp swings in air are large and fast and mostly unrepresentative of the temperature of the beer/wort.

 

[Khirsah17]

I think the problem with the first controller was just wide fluctuations of air temp in the freezer. That problem mostly went away when I submersed the probe into a pitcher of water. Enough so where I can use it to have stable fermentation temps.

However, with the second regulator I have, it just doesn't seem to ever turn the freezer off. I have never actually used a chest freezer for it's intended purpose, but the fact that I'm getting temps around -20F seems to indicate to me that the chest freezer is just running as designed, and the control unit isnt doing much more than displaying the inside temperature. I can understand and even expect some overshoot, but -20F? Could it be possible that the ETC is wired wrong, or that a wire inside isn't making a connection that tells the compressor to shut off?

 

[Bobby_M]

It very well could be wired wrong. Those nifty cordsets have a "hot in", "hot out", "neutral" and "ground". The hot in should go to one terminal and hot out to the other. Maybe the relay is stuck closed.

 

[Khirsah17]

Well, I had some time this morning to open the Ranco up and take a picture of the wiring. I sure don't see anything obvious that could be wrong. Maybe someone with more electrical expertise could advise.

 

[Yeast Infection]

Well, I had some time this morning to open the Ranco up and take a picture of the wiring. I sure don't see anything obvious that could be wrong. Maybe someone with more electrical expertise could advise.

Im not at home right now, so I cant say for 100%, but I just wired mine, works perfectly, and Im 95% sure it is NOT wired like that. I will look at it tonight when i get home.
I think the short black wire(going from the lower thing to the higher thing) should be coming out of the port to the right of what it is currently coming out of on the lower thing.
yup, im right, check the instructions out:
http://www.rancoetc.com/pdf/ranco_etc_instructions.pdf
goto figure 4

 

[Khirsah17]

Well, I feel pretty dumb.

Oh well, keeps me humble.. and hopefully now I'll have a working Ranco!

Thanks!

 

[Fingers]

It's wired wrong. Look at the black and white wires. They are connected together permanently. I'm at work right now, but I can get my Ranco schematic and talk you through it tonight if nobody else does it in the interim.

edit: Okay someone DID beat me to it. Hope it works for you now.