Question Using JLD612 With Freezer for Cooling

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DaveFla
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Question Using JLD612 With Freezer for Cooling

Post by DaveFla »

I bought a JLD612 to control a freezer for cooling.

The maximum control period (ot) is 199 sec or ~3 min according to the manual.

I assume this is the same as Cycle Time.

If so, is there a way to increase the max control period?

It is a very bad idea to short cycle a compressor.

It will considerably shorten the life of the compressor.
Last edited by DaveFla on Wed Jan 05, 2011 12:32 pm, edited 2 times in total.
richiem
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Re: Question Using JDL612 With Freezer for Cooling

Post by richiem »

Interesting question -- one with several possible answers; the cycle time defines the minimum wait for a cycle if temps have moved out of the control range -- if your cooling system is sized so that it runs for say 1/2 the time on average, then the actual cycle time will be much longer, and if your cabinet/enclosure/freezer is adequately insulated, then it will be quite a while before the system turns back on, so short-cycling may not be a problem.

But adjusting the P parameter value to a smaller number, which allows more temperature variation around the set point, may help -- try 1 or 2 to start -- but it's possible that the system will fail to control, depending on system variables that we can't really predict. If you actually experience short-cycling, then try increasing the value of the I parameter to increase the integration time, and play with the differential D value.

I'm just shooting from the hip here, but my experience of refrigeration is that optimum BTU capacity is when the unit has to run quite a while to achieve or hold the set temperature, so most systems won't short-cycle even with a short Ot.

That said, there are electronic ways to lengthen the cycle time involving the use of a CMOS 555 timer chip or two and relays, but are not for general use by folks who aren't experienced at building electronic gear....
Tech_Marco
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Re: Question Using JDL612 With Freezer for Cooling

Post by Tech_Marco »

There is a new output from the JLD612. Its seems that it's an ideal for your application. The control is relying on the "HY", the differenttial ouf temperature to turn on/off relay for controlling. HY = AH1- AL1. Per manufacturer, assuming control temp is 50'C and if you want the controller to take action at 48'C, then set the HY = 2. So, the controlling temperature is closed to 50'C.

There is important issue: SSR is disable and only Relay 2 is doing controlling. Relay 1 serves as an alarm.

I'll made up a new document and post it asap. In the mean time, set Outy = 4 will enable this mode

Marco
DaveFla
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Re: Question Using JDL612 With Freezer for Cooling

Post by DaveFla »

Thanks for the suggestions.

If Outy=4 does it turn the JLD612 into a simple on/off controller with hysteresis. In other words, is it no longer a PID?

If so, this will not work for my needs.

I have several on/off controllers and the overshoot is excessive.

My understanding of PIDs is that the freezer will be turned on for P / 100 * ot then off for ot * ( 1- P / 100) when the actual temperature is what I set it to.

The freezer will be off when the actual temperature is below what I set it to.

The freezer will be on when the actual temperature is above what I set it to.

I ran auto-tuning and the controller set the parameters to:

P = 1
I = 3
d = 0
Souf = 0.2
ot = 199
FILT = 0

I have not run it connected to the freezer other than to auto-tune to test if it is short cycling due to not having time to actually time it.
DaveFla
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Re: Question Using JLD612 With Freezer for Cooling

Post by DaveFla »

I connected the shield to the blue leads of the Pt100 sensor and changed the sensor type to P10.0 and reran the autoalignment.

The controller set the parameters to:

P = 0.7
I = 1999
d = 399
Souf = 0.2
ot = 199
FILT = 0

I lowered the set temp 0.1F and watched the results. The compressor cycled on approximately every 199 sec. I found if I cycled the compressor more frequently, power would be turned on to the freezer but the compressor would not turn on. So, there is some anti-short cycle protection in my freezer. Unless you know you have anti-short cycle in your compressor, I would not recommend the JLD612 for these applications. Also, the JLD612 needs much longer PID parameters for cooling applications. Perhaps the developers could create another outY method where I, d, and ot could be much longer.
equinox
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Re: Question Using JDL612 With Freezer for Cooling

Post by equinox »

Tech_Marco wrote:There is a new output from the JLD612. Its seems that it's an ideal for your application. The control is relying on the "HY", the differenttial ouf temperature to turn on/off relay for controlling. HY = AH1- AL1. Per manufacturer, assuming control temp is 50'C and if you want the controller to take action at 48'C, then set the HY = 2. So, the controlling temperature is closed to 50'C.

There is important issue: SSR is disable and only Relay 2 is doing controlling. Relay 1 serves as an alarm.

I'll made up a new document and post it asap. In the mean time, set Outy = 4 will enable this mode

Marco
Actually, Outy=3 is differential (on/off) mode as well, but keeps SSR on. I use this Outy=3 JLD612 mode to drive my beer fermenter via SSR and HY set to 2. To make whole system more stable I keep K Thermocouple hermetically wrapped using finger from latex glove inside 1" tube filled with gel from Ice pack. Actually, massive things inside fridge have almost constant temperature (+/-1F) with this setup. Fridge has pretty good cycle this way - 2-3 per hour.
equinox
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Re: Question Using JLD612 With Freezer for Cooling

Post by equinox »

DaveFla wrote:I connected the shield to the blue leads of the Pt100 sensor and changed the sensor type to P10.0 and reran the autoalignment.

The controller set the parameters to:

P = 0.7
I = 1999
d = 399
Souf = 0.2
ot = 199
FILT = 0

I lowered the set temp 0.1F and watched the results. The compressor cycled on approximately every 199 sec. I found if I cycled the compressor more frequently, power would be turned on to the freezer but the compressor would not turn on. So, there is some anti-short cycle protection in my freezer. Unless you know you have anti-short cycle in your compressor, I would not recommend the JLD612 for these applications. Also, the JLD612 needs much longer PID parameters for cooling applications. Perhaps the developers could create another outY method where I, d, and ot could be much longer.
Actually, PID controllers are not compressor friendly. You have to use differential mode for compressor cooling. JLD612 does it pretty good in output mode 3 (I use it with fridge-based beer fermenter). The real PID mode works pretty good with TEC (Peltier) coolers. I have one small fermenter box driven with PID controller and Peltier module (with fans on both sides). After auto-tuning the whole system becomes very stable.
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