New controler for my freezer to fridge conversion

[MaryB]

I use a chest freezer for a fridge and had been using a mechanical thermostat to control it. The temp swings were really wide and no way to make them smaller. I wanted to add a transfer switch to make it easier to drop back on grid power too. So I picked up a small 30 amp transfer switch, a PID temperature controller, an outlet and box, and a solid state relay and heatsink. Little construction and wiring later and I have a controller that holds my fridge within 2 degrees of set temps. It also includes a compressor delay so it will not short cycle and damage the motor/compressor.

Testing it with a lamp for a load, PID is Celsius only but for $17 I am not going to complain. I could have used the relay in the PI for switching but contact arcing as it cycles twice an hour would shorten the life. Solid state relay and heatsink were only $15 so I went that route and use the PID to switch it on and off. Same setup minus the transfer switch cold be used for temp control of your lead pot!

http://i226.photobucket.com/albums/dd248/maryalanab/IMG_20150318_2317263691_zpstlho88sa.jpg

http://i226.photobucket.com/albums/dd248/maryalanab/IMG_20150318_2317323431_zpsfcx2rngx.jpg

[bhn22]

Now that's thinking!

[DougGuy]

MaryB I have an RV fridge sitting in my shop that I need to do something with. I have tried various thermistors, and none of them work. I don't know if the control board in the fridge is gone wacko, but even thermistors that are within the range given by the mfgr don't work. The unit doesn't cycle until it freezes everything, then it cycles. There is a knob on the front, that serves as both an off/on switch, and a thermal adjustment range. Behind this knob is a pot that has a switch made into it, and then the back half of the pot is the typical control rheostat/carbon path type potentiometer. I could unsolder one leg of the switch, and use the two contact points for a relay to close the circuit, which would make the compressor run, and then when the relay opens this circuit, it will quit running. This would work if the vehicle is traveling and running off 12v, or parked and hooked up to an external 110v RV plug like a campground would have.

What do I need to do to be able to get a PID to make this unit cycle within say 34° - 40°? I can figure out the logic behind the controller, and I have some thermistors that I can mount inside the box that changes resistance as temps change. Would I be able to use this to control it with? Tell me what I need to do because I haven't ever worked with these controllers before.

[2wheelDuke]

That's good work. I built a PID for my lead pot and I'm quite happy with it. I've thought about doing another one for the toaster oven that I bake boolits in. I've wondered how they'd work on a fridge or freezer.

I'd love to have the money and space to have one on a fridge for lagering beer.

[lightman]

Some of the guys on one of the beer sites I'm on use a temperature controller from Johnson Controls for their beer fridges. It might be cheaper than a pid.

[Artful]

http://www.johnsoncontrols.com/content/us/en/products/building_efficiency/products-and-systems/commercial-refrigeration/commercial_refrigeration/temperature/electronic2/a419singlestage.html


Description
The A419 series controls are single-stage, electronic temperature controls with a Single Pole, Double Throw output relay. They feature a lockable front-panel touchpad for setup and adjustment, and a Liquid Crystal Display for viewing the temperature and status of other functions. A Light-Emitting Diode indicates the controls’ output relay (On/Off) status. The A419 controls are available in 24 VAC or 120/240 VAC models. The A419 controls have heating and cooling modes, adjustable setpoint and differential, an adjustable anti-short cycle delay, and a temperature offset (setback) function. The setpoint range is -30 to 212°F (-34 to 100°C). The controls feature remote sensing capability and interchangeable sensors. The A419 controls are available in either NEMA 1, high-impact plastic enclosure suitable for surface or DIN rail mounting or NEMA 4X Watertight surface-mount enclosures.
Features


Easy-to-read LCD displays the sensed temperature and control-function status clearly and custom icons on the display indicate the control and system status at a glance.
The 30° (F° or C°) temperature differential adjustment range allows precise (1F° or C°) temperature differential settings that are much tighter than electromechanical controls.
The Adjustable Anti-Short Cycle Delay (0 to 12 Minutes in 1-Minute Increments) ensures that the output relay remains off for a user-set time delay, and helps avoid hard starts, nuisance overload outages, and unnecessary equipment wear.
The Temperature Offset Function shifts the cut-in and cut-in setpoints by an adjustable offset when a user-installed, external switch closes the A419 control’s binary input circuit.
The high-impact thermoplastic type NEMA 1 allows surface or snap-fit DIN rail mount; the Noryl® high-impact thermoplastic type NEMA 4X enclosures allow watertight surface mount.
Lockable front-panel touchpad allows easy set up and adjustment of the A419 control setpoint, differential, and other functions; a concealed jumper locks the touchpad, and deters unauthorized adjustment of the control settings.
Low and line-voltage models provides options for almost any refrigeration or HVAC control-voltage application.


Applications
The A419 can be used to control a wide variety of single-stage refrigeration or HVAC equipment. Typical applications include:

Freezer control in convenience stores
Reach-in coolers
Supermarket display cases for produce or meats
Restaurant or convenience store walk-in coolers
Boiler control
Compressor lockout (disables the copressor when temperature exceeds limits)
Condenser fan cycling
Pump control for cooling towers

[MaryB]

All you need is a PID controller with temp sensor and a solid state relay. Wire the fridge to run constant then switch it with the PID. Pretty simple wiring.

http://www.amazon.com/TabStore-All-purpose-Temperature-Controller-Centigrades/dp/B00GNWTQ1I/ref=sr_1_5?ie=UTF8&qid=1426915319&sr=8-5&keywords=PID+temp+controller+STC-1000

Use the relay in the PID to switch this http://www.amazon.com/Omron-G3NA-225B-AC100-120-Indicator-Photocoupler/dp/B005T7XFDI/ref=sr_1_13?ie=UTF8&qid=1426915493&sr=8-13&keywords=solid+state+relay+25+amp

Power cable to PID power, grounds and neutral to the outlet. Hot goes to one side of the PID other side goes to outlet. PID control is neytral one side, hot to PID then PID to other side of SSR control terminals to switch it.


MaryB I have an RV fridge sitting in my shop that I need to do something with. I have tried various thermistors, and none of them work. I don't know if the control board in the fridge is gone wacko, but even thermistors that are within the range given by the mfgr don't work. The unit doesn't cycle until it freezes everything, then it cycles. There is a knob on the front, that serves as both an off/on switch, and a thermal adjustment range. Behind this knob is a pot that has a switch made into it, and then the back half of the pot is the typical control rheostat/carbon path type potentiometer. I could unsolder one leg of the switch, and use the two contact points for a relay to close the circuit, which would make the compressor run, and then when the relay opens this circuit, it will quit running. This would work if the vehicle is traveling and running off 12v, or parked and hooked up to an external 110v RV plug like a campground would have.

What do I need to do to be able to get a PID to make this unit cycle within say 34° - 40°? I can figure out the logic behind the controller, and I have some thermistors that I can mount inside the box that changes resistance as temps change. Would I be able to use this to control it with? Tell me what I need to do because I haven't ever worked with these controllers before.

[MaryB]

I fried the contacts in one of those in 2 years on another old fridge I no longer own.


Some of the guys on one of the beer sites I'm on use a temperature controller from Johnson Controls for their beer fridges. It might be cheaper than a pid.

[DougGuy]

Thanks.. Ok just a little twist here. This RV fridge is a dual voltage unit. I am not sure of the voltage at the off/on switch made into the temperature selector knob on the front. It's got to be 12vdc. If I use a relay (The STC-1000) to open and close that part of the circuit, it will still run on dual voltage. It would be just like me turning it off and on manually with the knob. The solid state relay you posted the link to would work great if the unit only ran off 110v and I understand how you are using the low voltage relay in the PID to trigger the 25A relay in the other part of it to control the switching of the load.

I need to measure the voltage at the switch I guess, since there is obviously a relay farther along in the circuit that turns the compressor off and on. This compressor is actually a 12v compressor, and even when the unit is running off 110v power, the control box on the back of the unit still converts it to 12VDC to run the compressor. So I got dual voltage going into this control box, but inside there must be an inverter to convert it to 12vdc.

Edit: I looked on fleabay at these STC-1000 controllers, they are 110v units. I think I would need a 12vdc unit if they make them. The fridge goes in a Sportsmobile camper van, and the fridge runs off a 12v marine battery when the vehicle is not plugged in to a an external 110v plug, runs off the alternator (charging the marine battery) when the vehicle is running on the highway.

Maybe this one? http://www.ebay.com/itm/Digital-STC-1000-All-Purpose-Temperature-Controller-Thermostat-DC-12V-w-Sensor-/191508087193?pt=LH_DefaultDomain_0&hash=item2c96c58199




All you need is a PID controller with temp sensor and a solid state relay. Wire the fridge to run constant then switch it with the PID. Pretty simple wiring.

http://www.amazon.com/TabStore-All-purpose-Temperature-Controller-Centigrades/dp/B00GNWTQ1I/ref=sr_1_5?ie=UTF8&qid=1426915319&sr=8-5&keywords=PID+temp+controller+STC-1000

Use the relay in the PID to switch this http://www.amazon.com/Omron-G3NA-225B-AC100-120-Indicator-Photocoupler/dp/B005T7XFDI/ref=sr_1_13?ie=UTF8&qid=1426915493&sr=8-13&keywords=solid+state+relay+25+amp

Power cable to PID power, grounds and neutral to the outlet. Hot goes to one side of the PID other side goes to outlet. PID control is neytral one side, hot to PID then PID to other side of SSR control terminals to switch it.




MaryB I have an RV fridge sitting in my shop that I need to do something with. I have tried various thermistors, and none of them work. I don't know if the control board in the fridge is gone wacko, but even thermistors that are within the range given by the mfgr don't work. The unit doesn't cycle until it freezes everything, then it cycles. There is a knob on the front, that serves as both an off/on switch, and a thermal adjustment range. Behind this knob is a pot that has a switch made into it, and then the back half of the pot is the typical control rheostat/carbon path type potentiometer. I could unsolder one leg of the switch, and use the two contact points for a relay to close the circuit, which would make the compressor run, and then when the relay opens this circuit, it will quit running. This would work if the vehicle is traveling and running off 12v, or parked and hooked up to an external 110v RV plug like a campground would have.

What do I need to do to be able to get a PID to make this unit cycle within say 34° - 40°? I can figure out the logic behind the controller, and I have some thermistors that I can mount inside the box that changes resistance as temps change. Would I be able to use this to control it with? Tell me what I need to do because I haven't ever worked with these controllers before.

[starmac]

Is their a benifit to converting a freezer to a fridge over just using a regular fridge???

[Screwbolts]

DougGuy, all the RV fridges I have seen and worked with do not use a compressor to operate they are the old ammonia system, a little heater , (Gas or electric (12V or/and 110)) to heat ammonia and a cooling grid. I don't think a PID will help you. what usually happens to them is a blockage from crystallization of coolant.

Ken

[Plate plinker]

We need pics of the unit guts and all. How old is this thing? Dies it also run on LP?

The newer units we use have 12v brains, but the compressor is 110 or LP.

By the way the middle to higher end stuff now gets regular refrigerators with a separate inverter. I suspect because the lp fired units are kinda junky (fire hazard). Only those who really want to go boondocking want the LP setup.

[DougGuy]

DougGuy, all the RV fridges I have seen and worked with do not use a compressor to operate they are the old ammonia system, a little heater , (Gas or electric (12V or/and 110)) to heat ammonia and a cooling grid. I don't think a PID will help you. what usually happens to them is a blockage from crystallization of coolant.

Ken

I didn't typo a whole 3 paragraphs. It has a compressor hanging right off the back of the unit. How much more plainer can I be? The unit cools REALLY GOOD! It runs until the inside cools down to 25° and then starts cycling.

Google Norcold DE-441. It is a discontinued unit, can't get a new control board for it, when you DO find parts for it, OMG they want half as much as a NEW fridge just for some of the parts..

Ok here's a pic of the backside. I did some further checking, the control board runs on 24VDC, there is 24VDC present at the switch terminals, see two tiny red arrows on the lower right hand pic. I would lift one side of this switch, and solder the PID controller across these two points so it would work much the same way as manually turning the switch on and off am I correct so far? Close the circuit, compressor starts. Open the circuit, it quits. I would still have the switch function in addition to the PID if I did it this way.

The COMPRESSOR for those who need pics to settle any doubts.. Is a Sawafuji swing motor compressor that runs off 20VAC. You can read more about it here: http://www.fridgefreezersite.com/sawafuji-compressor/

The inverter/converter/control box is shown, with 110vac and 12vdc inputs.

http://i1202.photobucket.com/albums/bb374/DougGuy/dumb%20stuff/NorcoldDE-441_zpscf65jzxw.jpg (http://s1202.photobucket.com/user/DougGuy/media/dumb%20stuff/NorcoldDE-441_zpscf65jzxw.jpg.html)

[JonB_in_Glencoe]

DougGuy, I have worked as a Electronic tech, mostly building industrial electronic control panels for over 20 years. I was hoping I could help you out, if I could find a wiring diagram. Well, I think I found a wiring diagram...but by looking at it, I can't tell you how to swap out the temp control board with just a PID and SSR. There seems to be more going on.

http://www.manualslib.com/manual/769898/Norcold-Dc440.html?page=11#manual

[DougGuy]

Thanks JonB and MaryB, apologies for steering the thread, at first all I wanted to do was ask a simple question..

I have the manual, with a schematic (I think) and it carries you through all the steps of troubleshooting to see which component is faulty, shows you how to check out the compressor, gives readings to check, gives a range of values for the thermistor by temperature range, been there done that, ran the electric bill up here by $75 in one month doing all the diagnostics and trying different thermistors, Grr.. It just runs too good to give up on it and replace it. It just wants to FREEZE everything inside it!

This is the bottom of the temperature adjustment circuit board. The two red arrows point to the terminals of the off/on switch for the whole unit. I wouldn't have to replace anything or swap anything out, all I need to do is wire a digital temperature controller's relay to these two terminals and it would then become the off and on switch. There really isn't any amperage to speak of on these terminals, so I think I would be alright without a SSR. I just have to do it with a 12vdc controller so it runs off vehicle current.

I could probably even connect it in series on one side of the compressor, leave the unit turned on and set on cold and it would still work like that but I'd rather connect it across the switch on the control board.


http://i1202.photobucket.com/albums/bb374/DougGuy/dumb%20stuff/DSC03716_zpsqdulm4d3.jpg (http://s1202.photobucket.com/user/DougGuy/media/dumb%20stuff/DSC03716_zpsqdulm4d3.jpg.html)

[MaryB]

Relay in the PID will likely handle the current okay, wiring diagram I found looks like it switches low current monitor circuits. If that doesn't fix it it might take some major surgery on the board to run the compressor inverter on its own. If you need to switch high current DC they do make DC SSR's http://www.ebay.com/itm/New-Solid-State-Relay-SSR-40-DD-DC-DC-40A-3-32VDC-Input-5-60VDC-Output-BYWG-/331511048495?pt=LH_DefaultDomain_0&hash=item4d2f99292f

[MaryB]

get your fet wet, stand in front of your fridge and open the door and tell me where all your cold just went. Now do the same with a chest freezer. Cold stays in the chest freezer so it cycles a lot less and when running via solar/battery that is critical!



Is their a benifit to converting a freezer to a fridge over just using a regular fridge???

[starmac]

LOL explain what wet feet has to do with it??? Are you saying cold air doesn't escape when you open a chest freezer?

[MaryB]

Yup you won't have cold feet opening one! lol

[lancem]

I use two of them myself, they are also better insulated being freezers. Great idea on the PID control, I'm using the mechanical Johnson controls currently but I know what I'll do now if they ever go wacko. Living off grid makes you think outside the box a bit :)

[6bg6ga]

Good Job Mary!!!

The correct parts the first time around. Properly thought out and implemented

[MaryB]

Still need to get the relay controller into the solar setup. Going to use it to monitor voltage and drop power to the inverter when needed. Transfer switch will drop back to grid then. Electric rates are not going down so I am cutting power anywhere I can.

[Screwbolts]

Very good job MaryB, I only use chest freezers for the very reason you simply demo using wet feet.

From Plate Plinker:
By the way the middle to higher end stuff ( that explains it perfectly, I don't have high enough ends or new enough middle, maybe not even middle, just an old 97 Sunline, OMG it's 18 years old! )now gets regular refrigerators with a separate inverter. I suspect because the lp fired units are kinda junky (fire hazard)( That Old style Low end stuff just kinda keeeepppsss wooorrrrkiiingg with out the need of electricity, now I better understand why I have not seen the new fangled RV fridges. I am not high ended enough. I must not rely on the grid enough) Only those who really want to go boondocking want the LP setup( perfectly sums up my Families camping, no hookups. ( Oh Yes, I run old school diesels, that don't require a computer to run also) (all of my added text is in purple , I do not want any confusion in case prior text is the to dark purple, it is still purple :-)).


Good job MaryB,

Ken

[MaryB]

Next off grid project is LED lighting. I picked up some 7 watt LEDS that are 500 lumens. Figure mount them on a heatsink, add a constant current regulator and a motion sensor to each then make a nice oak frame to hold it with some type of plexi front. 1,000 lumens is about 100 watts so it will be plenty bright in each room with only 600ma current draw per light. When I wire them in each room is getting 2 24 volt outlets for other stuff too.

[DougGuy]

Finally got around to modding a $13 PID controller and converting it's relay into just a dumb switch. New, the controller would switch 12vdc on and off at it's output so I cut the traces from the circuit board inside the unit lifting the 12v leg off the relay, and added a jumper so the unit just opens and closes a simple circuit like a single pole single throw switch. As the temperature changes, the controller opens and closes the relay which I have connected to the on/off switch of the RV fridge. This way there is not much current going through the relay in the controller so it might last a while, and the fridge gets to keep it's 12vdc/110vac dual voltage operation so it will work while running down the highway on 12vdc, or while parked on 12vdc, and then run on 110vac while hooked up to the power at a campsite.

So far, so good, fingers crossed that this thing can be tricked into operating at a temperature that will keep stuff cold but not freeze it. Before, it would cool down to 25°F and stay there freezing everything in the top half of the box. Not fun.

Controller:

http://i1202.photobucket.com/albums/bb374/DougGuy/dumb%20stuff/DSC03927_zpsdggmc5hy.jpg (http://s1202.photobucket.com/user/DougGuy/media/dumb%20stuff/DSC03927_zpsdggmc5hy.jpg.html)

Connected across the on/off switch of the fridge:

http://i1202.photobucket.com/albums/bb374/DougGuy/dumb%20stuff/DSC03928_zpsxcwmrtze.jpg (http://s1202.photobucket.com/user/DougGuy/media/dumb%20stuff/DSC03928_zpsxcwmrtze.jpg.html)

Will probably have to repurpose one of my 12vdc computer fans to circulate air inside the box to even out temps.

Edit: Setting the controller to 6.5°C with a 2°C swing, it cycles like it should, temps on the inside with a fridge thermometer show it staying within a low of 34°F to a high of 40°F which is about perfect, at least to start with. I think we're there! :bigsmyl2: I don't have to buy an $800 RV fridge! YET!

[MaryB]

Tested mine with a Kill A Watt meter. Old upright fridge was 2kwh a day, freezer to fridge with the new controller is running .41kwh, with the old mechanical controller on the freezer it was .45kwh a day so I am saving a bit each day and on battery that adds up fast!