Einstein Refrigerator

Building an Einstein refrigerator and hoping to use the arduino as the controller.

Have 3 arduino boards, 1 mega 2560 and 2 Duemilanove. Have 1 16x 2 lcd and a 20x4. Hoping to use the 16 x 2 to display 3 temp readings and a pressure reading. I have not located a pressure sensor yet that can work with arduino and be subjeted to the ammonia water mix…looks like I need a stainless pressure transducer. I am attempting to use an arduino controller to control 3 temp sensors. ( have 3 TMP36 analog sensors and 3 ds18b20 temp sensors). Not sure which are best to use…they will be inserted into thermo wells which will be in the fluid.The system will be powered by 2- 235 solar panels which will charge 2- 12vdc deep cycle batteries. The systen will use a 100 watt immersible heater for the bubble pump (water) and a 200 watt heater for the generator (ammonia water mix). As the system approaches steady state I need to be able to decrese the power to the heaters. I was hoping to use auto relays but do not think I can flicker the power effectively with them or decreses the power appropriately. Loooking to solid state relays. 200watts/12 volts is at 16 amps and the ssr’s look to be expensive. I am hoping to run the fans off the respective heater relays or they may need to have their own relays as they do not need to be controlled as much…on or off should be good.

Any guidance and or code/ appreciated

I have the 16x2 lcd working (can type text and upload program) but not sure how to show the 3 temperatures…cause I am not very code savvy. I do not have any of the sensors installed yet that is tonights project and I am hoping to get the digital sensors working (dallas type). Thanks Wiring diagram attached

Preliminary wiring diagram 2.pdf (107 KB)

For temperature the DS18B20 are very popular - http://milesburton.com/Dallas_Temperature_Control_Library -

waterproof version! - http://arduino-direct.com/sunshop/index.php?l=product_detail&p=151 -

Use a solid state relay to switch the heaters..

YOu can post the code you have sofar, and there will be comments and help to improve the "beast" :wink:

I too like the DS1820. They only require one line that can be used for both power and data along with a ground. However, I usually use a separate power line. Reading are faster. From that you can control as many temperature sensors as you would like.

You can also set up alarm thresholds so rather than the Arduino polling all sensors looking for situation that requires attention. You can set thresholds and then broadcast for alarm reports. You can then handle the alarm based on the ID of the reporting sensor.

If I could, I could try to keep the sensors out of any chemicals. I would think that you could bond the sensor the to outside of any tank or line and get a good reading.

SSR's are cheap if you are controlling AC. For DC I would look at power transistors and FETs.

I have a nice library that I use with my DS1320's if you don't have one you like.

Do you know of any potential problems with running DC across a A?C SSR?. I found some ssr's

http://arduino-direct.com/sunshop/index.php?l=product_detail&p=216
at above link. I figured as long as the amperage was below 25 amps this would work with DC flowing through the AC portion.

I was able to get the lcd configured last night and I soldered up the wires on the temp sensors and put into a bread board. Now just have to get the library right and see if I can get some readings on the LCD

Thanks

Thanks for the input and my ssr idea will not work, apparentlty once on with a dc load running through it will not turn off

It is an all DC system with DC immersible heaters, 100 watt and 200 watt. THe temp sensors will be inserted into thermo wells and will not contact the chemicals. The thermowells will conduct the temp to the temp sensor. See attached…then will use thermal paste on sensor and insert.

260_Commodity.pdf (344 KB)

30 volt 50 amp....$30.00

Hopefully I can use the arduino to control

Thanks for the input and my ssr idea will not work, apparentlty once on with a dc load running through it will not turn off

It's the wrong kind of SSR. AC solid state relays usually use a TRIAC, and they don't shut-off 'till the AC goes-through a zero-crossing, which may be a few milliseconds after you remove the control voltage.

DC solid state relays use something different (a MOSFET?) and they will turn-off as you expect. (I used some DC solid-state relays in a recent automotive project, and in-fact I used solid-state relays for the same reason... I needed to turn them on & off faster than 100mS.

As the system approaches steady state I need to be able to decrese the power to the heaters. I was hoping to use auto relays but do not think I can flicker the power effectively with them or decreses the power appropriately.

I don't know anything about Einstein refrigerators... But, typically in refrigeration systems there is a "gap", so that the system doesn't "flicker" or cycle on & off too rapidly.

For example if you are trying to hold 35 degrees F, you would hold the refrigeration system on 'till the temperature gets down to maybe ~34. Then, you shut it off and you don't turn it on again 'till the temperature creeps-up to maybe ~36. In electronics we might call this "hysteresis". In HVAC jargon, i believe it's called "swing". The greater the swing, the less-frequently the system cycles, and the less accurate it is.

samfred:
The systen will use a 100 watt immersible heater for the bubble pump (water) and a 200 watt heater for the generator (ammonia water mix). As the system approaches steady state I need to be able to decrese the power to the heaters. I was hoping to use auto relays but do not think I can flicker the power effectively with them or decreses the power appropriately.

Let's imagine your 100W heater is heating a gallon of water. The question then is how much time it takes to increase the temperature of 1 gallon of water by 1 degree with that heater.

1 calorie = 4.2 joules = raises the temp of 1 gram of water by 1 degree
1 gallon of water is 3780 grams
You need 3780 * 4.2 = 15876 joules of power
1 joule = 1 watt / second, so 15876 joules = 15876 watts for 1 second.
Your heater is 100W so you will need to drive it for 15876 / 100 = 158 seconds to raise the temp one degree.

...I think it's pretty clear that an automotive relay will be able to switch quickly enough to keep 1 degree accuracy.

Thanks. Not sure yet which way to go. I think I will need the ssr to pulse to maintain the necessary temps in the bubble pump and generator.

Heat excel calculatuions attached. Still not 100 % sure on the volumes of generator or bubble bump. It all relates to chemical ratios. Uses ammonia water and butane as refrigerant.

volume and heat calcs.xlsx (16.8 KB)

attached pdf of einstein refrigerator. Heaters go on lower left of drawing.

patent pdf.pdf (3.04 MB)

I just wanted to note that unless your are doing this for run or because it needs to be quiet or something a vapor compression cycle ( regular refrigerator ) would make better use of your energy input and would be simpler to construct ...

Otherwise great project ! I look forward to seeing how it works out ! Be sure to keep us updated!

Thanks, well aware of vapor compression vs vapor absorption and the resulting COP's. The COP of an EF is Around .17 and this project is attempting to increase COP with the use of heat exchangers.

Is it best to configure the 3 temp sensors with red and black common to ground and the white signal line attached to digital inputs with a resistor in front of all 3? How can you get the temp sensors to report to the lcd? I will have to read up on the library aspect
attached picture of breadboard w sensors and current lcd code.

lcd_placement_2.ino (1.79 KB)

1 gallon of water is 3780 grams

Only on one side of the Atlantic.
Here, presumably due to higher deuterium oxide content, 1 gallon of water is approximately 4546 grammes.

there is even a 3rd one - from wikipedia:

The imperial gallon
The imperial (UK) gallon, defined as 4.54609 L, is used in some Commonwealth countries and was originally based on the volume of 10 pounds of water at 62 °F. (A US liquid gallon of water weighs about 8.33 pounds at the same temperature.) The imperial fluid ounce is defined as 1?160 of an imperial gallon.
The US liquid gallon
This gallon is defined as 231 cubic inches,[2] and is equal to exactly 3.785411784 litres or about 0.13368 cubic feet. This is the most common definition of a gallon in the United States. The US fluid ounce is defined as 1?128 of a US liquid gallon.
The US dry gallon
This gallon is one-eighth of a US Winchester bushel of 2150.42 cubic inches, thus it is equal to exactly 268.8025 cubic inches or 4.40488377086 L. The US dry gallon is less commonly used, and is not listed in the relevant statute, which jumps from the dry quart to the peck.[2]

As an American, can we please just use the metric system now? ><

I try to use both side by side when talking to "non-metrics" inches /cm gallons / liters etc

could make a nice usefull Arduino sketch/lib - the metrics convertor -