Refrigerator Thermostat Replacement

[conachair]

14 hours in the life of a fridge

Next step is to add another couple of sensors, 1 on on evaporator and 1 near the top of the box, see a bit more of what's going on.

I think the lead to the compressor got pulled out for a while before 04:00

The pink line is compressor on/off, 5 in on, 4 is off.

[Richard Kollmann]

Your data logger chart would indicate very poor performance from compressor with excessive cycling. Compressor running 5 minutes and off 4 is not good. Each time compressor starts pump down electrical energy is wasted. The purpose of the BD35’s variable speed and a thermostat controlled evaporator’s extended Hysteresis is to prevent wasted energy. Any time compressor cycles near or more than 50% of the time the reason should be looked into especially if boat is to be moved to a warmer climate.
QUESTIONS
1.I am not able to understand the temperature range, is compressor cycling on a 2 degree differential? Where is temp probe located?
2.Describe thermostat and its installation?
3.Is this an Ice box conversion unit?
4.What is size of box?
5.Is condenser fan cooled?
6.What is ambient temp where boat is located?
7.If boat is a single hull Sailboat what is approximate seawater temperature?
8.What is air temperature interring fan cooled condenser?
9.Is air flow through condenser free of restrictions?
10.Has anyone tampered with refrigerant or connected pressure gauges to your unit?

[conachair]

Originally Posted by Richard Kollmann

[FONT=Times New Roman][SIZE=3]Your data logger chart would indicate very poor performance from compressor with excessive cycling. Compressor running 5 minutes and off 4 is not good.

The time at the bottom is actually in hours, the pump is running about 10 minutes on/30 minutes off.
(Edit, ah , see what you mean, the pink line is at 5 on the left hand scale when the pumps is running and at 4 when it's not)

1.I am not able to understand the temperature range, is compressor cycling on a 2 degree differential? Where is temp probe located?

So far there's just a sensor at the bottom of the box, compressor turns on at +5degC and off at +3DegC

2.Describe thermostat and its installation?

It's an arduino microprocessor, sensors are these..
DS18B20 Programmable Resolution 1-Wire Digital Thermometer - Overview
At the moment it's just turning on the compressor by switching a transistor, but it wouldn't be difficult to control the speed as well with a few transistors/resistors. No resistors in there at the moment so running low revs.
Cooling fins are barely warm to the touch.

3.Is this an Ice box conversion unit?
4.What is size of box?

No idea , it was on the boat when i got it, I took out an engine driven compressor which wasn't working and put in a bd35. Box is about 450mm depp x 300mm x 300mm.

5.Is condenser fan cooled?
6.What is ambient temp where boat is located?
7.If boat is a single hull Sailboat what is approximate seawater temperature?
8.What is air temperature interring fan cooled condenser?

Boat is out of the water, the fans has stopped working but plenty ventilation down there, ambient temp where the condensor is prob about mid teens during the day. Lower at night

10.Has anyone tampered with refrigerant or connected pressure gauges to your unit?

No gauges an hasn't been touched since new, about 6 years ago.

It's running now to see what temperature the evaporator plate cycles through. It will be easy to control using evaporator plate data, adding in pump temperature as well if that helps at all.

Thanks

[conachair]

And some more lovely data
Blue is temp near the bottom of the box, pick is evaporator temp and the little step in grey is when the pump is running.

So the question is ... what's the most efficient way to run a fridge?
With just 2 parameters, when the pump runs and it's revs. As far as I can see anyway.

Interesting little dog leg as the evaporator warms above 0Deg, could that be some frost on the plate sucking in a bit of energy it needs to melt?

[Richard Kollmann]

Mobile refrigeration in boats must be designed to meet a reasonable efficient standard of reliability, longevity and simple maintenance. Well designed basic boat refrigeration units perform properly in a wide range of conditions but adding gadgets that do not improve performance and reliability like electronic thermostats and water cooling on Danfoss BD compressor systems is a mistake.

Conachair, Your second chart provides a good freezer temperature but may be over powering evaporator lower compressor speed and see if you can improve daily power consumed. I can not see where I can help you with your project. Much has been done good and bad trying to improve pleasure boat refrigeration. The good is alternative energy from sun and wind along with high output charging systems. The variable speed compressors for small ice box conversions is a major breakthrough. Various size evaporators and compressors now allow a good application engineer to select components to provide a balanced refrigeration system tailored to each application.

Conachair, if you want to take on a project that could improve performance of small mobile boat refrigeration find a way to maintain condenser cooling regardless of cooling medium’s temperature air and water. On larger boats refrigerant pressure controls cooling water flow as cooling medium temperatures change. A good air cooled mobile unit for a boat is designed for worst case projected warm climates like Adler Barbour, SeaFrost, and the Cabri Models sold by Frigoboat. In cold climates performance can be improved by restricting some airflow through condenser. It is true that cold climate performance loss is not as important as tropical climates like the Bahamas. Frigoboat seems to have a solution to warm water on keel cooler models in tropical climates by adding a fan cooled unit in series with keel cooler to lower high refrigerant pressure.

[conachair]

Originally Posted by Richard Kollmann

but adding gadgets that do not improve performance and reliability like electronic thermostats and water cooling on Danfoss BD compressor systems is a mistake. [/SIZE][/FONT]

Possibly, but with no data on reliability it's impossible to know until you try, and at least with feedback on performance there's a chance of tuning the system for better performance.

Conachair, Your second chart provides a good freezer temperature but may be over powering evaporator lower compressor speed and see if you can improve daily power consumed.

No where to go there unfortunately, it's at it's slowest speed. Maybe switching between 4 and 5deg would make more sense?

Next stop a fan in the box to see how that helps with cooling.




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[BambooSailor]

So rather than order a new one I reckon a much better replacement can be made using a microprocessor with some temperature sensors for about the same money as a replacement.

I did something similar, except I added some features. My controller controls two separate units: refrigerator and freezer. Besides monitoring box temperature, it also control speed of compressor, speed of evaporator fan, speed of compressor cooling fan, it monitors power consumption and using some fancy algo it optimizes energy use (separately for freezer and refrigerator), it also turns on/off internal light, white during day, red at night, tells me when door is not closed properly, it controls box internal circulation fan, measures humidity (I am still working on algorithm that would detect leaking hatch/door and warn user - living in Seattle it is difficult to test), it detects charging/excess power and uses max power to deep-freeze a freezer. I still have several A/D ports available on the controller, I thought about monitoring coolant pressures in and out of compressor and plate for self-diagnostics and problem detection, but cannot find cheap transducers (I am too cheap). I control it through a web page. It cost me about $50 to build and yes, I can fix it anywhere in the world where Chinese will ship their components.

[conachair]

Originally Posted by BambooSailor

I did something similar, except I added some features. My controller controls two separate units: refrigerator and freezer. Besides monitoring box temperature, it also control speed of compressor, speed of evaporator fan, speed of compressor cooling fan, it monitors power consumption and using some fancy algo it optimizes energy use (separately for freezer and refrigerator), it also turns on/off internal light, white during day, red at night, tells me when door is not closed properly, it controls box internal circulation fan, measures humidity (I am still working on algorithm that would detect leaking hatch/door and warn user - living in Seattle it is difficult to test), it detects charging/excess power and uses max power to deep-freeze a freezer. I still have several A/D ports available on the controller, I thought about monitoring coolant pressures in and out of compressor and plate for self-diagnostics and problem detection, but cannot find cheap transducers (I am too cheap). I control it through a web page. It cost me about $50 to build and yes, I can fix it anywhere in the world where Chinese will ship their components.

Wow!

How do you know the internal light actually goes off

Optimising power I haven't got too far with yet, might end up a bit of trial and error, we'll see. But in general I'm happy with the direction, the last thermostat broke after about 6 years, solid state stuff lasts for ages so fingers crossed. The boards cost single figure UK pounds, having a few spare won't break the bank.

And since there's a clever box going in there I might stick some more sensors in, alternator, stuffing box and exhaust water trap spring to mind. With an alarm for each.

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[belizesailor]

Interesting discussion. Thanks all. Possible application to fridge on my boat and brewing beer ashore!

[Stu Jackson]

I've replaced the fan on ours with one from Radio Shack, 4" square, runs fine. Good luck.

[sy_gilana]

Originally Posted by HappyMdRSailor

I think you're making it more complicated than you need to....

Fully self contained PLC's with a display, 4-8 I/O, 4-20/TC in, relay out, can be had for $50...

Or something as simple as this, except find it in 12-24vdc, not 110...
FOR $17 !!!

Elitech 110V All-Purpose Temperature Controller+ Sensor 2 Relay Output Thermostat Stc-1000 - Hvac Controls - Amazon.com

If you want fancy... the latest BD series come with Bluetooth, so you can read compressor speed, temperatures etc.

Richard Kollman is probably "THE" Guru on these units so best take heed of what he says.

Agree with the Elitech, that one is a bit basic, we wend for the AKO version, its programmable, hysterisis etc. Best thing we did for the fridge. Even does a defrost cycle every 4 hours.

Please tell more about the PLC for $50!!!!! thanks...

AKOSYS - Industrial refrigeration components

[BambooSailor]

...reliability like electronic thermostats and water cooling on Danfoss BD compressor systems is a mistake.

I disagree re electronics. Reliability of solid state electronics very often exceeds reliability of mechanical components by order of several magnitudes. By optimizing usage of mechanical components (compressors, fans) and by detecting anomalies early, electronic controller can actually increase lifespan and reliability of mechanical components in the system.

[Richard Kollmann]

Originally Posted by BambooSailor

I disagree re electronics. Reliability of solid state electronics very often exceeds reliability of mechanical components by order of several magnitudes. By optimizing usage of mechanical components (compressors, fans) and by detecting anomalies early, electronic controller can actually increase lifespan and reliability of mechanical components in the system.

Bamboo Sailor, I do not think anyone will disagree with your opinion of electronics when used in the right application may be a better solution than mechanical controls. One must be careful with electronics in marine applications do to harsh environments. No matter how well electronics is protected on a boat a wise sailor always wants back up redundancy. It is not uncommon for voltage surges on a boat to damage electrical components even a lightning strike in the area can damage electronic components. Having seen lots of electronics damaged on boats from runaway alternators, lighting strikes and components not adequately protected from marine conditions I have formed a position that differs from yours. Use electronics on a boat only when required to enhance boating pleasures and then have the knowledge of a ways to bypass or do with out it for as long as necessary. Watch for creative advertising by manufactures who sell gadgets that do not enhance performance and reliability. Keep things simple efficient and reliable.

I trash many boxes of damages electronic modules a year all with failed electronic components inside.

[forsailbyowner]

I went the super simple route with my old adler barbour. I mounted this behind the evaporator. Then forgot it.


HVAC Refrigerator Thermostat Open 45'F Degree Close 25'F Degree Tube Mounting GE | eBay

[BambooSailor]

Richard, I agree with you 100%. (Yes, I bought two of your books and trust you implicitly ). I never rely on one system only, whether it is GPS, chartplotter, alternator, water tank, bilge pump, compass, refrigerator, dingy tow line, you name it, I have a backup system and/or plan. I just pointed out that mechanical thermostats are not necessarily more reliable than electronic ones. But I am talking about electronics properly designed for marine environment, otherwise they are almost guaranteed to fail in a very short time.