Mini Brushless DC Compressor

[marx290]

A friend of mine recently acquired a small brushless DC compressor for me to work with. He would like to develop some mobile cooling devices for a teardrop trailer he is planning. I was going to build a small air to air cooling system, but with the temperature dropping lately, and the relative humidity rising, I'm going after a dehumidifier for now.

Look at the pics; isn't it cute!?

It's a rotary compressor, 2.7cc, 1700-2900 RPM, 50mL oil, 12VDC

Other models are available which have a high speed of 6000 RPM, and other voltages as well.

eBay listing for 12VDC Refrigeration Compressor - Brushless DC

I've had an interesting time checking and changing the oil in the compressor. Displacing/burping the air is the biggest issue. I utilize a large syringe and needle, along with a very thin tube attached to the needle, for the job. Oil migration is an issue, I'm sure.

I'm running a capillary tube system right now. It is too long, so I'll be shortening that today.

Somebody else should buy one of these, and build something!

https://www.youtube.com/watch?v=aN6IQDzOLfI

https://www.youtube.com/watch?v=DH0XvfvGpuM

https://www.youtube.com/watch?v=MIAg8rhuV6A

[AC_Hacker]

Way cool work!

How are you varying the speed of the compressor??

-AC

[marx290]

Thanks, AC_Hacker! I'm not doing much in the way of varying the speed; running with all the power this little baby will take! There is a small potentiometer on the control board that allows me to vary the speed, with the aid of a small screwdriver.

I'm powering it with a deep cycle battery for now, but my buddy has a small regulated power supply to run it.

I've shortened the capillary tubing several times now. Down to 8 feet of 0.031 now. I'm getting fairly close to the right length, however I might have an issue with pressure drop across the evaporator. I will be adding another port on that side of the evaporator to look for the drop.

Oil migration is definitely an issue, I'm finding.

[AC_Hacker]

Originally Posted by marx290

There is a small potentiometer on the control board that allows me to vary the speed, with the aid of a small screwdriver.

That's pretty cool that you can change speed by analog means (Your pot could be replaced by an analog circuit to control speed). According to the fine print, you can change the speed through digital means as well.

Originally Posted by marx290

Oil migration is definitely an issue, I'm finding.

How are you detecting oil migration??

-AC

[TechShop]

That sure is a neat little unit.

It looks like the board that comes with it can run a complete system including the fans.
That must have an original application in RV refrigerators, portable coolers, etc.

[AC_Hacker]

Originally Posted by TechShop

That sure is a neat little unit.

It looks like the board that comes with it can run a complete system including the fans.
That must have an original application in RV refrigerators, portable coolers, etc.

I have an ice-cream machine that has a different, but tiny compressor. Very useful.

-AC

[marx290]

AC_Hacker, I will probably look into a better speed control. Perhaps, once I build refrigerator, or something like that, I will be more interested in variable speed. I am mainly interested in the small size, and at 80 watt input power, I don't need to turn it down anymore! An electronically controlled feedback loop that set the speed to match the load might be fascinating, but beyond my level of interest at this time. Another idea for the variable speed, is to give the operator of say, a refrigerator, some information about the power consumption of the unit, along with the run times and duty cycles; they could then turn up or down the the compressor speed, depending on their desires to gain efficiency or for faster cool down. Most people probably wouldn't care, but I think it would be neat.

Originally Posted by TechShop

That sure is a neat little unit.

It looks like the board that comes with it can run a complete system including the fans.
That must have an original application in RV refrigerators, portable coolers, etc.

Yes, the board will run a condenser fan, evaporator fan, accept some digital signals for run speed, has a temp sensor for compressor overheat, has a shunt for overcurrent protection, and of course has the little pot for manually adjusting speed.

I don't know of too many appliances that are using these compressors specifically. I've seen some pics of appliances that include refrigerators, freezers, dehumidifiers, portable refrigerators, liquid chillers, and more.

The company Purswave makes a very similar compressor to the one I have; so similar that it may be the same manufacturer, I'm not sure. Here's some of the products they make. Some of the compressors are larger, but many are DC.

Refrigeration Appliance -

Compressors this small and smaller, are being utilized a lot in personal cooling for people who must wear environmental protection suits of some sort. The US company Aspen has a military contract to produce tiny 1.9 cc rotary compressors for this purpose.

How are you detecting oil migration??

-AC

So, the oil thing is interesting. I don't have much experience changing oil in hermetic compressors; by that I mean none. I wasn't sure how much oil was in the compressor from factory, so I emptied it and charged 50 mL of POE with a syringe and needle. The copper lines I brazed on the compressor were going to make it difficult to check the oil level at a later time, but I figured it out. I utilized flare fittings in my system, since it is experimental, and they allow me to make quick changes, or do things like check the oil charge in the compressor.

The first time I pulled the refrigerant charge out, a good bit of oil came with it, from the suction line. I unhooked the compressor, an flipped it upside down. To force the oil out of the discharge line, I had to force air into the shell with a piece of wire insulation stuck to the needle of the syringe. Measuring the remaining oil, I found I had lost about 10 mL of oil; probably not enough to cause damage, but definitely oil migration. How this might play out in the long run, I don't know.

I have since moved the suction service valve, and I find I do not lose as much oil when recovering refrigerant. Whether or not it is returning to the compressor during operation, is another question. I must look into oil retun methods like traps, and wicks.

That is all for now, time for dinner.

Tomorrow night, I'll be adding some features, and nailing down the proper length of capillary tubing.

-Marx

[jeff5may]

Take a look at Jake's latest thread:
http://ecorenovator.org/forum/geothe...o-heating.html

He has been doing research on an oil trap/separator to use in his new concoction. As I write this post, he is gearing up for yet another build of groundbreaking (literally) and unconventional nature. His homework could save you some time and effort rigging up an oil trap.

I wish you both good luck and godspeed.

[marx290]

Thanks Jeff. It is an interesting thread. My little compressor is going to need some special attention when it comes to the oil. I will most certainly consider building a better draining system, but I don't want to rely on that. I'll keep my eyes open for more progress.

[pavel]

Thanks for posting