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Old 27-02-2024, 21:36   #1
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Making a DIY 12 volt compressor fridge copper tube size?

Hoping there are some experts that can assist. I am in the process of converting an icebox to a 12 volt compressor fridge with an evaporator. I have purchased a Chinese knockoff of a Danfoss compressor the same size as a BD50 (rated 650 BTU) that came with a condenser. I also purchased an evaporator. My issue now is getting the correct size copper refrigeration tube for this setup. I have been to 2 refrigeration shops and they showed me a myriad of small tube sizes (capillary tubes) but admit they are at loss for exactly what size I need. They assume that the low side requires somewhere around 1/4 inch OD but on the high side after the dryer they say cannot give an opinion.

Does anyone currently using a Danfoss BD-50 know the OD size of the tubing they are using on the system? I will need about 7 feet of tube to complete each side.

Please see attached pics of the compressor and evaporator
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Old 28-02-2024, 00:48   #2
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Re: Making a DIY 12 volt compressor fridge copper tube size?

Generally the high-side will use 1/4" tubing, the low-side 3/8".
The pic of the evaporator shows the cap-tube already installed.
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Old 28-02-2024, 00:59   #3
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Re: Making a DIY 12 volt compressor fridge copper tube size?

The discharge from the compressor to the condenser is usually 1/4". The return 5/16". The discharge goes to the condenser and the output from the condenser through a filter drier into the very small tube (capilary) which goes into the the evaporator. The 5/16" inch return from the evaporator goes into the larger tube on the side of the compressor.

The BD50 compressor can be run at a number of speeds which I think are controlled by a resistor in the circuit from the circuit to the thermostat. There are also various sizes of capilary tube and the length required depends upon the compressor speed and the ID of the capilary tube. There used to be a program for calculating the length of capilary tube required in the Danfoss site.
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Old 28-02-2024, 01:10   #4
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Re: Making a DIY 12 volt compressor fridge copper tube size?

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Originally Posted by RaymondR View Post
The return 5/16".
The OP might just as well put a pair of calipers on the suction side tube on the evaporator, 5/16" is not a "standard" size tube for refrigeration use.
But, stranger things do happen.
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Old 28-02-2024, 06:57   #5
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Re: Making a DIY 12 volt compressor fridge copper tube size?

Thank you for the input and information. So I am clear on this - from the dryer to the evaporator is only the capillary tube? I connect the dryer to the capillary tube then connect the capillary tube to the evaporator?

I did go to the Danfoss site and was not able to find any specific information on sizing a capillary tube. They sell them separately, 2 different sizes but no more details than that.

That is why I was hoping someone who has done a DIY with a BD50 could tell me the size of the capillary tube and the length used.
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Old 28-02-2024, 09:10   #6
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Re: Making a DIY 12 volt compressor fridge copper tube size?

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Originally Posted by hatyaiair View Post
Thank you for the input and information. So I am clear on this - from the dryer to the evaporator is only the capillary tube? I connect the dryer to the capillary tube then connect the capillary tube to the evaporator?
No, look at your own picture #2, it shows 2 connections, and it shows the capillary tube already wound-up like a little spring.
The cap-tube is already mounted/soldered in with a stub of tubing.
You simply connect some 1/4 tubing from the condensing unit to that stub connection.
The suction side is self explanatory.
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Old 28-02-2024, 17:23   #7
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Re: Making a DIY 12 volt compressor fridge copper tube size?

I sent a better picture of the connections on the evaporator and yes there is a few inches of a the tiny coiled tube but my understanding is that a capillary tube is somewhere between 4 and 9 feet long in a coil, not just a few inches long. But you are saying to just connect a 1/4" copper tube from the end of the dryer to the connection at the evaporator? I have attached a closer image of the dryer as well and the end of that is very tiny (about the size of a cap tube).
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Old 28-02-2024, 17:58   #8
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Re: Making a DIY 12 volt compressor fridge copper tube size?

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Originally Posted by hatyaiair View Post
I sent a better picture of the connections on the evaporator and yes there is a few inches of a the tiny coiled tube but my understanding is that a capillary tube is somewhere between 4 and 9 feet long in a coil, not just a few inches long. But you are saying to just connect a 1/4" copper tube from the end of the dryer to the connection at the evaporator? I have attached a closer image of the dryer as well and the end of that is very tiny (about the size of a cap tube).
Right after that wound section the tube goes inside the suction line and exits somewhere at the beginning of the evaporator coil.
The length of tube is predicated upon the size of the compressor, (its rating in tons or Hp,) and the inside dia. of the tube.
Yes, that strainer you're holding is designed for you to solder on your own cap-tube.
Yes, I could have read it wrong, it which case you would have to get a cap-tube.
But, you should contact the outfit that furnished the evaporator and find out the real info about it, like does it "really" have a cap-tube and if so what rating of compressor is it designed to work with.
And if not, what do they recommend for length/dia. of tube.
Be aware that the connection on that "wound" section of tube is sized for a tube that is far bigger than any cap-tube you would use.
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Old 28-02-2024, 18:09   #9
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Re: Making a DIY 12 volt compressor fridge copper tube size?

Seems really short for a cap tube. I'm thinking around 40" is more normal. Seems pretty large diameter.

See if you can find a pdf online by RParts. They sold a kit system about 12 years ago for awhile.
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Old 28-02-2024, 19:11   #10
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Re: Making a DIY 12 volt compressor fridge copper tube size?

Google "secop-capillary-selection-software.zip" without the quotes, and you should be able to download what was the Danfos program.

I think, as it's a while since I last used it.
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Old 28-02-2024, 21:55   #11
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Re: Making a DIY 12 volt compressor fridge copper tube size?

Thank you RaymondR for the link, was able to install the app the only issue is I really do not know what to enter for A (Heat Load of the System),B (Evaporating Temperature, C (Condensing Temperature) D. Return Gas Temperature. I only know that I am using R134a for the gas. Is there a general rule of thumb for these numbers? I am making a fridge but inside the evaporator it can freeze.
I greatly appreciate everyone's patience with me!
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Old 29-02-2024, 00:14   #12
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Re: Making a DIY 12 volt compressor fridge copper tube size?

Quote:
Originally Posted by Boatguy30 View Post
Seems really short for a cap tube. I'm thinking around 40" is more normal. Seems pretty large diameter.

See if you can find a pdf online by RParts. They sold a kit system about 12 years ago for awhile.
To further cool the liquid refrigerant before it goes into the evaporator they sometimes run the capillary tube inside the return tube from the evaporator to the compressor. The short piece of 1/4" tube soldered to the capillary tube would allow a flare fitting to be installed if one wished to use a readily replacable filter/drier.
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