on video I turn Fridge Compressor into a Air Compressor

 A few months ago I purchased a rig for surface mount (paste) type soldering which required a source of > 100 PSI compressed air. This left me in a difficult situation as I live in an apartment building, and compressors which provide this kind of output are almost all too noisy, far too obnoxious for my living situation.

A bit of googling around reveals an apparently simple solution of replacing the standard compressor of an air compressor unit with a fridge compressor. Perfect.

Having constructed one now, I can say from experience that in theory it's a simple idea, but to make something that's going to be safe, robust and will last lands a few more considerations and snags along the way.

General approach
In my example I've used a cheap ready made compressor from a DIY store and discarded the compressor unit it came with. This is a good approach because it's got everything you need, you just need to fit the actual compressor.

Many other guides on the internet start from a bare tank. If you want to go through the entire process i.e. sourcing gauges, check valve, safety valve, pressure cut-off, regulator, and mounting, wiring and plumbing it all then by all means do so, however I'd warn you that you are to unlikely save any money unless you happen to have all that stuff sitting around ready to go, but if you do have all of what I've mentioned, it's likely that you've just disassembled a full compressor anyway.

Compressor unit selection
The main thing we're looking at is displacement – effectively the throughput of the compressor, so, go big.

Displacements of these encased type compressors range from a 2cm² to 43cm². In my case I went straight for the one of largest, the SC21F; with a displacement of 20.95cm² it tips the scales at 14KG, and is about the largest practical encased type compressor usable for this application.

SC21F is also a good match for the 6L tank I have, filling it to 120 PSI in an acceptable 59 seconds. Sadly the whole lot weighs 23KG making the rig difficult to move around. This type of compressor is more likely to be found in a larger application like a supermarket freezer or an air conditioning unit.

Of course you can go bigger. Danfoss also make the GS34(MFX), with a displacement of 34cm² – weighing back breaking 21KG, assuming you also would have a larger tank to compliment it, the final setup would be an unwieldy, un-movable monster.

Beyond this we're getting into large, noisy, belt driven beasts, rendering the entire exercise increasingly pointless. If you need really big displacement, just put multiple smaller compressors on the rig.

Preparing the compressor
If like me, you bought one from a professional fridge recycling outfit, the compressor may come with all of its ports welded shut. This is done to prevent contamination and oil-spillage during storage and transport.

Due to the ugly, short, welded-shut, messy shape of the pipes on my unit, I had to hacksaw the ends of the pipes off, which inevitably resulted in metal filings falling into the compressor. This is very difficult to avoid.

Unless you have nice clean pipes and can use a pipe cutter, you'll end up getting metal filings inside it (cutting upside-down is not an option!) – once cut you'll then need to turn it upside-down and drain all of its oil, straining out any metal filings and other crud in the process. I used kitchen towel as a filter. Once done – re-fill with oil (see below).

No comments