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Calculating heat dissipation requirements for high pressure compressor... ?

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jmelson:
This is just insane!  The amount of energy required to compress air to 3000+ PSI is huge.  The only reason people do this is to carry large amounts of air in small packages, ie. SCUBA tanks and Scott air packs.  Compressing air to
3000 PSI and then regulating down to 80 PSI is an enormous waste of energy.  I'm not an expert in thermodynamics, but it seems like you compress 200:1 and then expand 32 X to get back to 80 PSI Gauge (95 absolute).  So, you recover
32 / 200 = 16% of the energy you spent compressing it.  This is skipping over the adiabatic effects, which are going to be huge, so it actually is much worse than these numbers.

Also, regulators can stick, leak or get debris holding the orifice open.  This will cause an explosion in your low pressure system!

Jon

jmelson:

--- Quote from: pipe2null on May 19, 2020, 11:22:06 pm ---  If you know of a cheap option for 240V->120V with decent amps I would be very grateful.

--- End quote ---
This one is easy.  Go to a scrap yard and ask for "step down transformers".  These are used on all sorts of industrial equipment, and usually have internal straps or connections for combinations of 480:240 and or 240:120 conversion.
They are usually scrapped for the copper, so they will sell them for about the copper value, by the pound.

Jon

pipe2null:
@jmelson:
If the incredibly electrically inefficient "Use HPA for everything" approach works out, it will save a significant amount of space in my cramped apartment.  It's trading one efficiency for another.  But I fully agree with you, the idea is at least a bit nutty.  To the best of my knowledge, no one has ever accused me of being 100% sane...   :D  But jokes aside, I take the safety factor seriously.

--- Quote from: jmelson on May 20, 2020, 01:49:47 am ---Also, regulators can stick, leak or get debris holding the orifice open.  This will cause an explosion in your low pressure system!

--- End quote ---
Excellent feedback, thank you!  Would this be the correct/safe way to do it (all pipe/hose/fittings prior to the LP hose connection point all rated for max pressure):
HP shutoff valve->HP to LP step down pressure regulator to 120-200ish psi-> LP over pressure relief valve -> HP-rated shutoff -> LP pressure regulator for LP adjustment (40psi vs 90psi tools) -> connection point for LP shop hose. 

I'm not sure if I'll need a small LP holding tank or not.  The only reason for needing one that I can think of is to help keep the HP/LP step down from freezing by reducing short term spikes in LP air flow demand.  If I end up needing one, I can make it from schedule 40 or 80 PVC pipe, with dimensions I can stash in the corner behind the closet door, literally.
Thanks for the junk yard tip, I didn't know they had those types of things.  The transformers I looked at were bran new on digikey, and very much not at all cheap to get normal household current capacity.

@NiHaoMike:
That booster is pretty cool, a bit more space than I have though.  And I am very very curious about the Prius inverter, maybe not as a 120V solution, but as a multi channel multi phase AC power supply for my lab.  Could it take un/rectified 240VAC direct?  How bad is the THD?  Where can I get tech and/or hacking info?  Hehe...  I think I need to attend a TEA meeting.  But seriously, more info please!

My issue with electrical power in my apartment is that decades ago they wired half the lights and outlets in the unit to a single 15A 120V circuit.  Nearly all the other circuits in the breaker box are dedicated to specific things, like dishwasher, kitchen outlets, water heater, etc.  My second bedroom/lab/workshop is not exactly wired to be a lab/workshop.  Even if it can handle my addition of an air compressor, I keep adding equipment and it won't be long before I'm tripping the breaker on a regular basis.  The property owner of my rental unit doesn't care about the improvements I make as long as they are up to building code and legally speaking do not require a building inspector visit.  So, I cannot modify the breaker box, but i can put an outlet on the existing unused 20A 240V circuit in my lab.  Good tip on the "flip the 110V->220V" switch on power supplies...  That didn't even occur to me.
What I consider a "cheap" solution for 120V:  The price difference between the 120V and 220V HPA compressors I've been looking at is around $150 for the same thing at different voltages, the 220V costs more.  So, a solution that let's me (optionally) stick with 120V equipment purchases that are easier to resell later is worth at least $150ish.

@coppertone2:
I would not use it to fill a scuba tank I intended to use for breathing without a minimum of 2 stages of filtering the output.  I am not a health nut, I just don't like the taste of oil.  Heh.  Supposedly the Yong Heng brand is the better of the cheapo HPA compressors.  Back in the day I got my tanks filled at a scuba shop that used cheap chinese "brand" compressors to save a few thousand dollars, I think it was Yong Heng or Tuxing, but I don't remember exactly.  Anyway, they used 3 or 4 filtering stages between the compressor and the holding tank and their air was always good.  So, the cheap compressor by itself probably not clean enough for your purposes without a few add-ons.  Did you happen to come across any in-line pressure regulators that can drop 4500psi to 200ish psi when you were looking into HPA before?

coppercone2:
there are tons of regulators that go from high pressure to medium pressure, you might be used to seeing O2 and acetylene regs, but they easily have 0-300-500 PSI stuff for nitrogen and other gasses used in medium quantities, commonly used for chemical analysis systems

my hydrogen tank output regulator was up to 300PSI iirc (way too high). Like it would be used for supplying forming gas to a huge kiln or something I think.

you might also want to consider a restrictor to increase safety, that is just a resistive dropper. (choke the flow by orifice restriction, its a precisely drilled hole) Beware of things like the supply pressure effect when dealing with high pressure and regulators (research this). It's almost like inductive kick if you think about it when dealing with certain regulators.

Keep in mind compressed gasses can be way more dangerous then hydraulics because they are compressible even if they run at the same pressures. The entire system pneumatics should be armored too, don't model after a SCBA pack because its designed for humans to do really crazy stuff in (its like at the limits of design of utility for firefighters dealing with insane situations).

You need alot of steel plate IMO

tautech:

--- Quote from: pipe2null on May 18, 2020, 02:08:07 am ---I have occasional use for high ~3000psi pressure,

--- End quote ---
Do tell what for ?  :-//  :scared:

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