How to make a small compressed air generator?

Last week I bought a silent air compressor for some planned air brushing of 3D printed objects and for cleaning the dust off my tools after using them. The "silent" just means it claims to produce only 59 dB while it's on though....so it's still making quite some noise but not so much you need ear protection

I was just wondering if it would be possible to build a small DIY proof-of-concept type of thing to use the compressed air to power a little generator. Efficiency is not really the point yet...just want to see if it works and is worth looking into. To me it would be similar to either a wind or water turbine from the electrical side...and connecting that into a victron system is a challenge to say the least. But I know at least for hydro generators some people use an MPPT to convert the voltage and charge their batteries.

It might be a stupid idea...or not. But since there is so much power in compressed air from what I have learned over the last week...it seems like a waste to just blow it out when draining the tank to let the water out. Even with my small 5L tank....and my portable 14L tank that just came in today.

Just curious what people here think about something like this.

Power in rarely equals power out. It is like buying nickles at a dime a piece. It only make sense if you get the dimes for a good price.

Mattb4 said:

Power in rarely equals power out. It is like buying nickles at a dime a piece. It only make sense if you get the dimes for a good price.

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I get that it takes way more power to compress the air. What I am talking about is when I have a "full" tank and need to drain it to let the water out....I am wasting all that energy that went into it anyway. This was a possibly stupid idea to get some of it back....as a proof-of-concept.

I timed the airflow at a low setting (20 psi) from full to empty using the airbrush and it took almost 5 minutes for both the 5L and 14L tank to drain all the way.That's a potential 5 minutes of running a small generator....maybe.

I know it's not efficient and it will be more of a gimmick than actually useful. I am just curious if it can be done and made useful somehow.

Any form of stored energy can be used. So yes you could use your tanks stored air to power something for a very short time. The best use you can effectively make of compressed air is in a tool designed to use compressed air. When you run your compressor and it takes 500wh to fill up it has stored that energy. Getting it back out is where loss occurs.

Several years back I saw where someone had made a car that ran on compressed air. Pretty nifty but not practical.

You can't get more energy out than what is put in..right...I remember that from somewhere! hahaha. I measured the compressor filling both tanks from empty to as full as it gets them. While running it's using about 500-600 watts at 230V and it took about 2 minutes and 22 seconds to fill both the 5L+14L tanks. I notice a pressure difference in the second tank but I think the connecting hose diameter might be to small.

My watt meter on the power cord shows 0.022 kWh of power is used. So that's just 22Wh of potential energy right? Not considering any losses for now...but I know they are there. If I can get about 10Wh of power from just "bleeding" the tanks by running the air through a small generator I don't think that is an unreasonable expectation.

It's not a lot...but these are really small tanks I have got now. Considering my ambient LED lighting seems to be using less than a single watt....I could potentially run it for 8-10 hours on just the stored compressed air. Or give my phone a 25% extra charge. Just a few things it can be used for

If that actually tuns out to work I might even get a bigger air tank...just for fun

Well just wildhat guessing; an air turbine could potentially mechanically recover nearly a third of the energy used to compress it, less conversion efficiency so maybe a . I don’t think I’d bother.

Here you go, build it and let us know. I couldn't find a commercial adapter to just hook up to your hoses.

Compressed air to electricity

Hmmm.
For one thing, you'd need a big compressor to achieve any kind of useful pressure. Like a scuba-diving one - 300 bar.
For another, dealing with the discharge cooling, and associated condensation, can be a bit of a bother.
Note that compressed-air vehicle engines were scrapped mainly for ice-formation problems.

Compressed air cylinders are mainly used by scuba divers and firefighters. In neither case is temperature drop/condensation a problem.
On a boat that had a scuba compressor, I charged a spare bottle to power tools when I didn't want to turn the generator on :·)
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12VoltInstalls said:

Well just wildhat guessing; an air turbine could potentially mechanically recover nearly a third of the energy used to compress it, less conversion efficiency so maybe a . I don’t think I’d bother.

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If it would be 75% efficient than I would be really happy....like I said this is just a little experimental project that popped into my head.

cs1234 said:

Here you go, build it and let us know. I couldn't find a commercial adapter to just hook up to your hoses.

Compressed air to electricity

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Thanks, I think I read it before...and might actually be why the idea got stuck in my head! hahahaa

I have seen a bunch of youtube video's already about this subject....just like I did when starting with solar actually. In one there was some kind of Amish shop I think it was where they had a big wind turbine that filled three big air tanks. And I mean REALLY BIG!! They also had big sealing fans in there powered directly from the compressed air! But also their workshop tools...forgot what it was but I think wood work and sewing machines.

Don B. Cilly said:

Hmmm.
For one thing, you'd need a big compressor to achieve any kind of useful pressure. Like a scuba-diving one - 300 bar.
For another, dealing with the discharge cooling, and associated condensation, can be a bit of a bother.
Note that compressed-air vehicle engines were scrapped mainly for ice-formation problems.

Compressed air cylinders are mainly used by scuba divers and firefighters. In neither case is temperature drop/condensation a problem.
On a boat that had a scuba compressor, I charged a spare bottle to power tools when I didn't want to turn the generator on :·)
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A big compressor is something I don't have the space for....the one I got is almost a little to big already! But I can just store it somewhere else when I don't need it....at least that was how I planned it.
But I did see a video of some guy that filed his scuba tank somewhere for $7 (not sure which dollar anymore) and then he could refill a paintball tank a couple of times at home. Then with a number of pressure valves/converters he lowered it from an insanely high PSI down to a more standard 100-ish psi to use with a nailgun. That makes a VERY portable setup...much nicer than my 14L tank that is also supposed to be portable.




I mean....you can carry it by the handle and it's with it's 9kg it's lighter than the compressor that weighs 17kg.



Either way, I think it all comes down to getting a really efficient low RPM high watt's wind turbine and then rebuild it somehow to work from compressed air. I have a 3D printer so I could try a few turbine and blade configurations that work better for this. So that is what I am going to look for I guess...a DC motor to build the compressed air generator. Another requirement for me personally is that it should not be making a lot of noise. That's one of the reasons I got that extra tank so the compressor does not need to run as often.

I'll also try to find those video's I mentioned again and link them here for those who are interested.

Thanks for the feedback and comments so far.

Just on a side note, here is a video I saw a few months ago showing an Amish homestead where they have both a pneumatic wind generator and a diesel compressor (for redundancy) to fill tanks, and run all sorts of pneumatic loads like tools and ceiling fans inside a workshop.

I didn't realize they use so many modern technologies. They are just like you guys on the forum, not wanting to use the public electric grid.. only they also abstain from forums like this one. Which is honestly probably for the best when one considers how much time can be wasted here.

Archerite said:

That's one of the reasons I got that extra tank so the compressor does not need to run as often.

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I think you’d be better off spending there.

I bought a dead 80-gal compressor for $50 just for that reason. Lots of storage so two things benefited me: use of tools a long time without electricity; air storage for the 120V harbor freight compressor so I could spray paint or use an impact without running into the slow recovery because the 240V ain’t portable; and in use 80-gallon of compressed air is not three times 26 gallons of compressed air, it’s way, way more usable CF in use. I can drain the 26gal very fast with an hvlp gun.
Well that was three but you get the point.

The wee bit of charge you’ll get is equivalent to not lighting the lamp at camp for three nights a week to save matches ?

I’m thinking you could buy a few panels for the air turbine setup costs and get more power the first day than a year of tank dewatering.

Samsonite801 said:

Just on a side note, here is a video I saw a few months ago showing an Amish homestead where they have both a pneumatic wind generator and a diesel compressor (for redundancy) to fill tanks, and run all sorts of pneumatic loads like tools and ceiling fans inside a workshop.

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Thanks! That's the exact video I was talking about. ?

cs1234 said:

I didn't realize they use so many modern technologies. They are just like you guys on the forum, not wanting to use the public electric grid.. only they also abstain from forums like this one. Which is honestly probably for the best when one considers how much time can be wasted here.

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It surprised me too that they had all those machines....but technically they still don't use any electricity for the work they do. Either way it's a really interesting and cool way to use alternative power. Especially those ceiling fans that run directly off the compressed air looked awesome!

Archerite said:

Thanks! That's the exact video I was talking about. ?


It surprised me too that they had all those machines....but technically they still don't use any electricity for the work they do. Either way it's a really interesting and cool way to use alternative power. Especially those ceiling fans that run directly off the compressed air looked awesome!

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Seems they use it for a bunch of stuff, they just use other methods as well.
Do Amish use electricity

12VoltInstalls said:

I think you’d be better off spending there.

I bought a dead 80-gal compressor for $50 just for that reason. Lots of storage so two things benefited me: use of tools a long time without electricity; air storage for the 120V harbor freight compressor so I could spray paint or use an impact without running into the slow recovery because the 240V ain’t portable; and in use 80-gallon of compressed air is not three times 26 gallons of compressed air, it’s way, way more usable CF in use. I can drain the 26gal very fast with an hvlp gun.
Well that was three but you get the point.

The wee bit of charge you’ll get is equivalent to not lighting the lamp at camp for three nights a week to save matches ?

I’m thinking you could buy a few panels for the air turbine setup costs and get more power the first day than a year of tank dewatering.

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Wow! 80 galons (almost 300L) that must be a beast of a compressor! hahaha. Nice deal on a broken one and then reusing it for extra air capacity. I was looking into a way to get an extra tank that cheap too...but the only one around here was that one I showed on amazon. It was like 90 euro's! But it does come with vales, gauges etc...?....I just consider the thing an oversized air battery I guess!

I am not exactly fluent in the compressed air units, but I try to compare it to electricity:
PSI/BAR = voltage
CFM = Amps?
Pressure valve = voltage converter
Compressor = charger
Air filter = capacitor?? sort of anyway...to clean nasty particles out the air.


Guess there is more to it but this is what I think makes the most sense to me.

300 bar compressors are common because of PCP air guns (I have one)

If one actually had a need for compressed air, and you had containers you could store it in that didn't rust out, and the space to store them, filling tanks with excess solar during the day would be useful.

All these ideas, while fun, really pound home how useful lifepo4 batteries are for their size/weight.

cs1234 said:

If one actually had a need for compressed air, and you had containers you could store it in that didn't rust out, and the space to store them, filling tanks with excess solar during the day would be useful.

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And if designed well, could build a compressed air system like dental oil-less air compressor style with air dryers right after the compressor heads, there shouldn't be any moisture accumulation, no water to drain from tanks, and no bad smell from the compressed air as it comes out.

Archerite said:

Pressure valve = voltage converter

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Voltage regulator…

Don B. Cilly said:

For another, dealing with the discharge cooling, and associated condensation, can be a bit of a bother.
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That is a solved problem.
Just use helium! ?

12VoltInstalls said:

Voltage regulator…

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Thanks! Off course that would be a but more accurate. The other things I got right then though...right?

cs1234 said:

If one actually had a need for compressed air, and you had containers you could store it in that didn't rust out, and the space to store them, filling tanks with excess solar during the day would be useful.

All these ideas, while fun, really pound home how useful lifepo4 batteries are for their size/weight.

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True. I would not have bought the compressor just for this experiment...but since I already have it now and see the possibilities I started to wonder. I have also read an article about CAES (Compressed Air Energy Storage) being actually used commercially somewhere in the US and Germany It think it was. (I'll link to it when I find the article again) But as said before efficiency is really low and it still relies on natural gas to heat the air before it get's to turbine. It's to get the water out of the air I believe.

For size, weight and capacity it's indeed not even a competition with lifepo4 batteries. But if you got the space for big huge air storage tanks...like you see in that video above...then it becomes a serious option to also use it for electricity. I am still learning about how air pressure works and all the measurement units involved so I am no expert by any means! It took me a few months to really get it for electricity when starting with solar...and I still consider myself a beginner in most cases. Maybe an advanced beginner though...

shot428 said:

300 bar compressors are common because of PCP air guns (I have one)

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That looks awesome and with such high pressure...if I get it right that is....in theory you have more air volume. right? And that stored in a much smaller container! Even with a few pressure regulators/converters to get it down to what pneumatic tools are designed for....it will still be much smaller than my current 14L portable air tank! Hahaha

Besides the high price tag of that compressor....it also makes a serious amount of noise it seems. Way more than my "regular" compressor I got now. But if the stored air volume is big enough that might not be a problem. Just fill it up during the day....and than use it in silence during the night! My biggest usage will be blowing dust of things and some air brushing....so that would be awesome to have a small tank like that.

For now though...the one I have is probably good enough. ?

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Small update on that is more on topic:
I really need to get a wind turbine / motor / generator that can give enough power at really low RPM's to keep the noise down a bit. The sound of airflow is not much of a problem....but when this generator makes more sound than the compressor itself...that would be too much right?
I am looking at getting a big 300W wind turbine generator from amazon...but it cost around 200 euro's. If it will work as I want it would be worth it...but I think I am going to experiment with some cheaper options first.

I have also seen that a stepper motor can be used as a generator, but it won't give many watts I believe. At least I could not find much info on it...most simple experiments only show voltage on a multimeter and some lights or LED's connected to it. That does not say anything without also knowing the maximum amps it can give at that voltage...and together how many watts it will generate. Guess the solar knowledge of electricity pay's off now, hahaha ?
Since I attempted to build a 3D printer from scratch a few years ago I have stepper motors in a box somewhere just laying around doing nothing! So can't hurt trying to see what kind of power they can generate! At first just hook up an electric drill or even a dremel like tool to get high RPM's to get the maximum power output capability! From what I have seen in the few youtube video's it should be about 8-12 volts per coil, but you can put them in series after rectifying the sort of AC output it generates. I am hoping to get anything between 18-24 volt's on the low rpm's I mentioned so a victron MPPT can lock on to it ( I know it's not built for it...but I have also seen people use them anyway for hydro installations)

Once I get to testing anything I'll post the results here. ?

This might not be the right place to ask...,but I'll try anyways (sorry if not allowed)

I drained my air tanks today to let the water out and that orange portable one...which is brand new and less than a week old...had some nasty rusty water comming out of it! Is this normal? Should I be worried? Should I return it?

At the very least I am going to ask the question on the amazon page for the seller to respond to. hopefully.

I do have high temperature and humidity at the moment (26-30 celsius at 50-60%)

The compressor itsef is also new and just two weeks old, but that water came out clear. Deffinatly going to put in filters between everything now!

Thanks in advance for any advice.

the inside of tanks are seldom coated

Hook up an impact gun to an alternator on a belt attached to a pulley.
Run wires from your alternator to a battery. Boom. There you have it.
Go to the junkyard now.
Old alternators on mk1-mk2 Volkswagens have an external voltage regulator. Brush type. Go get one of them Maybe. New brushes can be purchased and everything

Archerite said:

This might not be the right place to ask...,but I'll try anyways (sorry if not allowed)

I drained my air tanks today to let the water out and that orange portable one...which is brand new and less than a week old...had some nasty rusty water comming out of it! Is this normal? Should I be worried? Should I return it?

At the very least I am going to ask the question on the amazon page for the seller to respond to. hopefully.

I do have high temperature and humidity at the moment (26-30 celsius at 50-60%)

The compressor itsef is also new and just two weeks old, but that water came out clear. Deffinatly going to put in filters between everything now!

Thanks in advance for any advice.

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Pretty normal in tanks.
You do not want to use that air/water/rust
for airbrushing. You’ll ruin your gun.
Definitely put an in line filter and drain tank after uses like it sounds like you’re doing