What air compressor CFM and reservoir size needed to run a 50 amp plasma cutter

[curmudgeon]

Jim, earlier you reported that you are limited to 50 amps for the compressor, plasma cutter, lighting, etc. Compressors typically draw much more power during start up than while operating. Will you have sufficient capacity to run your plasma cutter and compressor concurrently?

That PA 120V compressor has a 12.2 amp rating, but also claims a 2.5 max HP rating - at 746 watts/HP, the math doesn't work. You also indicated that you were concerned about the compressor being able to keep up with long or repeated cuts. That PA compressor has a duty cycle of 50% which, as I understand it, means maximum 5 minutes on followed by a minimum of 5 minutes off.

Given the power supply limitations you've shared and the usage you plan, you should consider a 240V compressor to split the current draw over both legs, and look for a compressor motor with a higher duty cycle.

Installing an additional 240V receptacle and the trouble to find a friend to help with pickup/delivery are one-time events that could lead to years of problem free usage. I would be concerned that the start up current draw of that 120V unit while you're using the plasma cutter will trip your 50 amp breaker in the main panel.

g'luck

 

[JimGnitecki]

Jim, earlier you reported that you are limited to 50 amps for the compressor, plasma cutter, lighting, etc. Compressors typically draw much more power during start up than while operating. Will you have sufficient capacity to run your plasma cutter and compressor concurrently?

That PA 120V compressor has a 12.2 amp rating, but also claims a 2.5 max HP rating - at 746 watts/HP, the math doesn't work. You also indicated that you were concerned about the compressor being able to keep up with long or repeated cuts. That PA compressor has a duty cycle of 50% which, as I understand it, means maximum 5 minutes on followed by a minimum of 5 minutes off.

Given the power supply limitations you've shared and the usage you plan, you should consider a 240V compressor to split the current draw over both legs, and look for a compressor motor with a higher duty cycle.

Installing an additional 240V receptacle and the trouble to find a friend to help with pickup/delivery are one-time events that could lead to years of problem free usage. I would be concerned that the start up current draw of that 120V unit while you're using the plasma cutter will trip your 50 amp breaker in the main panel.

g'luck

Good points! Here are some of my responsive thoughts:

The 2.5 max hp claim is marketing hype. When you open up the online pdf of the manual on the Princess Auto webpage, you see that the current requirements is only 12.2 amps. Startup would of course bump that up closer to the 20 amps available in a 20 amp circuit, but since the compressor is sold to run on a 120 volt circuit, I assume it won't be popping a 20 amp breaker. The "2.5 max hp" in the advertising probably simply reflects the 2.5 hp x 745 watts/hp = 1862 watt startup current draw in fact. That 1862 is in fact about the max wattage that a 15, not 20 amp circuit will support.

Since my thickest and hardest cut with a plasma cutter is going to require only 30 amps, and my electrical available is 50 amps, the plasma and the compressor should be able to run simultaneously, especially if time delay breakers are used.

The 50% duty cycle doesn't bother me as usually that means "5 minutes work within every 10 minutes", and no long cut of mine will require more than 5 minutes. Even at a super slow cutting rate of 5 inches/minute, that's a 25 inch cut, and a 25 inch cut required to be done without a stop is as large or larger than I can foresee in what I do and want to do. I understand that plasma cutting should be done at 20 inches/minute - the 5 inches/minute is encountered when using a low powered plasma for a very thick material and settling for a "sever" versus "clean" cut.

As for the cost of another 240 volt outlet, I do have TWO 240 volt outlets available, one is a 50 amp and the other is a 20 amp. So, I COULD use a 240 volt compressor, BUT most of those (maybe all?) are oiled versus oilless, and I don't want to introduce oil into a system that is feeding a plasma cutter, because that necessitates an oil removal device in the line AND introduces more pressure drop.

Hmm. Adding an "inexpensive and simple" plasma cutter to my shop is looking more and more complicated and costly than most people, including all the plasma cutter Youtubers out there, have led me to believe! The plasma cutters are now cheap, but the infrastructure required to feed them seems to be NOT cheap.

Jim G

 

[phaxtris]

https://www.princessauto.com/en/20-gallon-portable-air-compressor/product/PA0008430043

thats a better option jim, it may have slightly less cfm, but the cast iron cylinder, oiled compressor head will outlive that oil-less by many many years, and make less noise while doing it

the first compressor i used for a plasma cutter was similar to the one you posted, it worked ok, loud (as most oilless compressors are), and wore out he pump in maybe 2 years of hobby level use, and that is not the only oil less compressor i have worn out, the worst part when they wear out you often cannot fix it, its new compressor time

 

[JimGnitecki]

https://www.princessauto.com/en/20-gallon-portable-air-compressor/product/PA0008430043

thats a better option jim, it may have slightly less cfm, but the cast iron cylinder, oiled compressor head will outlive that oil-less by many many years, and make less noise while doing it

the first compressor i used for a plasma cutter was similar to the one you posted, it worked ok, loud (as most oilless compressors are), and wore out he pump in maybe 2 years of hobby level use, and that is not the only oil less compressor i have worn out, the worst part when they wear out you often cannot fix it, its new compressor time

That compressor does offer some nice features:
- Cast iron, like you said
- Oiled versus oilless longevity
- Sanborn is a longterm brand name
- 75% duty cycle
- Runs on 120V 15 amp circuit breaker circuit OR consumes 7.5 amps at 240 volts, so could run on my 20 amp 240 radial arm saw circuit, for a total load (compressor + plasma cutter) of maybe 37.5 amps. Could even cut metal at 40 amps)
- Slightly lower cost

Also some negatives:
- Requires an electrician to convert from the as-shipped 120v to 240v operation (per user manual)
- Very heavy: 186 lb, which would be a hard unload from my pickup truck even with a strong friend helping (90 lb each man, and I am 72 yrs old!)
- CFM at 40 psi is still only 6.3 CFM, so not much margin, especially at my 3000 ft elevation
- Horizontal versus vertical tank, so the compressor consumes over 50% more floor space than a vertical tank
- Not rated as "quiet" - 78 db is not bad for a compressor, but still pretty loud compared to a "quiet" one

Also, would an oiled compressor potentially feed a bit of oil into the air, and thus necessitate an oil remover somewhere before the plasma cutter, since oil is a no-no in the air to a plasma cutter?

Lots to think about . . .

Jim G

 

[phaxtris]

here are some points for you that might help with your imposed negatives;

switching from 120 to 220 can be easily done without an electrician, the manual states an electrician for liability reasons.....that's a moot point anyhow, the procedure is similar for every dual voltage compressor

you only have to unload it once, pay some local teenagers or stronger adults to unload it if your not confident, couple beers or a pizza goes a long way for 5 minutes of their time...if you even have to pay them.....or make a ramp from a couple 2x6's

i know a few guys with similar style compressors, they easily fit, and often live under a bench, they are not as large as it appears and the horizontal package can be easier to hide

im not sure how the 78db of that one is measured vs the 58db @ 25ft of the oil less, but i can tell you i have never heard a "quiet" oilless compressor, i may be the pitch, but they always seem much louder than a belt driven oiled compressor, i would take those noise levels with a big grain of salt as manufactures like to manipulate how the sound levels are measured to suit their marketing goals

you should have a filter before your plasma cutter in either case, the oiled crank case is not a problem, the majority of plasma cutters fed by a piston compressor use an oiled compressor, oilless compressors are really a consumer level fill up your tires, run an impact once in a blue moon kind of thing, they are not built for heavy use like it would see with a plasma cutter and you will wear it out in short order

i doubt the oilless compressor puts out the air that it advertises, just like they have those goofy 2hp 10amp 120v motors that are the size of a soda can

 

[JimGnitecki]

here are some points for you that might help with your imposed negatives;

switching from 120 to 220 can be easily done without an electrician, the manual states an electrician for liability reasons.....that's a moot point anyhow, the procedure is similar for every dual voltage compressor

you only have to unload it once, pay some local teenagers or stronger adults to unload it if your not confident, couple beers or a pizza goes a long way for 5 minutes of their time...if you even have to pay them.....or make a ramp from a couple 2x6's

i know a few guys with similar style compressors, they easily fit, and often live under a bench, they are not as large as it appears and the horizontal package can be easier to hide

im not sure how the 78db of that one is measured vs the 58db @ 25ft of the oil less, but i can tell you i have never heard a "quiet" oilless compressor, i may be the pitch, but they always seem much louder than a belt driven oiled compressor, i would take those noise levels with a big grain of salt as manufactures like to manipulate how the sound levels are measured to suit their marketing goals

you should have a filter before your plasma cutter in either case, the oiled crank case is not a problem, the majority of plasma cutters fed by a piston compressor use an oiled compressor, oilless compressors are really a consumer level fill up your tires, run an impact once in a blue moon kind of thing, they are not built for heavy use like it would see with a plasma cutter and you will wear it out in short order

i doubt the oilless compressor puts out the air that it advertises, just like they have those goofy 2hp 10amp 120v motors that are the size of a soda can

Thank-you, phaxtris! So, it sounds like:

- I can find an online article, or even maybe a Youtube video on how to change from 120 volt to 240 volt, which eliminates the extra cost of an electrician

- The ramp idea for unloading sounds doable. I might even be able to rent a small portable scissor lift from a rental place for a couple of hours

Hmm. Sounding better.

Jim G

 

[phaxtris]

https://www.princessauto.com/en/600-lb-6-ft-foldable-utility-steel-ramp-hardware/product/PA0008667776

and you could probably use that in the future to help unload things

its even easier than looking up a you tube video, when you take that little plate off i have circled, there is a small diagram for "low voltage" and "high voltage", its as easily as moving a few spade connectors that are under that plate and changing the plug to the appropriate 240v plug, its most likely described in the manual as well



some options for you anyways

 

[Chicken lights]

I’m a fan of the vertical style, they tuck in a corner nicely. Don’t ask me the CFM or duty cycle, there’s no tags anywhere. I want to say I paid $700 or so, 12 years ago? The price per yer ownership is quite reasonable. Even if I have to replace the compressor, there’s no reason not to get another 10 years from the tank and motor. Other than the odd oil change there’s no maintenance costs

If I’m doing a lot of grinding or an air chisel, I will stop and let the compressor catch up. But in my experience unless it’s a full on commercial shop with multiple guys needing a fully commercial compressor, most “home” shop compressors can’t keep up to heavy usage

 

[JimGnitecki]

https://www.princessauto.com/en/600-lb-6-ft-foldable-utility-steel-ramp-hardware/product/PA0008667776

and you could probably use that in the future to help unload things

its even easier than looking up a you tube video, when you take that little plate off i have circled, there is a small diagram for "low voltage" and "high voltage", its as easily as moving a few spade connectors that are under that plate and changing the plug to the appropriate 240v plug, its most likely described in the manual as well

View attachment 30597

some options for you anyways

Sounds good!

Jim G

 

[Tom O]

I started out with the smaller compressor but later changed to the bigger upright for the air tools and have never looked back besides they basically take up the same space.

 

[phaxtris]

those 60g uprights used to be like 600-700, but man have compressors taken quite the hit with inflation! the one like @Chicken lights has is 1100$ now!

it seems like the 600-700 range is where @JimGnitecki is with his budget, and sounds to have space constraints, i think that one for 600$ is probably the best offering given that budget, i know they fit well under a bench

i have had the upright 20g ones, they do fit well in a corner, but unless you build shelves over top they kind of waste more space than a 20g horizontal hidden under a bench, defiantly when you get bigger, 40+g upright makes the most sense, i have an 80g upright, if it were a laydown i dont know where i would put the tank, outside maybe ? ive seen 80g and 100g laydowns, now that is a waste of space....unless your suspending it from the roof or something

 

[CWret]

Background: 25 years ago - more or less - i owned a rock drilling business and that included some large diesel compressors (750cfm @ 300 psi to 1300cfm @ 150 psi & 325 to 435Hp). These machines were oil flooded rotary screws with an oil separator / receiver tank.

Fast forward & retired - my hobby shop has a 1.5 Hp and a ultra quiet 1.0 Hp compressor (both oil less). A bit smaller but still compressors just the same.
I put them in tandem to feed the plasma cutter. I’m not concerned about a bit of oil because i have a good oil/water separator just before the cutter. I frequently give them a shot of chain oil lub to their air intake while they are running. My thinking is that it can’t hurt and will likely prolong their life (aside comment- i raced 2stroke dirt bikes using exotic injections oils). I wouldn’t recommend using WD40 or diesel fuel due to their much lower flash points (WD40 flash point 40C vs chain oil or motor oil flash point is over 200C). I’ve been doing this for awhile and had no issues. The Motor Guard air filter (great product & strongly recommend) i use has not needed a filter change after hours of plasma cutting.

 

[PeterT]

im not sure how the 78db of that one is measured vs the 58db @ 25ft of the oil less, but i can tell you i have never heard a "quiet" oilless compressor,

I suspect not all oiless are created equal these days. Not sure if they use different valves or some other noise abatement. I had a Dewalt upright, loved the power & small footprint. But noise drove me mental. I cant recall the advertised number but it was in the 80's. I remember some forums said 90% of the racket was in the diaphragm or flapper valve mechanism (might have the name wrong). I heard they are better now but its a good point, dB level is top of the shopping list IMO. I have a smaller California Air unit, I think it was listed at 55 dB. Totally tolerable.

5 Best Quiet Air Compressors in 2023

This post contains affiliate links and I may earn a small commission if you purchase through these links. An air compressor is a pneumatic device that generates pressure in compressible fluids or gasses. This device can operate pneumatic tools, like nail guns and paint sprayers and can even...

www.911metallurgist.com

 

[phaxtris]

I always thought a lot of the noise with oilless had to do with the higher operating rpms

Why i say take the db rating with a grain of salt, one mfg checks db at 10ft, the next uses 25ft to make it seem quieter, and another might even measure it as say 30ft or more, they may not be lying, but it's misleading, and of course it takes no account of the frequency of the majority of the noise

 

[JimGnitecki]

those 60g uprights used to be like 600-700, but man have compressors taken quite the hit with inflation! the one like @Chicken lights has is 1100$ now!

it seems like the 600-700 range is where @JimGnitecki is with his budget, and sounds to have space constraints, i think that one for 600$ is probably the best offering given that budget, i know they fit well under a bench

i have had the upright 20g ones, they do fit well in a corner, but unless you build shelves over top they kind of waste more space than a 20g horizontal hidden under a bench, defiantly when you get bigger, 40+g upright makes the most sense, i have an 80g upright, if it were a laydown i dont know where i would put the tank, outside maybe ? ive seen 80g and 100g laydowns, now that is a waste of space....unless your suspending it from the roof or something

My benchtops all have shelving underneath them, and in one 10 foot bench, ON TOP of them as well! No "under bench" room, available, which is why the uprights look better to me than the horizontal tank compressors!

But that $600 horizontal one at Princess Auto has a lot of other pluses going for it, and as you point out, compressor prices have skyrocketed way more than retirement benefits have! And i am not seeing any decent used ones - just ones that the owners have discovered the shortfalls of and are trying to unload.

Jim G

 

[JimGnitecki]

I suspect not all oiless are created equal these days. Not sure if they use different valves or some other noise abatement. I had a Dewalt upright, loved the power & small footprint. But noise drove me mental. I cant recall the advertised number but it was in the 80's. I remember some forums said 90% of the racket was in the diaphragm or flapper valve mechanism (might have the name wrong). I heard they are better now but its a good point, dB level is top of the shopping list IMO. I have a smaller California Air unit, I think it was listed at 55 dB. Totally tolerable.

5 Best Quiet Air Compressors in 2023

This post contains affiliate links and I may earn a small commission if you purchase through these links. An air compressor is a pneumatic device that generates pressure in compressible fluids or gasses. This device can operate pneumatic tools, like nail guns and paint sprayers and can even...

www.911metallurgist.com

Yeah, the noise level is important to me, but unless I can spend a lot more money than I want to, and can really afford to on what is a hobby, not a job, it does not look like i can get a compressor that has the output, the longer life, AND the low noise level ALL in one package. The compressors shown in the linked review are all pretty small.

Jim G

 

[JimGnitecki]

I always thought a lot of the noise with oilless had to do with the higher operating rpms

Why i say take the db rating with a grain of salt, one mfg checks db at 10ft, the next uses 25ft to make it seem quieter, and another might even measure it as say 30ft or more, they may not be lying, but it's misleading, and of course it takes no account of the frequency of the majority of the noise

In addition to what you noted, the size of the shop that a compressor is located within makes a bIG difference to how bothersome and tiring its noise level is. My entire shop is a rear detached garage of under 400 sq ft. My small pancake compressor sounds like a war zone within it.

I had been doing all woodworking until recently, and after about 60 years of it (including about 7 working with my professional woodworker dad, I've never liked the sound level of a radial arm saw, circular saw, or planer (nor the clouds of sawdust even with dust collection). When I started learning TIG welding recently, I was amazed at the quietness of the process, and am equally amazed at the quietness of plasma cutting - except for the air compressor.

A quiet air compressor would be wonderful, but if I want one that also has the output, durability, etc, it gets too expensive. It's too bad because I find plasma cutting rather relaxing otherwise. It's like cutting with a paintbrush or pen.

Jim G

 

[phaxtris]

In addition to what you noted, the size of the shop that a compressor is located within makes a bIG difference to how bothersome and tiring its noise level is

Yea thats a good point, im sure when they do those noise test they are in a sound dampened room with no hard walls for the sound to bounce back, that makes a big difference

 

[PeterT]

Before you build a noise reducing enclosure, this video kind of sums up what I read at the time.

 

[slow-poke]

FWIW, for those looking for more capacity. A friend used an old hot water tank for extra capacity, installed it up in the attic of his garage. Rated for 100psi so might need to tweak the regulator.