Air Compressor Sizing for Plasma Cutter

[arrabil]

Howdy. I'm about to purchase a plasma cutter. I've never had an air compressor before and don't know much about them. The plasma cutter says it needs 6 scfm @ 90 psi.

How close in size does the air compressor need to be? Would 5.3@90 be good enough or am I asking for trouble? Do I need a safety margin like 7 scfm? Or should I be looking in the 11 scfm range for a large safety margin?

Thanks.

 

[NC4AB]

For a plasma cutter more is definitely better.

I bought a Hypertherm cutter and planned on using my 3.8 cfm Campbell-Hausfield (Lowes branded) air compressor with a 30 gallon tank. Long story short, I wound up having to bypass the built in pressure regulator and purchase some commercial grade 1/2" air hose before I could get enough flow to the plasma cutter to even get it to start, and then it would only give me about 20 seconds of cutting time before the pressure dropped.

I found a used 3 hp 220V commerical grade air compressor that made a world of difference - pretty much gives me 100% duty cycle.

 

[Transit]

The more volume the better, some compressors rate their volume/min based on the volume of the storage tank and not totally on the ability of the compressor. That is half the story, plasma cutters demand DRY air. As air is compressed it also is heated lowering the relative humidity, the ability to hold water vapor. The air in the tank is stored at a high pressure, higher than the regulated 90 psi delivered to the cutter. When the high pressure air is expanded and the pressure is dropped to 90psi it is also cooled increasing the RH, water vapor now becomes water droplets passing through the cutting head doing all kinds of bad things. The fix is to add a dryer in the air line to the cutter. What type of dryer depends on the $$$ you want to spend; they range from filter cartridges to air coolers. Take your pick.

 

[arrabil]

I'm getting a package deal from the neighbor with a dryer. He says it uses beads (or maybe it was pellets) and it cost him $400 when he got it seven years ago. He's retiring from blacksmithing and I'm buying some of his tools. He isn't selling the compressor unfortunately.

 

[two_bit_score]

Howdy. I'm about to purchase a plasma cutter. I've never had an air compressor before and don't know much about them. The plasma cutter says it needs 6 scfm @ 90 psi.

How close in size does the air compressor need to be? Would 5.3@90 be good enough or am I asking for trouble? Do I need a safety margin like 7 scfm? Or should I be looking in the 11 scfm range for a large safety margin?

Thanks.

Sounds like you are getting a good deal on the plasma cutter. I'd go ahead and spend the money to get a good compressor with plenty of air. More is always better when it comes to compressed air.

 

[arrabil]

The key for me is that an 11 scfm compressor is 275lbs and as big as I am. So if I can get away with something smaller I'd very much like to.

 

[two_bit_score]

The key for me is that an 11 scfm compressor is 275lbs and as big as I am. So if I can get away with something smaller I'd very much like to.

Well, once it gets set up and installed in the shop/wherever it will stay there won't it?

 

[arrabil]

My "shop" is only so big......

And I only have one more double receptacle left in the electric panel but if I get a big compressor I'll have two more 240V tools to plug in.

 

[jimcolt]

Sizing a compressor for a plasma cutter depends on a couple of things:

1. The minimum flow/pressure requirements of the plasma cutter you intend to use. The manufacturer can provide the specs....and they can vary from model to model. A small Hypertherm Powermax30 will use about 4.5 cfm (cubic feet per minute) at 90 psi inlet pressure. A Hypertherm Powermax45 uses 6 cfm at 90 psi. If you have a small compressor with exactly the same cfm rating as the plasma.....then the compressor will run continuously when you are plasma cutting....the size of the air compresor tank will allow the plasma to run for a few seconds (or minutes if the tank is huge) until the pressure drops a bit (usually to about 90 psi)..then the compressor will run to try to maintain the pressure.

2. How much cutting are you planning to do? If you are a weekend hobbyist just cutting an occasional piece of steel for a project....then a compressor with a cfm rating slightly higher than the plasma will likely be adequate. If you are doing a lot of cutting, cutting thick plate (same air consumption but slower cut speeds = longer cut time) or are using the system to earn a living..then size the compressor at 1.5 to 2 times the plasma system requirement.

Another note on air for plasma systems....and all air tools: Compressors take air at atmospheric pressure and increase the pressure and store it in a tank. Humidity in the air is often condensed in the tank and in the airlines...more so during humid weather. Drain your compressor tank often, and if moisture in your air lines is at all noticeable, it is a good idea to add additional filtration to the air system that absorbs or removes moisture.

Jim Colt Hypertherm

Howdy. I'm about to purchase a plasma cutter. I've never had an air compressor before and don't know much about them. The plasma cutter says it needs 6 scfm @ 90 psi.

How close in size does the air compressor need to be? Would 5.3@90 be good enough or am I asking for trouble? Do I need a safety margin like 7 scfm? Or should I be looking in the 11 scfm range for a large safety margin?

Thanks.

 

[arrabil]

I'm going to be getting a 10.2 scfm model at Tractor Supply in a few hours (and the extended drain valve). I'll probably run the plasma cutter ten times a year at most but I'd really like to have one. I would have liked to buy a smaller compressor to match my usage but the only one I found actually costs more than what I'm going to get. I guess the "shop" is going to need some rearranging. Thanks for the tips!