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

JimGnitecki

Active Member
I recently got one of the lunchbox size 50 amp plasma cutters. The machine does a good job cutting on short cuts, but my current pancake air compressor is, I think, simply too small to support the plasma cutter on longer cuts or repetitive short cuts.

My current Bostitch pancake air compressor has only a 6 gallon reservoir tank and is rated for only 3.7 SCFM at 40 psi and 2.6 SCFM at 90 psi. It cuts out psi buildup at 150 psi, and cuts back in when the psi drops to 120.

The first few short cuts with the plasma cutter are fine, but then the air compressor starts up and has to KEEP running, and I can see the psi dropping on the palsma cutter's psi gauge (Glad it has one!).


The user manual for the plasma cutter has tables for cutting material that tells you the amps and psi to use, and cutting 3/16" test material apparently requires only about 25 amps and only 40 to 50 psi, but I am assuming I need more amps because the 3/16" material I am cutting is aluminum, and maybe also more psi? So, I am using 30 amps. The manual does not in the tables highlight the CFM required, but later, buried in text, it does say that 6 CFM is required! It also says to not exceed 75 psi (presumably because more psi is not needed and maybe because they don't want you blowing off internal air lines with 100 or 150 psi connected to the machine's inputs.

In addition, I need to mention that I live in a geographic area with VERY dry air (good) and at 3000 ft elevation (bad). The 3000 ft elevation apaprently degrades an air compressor's actual CFM output.

So, I THINK I need TWO things that my current air compressor does not have:

1. a CFM output of at LEAST 6 CFM at 40 to 70 psi, and maybe more because of the high altitude

2. A much larger air reservoir tank, so that the compressor is not forced to start running partway through a long cut. I am assuming that even when the air compressor is running to replenish the tank's psi, and thus also the air volume that feeds the CFM, if it is running, it is likely not sending a STEADY psi or STEADY CFM to the plasma cutter.

If any of you are knowledgeable and experienced with air compressors, what would you recommend?

Note that I know of course that I can simply overkill and get a really large air compressor, but the plasma cutter is the ONLY usage for a larger air compressor (the pancake air compressor works fine for my only 2 other uses: tire air pressures on 3 vehicles and a trailer, and feeding my finish nailer. Therefor I would feel silly buying a large costly air compressor to feed only my very inexpensive and only lightly used plasma cutter.

Also, most large capacity compressors are also oil-filled, and that necessitates maintenance, AND adds oil into the air which must then be REMOVED because it kills plasma cutter torch consumables. So, I'd like to stay away from oil!

Jim G
 

DavidR8

Scrap maker
Administrator
Moderator
Premium Member
I have a Speedaire 20 gal 1.5 hp compressor which runs my Cut50 just fine.
Adding extra volume is a trade off. If I add a 10 gal auxiliary tank I will have more volume at the expense of longer recharge time.
As a point of comparison I also use the 20 gal compressor with my HVLP spray gun. I can spray continuously for approx. 55 seconds before the pump cuts in. That may not seem like a long time but in reality it works just fine because I never hold the gun wide open for 55 seconds at a time.
 

JimGnitecki

Active Member
I have a Speedaire 20 gal 1.5 hp compressor which runs my Cut50 just fine.
Adding extra volume is a trade off. If I add a 10 gal auxiliary tank I will have more volume at the expense of longer recharge time.
As a point of comparison I also use the 20 gal compressor with my HVLP spray gun. I can spray continuously for approx. 55 seconds before the pump cuts in. That may not seem like a long time but in reality it work just fine because I never hold the gun wide open for 55 seconds at a time.
Yes, I get what you are saying. But, 55 seconds, at 10 to 20 inches per minute plasma cutting, is only 9 to 18 inches of cut. For a single cut, or cuts spaced apart by a few minutes, that would be ok. But when trying to do, say, 3 inch cuts quickly repetitively, it won't work well. And on a longer, curved-shaped 30 inch cut where you don't want an interruption in the cut, it's not enough air duration.

Your 20 gallon capacity tank is a big plus over my 6 gallon, but that 20 gallon tank needs to be backed up with a strong compressor for long cuts.

Jim G
 

JustaDB

Ultra Member
1. a CFM output of at LEAST 6 CFM at 40 to 70 psi, and maybe more because of the high altitude

2. A much larger air reservoir tank, so that the compressor is not forced to start running partway through a long cut. I am assuming that even when the air compressor is running to replenish the tank's psi, and thus also the air volume that feeds the CFM, if it is running, it is likely not sending a STEADY psi or STEADY CFM to the plasma cutter.
1. Princess Auto has decent enough air compressors to fit your requirements, and they frequently go on sale. Look for something in the 10 CFM @100PSI range. It doesn't really matter how big the tank is as long as the compressor can keep up, at least on home shop scale.
2. You need a pressure regulator between the compressor & the plasma. You can adjust the pressure between zero & WFO. Set it to say, 50 PSI, then even when the compressor is building air (assuming you have enough capacity), you still get proper requirements to the plasma.
 

DavidR8

Scrap maker
Administrator
Moderator
Premium Member
If those are your needs then a big volume backed up by sufficient power to quickly recharge is your only option.
I suggest figuring out what your longest cut might be, figure out the air volume required and go from there.
But be prepared to have to pony up for a pretty substantial unit to get the duty cycle required to sustain longer run times.
 

CWret

Ultra Member
Premium Member
I have a Hypertherm 45XP (45 amp machine). It self-regulates the pressure & volume it needs. This is my first plasma cutter & I'm new at it so my experience is inexperience.
My compressor is a 15 gal, 1.5 Hp, 135psi, 4.0cfm @ 90. Using this compressor (cutting 5/8" steel) the plasma cutter shuts down in 25 to 30 seconds due to lack of air. To improve the compressor reservoir's effective capacity I adjusted the (do not adjust factory setting!!) max pressure to 142 psi (that is what safety factors are for). The big benefit here is that this adjustment also raises the cut in pressure so that it starts up sooner at 105 psi instead of 98 psi. I also have a nice little ultra-quiet 4 gal, 1.0 Hp, 150psi, 2.3 cfm @90. I use it for most shop small tasks like the blow gun. I installed a Y hose connector just ahead of my air filter that feeds the plasma cutter so that both compressors are used to supply the plasma cutter. This gives me 6.0 cfm but I can still run out of air.
I do not have a plasma CNC table. On a table, the cutter can run for a much longer time than when just free-hand cutting. So if you are going to use it on a table you'll certainly need to upgrade your air.
I recommend a good air filter. I have a Motor Guard M-26, it was a good investment (can't recall exactly but I think about $100+ with a spare filter on Amazon).
 

curmudgeon

(Steve)

If you want long, uninterrupted cuts, or continual short cuts then you'll want to focus on SCFM flow rates and duty cycle rather than reservoir size.

If sufficiently sized, the motor cutting in/out while operating will not affect pressure and flow at the machine; set your regulator on the compressor to 90 PSI and install a another regulator set to 75 PSI (less if your machine does not have its own regulator) and a water/oil separator on the input to the plasma cutter. Many of our hobby shop compressors will have a 80% duty cycle, so you'll still be limited in how long you should operate.
 

JimGnitecki

Active Member
1. Princess Auto has decent enough air compressors to fit your requirements, and they frequently go on sale. Look for something in the 10 CFM @100PSI range. It doesn't really matter how big the tank is as long as the compressor can keep up, at least on home shop scale.
2. You need a pressure regulator between the compressor & the plasma. You can adjust the pressure between zero & WFO. Set it to say, 50 PSI, then even when the compressor is building air (assuming you have enough capacity), you still get proper requirements to the plasma.
Your comment on setting the selected air compressor's regulator gauge output psi to 50, when the cut-in psi is say 100 psi or more, is a really good suggestion, as yes, it means that even while the compressor is building psi back from 100 psi to its cutout psi, there will be no interruptions or wiggles in the regulated psi at the plasma cutter. Thanks for that idea!

And yes, I have seen that Princess Auto does sell a really large variety of air compressors. But it is hard to get and independent reviews on how well they actually perform versus their specs, since Princess Auto "private labels" many of their air compressors. For example, for one model that I read the customer reviews on, a buyer complained that although the specs claimed MORE than enough CFM to run his air tool, in practice it would not. This is why I like to read independent reviews by professionals who know how to properly exercise the test units. And professional reviewers generally review only brand names that are sold in many places, as they want lots of user clicks on their review webpages, not just users who are buying from ONE retail source.

You also cannot find who makes the "private labeled" compressors for Princess Auto, as they alter the designs enough that you can't find the actual manufacturer's comparable unit.

I'll keep a look out for sales on air compressors with strong specs and large tanks. And I'll also monitor Facebook's used offerings!

Jim G
 

curmudgeon

(Steve)
Also, short and fat air supply lines and high flow air filters water/oil separators are a plasma cutter's good friends.
 

JimGnitecki

Active Member
I have a Hypertherm 45XP (45 amp machine). It self-regulates the pressure & volume it needs. This is my first plasma cutter & I'm new at it so my experience is inexperience.
My compressor is a 15 gal, 1.5 Hp, 135psi, 4.0cfm @ 90. Using this compressor (cutting 5/8" steel) the plasma cutter shuts down in 25 to 30 seconds due to lack of air. To improve the compressor reservoir's effective capacity I adjusted the (do not adjust factory setting!!) max pressure to 142 psi (that is what safety factors are for). The big benefit here is that this adjustment also raises the cut in pressure so that it starts up sooner at 105 psi instead of 98 psi. I also have a nice little ultra-quiet 4 gal, 1.0 Hp, 150psi, 2.3 cfm @90. I use it for most shop small tasks like the blow gun. I installed a Y hose connector just ahead of my air filter that feeds the plasma cutter so that both compressors are used to supply the plasma cutter. This gives me 6.0 cfm but I can still run out of air.
I do not have a plasma CNC table. On a table, the cutter can run for a much longer time than when just free-hand cutting. So if you are going to use it on a table you'll certainly need to upgrade your air.
I recommend a good air filter. I have a Motor Guard M-26, it was a good investment (can't recall exactly but I think about $100+ with a spare filter on Amazon).
The dual air compressors idea is neat, but requires a high amp electrical panel that can feed the 2 compressors PLUS the plasma cutter at the same time. I am limited to 50 amps by the underground cable that the builder ran from the house panel to the rear detached garage, and the 30 amps being used by the plasma cutter, plus the 15 to 20 amps consumed by an air compressor, and the small draw for the laboraotry level LED lighting, mean that 1 air compressor is all I can run.

I have no plans for a plasma table. Space would be an issue anyway.

Jim G
 

JimGnitecki

Active Member

If you want long, uninterrupted cuts, or continual short cuts then you'll want to focus on SCFM flow rates and duty cycle rather than reservoir size.

If sufficiently sized, the motor cutting in/out while operating will not affect pressure and flow at the machine; set your regulator on the compressor to 90 PSI and install a another regulator set to 75 PSI (less if your machine does not have its own regulator) and a water/oil separator on the input to the plasma cutter. Many of our hobby shop compressors will have a 80% duty cycle, so you'll still be limited in how long you should operate.
My plasma Cutter, a Bestarc BTC 500DP, does have its own psi regulator, and the adjustment knob is right on the front right below the psi gauge! :)

Jim G
 

Chicken lights

Forum Pony Express Driver
Also, short and fat air supply lines and high flow air filters water/oil separators are a plasma cutter's good friends.
I’ve posted it before, but I was told by the air compressor repairman to mount the air dryer/separators as far from the compressor as possible, to try and cool the air and condense the water. In my case I ran about 25-30’ of 3/4” copper pipe between the compressor and water separator, then after that ran black metal pipe.
 

JimGnitecki

Active Member
Anything over 5 SCFM requires a 220 volt motor.
For high combinations of psi and CFM, that is true, but not for the psi and CFM combinations I need for my tiny plasma cutter. The user manual says 6 CFM BUT only 40 to 50 psi, depending on the specific material and thickness being cut. Many 120 volt air compressors can supply 6 CFM at 40 to 50 psi. It's the larger capacity plasma cutters that need the 220 V air compressor.

The other potential "solution" for me is to use the Argon clyinder I already have for my TIG welding. But, that's costly.

Jim G
 

JustaDB

Ultra Member
But it is hard to get and independent reviews on how well they actually perform versus their specs, since Princess Auto "private labels" many of their air compressors.
Over the last 30 years I've had two Sanborn compressors from PA. Both similar spec'd pumps, 11.5CFM@90PSI. Only difference was tank size. One is 60 gallon, first was ~40. I was stupid & never drained the first one, more a PITA matter of accessibility to the drain under the tank than anything, it rusted out after about 25 years. Current one working fine. Either of them will keep up to any air tool I throw at them, from 3/8"-3/4" impacts to die grinders to air ratchets to plasma cutter, save for this ancient rotary sander that consumes massive amounts of air. I can drain my tank in about 8 minutes with it. Luckily, I seldom use it. Recommended for residential/hobbyist use. As far as reviews are concerned, you're more likely to post a negative review than a positive one, so the sample is skewed.

As an aside, I put an elbow on the drain of my newer tank, attached a 1/4" hydraulic hose w/ MIP fittings, & routed it up to a ball valve mounted on the wall with a nipple pointing at the floor. It gets drained regularly.

I have the shop plumbed for air, but I don't have a water separator anywhere except for the one mounted to the plasma, along w/ a filter & regulator.
 

CWret

Ultra Member
Premium Member
Good point about the drain. One of the things i like about the Ultra Quiet (King Canada) i got from KMS is it has a pair of aluminum tanks.
Under 50 pounds so free shipping by KMS and on sale so it was a good deal.
On my very old ( inherited) air pig it got some rust holes. I’m no certified welder but what the heck it’s only 100 lb and you only live once. Years ago i welded it and no issues. I figured a rust leak was no more dangerous than a weld leak.
 

SomeGuy

Hobbyist
Anything over 5 SCFM requires a 220 volt motor.

Well no, you could find a 120v 20 amp or 30 amp compressor that can do more...less efficient, but you can still get more than 5cfm out of a 120v circuit technically.


Anyway, to the point, 60+ gallon 5+ hp, is the way to go, in my case 2 stage and 100% duty cycle...just buy a big one and be done with it.
 

JimGnitecki

Active Member
Princess Auto has this "silent" model:

The specs look impressive:
6.0 CFM at 90 psi
7.9 CFGM at 40 psi
(Recall that my plasma cutter requires only 40 to 70 psi, depending no thickness being cut)
20 gallon tank
Twin cylinder
120 Volt, so my electrical branch panel and 115 volt outlets would handle it
VERY quiet, which would be a nice change from most air compressors

One of the reviews on Princess Auto's other compressors mentioned that some of their compressors are "Eagle" brand compressors being private labeled by Princess. That looks to be the case here; This looks identical, outside of paint colour and brand decal, to the Eagle EA 6500.

This is a twin piston, oilless compressor. The Eagle user manualsays it apparently weighs 132 lb, so I suspect the Princess spec sheet is wrong, as it show 176 lb which seems very high for this size of compressor.

I'm wondering if this one would have enough capacity for the plasma cutter (which is my highest CFM requirement now and in the forseeable future as I don't use air powered tools except for my low-CFM finish nailer).

Princess Auto has it on sale right now for $650 CDN, which seems like a bargain price compared to what the identical Eagle EA 6500 seems to sell for. It's a lot more money than I want to spend, but IF it would really eliminate the current limitations on using the plasma cutter, if it is really that quiet, and if it is really that good a price for a twin cylinder Eagle in disguise, maybe it is worth sucking up the price and buying it, despite the fact that for all my other air needs except the plasma cutter, it is way overkill.

The weight would still be an issue for bringing it home. Eagle says the weight is 132 lb, which is already a lot for one man to get off of a pickup truck tailgate alone without damaging either the tailgate or the compressor. if the Princess stated weight of 176 were actually true, it would be a REAL challenge for one man, but I think that 176 lb HAS to be an error!

Jim G
 
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