Air Compressor Help

What really matters is CFM. That is the amount of air your compressor will make at a given pressure. If you want to run a tool that hogs air continuously, your compressor must create more air than the tool uses. If you still have the books on your tools, they will probably tell you how much air is needed. Then, you can buy a compressor that takes care of the issue.

Here's another thought. What about buying another small compressor, and running them at the same time. Let's say you set your main compressor to kick on at 75 psi. Then, you set your auxiliary compressor to kick on at 90 psi, and hook them both into the same manifold. This way, your main compressor still carries most of the load, and your cheaper, lighter weight compressor only kicks on when the main one can't handle the demand. This may take up less room in your shop, and give you a small portable compressor for those times that you may need it.

BTW, you shouldn't be tripping breakers. Make sure your breaker is the right size, and your wires are large enough for the load.

I know that it is labeled "5HP", probably "5 peak maximum developed HP" or some such, but it is not 5 HP in reality. If it is 110 volt, it is probably just 1.5 real, honest HP.

That's what I have (I initially thought that mine was 80 gallon).

I think that size of the tank does matter a lot, to make the compressor run less often or to handle extreme but intermittent demands. I am very happy with my 60 gallon vertical compressor. I would look for stuff that does not advertise fake HP like those Sears compressors.

Thanks for the idea Dave. I didn't think of that route. To the above thought, this is a new occurance. I actually used my cutters weeks ago and didn't have this problem. It is an old compressor and I understand that the oiless units use a piston and do wear out over time. I was thinking this may be the case and the motor is just over working itself to keep up with the pressure. Also, I need to correct one thing. When I said "tripping the breaker", I was talking about the breaker on my surge protector strip, not my home's fuse box. I don't know if that matters but this has never happened before. It may just be time for a new unit after all. Let me see if I understand this. The large compressor I was looking at, for instance, stated that it produces 10.5 CFM at 90psi. One of the sanders I use says it uses 4 CFM @ 90psi. Does that mean that when running my sander non-stop, the compressor should not have to run steady because it produces more than twice the CFM? Thanks again. Rich.

Hook another air tank to your existing tank... A broken compressor from a yard sale could be a cheap source for a tank... Two or three el-cheapo compressors from yard sales, added to your existing compressor will help...

denny

If the sander really uses 4 CFM (they are often underrated) and the compressor really makes 10.5 CFM (make sure that it is not Sears CFM), then yes, the compressor will be idle about half the time. I would look into getting a 12 CFM unit, honestly rated.

Exactly. Assuming you have no leaks, you should be able to run 2 1/2 of those sanders at the same time and not run out of air. In your case, it means that your compressor will kick off for a while, and then back on while you're using it. The cycle time will depend on the size of your tank.

What kind of surge protector strip are you using? This may be a good place for one of the guys with electrical experience to chime in, but I'm not sure I would be using one on a compressor. I would think that even a small compressor would need more power than a "computer" type surge protector strip could supply. Robbing a motor of power by using long underrated extension cords will cause them to overheat, and not work to rated performance.

A minor variation: instead of the compressor(s), use portable "carry about" tanks.

I'd changed my carry tanks to use quick disconnects and found that by using a "T" [2 males and a female] to attach linking hoses, I can "add-a-tank" to both provide additional capacity AND to provide a reservoir closer to the work site.

This way, I can, also, continue to use the portable tank AS a portable and, when needed, as an additional reservoir.

Just make sure that the portable tank is rated for the pressure that you're supplying...

Blink blink..surge protector strip....you are running an AIR COMPRESSOR on a surge protector strip??

At max..if its the usual type..it has a 15 amp breaker built into it..chinese made..and they do get tired when overloaded repeatedly.

Blink...I keep forgetting that there are toy air compressors out there that one can maybe get away with this for a while. Sounds like you got your $5 worth on the strip.

Gunner

"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences."

- Proverbs 22:3

AND his $39.95 on the compressor! 5HP, indeed!

LLoyd

Remember that "5 Sears Horsepower" is probably 1.5 or 2 Real HP. Stall Current is not the way you rate a motor, but they do. If yours plugs into a normal 15A 120V receptacle it is *NOT* 5 HP.

The size of the compressor is the continuous air output of the unit in Cubic Feet per Minute. If you want to work non-stop, it has to be bigger than the tool ratings.

The tank size gives you a cushion so you can run tools that use very high CFM ratings, but only in short bursts like an impact wrench. The bigger the tank, the longer the intermittent heavy blasts you can use.

Many of the tools you mention like nibblers grinders and shears are somewhat bursty, so you can get a compressor slightly smaller than their rated continuous CFM draw. During the time you aren't actively pulling the trigger the compressor is chugging away catching up.

Two stage compressors gets you higher storage tank pressures, which increases the effective air storage volume of the tank - better for those big burst tools, because you can regulate at the main tank output to 90 PSI and the tank can fluctuate from 150 down to 100 without the tool ever seeing it.

Belt drive compressors run the pump at a slower speed for better efficiency, longer life, and lower noise.

Oil lubricated compressors run cooler and live longer between rebuilds or replacements, especially if you change the oil occasionally. The small ones are splash lubricated like a lawnmower engine, but when you go to the serious commercial units they are pressure lubricated with a pump - and sometimes even an oil filter.

(After several years and 5,000 or 10,000 running hours you will notice that it chugs away a lot longer before shutting off, and putting out that last 10 PSI takes forever - time for a rebuild. But on an oilless pump you can hit that point at 1,000 - 1,500 hours.)

The minimum for a decent home shop IMNSHO is a real 3-HP 60-gallon or 80-gallon compressor in the 9 CFM range, two-stage oil lubricated pump, belt drive. (I went for the 80-gallon.) Will run off a 30A 240V circuit, which most all house power panels can supply - steal the clothes dryer circuit.

If the CFM ratings sound low for your uses, go to the 5 HP unit, the one with the magnetic motor starter. But you need a 50A circuit.

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Highly unlikely to be a 2 HP output on the shaft, given that motor efficiency of that size is quite a bit below 100%.

Also, considering that these "oilless" compressors are inefficient, the output of that POS is less than that of a compressor with a better pump.

Here's how a real 3 hp compressor looks like

Sears' abuse of horsepower ratings is very outrageous.

Thanks to all for the great input and ideas!!! You all have been extremely helpful. I did throw one of those cheapo power strips on the wall so I can keep multiple tools plugged in. I will bypass that strip and use my air tools and see what happens. I had taken it off the power strip but did use one of those cheapo Harbor Freight roll-up extention cords with a breaker on the reel. That one popped as well. I will run the compressor straight into the wall and try it again. Thanks again to all.

I just recently did a compressor upgrade in my shop. I was tired of waiting for my compressor to build up pressure. I was spending a lot of time just waiting, or having to go do something else while my compressor was building up pressure, so I could resume work with my air tools. I use die grinders a lot, and they are air hogs.

I replaced a high end dual stage 120 volt compressor with a basic single stage 240V compressor. Both drew 15 amps, but of course 15 amps at 240 is twice as much power as 15 amps at 120 volts. The CFM was also double, going from 5 cfm to 10 cfm. The tank size also doubled, from 25 gallons to 60 gallons. However, since the smaller tank went up to 175 psi, while the larger tank only went to 125 psi, I figure that the effective tank size was about the same. (Yes, I know that 175 psi is not double 125, but the calculation relates to the difference between the tank pressure and the regulated pressure).

A simple experiment will tell you how much air your tools draw relative to your compressor output.

1. Turn off your compressor after it is up to pressure. Turn on the air tool. When the tank pressure gets to 120 psi, start the stopwatch. When the tank pressure drops to 90 psi, stop the start watch. Let's say that it took 15 seconds to drop 30 psi. Run the pressure a little below

1. Turn on your compressor. Do not run any of your air tools. Start the stopwatch when the tank pressure gets to 90 psi, and stop it when it gets to 120 psi. Let's say it took 30 seconds to build up pressure.

2. Take the tool time from step 1, and the compressor time from step 2. Divide tool time by compressor time. In this example, 15 seconds divided by 30 seconds is 1/2, or 50% duty cycle. You can run that air tool about 50% of the time, and the other 50% of the time you cannot run the air tool, you need to wait for the compressor.

With my old compressor, I was around 25% duty cycle, so I did a lot of waiting. With my new compressor, I am around 50% duty cycle. In practice, you rarely run an air tool at 100% duty cycle. You stop to look at your work, to get another tool, to reposition the work, to change sanding disks, whatever. The net is that I no longer spend my time waiting on the compressor.

I have not had my new (used) compressor long, but I am very happy so far. In the future, I am sure that I will sometimes get ahead of my compressor, depending on exactly what I am doing, but at least it is not happening all the time.

If you are using air die grinders, dual action sanders, or angle grinders, you need a 240 Volt compressor. The world's best 120V compressor is not going to provide enough air to run those tools without a lot of waiting around for the compressor.

Richard

snipped-for-privacy@cfl.rr.com wrote:

Not necessarily true. I used to have an Ingersoll Rand oilless compressor that was rated at 2 Hp. It delivered 6.4 SCFM, which is quite consistent with a HP single-stage compressors. It drew something like 14.8 A, so you couldn't even run a 100 W light bulb from the same outlet or it would trip the 15 A wall breaker.

I got rid of the damn thing because of the noise, of course!

I now have a Quincy 2 Hp oil-bath 2-cylinder single-stage compressor running off a 2 Hp 220 V compressor-duty motor, and get about 6.3 SCFM. So, the IR oilless was pretty efficient. The downside, of course, was the noise.

Of course, the stuff Sears was selling a few years ago may have been much worse, the IR I got in 1989.

Jon

On Wed, 27 Sep 2006 15:58:18 GMT, with neither quill nor qualm, Gunner quickly quoth:

That's a FIVE HORSEPOWER compressor running at 120v on a surge strip. Ayup, it must be Searz...

See my page at:

It's worse than that. Some theoretical calculation that is beside reality.

Many manufacturers are rating tools at a % of duty cycle. In other words, running the tool constantly it will consume more the air they claim. My bet is you sander is rated this way. 4 CFM in a sander is pretty low! Tank size is not real important, CFM rating at 90 PSI is. Look for something around 10 CFM minimum! More is better, but it costs more too. My compressor is rated at 9.6 CFM and it takes all I can give it with air drills and air sanders. Greg

Just remember - Tool manufactures often give average air requirement based on