Compressors

[Charlie_in_TX]

You have got'n some good advice so far. I will put it a little diff.

Oilless, pros-cheap, usually more portable, um thats about it. cons-LOUD, short-lived, cheaply made, the hp rating is a lie

Belt drive, pros-long lived (so buy the right one the first time), relitively quite, universal parts.
cons-initial cost, um thats about it.

If I were in the market, I would get a 5hp, single stage, 80gl, belt drive, plumb the barn, and get a small 5gl portable tank for remote filling.

You will be amased at how much air a drill or random orbit sander will take.

 

[ELMO67]

Tracy, the best advice I can give is based on years of working at an automobile dealership, and a hobby of custom and restored cars. I purchased a compressor in 1984 when I started to restore my 1968 VW. I purchased a T20 compressor( I won't name the brand because I won't recommend or buy another product from them, but their new compressors are labeled as "T30"). At the time, it was a major purchase for me, what I considered to be a lifetime investment, but it only had approximately 100 hours on it when a rod broke, and that was that ( yes it had oil in it). To add insult to injury, this compressor line was sold to another manufacturer because of all the problems associated with it. The worst part is, replacement parts are not made for it, no one wants to talk about parts interchangeability, all anyone wants is to sell a complete new ccompressor assembly. As it turns out they were designed as " throw-away" units, sent out to bid by the manufacturer for the lowest possible price to be their price- leader. I've been told that all the units on display at home centers and large retail outlets are made the same way. Soooo..., to make a long story short, if you value your investments, ONLY buy a compressor from a place that ONLY sells compressors, not a box store. A 2 stage, 5hp, 80 gallon tank will do most any job quite well. Make sure that the motor is rated at a " true" hp, not a peak hp, the pump will be more durable if it is cast iron, add an automatic water drain, and a low oil warning or shutdown- DO YOUR RESEARCH- don't buy because it is easy and convenient. Good luck, and have fun dreaming up projects for your new compressor!

 

[Phred]

Bob,

If you have a lot of remote use of air tools then the small portable oiless make sense. But for tire fill ups you can use a portable tank that is a lot cheaper. Also keep in mind that you can't really run alot of air tools with one of these portables since they can not deilever the air volume.

I went the small portable route and wish I had not. I was in lowes the other day drooling over the large oil units. This would have been the way to go in my humble opinion.

I will be buying one of the larger units and trying to sell my oiless once the budget allows.

Fred

 

[Bird]

<font color=blue>he has a newer PUMA compressor with a vertical tank</font color=blue>

I've sure been well pleased with my PUMA, even though there doesn't seem to be near as many of them around as some of the other brands. But since we're moving back to town, it'll probably go in the garage sale this weekend./w3tcompact/icons/laugh.gif I think someone will get a bargain, but the guy who's buying our place says he already has an even bigger compressor to set in the PUMA's place.

 

[Rockyroad]

Tracy-

ABout 5 or 6 years ago I purchased a Rand 4000 single stage with upright 60 gallon tank. It is not a cast iron compressor, but it supposedly has an iron bore liner. It is 220V, 5 HP.
I bought it from a "big box" store for about $600 (if memory serves).

I know that a cast iron compressor would be better, and I would like to have a 2 stage machine, BUT it has been perfectly adequate for everything I do with it. It is one of the most handy machines I have in my barn. I run pneumatic tools (sander, die grinder, impact wrench, paint gun, pneumatic chain hoist, etc.) with it. I use it to clean my machines after use, inflate tires, blow out filters, blow out my wife's vacumn cleaner filter, etc, etc, etc.

I know more expensive rigs would be desirable, but this machine has been perfectly adequate for my purposes. I am a weekend warrior and the compressor does not get tons of hours on it as would be the case if I were using it on a daily basis. I just keep the oil changed, the tank drained, and the filter clean.

If you can afford a grand and up for a better machine that's great, but the sincle stage lower priced machines will do a lot of work for less money.

If I have the bucks someday, I will buy a cast iron 2 stage for my barn and put the Rand 4000 in the basement of my house to use there.

 

[Darren]

Depending on how much you'll be using it, consider the quality. I was given a thirty or forty year old Kellogg air compressor that spent it's previous life in the back of a tire truck. After that it laid behind a shed for years out in the weather. To get to the point, the Kellogg, recently refurbished, has more life left in it than any new compressor you'll find in a store. Finding parts was not a big deal unlike some of the cheesey stuff being sold today.

The old units were built like battleships. They can be passed down to your grandkids. Not so with the new stuff. Besides that old used compressors aren't hard to find nor are they expensive. You'll probably pay less than a new vertical model with a pot metal compressor.

 

[Rockyroad]

Darren is right. There are some good old compressors out there. A buddy of mine wants to all but give me one he has in a shop that he bought. It is a monstrous oldie but goodie that I would really like to put in my barn. Only problem is, it is 3 phase, and I don't have 3 phase in my barn. I am told you can put a 220-volt single phase motor on some of those old 3-phase machines, but I don't know that I am really qualified to do that.

I am on the lookout for a good oldie that runs 220 volt single phase, then I will put my Rand 4000 down in my house basement for occassional use there. Or, if I have the bucks I will just step up to a better machine in the future that is brand new.

FYI, there is some guy on e-bay who is selling a book that claims to give plans to make a rig that will run a 3-phase motor on 220 single phase. He claims that there are three different ways of doing it. All you have to do is buy the book to learn how. Anybody out there ever heard of such a thing being possible? If it is, then it may be possible to use some of those older 3-phase compressors.

 

[Darren]

You can either use those directions to build a convertor (single phase to 3 phase), buy a convertor (expensive unless you find one used), or buy a single phase motor (not cheap). I've seen three and five hp single phase motors. In the past Sears had them on their tool catalog.

 

[MJB]

Here is a site that describes a few methods of running 3 phase motors from a single phase source: <A target="_blank" HREF=http://www.metalwebnews.com/howto/ph-conv/ph-conv.html>link</A>. I have not tried any of this myself but it does look interesting./w3tcompact/icons/smile.gif

 

[Hank]

<font color=blue>I am told you can put a 220-volt single phase motor on some of those old 3-phase machines, but I don't know that I am really qualified to do that</font color=blue>

If you can match up the HP with a single-phase motor it should work simply; just bolt it on and make sure the rpm's and drive pulley are the same (or compensate for rpm's with a different sized pulley).

I'm definitely no electrical engineer, but my limited understanding (and I am sure I will {gladly} receive an education) is that within an overlap range (3-7 HP) single phase and three phase motors are interchangeable for the driven device. Single will run a bit hotter, be a bit more expensive/HP, draw a bit more current/HP (be less efficient), and have a bit bigger motor winding, but either will work. Beyond 7-8 HP, you only see 3-phase motors, due to that single phase is simply no longer efficient at that level.

 

[FamilyFarm]

I found an Emglo unit only 3 years old for about $100. It is $800 new and puts out a ton of air volume, and is very quiet also. It is a small tank unit (twin tanks), but also more portable than some - if you consider 195lbs portable - wheelbarrow style.
Learn how to compare the ratings, most are exaggerated. Large tanks are nice, but true CFM displacement is more important for heavy-duty use.

 

[Anonymous Poster]

When you convert to single phase, keep in mind that the running current for the same HP is slightly higher in the single phase units. For example, a 5 HP three phase motor is 15.2 AMPs, and the same HP on single phase is 28 AMPs. The inrush AMPs....that's starting load......is not much different percentage wise than three phase, but of course it too has to be higher. If you are thinking of going single phase, a smaller motor may be necessary if you have limited electrical power. I JUST FINISHED installing an electrical service to my "new" shop and it is 100 AMPs. If I get a 5 HP single phase compressor, I'm covered. There ARE several ways to run three phase motors on single phase, but aside from the expense of actually changing the motor, it actually doesn't save you any money. If you DO go single phase, BE SURE that the unloader is working perfectly and that the compressor has ample time to get up to speed before the load gets on it. That is a big help in prolonging the life of both single and three-phase motors. And another thing....take my word for it as an Infrared Thermographer......compressors want YOUR BEST electrical. If you think one particular size wire is sufficient, jump it up TWO sizes. You'll be glad you did.

 

[Charlie_in_TX]

Go to the forum http://www.practicalmachinist.com/c...opics&forum=Phase+Converters+and+VFD&number=3. You can find used/ask question about variable frequency drives. That is the best way to drive 3 phase motors. There are people there that have BTDT.

 

[Anonymous Poster]

Hmmmmm....VFD.....not a bad way to go, since the drive can be set up to accept single phase input. It might be a bit spendy, and they do have to have a fan and an air filter, but they ramp up slowly and that reduces the inrush current. What is BTDT?

 

[jima1]

BTDT = "Been There Done That" /w3tcompact/icons/smile.gif

 

[kevinro]

I have been considering putting my compressor outdoors and running the pipes indoors. One concern I had was the temperature of the air. As you might already know, when air is compressed, the air gets hot because you squeeze the heat energy into a smaller space. The inverse is also true. When the air expands, it gets colder.

My thought, and I was hoping someone who has an outdoor compressor could comment, is that if the outside air is cold (30 degrees for example), and has time to cool, is the expanding air too cold to use?

Kevin

 

[Anonymous Poster]

Since this thread began and since we are in the process of putting a shop together, I have been noticing air compressors that are offered for sale in farm supply stores. I recently looked at one that had "6 HP" on the label, and when I looked at the motor it was quite small. The nameplate on the motor did not give the HP, but instead it said "Spl Duty". What a complete crock! Farther down on the nameplate was the "truth", and where it listed running AMPs it had 15.6, which is................about THREE HP on 230Volts. If that isn't false advertising, I don't know what would be. 1 HP is 16 AMPs on 120V, 1-1/2 HP is 10 AMPs on 230V, 2 HP is 12 AMPs on 230V, 3 HP is 17 AMPs on 230V, and 5 HP is 28 AMPs on 230V. Where they can possibly get SIX HP is completely beyond me.

 

[Charlie_in_TX]

CJDave, yes it is a crock, lie, whatever adjective you want to discribe.

volts X amps X power factor = Power
240v X 20a X .8 = 3840watts
3840 X 80% effiecency = 3072
3072 / 750 = 4.1 HP at the output shaft

That same motor is rated as a 10 HP motor because, under lab conditions, with a locked rotor, the motor pulls 31 amps @ 240 volt. Air compressor manufacture rate there motor by how much power they can consume (just before they blow up) not how much they produce.

 

[Soundguy]

Any gear reductions taking place.. or were they really stretcing the limits.. like car amplifiers advertising peak to peak measurements, rather than rms...


Soundguy

 

[Anonymous Poster]

Hmmmmm.......Root Mean Square? I'll have to try and remember how to use that. Gear reductions will actually only reduce rpm, they can't literally make more HP. Oh yeah, and one more troubling thing...the motor was 3450 RPM instead of 1760, so everything is turning wayyyyy faster than what I would like to see. I like the throb-throb-throb of an ancient , slow speed Kellog anyday to the frantic pace of these modern high-attrition, high-speeders.