I'm thinking about buying a used electric air compressor for light use around the house.
I've owned a compressor before, but I've never bought a used one before. What should I watch out for, apart from the obvious points of avoiding anything that doesn't work or is heavily worn or visibly damaged?
=3D=3D I've seen new light duty ones made in China for $88 with 25 foot hose and various attachments. If you're not in a hurry watch the ads. New at that price complete with hose is a better deal than used. =3D=3D
You really need to figure out what you will do with it to know what size you need. Just about anything will air up tires. Once you get into air tools, you need a big enough compressor to run them. Nail guns and such need 100 PSI or so but they don't need a lot of volume. Painting, OTOH usually needs a lot of volume. Things like air chisels are also air hogs.
I agree with the other poster. it is better to get a good used machine than a cheap new one.
Ignore "HP" rating stickers, they are usually just BS. Look at the electrical requirements and go from there. If it is 120v it will not be more than 1HP. A true "5HP" machine will be 230v 30a or so.
1HP is about the minimum you can take seriously if you want to use air hungry tools but you still need a big tank and you will have an intermittent duty cycle.
You can get some good deals at pawn shops. Buy a brand name, and buy one that looks clean, that's about all I can suggest. If you're just going to use it for nailers, etc, you don't need much, and as long as it will build up pressure, and doesn't leak, there isn't much else. Take a bottle of Windex, and pressure it up, and test for leaks. Open up the bleeder valve on the bottom once it's pressured up, and see if any water comes out. If it does, pass. It means the owner hasn't bled it regularly, and there will be water and rust inside the tank.
Steve
Heart surgery pending? Read up and prepare. Learn how to care for a friend. Download the book.
Lots of tires today take more than the 32 psi than our father's cars and the ones we drove in our teenagerhood. But yeah, most compressors will put enough air in them to get to the tire store even if they do have to work a while. And anything will blow up bikes, motorcycles, those temporary plastic dates, etc.
Steve
Heart surgery pending? Read up and prepare. Learn how to care for a friend. Download the book.
My feelings exactly. For my intended uses I could probably get away with an $88 piece of junk, but I prefer to buy good tools and keep them as long as I need them.
Nonsense. The guy I bought my compressor from sold it to me because he wanted a bigger compressor (bigger tank/more air output). I got a good deal on it because the regulator was busted, which was no big deal to me (I used the regulator I had purchased for my previous compressor).
Like the fellow that I purchased my current compressor from, I sold my smaller compressor because it failed to deliver the output that I needed.
Some tools are sold because the owner grew out of them: it's the same deal with my drill press, too; I sold the little one once I bought a bigger one, and didn't have the need or space to keep the old one around.
Your motor is rated wrong. Some call it "peak horsepower". A real 3HP motor at 115VAC will draw 19.46 amps.
I have a ~ 35 year old 1HP Sears compressor. I also have a "2HP" craftsman compressor (someone gave it to me). The older 1HP one puts out over 2 times the CFM than the newer 2HP one. Forget the motor rating, the CFM is what matters.
No, the motor is rated correctly; your confusion arises because you do not understand the nomenclature used on electric motors. especially those used on air compressors. As I stated previously, the motor is a 3HP SPL, and is rated 15 amps at 115 volts. 15 amps at 115 volts is 1725VA, or 2.3HP continuous duty.
Because this is a compressor, the 3HP SPL refers to the fact that the motor will safely deliver 3HP during an overload condition when it called on, namely for the last few minutes of filling the tank up.
No, it is still a current model, and there is no inaccuracy with the way it is being marketed or sold. Perhaps you might want to learn more about motors before you spout off about things you do not fully understand.
I suggest you put a clamp on ammeter on your compressor some time. The last few pounds going in the tank is actually less of a load on the motor than the mid range. That means if you are using air about as fast as you are making it, that is continuous duty.
The fact remains, manufacturers played fast and loose with HP numbers and got sued for it. A HP is still 550 ft/pounds a second and any "peak", "instantaneous" or other quibble is simply a lie.
one horsepower *is equivalent to* 746W. (both HP and Watts are units of power, just in different measurement systems.) Therefore a 3HP motor, if 100% efficient, would draw 2238W or 19.46A @ 115V. IRL it would either draw slightly more, or put out slightly less than 3HP. Pesky laws of thermodynamics.
a 15A circuit by definition cannot provide more than 1725W @ 115V, and it would be a bad practice to expect it to do so. A load that large should really be connected to a 20A or larger circuit.
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