Buying a used air compressor: tips?

[Nate Nagel]

We're still not sure.

nate

[Vic Smith]

Nice explanation. Might be able to use it when I buy a compressor. Want a cast iron, as heavy duty as possible on 120V, 15 amp. Light use for impact wrenches, filling tires, etc. The garage circuit also carries 6 2-tube 4' fluorescents. Don't want to be running to the basement because of the breaker tripping. Any way to spec a 120V compressor motor for this? Stay under 15 amps? 13? I could pull a 220V service to the garage if I had to. I'd get an electrician for that. I stay away from electricity.. Don't want to if not really necessary though, because the 1/2" condiuit is 50 years old and runs under fairly new and good sidewalk. That might cause issues.

--Vic

[clare]

I just switched mine over to 220 - now I can start it when it is cold. It is rated at 14 amps on 120, and 7 on 220, but it was popping

15 amp fuses on a normal startup, and 20s if it was at all cold.

On 220 the 15s start it when cold.

[Vic Smith]

Thanks for that advice. Pretty much settled on this. Should be all I'll need.

Sears has had it for $449 so I'll wait for that. Not ready to pull the trigger anyway. Been complaining to my wife about much she spends on groceries. Best to let that settle down. Still don't know if my 15 amp garage circuit will handle it though. Don't know how start-up amps work, how many amps the lights are pulling, etc. But since folks are using it on 15 amp circuits, I guess that's just worrying too much. Read plenty of reviews, and only one guy said his lights flickered.

--Vic

[gfretwell]

Look around in the IR web site and get the installation/user manual PDF. I bet they recommend this should be on a 20a dedicated circuit. I have a similar compressor and that is what my book says.

If you have an amp of lights on a 15a you are pushing it. I guess pulling in another circuit is going be hard.

[Vic Smith]

No recommendation except call an electrician.

Might not be for an electrician. Don't know why I spent at least 50 bucks on fish tapes. Maybe I'll use them some day. I was going to pull 220 to the garage for a compressor some years ago. My brother said I could have a problem with corroded conduit. It's 1/2" I think, and underground the 30' from house to garage. So I just never got around to tackling it. Maybe I never needed the compressor so much?

But thanks. You mentioning 20a made me check my circuit box. Thought it was all 15's but there are four 20's.. When it's dark and my wife is home I'll turn on the garage door light on have her watch while I trip the 20's. Maybe I'm good to go. Now, do I really need that compressor.

--Vic

[bud--]

Is there any reason to believe that these motors have different characteristics than other cap start cap run motor (which is what this motor is)? Is there a reliable source that says compressor motors have a different characteristic? That is, is there any reason an honest company wouldn't use the real HP?

Perusing the Grainger catalog (real paper), many of the smaller compressors (maybe 6HP max) have a "peak HP" and a "run HP". Peak HP was what was used by companies that were sued in the class action. It is likely what "SPL" is. "Run HP" is the mechanical HP used at the rated air output (the real HP). "Run HP" generally ranges from about 30 to 65 % of "peak HP". In general the higher the HP the lower the percentage.

The companies in the class action presumably agreed to not mislabel their compressors. That puts them at a disadvantage to companies like Jon's.

It started when gfretwell said 1HP was about the max you could run on a

15A circuit. You said "nonsense" you run your 3HP motor on a 15A circuit. In the quote above clare told you it is not a 3HP motor. That is what everyone else has been telling you.

Then you said it was a 2.3HP motor - also wrong.

Nobody seems to know what you are saying, including you.

[Jon Danniken]

It says it's got a 2HP motor on a 115V circuit, which is impossible according to a number of people on this newsgroup.

You might want to call IR and tell them they have a misprint.

Jon

[Jon Danniken]

Bullshit. I never stated that I had a 3HP motor.

I did state that I had a compressor with a 15A motor, and that it was a "3HP SPL" rated motor.

At no time did I claim that I had a 3HP motor.

Nice troll, though, as with the other trolls in this group. You guys had me going for a bit, shame on me for falling for it.

Jon

[gfretwell]

If it is really a 20 you should be fine although you may see the lights dim when the motor is in locked rotor for the first half second or so on the start. Where you could have problems is if you had something else running and the compressor kicked on. I just looked and mine says 6.1 SCFM @ 90psi with the bogus "6.25" hp thing. Based on the nameplate FLA, I peg it around 1HP in an honest world compared to other motors. It might be 1.5 but that would be optimistic.

In real life who cares. The SCFM at the pressure you use most is what you care about. This thing will run an impact wrench if you have a fairly short duty cycle. The air chisel even has a shorter duty cycle (35-40%). Using a big paint gun is pushing it but if you watch your secondary regulator and stop when you see the pressure drop, you can paint. My big cup gun will usually go with about 75% duty cycle. Just about any compressor with enough pressure will run nail guns and such. I had 4 roofers, going as fast as they could go and the compressor was only cycling about 20% of the time.

I will warn you, once you get hooked on air tools, you will wonder how you lived without them. There is nothing better for working around your dock. You have no electrocution fears and lots of power. I borrowed a big air drill and I was spinning a 3/4" ship auger through SYP pilings. The only trick was holding on so you didn't get thrown in the water. They are air hogs. About half way through, I needed to stop and let it catch up.

[N8N]

Won't work on a 15A, 115V circuit. Should work OK on a 20A, 115V circuit however if there are no other loads connected. Note that current draw is listed @ 15A. You should not connect a motor that draws 15A, running, at full load to a 15A branch circuit.

Theoretically speaking, 2HP is 2*746W =3D 1492W or about 13A @ 115V, so even if the motor were 100% efficient it would still not be acceptable on a 15A circuit. (shouldn't load a circuit to more than 80% of its OCPD rating as a general rule, not sure if rules are different for motors or not. In the case of a 15A 115V ckt. that would be 1380W or

12A.) The compressor you describe draws 15A which is less than 20*0.8 or 16A so that is why I say that that should be OK, although it still might blow a fast-blow fuse on startup.

So, no, in short you shouldn't connect a 2HP motor to a 115V, 15A circuit (typical household circuit.)

nate

[Jon Danniken]

Not according to [e-mail], who stated "If it is 120v it will not be more than 1HP."

Surely you're not questioning the word of the almighty gfretwell?

Jon

[N8N]

I don't claim to be an expert on motors, but based on some cocktail napkin calculations, he's probably about right. Maybe a 1.5 HP motor would be OK, maybe it wouldn't, but 2 HP is definitely right out.

nate

[krw]

It ain't 2.3HP, either.

It's unseemly to pat yourself on the back in a public forum.

[Ashton Crusher]

I can think of another. It possible that there is some design difference in how the motor is wound or some other aspect that makes it more difficult for it to stall if someone shuts it off and then immediately back on when it's pumping under high pressure.

[Ashton Crusher]

I've understood what he's been saying since the beginning of the thread. He's never said it's anything other then what it's labeled as, a 3hp SPL and he's acknowledged that he's not claiming it's a 3hp continuous duty motor. He's simply said, several times, essentially the same thing clare just posted. Maybe there is some history here I'm not aware of but it seems like a lot of people went out of their way to attack him for pointing out there is a difference between a 'compressor' motor and a 'regular' motor.

[Tony Miklos]

I think Clare had the best idea about changing your single 115 line to a

220-240 line. Although I don't know if that calls for a third wire or if you can use the ground as a neutral and drive a ground rod in at the garage. If possible, that is your best bet for now and down the road. Double your capacity through the same wires.

[Vic Smith]

I don't have a dock, but one of my kids is a mechanic and has been doing all my car work. He's got plenty of air tools at work, but has no problem doing plenty of car work in my garage without them. A lot of cars, and doing stuff he would use air for if he had it. I wanted the compressor mostly for tires and sandblasting. Never had a problem turning a wrench or breaking a nut manually. He called yesterday and said his offer on a house was accepted. House has a nice garage. And he'll be farther away. I got a feeling at some point he'll ask to "borrow" the compressor for use in that garage, and I'll say "sure" because he does so much for me. But it will bug me a bit when I want to use the compressor and it's at his place. It's happened with other tools of mine. But like the other tools, I always end up figuring he's putting them to more use than me. And he's a good kid. So I get over it. He got most of my wrench sets, and what I did was eventually buy some new sets and lay down the law "These are mine, and mine only."

So now I'm thinking I'll get him the compressor as a "housewarming" gift after he closes. Avoid all the in-between stuff. Then see if I want to buy one for myself.

--Vic

[clare]

IF the circuit is dedicated to the compressor you can get away with L1 and L2 and ground with no neutral as you do not need any 110 volt capability. No ground rod issues ar anything, assuming you have a grounded cable now. You do need to mark the white wire red, or pigtail a red wire to it to identify the former neutral wire as a live conductor.

[Ralph Mowery]

Sometimes it is an 'investment' to get a son or son-inlaw some tools. Last Christmas I bought my son-inlaw a wire welder he had been looking at. Way more money than I wanted to give for a gift, but if I want something welded, he is only about a 15 minuit drive from the house. Beats me trying to learn how to weld to do a job I want done maybe once every two years.