need compressor motor choice advice

[Great white]

First off, I will freely admit I'm no expert on building compressors. I know enough to select a cfm/size for a tool/job and how to take care of them, but building the entire setup is something new to me. Fabricating stuff isn't an issue for me: MIG/Tig, Metal lathe and Mill in the shop.

I've got a "compressor", but it's nothing special. It's one of those cheap direct drive jobbies that you can't even be in the same room with when it's running. I knew it wasn't anything special when I bought it, but it was cheap and had an upright 60 gallon tank so I thought I'd give it a try. Can't be that bad, right?

Turns out the bigger tank just means that horrible oiless thing runs even longer. OMG do I hate that pump!

Had a dental appointment yesterday and arrived far too early to sit in the waiting room that long. So I thought I'd burn off a little time walking around an "overstock" type store that was a few doors down. In the back, they usually have some tools, so I made my way back there.

Now, I've been wanting to replace that noisy cheap compressor for a while, but the prices are just crazy for anything that's not a cheap direct drive thing like I already have. But sitting there on the shelf, hidden in the back, was a v-twin compressor. Nothing special, obviously a Chinese import:





Tag says "4hp" but the part number on the sales tag googles up to a 3hp. Single stage. Seems it's at least good for 8.8 cfm at 90 psi, which woudl be great for what I woudl use it for. I'm looking at it and thinking of ripping off the direct drive noise maker and reusing the tank for this vtwin pump. Also possibly reusing things like the pressure switch and such. Price tag says 75 bucks, far less expensive than anything I've found yet.

So I grab it, drop it in the truck and go to my appointment. This store is one of those "but it if you think you want it because it won't be there when you come back in ten minutes" type of places. People tend watch what you show interest in and if you walk away, they grab it and it shows up on marketplace or Kijjji or the like for (usually) double what they paid for it.

I get home and start looking around for a motor. Nope, everything I have lying around is fractional. Then I remember the clutch motor from the industrial sewing machine I replaced with a servo (walking foot and I use it for sewing leather). That clutch motor was monstrously heavy, it must be a couple HP at least. Nope. 60-70 lb (as big as my thigh) and rated at 1/2 hp.


So I need a motor. OMG they're not cheap up around 3hp! evn used they want almost the same. Most are also 220v and/or 3 phase. The compressor is right next to the panel in the utility room, but I'd still have to have an electrician come in the wire up a 220 socket. 3 phase is out of the question.

Do they even make a 3hp 115v motor?

And one that doesn't cost 300-400 bucks?

I've also seen a picture on the internet where a guy took the direct drive motor off his cheapo compressor and adapted a pulley to the shaft to run the same type of pump. But my oiless only says "2hp peak" on the data plate, so I doubt it's even a 2hp.

There will be no welding on the pressure tank, I know enough not to mess with that stuff! All the "mounting" work will be done to the existing rails already factory welded on the top of the tank.

What woudl happen if I put one of these under rated motors on the pump? low/no cfm? Lock up the motor once pressure builds? Just flat out burn the motor out?

I can spin the pump easily with no load, but I'm assuming that's where the Hp rating comes in: under load as it build psi.

I'd like to get this set up inexpensively, but I'm starting to think I'm going to be into it for at least another 300-400 bucks.....

 

[micromind]

3HP motors are made that'll run on 115 volts but the current will be more than 20 amps (more like 30ish) so you'll need to run another circuit anyway.

Compressor pumps have a m minimum and a maximum RPM. Too slow and oil doesn't get splashed around enough to lube it properly. Too fast....well, that's obvious. The minimum is often around 400 RPM, the maximum is usually around 1500 or so (Of course, someone will pipe up and say 'my compressor runs at 5,247,366 RPM so you don't know what you're talking about').

Make sure the nameplate of the motor actually states 3HP and not blank or SPL. A motor that runs at a bit less than 1800 RPM is better than one that runs 3600 or so.

As a wild guess, I'd say a 3HP motor would run that pump at 125PSI at around 700 RPM. Wild guess though......

 

[Great white]

All my garage plugs are 20 amp. Had the electrician build it that way when we were building the house. Only 30 amp stuff is the trailer plug in and I can't remember what the welder plug was, I think it was 35 but memory fails me right now.

All the info I can find on the part number indicates it is spec'd to run at 1070 rpm.

easy enough to adjust with pulley diameters as long as the motor doesn't run stupid high rpm....

 

[mark-NJ]

Yes, single-phase 3HP motors are available.

Per the tables in NEC, a 3HP @ 120V is going to draw 34A. Now, that's a "one size fits all" answer, and actual motor currents will vary between different makes & models, but yes: a 3HP @ 120 draws a lot of current. At 240 it's about half that, which is manageable.

 

[Great white]

well now. Pulled the cover of the cheapo "2hp" compressor and was greeted by this:



No data plate, just the sticker on the tank that says "2hp peak". The tiny little compressor is built into the front frame, but it's still a belt and pulley.


I remember where I'd seen it one before. It was a picture on harbor freight:



I think it was 2hp rated pump on HF, although it looks identical to the model I bought. HF:



Mine:




Doesn't mean it's the same internals though.

Looks like he pulled the compressor off the frame and his mounting choice isn't exactly what I woudl do, but it must/might work for him.

So I may give it a try. Nothing to loose as the little compressor isn't much good for me as it is. Might as well at least try and repurpose it rather than just toss it out. I'm no further behind if it doesn't work....

 

[Great white]

well screw it.

Decided to do it right first time around and found a 3hp single phase compressor motor (new) that didn't break the bank.



Nothing overly special, but will get the job done well enough.

I've got a 3.2" pulley with 5/8's shaft here on the bench already and it works out to right around 1100 rpm at the pump. I'll reuse the original 26 tank and have a new 230v plug wired into the utility room (lots of space still in the panel) in the new year.

I thought it was a 60 gal vertical tank, but I was wrong. It's only a 26 gallon, which fits in the space I have available nicely. Just means the pump will come up to pressure faster, even though it will likely have to run more often while in use.

Maybe I'll see if I can sell on he original oiless direct drive pump. Might be someone who'll give a couple bucks for it. Couple bucks would still be better than tossing it in a landfill.....

 

[The Cobbler]

Maybe I'll see if I can sell on he original oiless direct drive pump

List it on Kijiji , would be good for someone looking for parts even . Or, hang on to it and make it into a small unit without a tank for airing up tires, or a pony pump for when you need a bit more air than your new system provides .
can you tell I have hording tendencies?

 

[The Cobbler]

There was just a thread on here re Vevor 5 HP motors not lasting. I hope you have good luck with your 3 hp !

 

[Great white]

There was just a thread on here re Vevor 5 HP motors not lasting. I hope you have good luck with your 3 hp !

It's not going to get very hard use. My air tool demands have really dropped off in the last 4-5 years. Getting old *****.

But, when I need them I need them. And then there's also the horrible racket that oiless compressor makes......will be nice to at least be in the next room and not want to run out screaming when it turns on.....