Compressor Motor Sizing

[TheClaw]

I've to a 3hp 9.3cfm at 90psi compressor with a 30gal tank. The tank has a leak on the bottom near the drain. Yeah, I know that's fatal.

I've found a 5hp 60gal compressor, the US General US660V that has a motor that runs hot and shuts down, for a price too cheap to pass up. What's the chance I can make that work with a 3hp motor?

Jeff

 

[Showkey]

Chances............I vote slim and none.......

 

[MacMcMacmac]

I've to a 3hp 9.3cfm at 90psi compressor with a 30gal tank. The tank has a leak on the bottom near the drain. Yeah, I know that's fatal.

I've found a 5hp 60gal compressor, the US General US660V that has a motor that runs hot and shuts down, for a price too cheap to pass up. What's the chance I can make that work with a 3hp motor?

Jeff

Easy. You just need the proper pulleys for the rpm and amp draw that will give you 3hp performance out of that 5hp pump, barring any other problems with the pump itself. You will lose some performance from the US General compressor, but you have to weigh that against the cost of a new tank, or whole new compressor. It might be something simple wrong with the motor on that one as well. Depends on how cheap you can get it for, and how cheap you can build up the "new" unit.

 

[DIC]

You will probably need to turn the US General down to 85 or 90 pounds

 

[larry_g]

Easy. You just need the proper pulleys for the rpm and amp draw that will give you 3hp performance out of that 5hp pump, barring any other problems with the pump itself. You will lose some performance from the US General compressor, but you have to weigh that against the cost of a new tank, or whole new compressor. It might be something simple wrong with the motor on that one as well. Depends on how cheap you can get it for, and how cheap you can build up the "new" unit.

I agree with 3M in that it can be done with pulleys. Another knob you have to play with is cutout pressure. You can decrease the cutout pressure to limit the max current draw. You need to reduce the pump speed ~30% or cut out pressure~30% or some combination of the two. Me I'd grab a pulley that slowed the pump ~20% and then lower the pressure till the amp draw on the motor is at FLA. The FLA is the bottom line in what you can do.

lg
no neat sig line

lg
no neat sig line

 

[Heavymetalmechanic]

Why not swap the pump/motor pair from the bad tank to go tank?

 

[LS6 Tommy]

Why not swap the pump/motor pair from the bad tank to go tank?

^^^This^^^ Done it a few times.

Tommy

 

[larry_g]

The last two posters bring up something to think about. A 3hp motor is only capable of so much work, or raising the pressure of so much air in a given time. So putting a bigger pump on the 3hp motor will not give you any advantage in air delivery. The basic of ~4cfm per HP still stands. The amount of air a compressor can deliver is determined by the motor hp.

lg
no neat sig line

 

[TheClaw]

Why not swap the pump/motor pair from the bad tank to go tank?

That's probably what I'll end up doing. Just have a smaller motor/pump on a bigger tank. I'm getting the other setup pretty cheap.

 

[JACDes]

You will store more air in the larger tank so your 3HP motor will cycle less often
however it will take a bit longer to fill the tank than the 5HP did.

The larger motor also provided more "working pressure" (SCFM ) since it could compress more air in the larger tank.

but if you were OK with the SCFM your smaller tank with 3 HP setup provided the larger tank with same size motor should deliver the same performance.

 

[TheClaw]

Since it slow, I've been searching the forum most of the morning and been online looking for used or new ones in my price range (which varies who asks, GF or SWIMBO). The difference between a decent used one and new is not that great. At least not great enough to sacrifice a warranty and known history. Still, I'm checking CL for a used unit but also looking at some new ones.

I posted this in another thread but In the $500-$700 range they all look the same,

Single stage,
3.0-5.0 hp
60gal tank
Some oil less some not
Max psi 135 to 155

Except for the IR SS5L5, they all weight about the same. The IR is hefty 450lbs.

In this price range, all they are going to be pretty much the same? Mexican motors, steel tanks, single stage? Are there brands more reliable than the others? Husky, IR, industrial air, Puma, powermate?

Thank you,
Jeff