Air Compression Motor

[tablesawtom]

I need to replace the motor in my vertical 60 gal. air compressor. It has a 3 hp,  3450 RPM,  single phase 220 volt motor on it. Harbor Freight has a 3hp 220 motor that is rated for air compressors, but it is 3600 RPM instead of 3450.

All of the compressors I have looked at are 3450. So I guess I am wondering why a 3600 for a replacement and will the 3600 RPM motor work for me?  And why would it be listed as rated for air compressors. Why can't any 3 hp 220 volt motor work on a compressor? 


Tom

[The Tinman]

The short answer is that the 150 RPM difference shouldn't cause any problems. The long answer is that there are too many variables to say that this motor should work. The first has already been addressed in that it is compressor rated, but will it bolt up to your tank and accept the pully that you have isn't certain yet. Look on the motors and see if they each give a frame  classification, they need to be the same. The frame will tell what the bolt pattern is and the shaft diameter.

[tablesawtom]

The short answer is that the 150 RPM difference shouldn't cause any problems. The long answer is that there are too many variables to say that this motor should work. The first has already been addressed in that it is compressor rated, but will it bolt up to your tank and accept the pulley that you have isn't certain yet. Look on the motors and see if they each give a frame  classification, they need to be the same. The frame will tell what the bolt pattern is and the shaft diameter.

THank you for taking the time to reply. I checked out the shaft size and frame and it is compatible. I just didn't think to post it. I don't heat my shop so it was 5 or 6 months ago checked it. I didn't buy it at the time because I wouldn't be needing it until it warms up and we are still waiting for that.  That and a broken finger that is bad enough that the doctor says no use not even driving.

So I am just asking.

Tom

[daddo]

I have a 1.5 hp HF motor running a grinder and it's been performing perfectly for three years now. I'd say it's a good buy- get a warranty if you can though.

[Roly]

I need to replace the motor in my vertical 60 gal. air compressor. It has a 3 hp,  3450 RPM,  single phase 220 volt motor on it. Harbor Freight has a 3hp 220 motor that is rated for air compressors, but it is 3600 RPM instead of 3450.

All of the compressors I have looked at are 3450. So I guess I am wondering why a 3600 for a replacement and will the 3600 RPM motor work for me?  And why would it be listed as rated for air compressors. Why can't any 3 hp 220 volt motor work on a compressor? 


Tom

It will work fine and will be 3450 rpm.   Enlarge the HF picture and read the label.    3600 rpm is the synchronous speed (which means nothing) because there is slip on this type of motor which brings the actual speed to 3450 rpm.   Roly

[barryvabeach]

Tom, to answer your second question,  compressor duty generally means that it is not designed to run continuously.  You can turn your table saw motor on in the morning, and run it for several hours, and it won't be much warmer than it started.  A compressor motor would keep getting hotter, which would shorten its life.  In use, the compressor more cycles on and fills the tank, then shuts down and cools off while you draw air from the tank, then it comes on again.   Other applications require that a motor run for long times without a break to cool down

[Bobby Thompson]

I need to replace the motor in my vertical 60 gal. air compressor. It has a 3 hp,  3450 RPM,  single phase 220 volt motor on it. Harbor Freight has a 3hp 220 motor that is rated for air compressors, but it is 3600 RPM instead of 3450.

All of the compressors I have looked at are 3450. So I guess I am wondering why a 3600 for a replacement and will the 3600 RPM motor work for me?  And why would it be listed as rated for air compressors. Why can't any 3 hp 220 volt motor work on a compressor? 


Tom

All 2 pole motors will run 3600 less certain losses. There are windage loss from the fan and frictional lossed in bearings so the motor runs a little less than 3600 rpm. I really doubt the HF motor will run a true 3600. Check the frame sizes. They are a NEMA standard. If they are the same they will interchange.

[TDKPE]

As stated, 3600 rpm is the synchronous speed at 60hz power. If on 50hz power, it would be 3000 rpm. Synchronous speed is the industry standard identifier as is the number of poles, which translates to synchronous speed.

The rotor must turn slower than synchronous speed in order to induce a current within it (hence the term induction motor) and the slower it turns relative to the synchronous speed the more current is drawn and the more torque the shaft outputs. The speed difference is called slip and is normally no more then about 4-1/2% though there are some very high slip designs usually used in Hoist’s and similar conveying machinery. But normal full load speed is about 3450 rpm or thereabouts, while unloaded speed is just a few rpm below synchronous speed.

Compressor duty usually means less expensive. Any continuous duty motor of the same output rating and number of poles (2 in this case) will be fine.

[Reverb]

Compressor duty usually means less expensive.

Doesn't it also usually mean that it's an ODP (Open Drip-Proof) type motor as opposed to (for example) TEFC (Totally Enclosed Fan Cooled) like what one might use for a table saw?

[daddo]

Some compressor duty motors are made for continuous duty. I know US motors makes them. You have to look at the specs.