Single phase 5hp motors - Baldor vs WEG?

[FlyFishn]

It just requires a motor teardown. But there could be other damage to the motor also. Frankly I never looked at the motors beyond confirming the centrifugal switch was fried, before I tossed them in the scrap bin.



At 240V, the max load on my single phase line is 23 amps, right at the nameplate amps for a 5HP motor.



Most modern motors with class''H'' insulation are just fine on a VFD. Consider that most 3 phase motors are dual voltage (230/460 in North America). What kills motors is the ''spikey'' output from a VFD, actually punches through the insulation. Since we are running them at half of their max rated voltage, it's really not an issue. The actual insulation in the motor is most likely rated at 1000 - 1200 volts. In my 40 or so years of hanging VFDs on motors, I have never seen a failure. I have been running VFDs on my machine tools for years, and have installed many on non-inverter rated motors over the years in many applications.

I didn't ask for any guidance from WEG, in fact, I purchased that motor from a guy on Craigslist for $125. It was brand new, never used. I know the brand so just went off of my experience.

I did some searching on VFD's this evening. It looks like the highest HP rating for a single-phase input/3-phase output VFD is 5hp.

I was tossing the idea around of a 7.5hp compressor motor with 3-phase via VFD. However, it does not appear there is such a VFD to handle the size motor from a single-phase service. So that puts me back to the 5hp class.

 

[mksj]

You can use a 15Hp 3 phase input VFD on single phase but it needs to be derated around 2 to do so, this varies by manufacturer/model. Basically when you purchase a single phase input VFD it is similar to a larger 3 phase input VFD. It has to do with the amount of ripple/THD and current spikes generated when feeding it single phase as opposed to 3. Problem with that route is it is a tough load, and a decent 15 Hp VFD is going to run you quite a bit and require a very big breaker/wiring. Technically the input wiring has to be rated for the total VFD capacity and not the load it is driving, the rating for the WJ200-110LF specifies 80A fusing with #4 wire. You would be much better off just getting a 7.5Hp single phase compressor which would be about 1K cheaper, take a smaller breaker and be a lot easier to install.

You can buy HY VFD's supposedly rated for single phase input, but others have pointed out that it is a bit misleading advertising. Compressors are a difficult load, most people using these generic VFD's significantly up-size them. If you read the reviews on say Amazon, they are not favorable in this application.

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[FlyFishn]

I decided on 3 phase because what was failing on the single phase motors is the centrifugal start switch, in all 3 cases.

It sounds like the mag start option is in addition to the centrifugal start switch and is adjustable. Would the mag start alleviate the wear on the centrifugal start switch if it is set for lower inrush current?

I am thinking just keeping things single phase and having all the necessary parts on hand to swap in should something go is going to be the route Ill go. I suppose having a 2nd motor would be the next option for a quicker way to get back running then rebuild the other one. Im not sure a 2nd motor is in the cards off the bat, though.

I talked to a guy at Saylor Beall today and he said they like to stick to Baldor in the 5hp class then switch to WEG with 7.5hp on up. I didnt get many details as to why other than Baldor seemed to have a good product there and they like to keep everything made in USA as best they can, where WEG is not US made.

 

[Janderso]

the Baldor motors are still good.

Mike, don't you think the industrial baldor motors are still excellent motors? The reason I say that, we have Baldor Industrial (10hp) in our stationary high pressure pumps that run the two car wash wands. They go 9-10 hours a day 6 days a week almost non-stop. Never an issue with the Baldors.

 

[JimDawson]

It sounds like the mag start option is in addition to the centrifugal start switch and is adjustable. Would the mag start alleviate the wear on the centrifugal start switch if it is set for lower inrush current?

No, not at all. Also there is no adjustment on a mag starter, it's just a big relay. Either on or off.

Edit:
You may be thinking about the overload adjustment, this is only for motor overload. Has no effect on the inrush current. The centrifugal switch sees motor locked rotor current on startup.

 

[FlyFishn]

Also there is no adjustment on a mag starter, it's just a big relay.

Either I was told wrong or there was a miscommunication/misunderstanding when I talked to the guy at Saylor Beall. He said the mag start was "adjustable". Maybe I didn't interpret what he said correctly then. How I interpreted it was the mag start being "adjustable" would allow the inrush current to be adjustable = softer start if desired.

 

[pacifica]

I did some searching on VFD's this evening. It looks like the highest HP rating for a single-phase input/3-phase output VFD is 5hp.

I was tossing the idea around of a 7.5hp compressor motor with 3-phase via VFD. However, it does not appear there is such a VFD to handle the size motor from a single-phase service. So that puts me back to the 5hp class.

You can also look at a 2 stage compressor to get more cfm from the 5 hp and a larger tank.

 

[JimDawson]

Either I was told wrong or there was a miscommunication/misunderstanding when I talked to the guy at Saylor Beall. He said the mag start was "adjustable". Maybe I didn't interpret what he said correctly then. How I interpreted it was the mag start being "adjustable" would allow the inrush current to be adjustable = softer start if desired.

A motor starter consists of two parts: The contactor, just a big relay. And the overload relay. Some overload relays are adjustable for current, but has nothing to do with inrush, only the motor running current. Are normally set to trip at a 125% overload.

The only way to get a soft start is with a soft starter, a rather expensive device. https://www.automationdirect.com/adc/shopping/catalog/motor_controls/ac_motor_soft_starters

 

[pacifica]

It sounds like the mag start option is in addition to the centrifugal start switch and is adjustable. Would the mag start alleviate the wear on the centrifugal start switch if it is set for lower inrush current?

I am thinking just keeping things single phase and having all the necessary parts on hand to swap in should something go is going to be the route Ill go. I suppose having a 2nd motor would be the next option for a quicker way to get back running then rebuild the other one. Im not sure a 2nd motor is in the cards off the bat, though.

I talked to a guy at Saylor Beall today and he said they like to stick to Baldor in the 5hp class then switch to WEG with 7.5hp on up. I didnt get many details as to why other than Baldor seemed to have a good product there and they like to keep everything made in USA as best they can, where WEG is not US made.

Also might be that the Baldor's cost more.

 

[mksj]

How many hours per day and the type of CFM or cycles/hr are you looking at? Single phase motors go for many years, and in my limited experience the start capacitor is the first to go. Never had to replace the start switch, but they are available for the WEG motors on-line for $35-50. Certainly a lot less expensive than replacing the motor. As Jim pointed out, there are thermal overload devices that attached on the contactor typically seen with the better compressors at 5 Hp and higher. This can be either fixed overload heaters or variable overload relay with a limited adjustment range and set by the manufacturer. Adjustments do not effect starting current. Soft start would be overkill and costly, they cost as much as a VFD and not sure how they would effect the start switch life. There are also solid state single phase motor starters, although I have only read about them.

With a two stage compressor, you have an unloader which softens the starting load, you can also set them for continuous run if you were doing something like sand blasting.