# 10hp Motor Help



## Hamstn (May 23, 2015)

I purchased a lathe with a 10hp motor. I am running it off a VFD with single phase 220 input. I now know after reading that I really should have bought a larger VFD then the 10hp rated one. But so far it is holding up fine with no errors and I have stayed below the current ratings of the drive.

The problem I have seems to be the motor. It runs fine at 60hz even taking a .300 DOC at .5 in/min. 217rpm?. The problem seems to arrive when I go much above 60hz. First I start to get a vibration in the lathe. Maybe a balance issue? I also loose torque. Taking the same DOC as above it will start to stall the motor. Also I can't run the lathe in the next higher gear even with no load as the motor will start to slow down and amps rise. Previous owner did say the drive pulley is bigger then OEM so the speeds are 15-20% faster then on dial. Just not sure if I need to look at a different motor or what, and if so would a 7.5hp be enough or I need to stick with a newer 10hp.


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## Ulma Doctor (May 24, 2015)

7.5 hp even sounds like a lot of HP for a lathe i'm accustomed to, it must be big...
What size and brand of lathe are we working with here???


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## Tony Wells (May 24, 2015)

First thing I would do is put the OEM sized pulley back on the motor. If the PO did this because he needed a higher spindle speed, that's one way to get it, but at the expense of torque, and possibly bearing/gearing damage from higher speeds than designed for. I have seen this done on older lathes that were in use before carbide caught on. I never was comfortable with the idea though. 

As far as getting a new motor, unless you need to work the machine that hard, you don't need 10 hp. There are times when it's really nice to be able to peel off material in a hurry when you are in the business, but most hobbyists have time.


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## Hamstn (May 24, 2015)

The lathe is a Monarch CM20 with 22.5 swing made in 1941. It's huge so it's much more then those who have one just for a hobby. I don't use it for a living but do have a need at times for my equipment repairs and I may in the future do some outside work. It did have a 15hp on it at one time. I am not concerned with turning it say up to 25% faster. Speeds range from 10 to 450 so it is on the slower end for carbide on smaller work, but that is what I have a smaller lathe for.


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## Karl_T (May 24, 2015)

I'd suggest a bit more diagnosis before acting. What is spindle load, or motor amps doing?  Both while cutting and free running.  I'd also suspect a bearing problem someplace. A poor man's bearing noise instrument is a length of tubing, one end at the ear, the other poking around for a noise source. Can you rip the belt off and run the motor up by itself?


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## mksj (May 24, 2015)

Hamstn said:


> VFD with single phase 220 input



What size VFD are you using, usually the largest single phase unit is 5Hp? A 3 phase input VFD used on single phase would need to be up sized considerably (probably 20HP). Hitachi AN032404-1 recommendation for 3 Phase VFDs used on single phase: "The rule of thumb Hitachi recommends is to start with the 3-phase motor’s nameplate full load amperage (FLA) rating and double it. Then select an inverter with this doubled continuous current rating. This will give adequate margin in the input rectifier bridge and bus capacitors to provide reliable performance. NOTE: Fusing or Circuit Breakers should be sized to match the INVERTER input current rating, NOT the motor current rating!"

Similar issue: http://www.practicalmachinist.com/v...single-phase-10-hp-3-phase-vfd-output-102887/


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## JimDawson (May 24, 2015)

I'm with Tony and Karl on this one.  It sounds like either there is some mechanical problems, and/or the VFD is current limiting.  When not cutting, that motor should turn the lathe at any speed the machine is capable of.   Above 60Hz the torque will start dropping off and the current will go up.  If the VFD is not single phase input rated, then you would have to de-rate the VFD by about 1/3.  It is possible that the VFD is sensing high input current and is cutting back to protect it's self.  You should put an amprobe on the input and see if it is exceeding the rated input current.

Not sure what the vibration is, at spindle speeds that low I wouldn't expect much.  Maybe it's coming from the motor. The best way to determine that would be to pull the belts off and run it.


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## Smithdoor (May 24, 2015)

I had 10 hp single phase 220 on lathe use for 30 years work great till sold the lathe
Work great
In the shop I had phase converter and replace a few times

Dave


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## Hamstn (May 24, 2015)

> 'd suggest a bit more diagnosis before acting. What is spindle load, or motor amps doing? Both while cutting and free running. I'd also suspect a bearing problem someplace. A poor man's bearing noise instrument is a length of tubing, one end at the ear, the other poking around for a noise source. Can you rip the belt off and run the motor up by itself?



No need to take belts off as this lathe is clutch driven. At idle motor is quiet and has had new bearings a few years ago. Spindle load, reading amps on the VFD is around 8-10 amps. Cutting I think it was around 12-14 amps. Idle I think was 5-6 amps. When I shift up the spindle or try to run over 60 hz the motor slows and the amps slowly climb. On test I did I shut off the motor when it reached 24 amps. Motor was running good with  10 RPC in the shop I purchased it from. Maybe this is the route I should take.

The VFD will operate on single phase but it says performance will be degraded and it should be derated to 5hp. I only found the rating after I bought it and very little in the manual on the subject. I can turn off phase loss but I have not had to as it also lists to hook single PH to T1 and T3. Hooking to T2 will throw the error code.

Now that it is mentioned it may be very likely that the VFD is cutting back. Reading the link provided they were recommended a 100 amp single PH at 10 hp? I need to check voltage drop under load.


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## mksj (May 25, 2015)

At 24A you VFD is most likely cutting out, and as you exceed 60Hz, as the voltage is constant and you are loosing torque (and current if I understand the VFD parameters). I am actually surprised the VFD worked under load at 60Hz. I would be concerned about the longevity of the current VFD (rated at 5Hp on single phase), as the input rectifiers and capacitors are likely to fail (see attached documents).  Based on the current draw, you would most likely need a 20Hp 3 phase input VFD to use on single phase at 230V in. A 15Hp VFD is almost the same price as a 20Hp and that would be pushing the long term reliability. The Yasakawa document provides some additional information on single phase draw and fusing for your sized motor (P9, Table 2).


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## Reeltor (May 25, 2015)

If the previous owner was using a RPC and it was running fine, I'd have to agree with the others who posted--- that it's the VFD that is the issue.
I've never had a VFD so I can't comment on how "great" they are.  Only thing is, I am a fan of rotary phase converters; a properly sized RPC will run any 3-phase motor that you currently own or may purchase in the future.  No programing, Yada, Yada, Yada, you get the picture


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## merlewagner-2 (May 27, 2015)

I would think the VFD is cutting out. Surprised the unit is running under load. I have a 20HP VFD running a 10HP AIR COMPRESSOR  and it runs great, at least the last 10 years. I have it setup to ramp up on startup and the lights in the shop are never flickering, etc. 

I would be careful running an old motor at a different cycle as they will get pretty hot fast. Old motors were not designed to run that way.

Merle


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## ChrisW (May 27, 2015)

I did a quick search on a CM20 and found that it was equipped with a 20 hp motor.  Yours has a 10 hp motor with a larger drive pulley and an undersized VFD.  Sounds like it's way under powered.  No wonder it wants to stall.

Chris


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