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1HP Bridgeport, low power using VFD for RPM

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Janderso

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#1
Maybe this is a dumb question but here it is.
Using the BP over the weekend, had a 3/4 end mill, it had low power where I could have easily stopped the motor. Took light cuts and got the job done.
Should I be changing the belt ratio for more torque, slower speed vs. using the VFD in a case like this?
Thank you for your advice.
 
D

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#2
I don't know a lot about vfd's so someone who does is sure to correct me .
I think slow speed torque depends a lot on how your vfd is set up and the motor it's self .
But if it's set up right and your running the motor slow enough to stall yes you should be changing the belt to a lower ratio

I have a 1hp inverter rated motor on my lathe with a Hitachi wj vid
If I set the belt for 750 rpm spindle speed @ 60 hertz I can slow the motor down to 5 hertz and make the belt slip before the motor even thinks about stalling
 

Dave Paine

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#3
The motor will not have much torque at low RPM's as you experienced.

MrPete222 has videos on refurbishing a Pull Gear to achieve lower speed with good torque. He removed his VFD from this drill press due to not having sufficient torque as low Hz/RPM.

You will get better torque is you change belts so that the VFD is running the motor as higher RPM's.

FYI, an Australian fellow was inspired by MrPete to make his own Pull Gear. Several videos. I found these very interesting. Part 1.

Mark Presling Pull Gear part 1 video
 

macardoso

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#4
A standard Volts/Hertz VFD will provide constant torque down to roughly 1/2 of the nameplate speed. As you use fancier VFDs with Field Oriented Control (FOC) or Flux Vector Control (FVC) you can get constant torque down to 1/100 or even 1/1000th of the nameplate speed.

If you didn't pay top dollar for your VFD it probably will not have these control strategies. I would change pulleys for increased torque at low speed.
 

Janderso

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#5
My VFD is a Teco, Fluxmaster FM50.
I have no idea if it is a good VFD.
I will try the pulley method and see what difference it makes.
To be honest, I looked at the programming of that thing and I just don't know enough about it to make any changes with confidence.
I am concerned I will screw it up.
 
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#6
For my lathe I tend towards using the step pulleys for spindle speed changes and use the vfd to fine tune the actual speed .
Biggest benefit is being able to take a much better guess to actual speed and material removal rates without having a tachometer.

And I thinks it's also a good idea to keep the motor speed fast enough for the cooling fan to be effective.
 

Modelmakerbue

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#7
Is the motor wired correctly to the VFD, I had the exact same problem.
 

JimDawson

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#8
Unless you are using a sensorless vector VFD, the torque will drop off as the rpm is reduced. In this case changing the belts is the way to go. Using low speed (back gear) would be the best way to run a 3/4 endmill.
 

Janderso

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#9
Is the motor wired correctly to the VFD, I had the exact same problem.
I did verify the wiring is correct.
The motor speed regarding cooling benefits makes sense.
I have never moved the belt.
Determining speeds using the belt is a bit of a challenge as I do not know the step RPM rates.
I imagine there is a diagram in the manual?
1971- J Head, step pulley 1 HP.
 

JimDawson

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#10
Here are the speeds. The low speeds are in back gear.
1534358679766.png
 

P. Waller

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#11
We have a Trak FHM7 mill with a 7 1/2 Hp spindle motor, a 1" drill will stall it at a speed slow enough to use it.
No back gear
 

BaronJ

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#12
Hi Jim,

Is the motor wired for delta ?
 

Technical Ted

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#13
Maybe this is a dumb question but here it is.
Using the BP over the weekend, had a 3/4 end mill, it had low power where I could have easily stopped the motor. Took light cuts and got the job done.
Should I be changing the belt ratio for more torque, slower speed vs. using the VFD in a case like this?
Thank you for your advice.
I have two of those Teco FM50 VFDs. Running the motor at 60 Hz should give you full HP. Select spindle RPM with your pulleys. This should give your full power.

Sometimes you can get away with leaving the belt/pulleys alone and just vary the VFD, but sometimes you can't especially in a non-vector rated motor like these old Bridgeport motors. Running at lower Hz can cause overheating and loss of power/torque.

Monitor how hot your motor gets while working as well. If you put your hand on it and it's getting really hot, I would up the Hz to 60 (not much over) and keep it there so things will cool off and run the way the motor is designed. Use the step pulleys for big variance in spindle RPM and stay fairly close to 60 Hz in these old motors.

Just my two cents,
Ted
 

Janderso

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#14
Great advice, I appreciate it.
I'll up the Hz. and change the belt position.
Thanks for the belt chart, mine is gone.
I'll see how it improves the torque/power this weekend.
 

BaronJ

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#15
Hello Jim,

Since you didn't answer my question, I'll assume that you don't know. The motor can be wired in two configurations, star and delta. For best results with a VFD it needs to be wired in delta.
 

Janderso

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#16
Hello Jim,

Since you didn't answer my question, I'll assume that you don't know. The motor can be wired in two configurations, star and delta. For best results with a VFD it needs to be wired in delta.
Sorry,
I have no idea. I do have the manual on the VFD. I am so limited when it comes to anything electrical.
My son works for a commercial electrical contractor, but he does not get involved in motors or machine wiring.
 

BaronJ

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#17
Hi Jim,

If you look on the side of the motor you should see a label indicating the two possible configurations of the motor. Now if you look inside the motor connecting box you should see jumpers on the terminals. Those jumpers correspond to the label. Please make sure that you remove the power to the motor before looking in the connecting box.

Somewhere I have a picture showing the label. I'll post it if I can lay my hands on it.
 

JimDawson

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#18
Hi Jim,

If you look on the side of the motor you should see a label indicating the two possible configurations of the motor. Now if you look inside the motor connecting box you should see jumpers on the terminals. Those jumpers correspond to the label. Please make sure that you remove the power to the motor before looking in the connecting box.

Somewhere I have a picture showing the label. I'll post it if I can lay my hands on it.
There are no terminals on this motor like a European motor. In this case this is either a 9 lead motor if it is a 230/460 dual voltage, or if 230V only, has 3 leads for the input connection. Bridgeport used both motor types. You don't have a choice to connect Y or Delta.
 

BaronJ

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#19
Hello Jim,
Thank you for the information.
I do apologize, I had no idea that the USA market had different motor configurations. I've only ever had experience with the dual voltage motors.

I posted that information based on experience with people that wired in a VFD without changing the motor to delta and suffered loss of power.

To Janderso, I'm sorry if I mislead you ! I was unaware of a single voltage Bridgeport motor.
 

JimDawson

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#20
Hello Jim,
Thank you for the information.
I do apologize, I had no idea that the USA market had different motor configurations. I've only ever had experience with the dual voltage motors.

I posted that information based on experience with people that wired in a VFD without changing the motor to delta and suffered loss of power.

To Janderso, I'm sorry if I mislead you ! I was unaware of a single voltage Bridgeport motor.

In doing some research I did find a diagram to connect a 9 lead motor as delta, so it may be possible. But I have never seen that connection diagram on any low horsepower motor data plate.

To really get low speed performance out of a VFD driven motor, you need a sensorless vector VFD. With that you get 100% torque down to near 0 RPM. That gives you constant torque below the base speed, and constant HP above base speed.
 

BaronJ

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#22
Hi Jim Dawson,

The information that I gave is common to most if not all three phase dual voltage motors. In an industrial setting, a three phase motor would normally be connected to a mains supply voltage of 440 volts AC at 50 or 60 Hz. I believe in the USA it is a little different voltage wise. At this voltage the motor windings would normally be connected in a star configuration. By connecting the three motor windings in a delta configuration, the motor will run on a 220/240 volts three phase supply at full power. Nowadays 220/240 volt three phase in the UK is virtually non existent.

There are few VFD that will step up the voltage from a 220/240 volt single phase supply to the 440 volts. The vast majority of VFD will however produce a variable frequency three phase supply of 220/240 volts. Since the motor speed is determined by the supply frequency, being able to change the supply frequency by means of the VFD means that the motor speed can be varied.

By changing the motor windings configuration to delta the motor can run at full power on the 220/240 volts supplied by the VFD.

This works because when the motor is wired in star the whole 440 supply volts is shared across two motor windings. When wired in delta the supply voltage is across just one winding.

Very often the information of how to change the motor configuration is either inside the lid of the connection box of the motor, or in the case of the dual voltage Bridgeport on a label attached to to side of the motor.

A clue is if there are six terminals inside the connection box with jumpers going between or across the terminals. Somewhere I do have a picture of the label attached to a Bridgeport motor.

Ted: The link you gave demands that you register to view ! I don't want to. But thanks anyway.
 

Technical Ted

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#23
[QUOTE="BaronJ, post: 605428, member: 51560"
Ted: The link you gave demands that you register to view ! I don't want to. But thanks anyway.[/QUOTE]

That's interesting... I didn't register. It did come up grayed out with some banner on it that I didn't take time to read. I left the site and then went back to it and I got right in.

Oh well, there are other sites that give the same information. Just do a Google search and you'll find more information than you want! ;)
Ted
 

BaronJ

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#24
Hi Ted,

Thanks for that, I'm in the UK so they probably have different rules for us.
I doubt that the information I gave would be very different anyway.
 

Technical Ted

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#25
Here's a YouTube video with about the same info. The 3 phase motors I'm familiar with are internally configured for delta or wye as the video explains and he demonstrates a method for determining how it is configured if no nameplate info is available.

There may be and probably are other types of 3 phase motors used in the USA that are different, but this type are typical/common and the only dual voltage 3 phase motors I've come across in my travels.


Ted
 

BaronJ

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#26
Hi Guys,

Still haven't been able to find the Bridgeport picture that I was looking for !

However I did remember that my ML8 lathe had a half horse power three phase motor and needed to check that it was correctly wired in delta. So I took some pictures of it. It is a Brooks motor made shortly after Crompton Parkinson took them over in the 70's or 80's. I don't recall.

Any way the motor is rewirable for star or delta connections, the information being on a label attached to the inside of the terminal box cover.

17-08-2018-004.JPG
You will notice that the rating plate indicates that this is a dual voltage motor and shows the star and delta symbols. Also the plate indicates that the motor rating is CR (continuous running). Ideal for use with a VFD.
17-08-2018-005.JPG
This picture is of the label under the terminal box cover. It describes the wiring changes needed to alter the voltage and the winding configuration.
17-08-2018-006.JPG
17-08-2018-007.JPG
 

Technical Ted

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#27
Interesting. It would be nice to have that flexibility here in the USA, but we have to take what the manufacturer gives...

Ted
 

BaronJ

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#28
Hello Ted,

Thank you for your comment. I was of the, it seems, mistaken impression that some machines, particularly Bridgeport, had this flexibility. I was unaware of the single voltage, single speed motor fitted to some of these machines.

However I have knowledge of a number of people that have taken the trouble to make modifications to motors that didn't provide facilities for the user to alter the wiring configuration in a simple way. These users have altered the winding configuration internal to the motor and brought both ends of the three stator windings out so that they can use 440 volt star wired motors in delta on 220/240 volt supplies from VFD.

But if you don't have the knowledge or the skills to do this yourself, taking the motor to a motor rewinder and letting them do it for you, would be one way.
 

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#29
However I have knowledge of a number of people that have taken the trouble to make modifications to motors that didn't provide facilities for the user to alter the wiring configuration in a simple way. These users have altered the winding configuration internal to the motor and brought both ends of the three stator windings out so that they can use 440 volt star wired motors in delta on 220/240 volt supplies from VFD.

But if you don't have the knowledge or the skills to do this yourself, taking the motor to a motor rewinder and letting them do it for you, would be one way.
I have just done this on my King Rich 5hp 415V motor, It is not difficult, you need to find where the 3 windings are stared and bring these out.

BTW a 415v 50hz motor will run at full torque at 240V 30hz but run at 60% speed because the motor is still in the V/Hz curve.
 
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