Machine electrical testing

[Mmfh]

Hey there,

I'm having a problem with my automotive surface grinder, high speed for the cutter head is not working properly. This is a two speed cutter head and has a switch on the console for low, neutral, and high.

When you turn it to the high position it just growls and grumbles, and tries to turn but very slowly. I turn it off quickly as it sounds very wrong.

This is 220v 3 phase, I'm making the 3 phase with a Rotary Phase Converter, 25hp idler motor. Tested voltage and between the legs I have 212v. 214, 237v.
That's measuring between 1 and 2, 2 and 3, and 3 and 1.

I don't see what changes the speeds for this 6hp motor, its something in the console, but the console is full of contactors and relays and just basically crammed full of stuff.

What would you check first to see what's going on with this high speed problem? I just don't know what to look for, low voltage controller?

Any help would be great!

Thanks

Mm

 

[ddawg16]

There are typically 2 ways to vary the speed without using a VFD....step down transformer or seperate windings in the motor....chances are your motor is wired two speed....

Pretty easy to confirm....see what is between the switch and the motor....and look at the motor name plate....if there is nothing but wire going to the motor...then your nameplate should show the connections.

If so...chances are you have an issue with the high speed windings....or it could be something as simple as bad contacts on the switch.

To confirm....bypass the switch following the wiring notations on the name plate....if it works fine...switch...not fine...motor.

 

[larry_g]

First question here is, Have you ever had it working at this place?. A two speed motor has two sets of winding's in it and the switch selects which set is working. Most likely the switch is setting a contactor so you have to determine which contactor is the one that is supposed to be doing the switching. Do you have schematics?

lg
no neat sig line

 

[Mmfh]

I have a very basic diagram but its really of very little help. I took the plate off the motor and inside is a block afair, 6 screws, both sets of 3 screws has leads that seem to go back from the motor to the console. Like maybe it is a two speed motor.

I have not used this machine at this location, I bought it a while back and have been working on the shop getting it ready and setup for work. When I bought it he told me that to run in high speed you had to first get it going on low speed. I thought that was very strange but I let it pass as something I would deal with later. Price was right.

Now when you get it going on low speed, and quickly turn the switch to high speed it slows down and makes ungodly noises. Sounds like a bad connection somewhere to me, probably in the console.

I took the lower cover off the console, one I hadn't seen before, when you try to start it on high its like a blue fireworks display inside behind and those contactors. It has 6 contactors and now that I type this I think I verified that it is a two speed motor.

How do I find which one it is? At this time I can't even see what holds in this group of 6 contactors, just a large assembly of componnets and I can't see what hold them all in there.

Sorry about the length of this, any more suggestions after reading this?
Do two speed motors often go bad? Contactor maybe? Hopefully bad connection!!

Thanks again!

Mm

 

[Mmfh]

Can I take power straight to the terminals inside the motor plate and test it that way? No contactor, no starter, just power right from the RPC to the motor terminals?

Thanks

 

[larry_g]

Can I take power straight to the terminals inside the motor plate and test it that way? No contactor, no starter, just power right from the RPC to the motor terminals?

Thanks

Probably, if you know the correct wires to use. I can't seem to find my 'Electrical Motor Repair' book off hand or I would post a picture/diagram.

This book http://www.amazon.com/dp/0030790905/?tag=atomicindus08-20

on edit Make sure that the controls of this machine are not powered by the generated leg of the RPC. That Dufore mill I have would chatter and bang when the controls were connected to the generated leg because the start/inrush current would drag the voltage down on the generated leg to a low level and the contactors would then drop out loosing power to the motor. I ended up moving the power wires one spot to the right and all was good.

lg
no neat sig line

 

[Mmfh]

That's interesting about not using the generated leg for the controls. When I first hooked this up the low speed worked fine but spun in the wrong direction. I switched a couple of wires and now it spins the right direction. Maybe if I change the another one.

Something to try for sure. Its been so long since I've been inside of a machine like this, I feel stupid but starting to remember a few things.

Thanks

 

[W-Cummins]

Yep, NEVER use the generated leg to run ANY thing but a motor load. It's normally running about 200 volts to ground and will mess up stuff. It may be that you will have to re-wire the machine, as it may use one leg for some control voltage and another for another control segment ( this would not cause any problems with normal non-high leg 3 phase power ) but will cause lots of grief when you have both a high leg and directional conflicts.
Did it run backwards on both speeds?? If it did and will not on another rotation of the phases, Change it back to the reverse condition and rotate the sets of motor leads at the motor ( both sets).

William....

 

[PRH44]

If you have a two speed two winding motor you should have two 3 pole contactors.
As ddawg and others have stated taking power directly to the windings can be a way of testing.

Normally the terminals at the motor will be labeled T1 T2 T3 for low speed and T11 T12 TT13 for high speed. Some MFG may have T6 T7 T8 for high speed.

Always test live with all covers closed as a short could cause and arc flash of large magnitude.

You could have a Wye-delta motor. You would have (3) 3 pole contactors with one contactor having what appears to be jumpers from phase to phase on the load side.

This would be a different type of test.

 

[Mmfh]

Well, I didn't have time to do much to the machine today, but I wanted to upload the schematic for anybody to see and possibly give me a couple of idea's if they wanted too.

This is all the electrical info I have for this machine. I was going to switch the wires around today but after the day I had I'm not up to it. I'll try to do it tomorrow if I get a chance with Easter dinner and family coming over.

Thanks for any info you may have for me!

Mm

 

[larry_g]

Well I've got to do a bit more studying of that but I'm sure that the generated leg from the converter should connect to the T connection point. Do you know which motor your having problems with as it looks like both M1 and M2 are two speed motors, but of different styles. I assume the M3 is a pump for coolant.

lg
no neat sig line

 

[71flh]

If we think about what's going on, the switch you press to actuate the thing is the most often used mechanical device, so its most likely to be the problem. Since its 3-phase, next would be the device that pushbutton is controlling, probably a contactor, that has a bad set of contacts.

Of course I'm guessing, but it sounds like maybe one leg is missing.

 

[PRH44]

Motor one is Wye-delta. Motor two is a Wye-delta wired for forward and reverse control.
Motor 3 is an across the line start single speed.

Which motor is giving you the trouble #1 or # 2 ?

 

[PRH44]

Are the other 2 motors functioning properly?

 

[Mmfh]

Are the other 2 motors functioning properly?

Yes, the other two motors are working as they should. One is a table traverse motor, two speed, the other is a single speed coolant pump.

The main motor, 6hp, runs the cutter head, its the one with the problem and from the diagram I'm not sure which one it is, but I assumed it was M1.

I used the machine yesterday on low speed for the cutter head, sounded fine, ran very quiet and strong. High speed, not so much.

I'm sorry I wasn't able to do much checking yesterday, I had a lot to do and wasn't feeling good after that. I'm hoping to move wires around today.

Thanks

Mm

 

[PRH44]

I also think M1 is the culprit. If the other three phase motors run fine that rules out 3 phase voltage issues.

Do the controls seem to work fine on the other two motors?

The high speed on this motor requires the windings to be be configured in a delta configuration.

I can tell you how to test this but first we need to clarify the following.

Did you reversed two wires on just this one motor to change direction? If you did where did you do this? You must be very careful of the phase relationship.

 

[Mmfh]

I also think M1 is the culprit. If the other three phase motors run fine that rules out 3 phase voltage issues.

Do the controls seem to work fine on the other two motors?

The high speed on this motor requires the windings to be be configured in a delta configuration.

I can tell you how to test this but first we need to clarify the following.

Did you reversed two wires on just this one motor to change direction? If you did where did you do this? You must be very careful of the phase relationship.

Everything on the machine seems to work as it should, except for the high speed for the cutter head.

When I reversed the wires to get the cutter to turn the correct direction I did it right where I attached the cord from the machine to my Phase Converter. Nothing inside of the machine.

The direction of rotation for the cutter head at first was the wrong direction, also the table direction of movement was also going the wrong way. When I switched two of the wires at the end of the power cord everything started turning and moving in the correct direction again.

As far as a Delta, or WYE motor, truthfully I don't know what that means although I've heard of it before. Not sure what it means.

Thanks

 

[MBfreak]

I am the happy owner of a fantastic book, " Electric Motor Repair" by R Rosenberg. In it is some illustrative diagrams on two speed three phase motors. Pse send me a PM with your email if you want a copy of the drawings. Two speed three phase motors can be achieved in differenr ways.
Check the inside of the motor terminal box for a diagram of the motor you have.
However, since the machine basically works correctly except in the hi-speed M1 mode it is quite likely that the M1 motor itself is all right.
My guess would be :
The phase converter is not stable enough to supply " simulated" three phase in M1 hi speed mode. Try shifting the incoming wires one step ahead ( ie L1 to L2, L2 to L3 and L3 to L1. ) Test , you may be lucky . If no success, another step ahead, then try.
If still not OK, examine the M1 contactors very closely. They should be silent when energized with no chatter and show no sparks in either lo or hi speed mode when runnig the motor.
Disconnect incoming power and use an ohm-meter across each contact. Push the contactor to close and verify that you get zero ohms( below 0,2 ohms) on each contact as you push it closed.

Best regars

Ola

 

[PRH44]

MBfreak raises some good points concerning the phase converter and contactor condition. The contactors should never chatter or arc while running. They could be in rough condition and causing a problem.
After reviewing your schematic It appears the nomenclature is an older IEC using UVW, XYZ.
The contactor control scheme is using what is known as a High speed (2) WYE (parallel configuration) and Low speed (1) WYE (series configuration) The low speed could be delta for constant torgue application. Non the less
The motor windings appear to be OK if you are running on slow speed wth no events.

When you switch to high speed you will be creating more current. Your current should be a 1 to 2 ratio from low to high. Contactor T1 and T3 closes for high speed and is suspect to be bad.
The wiring should be as follows. Should you want to test the motor directly.

High speed
L1 = U L2= V L3= W ZXY connected together

Low speed
L1=Z L2=X L3=Y UVW open

 

[Mmfh]

I did the switching of the wires to see what happens. L1 to L2, L2 to L3, L3 to L1, tried it and same thing, no high speed. It didn't seem to chatter and growl as much, just a electrical humm and the cutter started slowing down, I shut it down right away when it slowed down.

I think I said this earlier but it beirs repeating I think, for some reason with the machine you have to get it up to speed on low, and then switch over to high speed, designed that way is what I'm told.

So, that is what I'm doing, bringing it up to speed on low, then quickly switching over to high and cutter *******, moans, slows down, and I shut it off.

Since moving the wires one space forward didn't work, I did it again, another step forward to the next position. I'm taping into the T1, T2, T3, as the wires are banded coming right out of the 3 phase motor, (25hp).

I should also probably say, this is a very basic Phase Converter, pony motor, idler motor. That's it, no caps for running or starting, or balancing or whatever. Just the two motors and that's it.

I've used it this way with several machines, for many years, always started everything just like it had the real thing. My jet washer has a 7.5 hp pump for moving cleaner for the spray wash cabinet, that starts under load, and it didn't mind the Home Made power at all.

Now I think you know all there is to know. If you are still with me I'd love to hear what you have to say.

I'm going to dig into the contactors tomorrow and try to figure out which one controls the high speed of M1, low speed too for that matter.

I appreciate your help, its been a long time since I've been inside of one of these and I was barely competent back then. No budget for bringing someone out.

Thanks very much!

Mm