[pwpeterson]

Hi, I hope someone can help troubleshoot a problem that has arisen over the weekend with my lathe. It's an older Sheldon manual lathe with a three phase motor. For some reason the lathe will not come up to speed and power.

That is to say, I turn on the RPC and then the lathe. The RPC sounds like it's under a load, which is normal until the lathe comes up to speed, however, the lathe's motor will not start turning on its own.

I removed the belt from the motor and if I spin the motor's pulley by hand it will come up to speed but has no power as I can easily stop the motor by slipping the belt back on the pulley holding the belt lightly with my hand.

I have a 5hp RPC that's worked well for several months and doesn't seem to be the cause of the problem as I get adequate voltage to the three contacts on the lathe's junction box.

Any idea what may be causing this problem?

[Al_The_Man]

Check the resistance across all three phases of the lathe motor, normally when a 3ph motor fails it causes excessive current, but in your case, it does not sound like it if the RPC voltages are up to normal, check if one pair is high resistance.
You may have an open winding on the lathe motor.
If you have a clamp on ammeter check the 3 motor phases.
Al.

[pwpeterson]

Al. Thank you for the quick response. I'm not an electrician and want to make sure I understand what you want me to check. I am going to disconnect the three wire to the motor and check resistance across each of the motor's connection with each other, correct? 1-2, 1-3, 2-3?

Paul

[Al_The_Man]

Thats the first thing I would do.
Al.

[pwpeterson]

Ok, Al. Here are the results...

There are nine wires in the motor's junction box. Three are twisted together and the other six are divided in groups of two each with a power wire. I'll arbitrarily name these connections T1, T2 and T3.

T1-T2 no leakage
T2-T3 no leakage
T3-T1 major leakage.

Am I suppose to turn the motor while I do this? I didn't.

Paul

[Al_The_Man]

Not sure what you mean by 'leakage' but the resistance (use an ohmmeter) measured should be the same between any of the three combinations you show, i.e. very low resistance.
Do not switch on when checking resistance.
If you check current with a clamp on ammeter, then the power should be applied, and all three phase conductors should be close in current reading .
Al.

[pwpeterson]

I apologize for the confusion...

T1-T2 high resistance
T2-T3 high resistance
T3-T1 no resistance

pwp

[Al_The_Man]

No where near what it should be, I can't see them all being open, there should be a couple of ohms at most across any phase pair.
Check the connection of the three that are twisted together, this is the common point of all the coils.
Al.

[pwpeterson]

Al, I checked the motor's three wire group and put a wire nut on them. (It was black taped.)

I did some more testing this morning. Please disregard yesterday's results as I took a short cut and was measuring across the wrong connections.

At the motor:
T1-T2 no resistance (The ohm tester's needle pegs far right.)
T2-T3 no resistance (The ohm tester's needle pegs far right.)
T3-T1 no resistance (The ohm tester's needle pegs far right.)

There is voltage on all three lines from the RPC at the 709 automatic starter but only T1-T2 has voltage at the motor. I suspect the 709 has failed. I have another, slightly different 709(AAA) here and will try to connect it next weekend.

thx

pwp

[Al_The_Man]

The right description of the reading you get (sounds like you have a moving coil meter).
Is very low resistance, not No Resistance. They appear OK, on the surface.
Is this 709 an automatic starter of some kind?
Obviously you need the RPC output to all three motor phases, so it sounds like it is up-stream of the motor.
Al.

[pwpeterson]

Yep, The 709 is an automatic starter. I know how to connect the Lines in and the terminals out but not sure where the wires from the start, stop and jog buttons go.

pwp

[pwpeterson]

Al Can you tell me where the three wires from the lathe's start switch go on this 709 AAA automatic starter?[IMG]file://temp/709aaa.jpg[/IMG]

[pwpeterson]

[Al_The_Man]

If you use this set up shown in this link,
http://www.cnczone.com/forums/showthread.php?t=47948
it is for a standard stop/start connection, the two terminals either side of the coil label are the contactor coil and right above it is the normally open contacts to latch it in, a resistance check should confirm them, the coil should show about 60 ohms and the NO contact will show open, if you push the contactor in manually the contact should show closed.
It might pay to get an electricians help if you have doubts.
Al.

[pwpeterson]

Thanks, Al.

I think this may help. I'll spend some time with my ohms tester and check things out.
The jog button on the lathe's control didn't work before and I don't think I would miss it. However, since it's on the machine I'd like to get it working.

This is my very limited understanding of what the 709 Auto Starter does:

Three power lines come in on the top. Three terminals to the motor's contact are on the bottom. In between them are contacts the keep these circuits open.

When the coil (in the center) is energized these line/terminal contacts are closed and electricity flows to the motor.

My task is to connect the stop and stop wires (perhaps jog button's as well) between L1 and L2 to control the closing and opening of the contactor.

One of my problems is there are too many contacts. What's with all the screws?

Also, what do O/L and M1 mean?

I have an electrician who can help if I get in too deep.

thx

pwp

[Al_The_Man]

In the last link, M1 is the coil of the contactor, in your case it is an Allen Bradley.
I am not sure what you have in the way of PB's right now, but the attached PDF is one way of doing it.
I believe the AB may have the OL contact built in, you may have to get the AB bulletin on the contactor to find out exactly what the configuration of it is.
The white semi-circular devices are for reseting the overloads, the sensing heaters of which are right below the resets.
Hope this helps.
Al.

[MrWild]

I think a schematic for a latching selenoid is in order. The extra screws are confusing if you think they have a purpose, but the only four important ones are the two on either side of the 120v 60 cycle/110v 50 cycle label (activating coil) and the two directly above it for the latch part of the latching circuit. All other screws (except the in/out 3 phase) are to be ignored.

I've had one laying around for some time. Have seen them several times in cabinets but never bothered to understand their workings. I follow the schematic, but wonder what "1 CR" stands for. It is used in the jog circuit and then in the main power line after the O/L. At first glance I thought it was referring to the capaciter in the jog circuit, but the second 1 CR says that isn't right.

Thanks

Stuff a 5th grader for sure don't know.

[Al_The_Man]

ICR in the circle refers to the coil of the contactor, and the normally open contact 1CR refers to the NO terminals above the coil.
The jog PB will only hold the contactor in when pushed, the start PB latches it in , as normal.
Al.

[MrWild]

THANKS Al! :rainfro: (We really need a dancing banana.)

It all went click! The NO are contacts in the relay are normally open (of course), but when the contacter homes and allows 3 phase to flow, it is also closed.

Juice flows from the leg with the E-stop through the NC side of the jog button and keeps the flow going after the start PB is released and goes back to NO. This keeps the coil powered up and contacter homed. I figured this all out once for a home brew EDM, but the three phase switch with it's larger and yes, imposing shape becomes nothing more than the small one I used before.

ICR threw me off though. What I thought was a capaciter in the circuit, was the NO contacts in the ICR. ICR = Induction Coil Relay? The back panel I've been avoiding makes a lot more sense now.

[Al_The_Man]

BTW the 3 items screwed in labeled N31 on the contactor are the OL 'heaters' they are thermal sensors that are selected by current value according to the current rating of the motor. You should by rights, use the correct heaters for the motor.
Al.