Reversing controls - single phase. 2

[itsmoked]

I have a 240Vac 2hp single phase reversible motor running a lathe. In the motor controls there are two contactors not mechanically linked. They are obviously set to reverse leads to the motor.

They each have their coils run thru the opposing relay's N.C. contacts so both contactors can't be commanded closed at the same time.

There is an E-mushroom and an ON switch. The only motor control is two microswitches run by an operator's lever. Up->REV Dn->FWD Middle->STOP.

Question: There is a smaller associated contactor next to the aforementioned two. What is it's purpose and (generally) how is it connected?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[wayne440]

My WAG is that it prevents a direction change until the machine comes to (or close to) a stop. Similar to an anti-plugging relay in a 3 phase machine.

 

[waross]

Could it be to run a cutting oil pump whenever the lathe is running? Generally full speed reversing is not an issue with capacitor start motors. The centrifugal switch keeps the capacitor out of the circuit until the motor is almost stopped or at least turning slow enough that the motor may be reversed. If an attempt is made to reverse the motor before it has slowed enough for the centrifugal, switch to close, the motor simply accelerates in the direction that it is running.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[wayne440]

An oil pump is a good possibility.

My thinking was that the relay might be intended to prevent exactly what you describe, in other words to insure that the lathe always turns in the indicated direction. One would think the operator would be aware but, you never know.

 

[itsmoked]

I thought "oil" too. But there isn't any provision for it.

A cursory investigation showed no capacitor(s) on the motor.

Here's a picture of the control with the left failed contactor removed. The smaller relay is the one on the right.

Notice there are three wires being swapped between the left two contactors. Three? It's single phase..


Keith Cress
kcress -

http://www.flaminsystems.com

 

[OperaHouse]

I would imagine the contactor on the right is the stop/start contactor and one set of contacts inhibits power to the reversing switches so the direction can not be changed when the motor is running.

Operation would be lik this. Master contactor off. Power supplied to fwd/ rev pushbuttons. Pressing one latches in one direction. Pressing start powers master and latches it on and removes power from direction PB. Off unlatches master

 

[wayne440]

Looks to me like it was made by a water heater factory...

 

[waross]

Three wires:
Two contacts interchange the leads from the run winding.
The third contact supplies power to the start winding.
Third relay:
A master control relay tripped off by the E-mushroom button.
I have seen quite a few single phase reversing motors, Keith, and I don't remember seeing any with a reverse inhibit relay.
BUT that sure looks like a three phase setup from the picture.
Does the O/L relay have differential protection? If it is set to protect the motor and has differential protection it will be tripping when the centrifugal switch cuts out and the only one set of contacts are carrying current.
Many 230 Volt single phase motors may be reversed with three conductors. The start windings are often 115 Volts and one end of the winding is connected to the center tap.
The other end of the start winding may be connected to line one and the run leads interchanged between L1 and L2.
If this is for single phase there should be a jumper between two of the line terminals on the reversing contactor.
An alternate control scheme would require the yellow wire to be connected and two wires carried to the start winding instead of using the center tap at the motor. The three wire scheme will only work with a 230 Volt supply with a 115 Volt start winding. The four wire scheme will work with 115 Volts or 230 Volts.
"
A cursory investigation showed no capacitor(s) on the motor." Split phase motor??

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[OperaHouse]

I imagine this has three buttons forward, reverse and stop. The third relay is the master on off. The reversing relays each have three contacts for motor, one coil hold in, and one to inhibit other direction relay. The master relay has one hold in and two contacts to insure the master is on before powering direction relay. I've seen worse designs. Master must be off before new direction can be pressed.

 

[itsmoked]

Thanks for the discussion!

Bill; One probably doesn't want a lathe 'snapping on' as it could throw your workpiece or at least cause it to move. So, I bet this is a low starting torque split phase motor.

And. Yes! There is a jumper on the LEFT contactor between R and S. (see it laying down on the box bottom)

The power cord has only three wires. GND, L1, L2

Opera; I think you may have something there with the master relay. There are no "buttons" it's more like switches since a direction is essentially a switch held ON. There isn't a need for 'latching'. I guess it could still operate in a latching way -non-retained push buttons- but just have the buttons remain pushed in one direction.

One other puzzling tidbit of info. Each directionandrun SPDT ON-ON microswitch has two wires running to it from the contactor box. Both have wires coming to the N.O. contact and then one has its common wire leaving and the other has its N.C. contact routed to the contactor box.

The switches have the remaining N.C. and COM jumpered together.


Looks like I will be drawing the schematic from scratch tomorrow. I was hoping to avoid this since the machine seems to have several problems and I'm concerned it's been re-wired by some hack. I was hoping for a definitive, "that's called an XX setup and it's wired this way'.

I've looked at about 40 web sites and not seen anything like this.

I'll let you know what I find. Maybe we can all learn something.




Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

Mission accomplished so I'm back to report.

I finally stopped and drew the schematic for the lathe.

Here's the power side. This helped me figure out what the 3rd Mystery Contactor was for.

This is the control side. They had this switch obviously mis-wired. I modified the circuit to require they push a button to latch-in the auxiliary contactor. It will only pull-in if the direction lever is in the center all-off position. That means the power coming on, can never spontaneously have the lathe spin.

Thanks all for the help!



Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

Erk.

Here's the control logic!

Keith Cress
kcress -

http://www.flaminsystems.com