View Full Version : Need help rewiring lathe from 120v to 240v.

09-11-2010, 09:31 PM
I just finished my new shop and am moving my Jet 1024P lathe in. It has a 120v/240v motor and the manual has diagrams for wiring and the high amp draw on 120v. The motor was wired 120v but I wanted to change it to 240v since I have plenty of 240v receptacles. I wired it this afternoon following the diagram in the manual. The 120v diagram matched up with what was on the lathe so I figured the 220v diagram should be right.

Turns out it was wrong. Now the motor only turns in reverse. Forward does nothing. The last time I ran the motor in reverse I heard a significant "pop" noise :eek: and I shut the lathe of immediately.

As far as wiring AC motors, I can follow a diagram and that's about it. I don't understand the significance of the different leads. I need some help. Below is the wiring diagram page out of the manual and a picture of the plate on the motor. The diagrams seem to conflict to me. Thanks!


Right now my lathe is wired as show above, with motor leads 2 and 3 wire-nutted together as the diagram seems to suggest.



09-11-2010, 09:52 PM
That pop was probably one set of contacts being toasted in the drum switch.Which would explain why you now have reverse and nothing.

That it's running in reverse is probably due to the polarity of the start coil being reversed when you swapped to 220v.

Does the diagram show what motor leads connect to the capacitor?

09-11-2010, 10:07 PM
There are two unmarked yellow leads that go to the capacitor. The diagram simply shows two unmarked wires.

To clarify, since rewiring I have only had reverse. Even after the"pop" reverse continued to operate seemingly fine until I shut the power off.

09-11-2010, 10:21 PM
Okay,after the pop it worked fine until you turned it off,or the next time you used reverse it worked?
Reason I ask is contacts will actually weld together and will break apart once they are opened (switched to off)the next time they are brought together tey can either work like normal (10%) not work at all (30%) or pop again and maybe work or at least shoot sparks and sizzle (60%).

The fact that the motor is now starting and running in reverse,but not forward tells me that the wiring is right(except for being reversed)and the switch is shot.

How comfortable are you with an Ohm meter?

09-11-2010, 10:31 PM
I went out and tried the lathe again. It ran in reverse just the same as it did before (seemingly fine).

I am extremely comfortable with a DMM. I also know single phase AC wiring quite well (just wired my new shop), just not with motor wiring.

09-11-2010, 11:18 PM
Okay,looking at the diagram 1,2,3,4 are the run coil ends.

That leaves 5 and 6 as the start winding.

If I'm right you should be able to swap 5&6 and have the motor run FWD.

If I'm right on the switch then you will have FWD and not reverse.

If I'm wrong you will need a flashlight to reset the breaker:)

09-11-2010, 11:29 PM
Ok, I swapped 5 and 6. Motor now turns in the FWD direction with the switch in rev. FWD switch position still produces nothing.

ETA: Didn't think of this earlier, leads 1-4 are red, 5-6 grey, and capacitor leads yellow so I am guessing your breakdown in post #6 is probably on.

09-11-2010, 11:55 PM
Okay,good,if it were me I would replace the drum switch with a new one.Maybe a beefier model if you can fine one with the same connections.

I would also solder a 1/4 watt 20-24k ohm resistor across the capacitor terminals.That will discharge the cap after start,assuming it's a capacitor start motor.Discharging the cap makes the switch contacts last longer.

09-12-2010, 12:04 AM
Thanks for all the help. Strange to me that the switch is bad, from what I remember it worked fine before.

Knowing what we know now, what do you think that pop might have been? Possibly a figment of my imagination? For what it's worth, the lathe has been dissembled for the last 5 months and sitting in an enclosed trailer since I hauled it out of the basement at my old house. Very well could have had a metal shaving or some other contaminant fall inside the housing.

09-12-2010, 11:38 AM
STOP! Do not run the lathe. The wiring diagram on the lathe may be hazardous to the motor. It seems to conflict because it does.

1 and 2 are one half of the main winding and 3 and 4 are the other half. You wire those windings in parallel for 110V and in series for 220V. 5 and 6 looks like the starter winding, with a hidden diversion of one through the capcitor leads. The starter winding isn't split like the main winding. Which means it isn't a 110/220V winding. Instead, what motor manufacturer intends that you do is connect it across one of the main winding halves (where it will see 110) rather than across both/main power. But your switch was probably designed to switch the starter across the AC mains either forward or reverse - full voltage. The trick around that is to run one side of the start winding to the center tap of the main winding and leave it there and leave one side connected to the switch where it will get connected to either L1 or L2. This will effectively reverse the voltage on the starter winding without cooking it with 220V. So connect #5 to #2 and #3 as shown on the motor diagram and leave 6 connected to the switch (if you don't like the direction it turns, move it to the other starter terminal on the switch or if it is fried swap either wires 5 and 6 or wires 1 and 4 but not both). You may also have blown the cap which may not be rated for 220V.

The lathe diagram puts 4 times as much power on the starter winding as it was apparently designed for and twice as much on the cap. They might have compensated for this by putting a lower capacitance, higher voltage cap but then starting on 110V would be too wimpy.

Meanwhile, you probably have a bad contact on the forward side of the switch.

By the way, when motors sit without use they can absorb humidity into the windings and need some eat to drive it off or the insulation can fail. Just an example of how "just sitting" can actually be bad for it.

They also screwed up the switch winding on the lathe 220V diagram
They swapped pins B and 4, which they should not have done.

Potential consequences of the bad lathe 220V diagram:
- Fry the motor starter winding by putting too much voltage/current/power into it.
- Fry the starter cap by too much voltage
- Fry the switch by not using the contacts for the purpose they were intended for.
You are lucky that only one of those has happened so far.

Anyway, I am just guessing from what little info is available.

I am guessing you have a drum switch like this.

Hot A ******** B Run 1 A ****** B
* *
Start 1 C * * D Start 2 C * * D
* *
Neutral E ******** F Run 2 E ****** F

On yours the contacts shown above may be laid out as follows

1 A A 1
2 4 OR 4 2
3 B B 3

I suspect the switch manufacturer envisioned the configuration on the right when they numbered the contacts but the lathe manufacturer appears to be using the one on the left for 110V (no big deal) and complete garbage on 220V.
Note: this swapping of 4 and B may be all that is stopping the motor from running in both directions. The switch may have survived. With those pins swapped, in one direction the motor will get no power to the run winding.

Here is the 110V diagram edited for how I suspect it should be wired for 220V:


09-12-2010, 11:55 AM
Here is a picture of the switch wiring diagram directly off the bottom of the switch. Can anyone tell me how this should test out with an ohm meter so I can 100% verify if the switch is a problem? Thanks


09-12-2010, 12:07 PM
Whitis could be correct,one way to tell is by looking the drum switch over for jumpers.

Since don't have the contact layout for the switch or the rest of the diagram it's hard to do this long distance.This is one of those times where if we were standing there it could be sorted in 5 minutes.

Edit,okay,that looks like REV would connect 3,B,2 AND 4,A,1 and FWD would connect 4,3,B and A,1,2

09-12-2010, 12:12 PM
I know exactly what you are talking about and appreciate your help.

09-13-2010, 11:14 AM
Investigating the switch - good.

Take it a different way; rather than us telling you what to expect, you tell us what you find.

Open the switch up and look at the innards if you can.

Put one lead of an ohmmeter on pin 1, check continuity from there to all other pins in each of the three positions, record results. Repeat in each switch position.

Repeat for pin 3.

In each of the three positions, check continuity between each pair of adjacent pins on the diagram. This is likely to confirm the data from previous tests as well as give additional info on the off state. The diagram does not inspire confidence that the switch doesn't short the motor windings together in the off position;which may not be bad but is something you should be aware of. The diagram suggests 6 contacts arranged at 60 degree spacing. However, inside there may be 6 contacts arranged at about 30 degree spacing in two groups on opposite side (11,12,1 and 5,6,7 o'clock positions). This arrangement would not engage run and starter windings simultaneously.

Or the drawing could be purely symbolic and it might look like this (see second pic):
Or other configurations with the same effect, like a drum with cams and microswitches or irregularly spaced contacts

Or just make yourself three 6 x 6 grids of pin numbers on a sheet of paper and simply probe each possible combination of pins, and repeat for each of the three positions. Technically, you only need to do about half of them (i.e 1 to 2 and 2 to 1 are equivalent). This should be very fast - 45 combinations at about 1 second each. Just fill in the section above the diagonal lines.

Reverse Off Forward
|2|B|3|4|A|1| |2|B|3|4|A|1| |2|B|3|4|A|1|
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+
2|\| | | | | | 2|\| | | | | | 2|\| | | | | |
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+
B| |\| | | | | B| |\| | | | | B| |\| | | | |
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+
3| | |\| | | | 3| | |\| | | | 3| | |\| | | |
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+
4| | | |\| | | 4| | | |\| | | 4| | | |\| | |
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+
A| | | | |\| | A| | | | |\| | A| | | | |\| |
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+
1| | | | | |\| 1| | | | | |\| 1| | | | | |\|
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+

Likely results:
Reverse Off Forward
|2|B|3|4|A|1| |2|B|3|4|A|1| |2|B|3|4|A|1|
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+
2|\|*|*| | | | 2|\| | | | | | 2|\| | | |*|*|
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+
B| |\|*| | | | B| |\| | | | | B| |\|*|*| | |
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+
3| | |\| | | | 3| | |\| | | | 3| | |\|*| | |
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+
4| | | |\|*|*| 4| | | |\| | | 4| | | |\| | |
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+
A| | | | |\|*| A| | | | |\| | A| | | | |\|*|
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+
1| | | | | |\| 1| | | | | |\| 1| | | | | |\|
-+-+-+-+-+-+-+ -+-+-+-+-+-+-+ -+-+-+-+-+-+-+

09-13-2010, 11:15 PM

I tested out the switch. My results match your "Likely Results" perfectly.

09-15-2010, 10:54 PM
Shameless bump for more input.

09-19-2010, 11:52 PM
Ok, you should be able to rewire the lathe according to the modified wiring diagram I posted and the lathe should run in forward and reverse.

If you measure the voltage on the starter winding while starting the lathe, it will probably be somewhere between 1/3 and 1/2 of line voltage. If you get full line voltage, you have a problem.

09-22-2010, 10:21 PM
The lathe is up and running, forward and reverse. Thanks again to everyone who help me out. I greatly appreciate it!