Wiring an old Century 1/4hp motor to a drum switch

[lin842]

I know this has been beaten to death and I have searched, believe me. I have a 1943 South Bend lathe that I am trying to restore. The motor is a repulsion start induction type RS single phase motor. I got this lathe in pieces and I'm now trying to get it running so I can at least see what I have before I spend a lot of money making it pretty.

The motor has a 110v power cord that is hooked up with a short lead pigtailed that is just hanging. The drum switch is mounted to the side of the gear train cover. It has 9 terminals, 3 down each side and 3 in the middle. When I got it there were only 3 screws in the middle It's a CH switch. I'll post a crude pic of what wiring I see.

The motor has 4 wires that have no markings but the way it's now wired is two of the 4 wires are tied together to the black wire in the cord with the plug. The other 2 are tied to the black wire to the short cord that is just hanging. the white wires are tied together between the two cords. This wiring looks to have been done many, many years ago and it must have worked until somebody pulled the plug.

The short cord is just long enough to go from where it connects to the motor to where the drum switch is mounted so I assume it went to the switch. Here are some pics and hopefully someone can help me connect the dots. It wouldn't let me post the drawing but there is a pic of the actual wiring. Thanks........

 

[Bob-J-H]

For an RI motor, I believe you reverse it by changing the brush position. If I am right, that switch won't work for you. But I could be wrong.

 

[lin842]

For an RI motor, I believe you reverse it by changing the brush position. If I am right, that switch won't work for you. But I could be wrong.

I had read that in one of the old Century books but it also said there was an optional motor that you could buy that was reversible by the use of a #791 drum switch whatever that is. I didn't see how that motor was identified though. I've also been wondering if this lathe even had reverse on it. The old papers on these things are hard to follow and probably written for people much smarter than I.

 

[dalmatiangirl61]

I'm questioning if 1/4hp is enough to be usable on a lathe, how big is the lathe? I'd bet if it was working before on that switch, it was just as an on/off switch. You need to figure out how to wire motor for CW rotation, then CCW rotation (without the switch). Then map out the switch to figure out how it works, then apply that to how motor needs to be wired.

 

[jim rozen]

Odds are very good the four wires are set so in parallel it will be 120 v operation, in series (two tied together, line to the other two) it will be 240 volt operaton. Reversing as said is via the
brush shifter visible in one of the photos.

Your three pole drum switch only needs to have two wires go it it, if you using 120 volts. A simple single pole light switch will do the job also. You cannot reverse this motor via the drum switch.

For a small lathe, that motor will work find. By small, say a 9" southbend or atlas.

 

[jim rozen]

Damn that's a lot of typos. Forgot to add: you could purchase a new capacitor start 3/4 hp motor for this, and use that drum switch, although it won't be instant-reverse.

 

[lin842]

I'm questioning if 1/4hp is enough to be usable on a lathe, how big is the lathe? I'd bet if it was working before on that switch, it was just as an on/off switch. You need to figure out how to wire motor for CW rotation, then CCW rotation (without the switch). Then map out the switch to figure out how it works, then apply that to how motor needs to be wired.

It is a 9A and the 1/4hp motor is plenty because of the way these motors are designed. They develop a ton of torque on startup and reach max RPM in an instant. They also last forever. From what I have read there are some of these motors that were built in the 1880's that are still in use today in factories.

I feel certain that this motor is original however I'm not to sure about the switch. I wish I could get up with the last person that had this lathe and actually used it so I could pick his brain about the what and why configuration that is now on this lathe. All I have to go on is what I see and I'm thinking you may be right about the on/off part.

 

[lin842]

Odds are very good the four wires are set so in parallel it will be 120 v operation, in series (two tied together, line to the other two) it will be 240 volt operaton. Reversing as said is via the
brush shifter visible in one of the photos.

Your three pole drum switch only needs to have two wires go it it, if you using 120 volts. A simple single pole light switch will do the job also. You cannot reverse this motor via the drum switch.

For a small lathe, that motor will work find. By small, say a 9" southbend or atlas.

Yes it is wired for 110v according to drawings I have seen. I'm going to post a manual if the site lets me and you can page down to page 23 and it shows an instant reversing repulsion/induction motor that was optional that could be used with the switch I mentioned above.

AS I figured it wouldn't let me post it because of the size. I'll try posting just the link. make that page 21.
http://vintagemachinery.org/pubs/1617/15133.pdf

 

[lin842]

Damn that's a lot of typos. Forgot to add: you could purchase a new capacitor start 3/4 hp motor for this, and use that drum switch, although it won't be instant-reverse.

I wanted to keep this original if possible. I probably don't need a reversing motor anyway because I probably wont be doing a ton of threading. I'm mainly going through this lathe to be sure it's good to go and I plan on selling it and my Atlas to help fund a little larger lathe.

 

[johansen]

The brushes are cross wired. Use a dpdt switch to reverse the brush connection and a single pole start stop switch to turn on the motor.

So 3 switches. One dpdt switch. One push button on switch wired to a 3 or 4 pole motor starter, and one normally closed stop button switch

 

[lin842]

The brushes are cross wired. Use a dpdt switch to reverse the brush connection and a single pole start stop switch to turn on the motor.

So 3 switches. One dpdt switch. One push button on switch wired to a 3 or 4 pole motor starter, and one normally closed stop button switch

I'm sitting here reading this and asking myself, what the hell did he just say. I'm wondering if somewhere, some kind of wiring diagram may be found. I've always had a hard time with wiring and don't mind saying it.

 

[Just a Sparky]

The brushes are cross wired. Use a dpdt switch to reverse the brush connection and a single pole start stop switch to turn on the motor.

So 3 switches. One dpdt switch. One push button on switch wired to a 3 or 4 pole motor starter, and one normally closed stop button switch

Bullshit.

All four brushes are short-circuited together and bonded to equipment ground via the motor frame.

A standard repulsion start induction motor cannot be electrically reversed. Two 120V windings. Series for 240V, parallel for 120V. Polarity sensitive. Reversing one pole with respect to the other will cause the motor to hum and overheat.

An electric-reversing repulsion start induction motor will also have four wires*. One inducing winding and one field winding*. They must always be connected in series. Reversing the polarity of one with respect to the other will reverse the starting moment of the motor. It is my understanding that the field winding in these motors is arranged to shift the magnetic field slightly clockwise or counter-clockwise relative to the brush cage.

Yours is a standard repulsion start motor. It can only be reversed by shifting the brush cage. Electric-reversing repulsion start motors are usually clearly marked as such.



Whatever you do, don't scrap that motor. Pre-1930s Century motors are collectors' items.

Also note that the end bells are installed incorrectly on your motor if it sits as pictured when mounted. The oil sumps should always face down. Century type RS motors were designed to be bottom, side or top mountable by removing the end bell bolts and rotating the end bells in 90* increments. 4 pole motors like yours (1800 RPM) do not require any extra hardware since they have 4 brushes 90* apart. 2 pole motors on the other hand (3600 RPM) require an accessory brush cage for side mounting iirc because they have 2 brushes 180* apart, which doesn't divide into 90*. Can't remember 100% if the 6 poles (1200 RPM) need a different cage or not but I don't believe so - 4 brushes 60*/120* apart.

(*Three wire motors also exist. They use two field windings for forward and reverse instead of reversing the polarity of one common field winding.)

 

[lin842]

Bullshit.

All four brushes are short-circuited together and bonded to equipment ground via the motor frame.

A standard repulsion start induction motor cannot be electrically reversed. Two 120V windings. Series for 240V, parallel for 120V. Polarity sensitive. Reversing one pole with respect to the other will cause the motor to hum and overheat.

An electric-reversing repulsion start induction motor will also have four wires*. One inducing winding and one field winding*. They must always be connected in series. Reversing the polarity of one with respect to the other will reverse the starting moment of the motor. It is my understanding that the field winding in these motors is arranged to shift the magnetic field slightly clockwise or counter-clockwise relative to the brush cage.

Yours is a standard repulsion start motor. It can only be reversed by shifting the brush cage. Electric-reversing repulsion start motors are usually clearly marked as such.

View attachment 340236

Whatever you do, don't scrap that motor. Pre-1930s Century motors are collectors' items.

Also note that the end bells are installed incorrectly on your motor if it sits as pictured when mounted. The oil sumps should always face down. Century type RS motors were designed to be bottom, side or top mountable by removing the end bell bolts and rotating the end bells in 90* increments. 4 pole motors like yours (1800 RPM) do not require any extra hardware since they have 4 brushes 90* apart. 2 pole motors on the other hand (3600 RPM) require an accessory brush cage for side mounting iirc because they have 2 brushes 180* apart, which doesn't divide into 90*. Can't remember 100% if the 6 poles (1200 RPM) need a different cage or not but I don't believe so - 4 brushes 60*/120* apart.

(*Three wire motors also exist. They use two field windings for forward and reverse instead of reversing the polarity of one common field winding.)

Thanks, that's what I needed to know and no it would not be mounted in that position. The way it's sitting on the bracket footrest get mounted to another bracket that is angled on a pivot so that you can adjust/tighten the belt. Once it is mounted and the belt is tight it will be in the upright position with the oil cups facing upward.

And yes, I would like to keep this motor on the lathe even if you can't reverse it.

 

[Just a Sparky]

Would be interested in seeing it run once you get everything put back together.

Looks like it's got plenty of carbon built up. Might be worth wiping down the commutator and cleaning up the brushes while you've got it apart. Nothing aggressive - just a mild solvent and some paper towels & 'q'-tips to remove carbon from the commutator and grease from the brushes & their holders so they float freely. I like to add just a touch of grease to the spring barrel ring (#55 on page 13 of the publication below) to lubricate it and quiet it down during operation.

The rear end bell pops off pretty easily with those four bolts and some gentle encouragement. The brushes aren't retained so they may fall out. 'M' frame motors usually have yarn packed oil sumps, but on the off chance it has oil rings, simply invert the end bell 180* to slide the bearing back over it's journal. The top cover should be removed on yarn lubricated motors to relieve the spring pressure on the yarn.

Watch and listen for excessive sparking/arcing during startup. Those are warning signs of a commutator in need of grinding and/or incorrect brush position. Verify that the brush position pointer is aligned with one of the two factory marks staked into the end bell.

Good commutator

Bad commutator

http://vintagemachinery.org/pubs/2461/4520.pdf

 

[loggerhogger]

Century Repussion start motors are reversed by changing the position of the brushes. I dont think they can be reversed with a drum switch.
As far as the four wires are concerned. Look where they come out of the motor casing. They are usually in a porcelain block and in a straight row. For convenience sake. Just number them 1,2,3,and 4.
These motors are usually duel voltage. They will run on either 110V or 220V.

For 110V operation, tie wires 1&2 together, then tie wires 3&4 together. Hook 1&2 either the hot or neutral, and then 3&4 to the other.

For 220V operation, hook wires 2&3 together and insulate the joint with a wire nut or some other means
Connect wire 1 to one of your hot leads, and wire 4 to the other.

Hope this helps.



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