DC motors and speed control

[Jarred Hoffpauir]

There must be some machine people around here! I just bought a Nova 3000 lathe that needed a motor. Well I found a nice 1hp DC motor for it and its rated at 180v 5amps. Its a two wire hook up plus a ground. Can I just hook that up to the lathe and run a 220v type plug and on/off switch? I dont quite understand how the power goes from AC to DC to run the permanent magnet motor. Also if I add a Leeson speedmaster controller to the unit do I simply hook one side up to the power and the other side to the motor? That seems too simple...

Any help would be greatly appreciated.

Thanks,
Jarred

 

[Dennis J Gooding]

If it truly is a DC motor, you will need a separate unit to rectify the AC source to produce DC. Some very small motors are universal motors that can run on either AC or DC. However, any motor that uses a permanent magnet to produce the field will require a DC input. I am not familiar with the Leeson controller. Possibly it incorporates the necessary rectifier. Check with Leeson for details on the usage of the product.

Dennis in Southern Oregon

 

[john lucas]

I just hooked up a DC motor to a Leeson controller. You must have a controller of some sort that converts AC to DC to run that motor. The controller will have an input side (AC from the wall) and an output side which will be the rectified DC. Hook the 2 motor wires up to that. If you want reverse you will have to look up a schematic diagram on how to wire a switch to get reverse and forward. It isn't hard. If I get time I'll try to look it up or draw one up for you.
I have run a DC motor in an emergency with just a Bridge diode but the motor only has one speed, full on, when you do that.

 

[Jarred Hoffpauir]

Thank you guys, that is exactly what I am looking for. I will look up what a bridge diode is and see if that will work until I get my controller back from the place that is repairing it.

 

[john lucas]

Scan down this site to the bridge diode. It has an excellent description of how they work. You will need to buy one for 120 volts of course. They are pretty cheap at Radio shack.
Bear in mind that you only have one speed and that is as fast as the motor will run. If you have step pulleys it's not a major problem. If not I would not hook it up. Your lathe will simply run too fast to be safe.

 

[Jarred Hoffpauir]

I do have pulleys but I found out where to send my Drive into and they are going to fix it and send it back to me. Maybe two weeks tops. I can hold out that long.

 

[Bill Boehme]

A bridge rectifier is simply an array of four diodes connected in a "diamond" configuration to get full wave rectification of the AC power.

 

[Jarred Hoffpauir]

I went by Raido Shack and there are lots of different kinds of Diodes. The big differences on them seem to be the volt and amp ratings. Not sure which ones I should be looking at. This project may be a bit over my head but it sure has been interesting to read up on.

 

[Dennis J Gooding]

Jared, speaking as an electrical engineer, if you are not an experienced electronics person, I would strongly recommend that you do not attempt to build a rectifier system without expert supervision or a detailed plan produced by a knowledgeable person. This is particularly important if you are considering using a 240 volt AC input. The risk to life and the fire hazard that can result if you get it wrong are just too great for any savings you might realize.

Dennis in Southern Oregon

 

[Bill Boehme]

..... This project may be a bit over my head .....

I would say that it is completely over your head, but just FYI, a designer would need more than the paltry amount of information that RS has given. The voltage rating is the reverse EMF and you need to know if it is peak or RMS. If a diode is designed for rectifier duty, the value might be stated as RMS, but in general the value is peak. The Amperage rating is maximum forward current, but you also need to know at what temperature. Specs are typically given at both 25°C ambient as well as max rated environmental temperature, which might be 40°C or something else. Of course, you also need to know what the application requirements are for the part.

A circuit diagram is just one tiny piece of the complete design. The mechanical design and safety are just as important. Also, consider whether your modification might pose a lethal hazard to an unsuspecting person who acquires the lathe in the future. Here is a good example to illustrate the reason why: My dad acquired a hand drill that had belonged to his next door neighbor. The neighbor didn't know squat about electricity, but that did not stop him from "repairing" the drill to replace the worn out trigger switch. This was back in the days when drills and other tools had metal rather than plastic housings. During the "repair", he had managed to connect one side of the power to the metal shell. My dad gave the drill to me since he already had a drill. I was doing some maintenance work next to my patio door and everything seemed fine until I laid the drill down on the patio door frame. There was a bright flash, a loud pop, and finally a tripped circuit breaker. The only casualties were a drill welded to the patio door frame and the need to make a change of clothes. Had I touched the patio door frame with one hand while holding the drill in the other, I would have been dead. I opened the door earlier by grabbing the plastic door handle while holding the drill -- that was about 37 years ago, but it still gives me the willies to think about it.

Jared, speaking as an electrical engineer, if you are not an experienced electronics person, I would strongly recommend that you do not attempt to build a rectifier system without expert supervision or a detailed plan produced by a knowledgeable person. This is particularly important if you are considering using a 240 volt AC input. The risk to life and the fire hazard that can result if you get it wrong are just too great for any savings you might realize.

Dennis in Southern Oregon

I will add my amen.

 

[Jarred Hoffpauir]

Bill, I came to the same conclusion and am just waiting for the speed controller to come back from the repair shop. Ill know next week. BTW you may as well have written the first paragraph in French. I do not understand much about electricity and while I do not think I will end up welding my lathe to the door frame I get your point.