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  • Controlling DC motor

    I found a DC motor that should work for my quill feed. It's 1/8 hp 90 v dc field and 100 v dc on the armature. Any advice on how to make the electricity this thing needs? I'd like it to be variable from 0-250 or so RPM. I'm guessing that since it has wires for field and armature that it's designed to be a variable speed reversable motor.

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    Hoffman in Warner Robins Ga
    Techno-Anarchist

  • #2
    Hi Hoffman
    There's a good bit here about such a thing

    http://www.truetex.com/dcdrv.htm

    all the best.....mark

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    • #3
      Thanks Mark. I looked on ebay for dc controllers but I'm not sure what I need. This motor has 4 wires, 2 go to the brushes and 2 go to the field windings. From what I've read the field voltage remains constant and the voltage to the armature is varied to control speed.

      ------------------
      Hoffman in Warner Robins Ga
      Techno-Anarchist

      Comment


      • #4
        Sounds like it functions just like the old car dynamo's...but only in reverce ......you sure it is a motor you have there , not one of these old lucas dynamo's or something .
        me not knowing much at all on this subject .
        all the best.mark

        [This message has been edited by aboard_epsilon (edited 01-02-2005).]

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        • #5
          Use a Dart or a KB DC motor control like this one:

          http://cgi.ebay.com/ws/eBayISAPI.dll...863953616&rd=1

          It has an on-board field supply. You can pad it down to 250 RPM but the motor performance may be a little lumpy for a smooth uniform quill feed. I suggest you rig up a 5 to 1 belt reduction from motor to quill handwheel.

          Search eBay under "DC Motor Control"

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          • #6
            It's an RA Boehm 4640. Tag reads: 4.6 amps Volts: 90 DC-A 100 DC-F.
            It came off a mystery machine feed. Probably a table feed for a mill. Serious chunk of iron...
            Thanks Forrest. I just bid on the one you provided a link to. Just finished reading your chuck article. Good stuff
            ------------------
            Hoffman in Warner Robins Ga

            [This message has been edited by hoffman (edited 01-02-2005).]
            Techno-Anarchist

            Comment


            • #7
              well I did a search on your motor
              and acording to here it is a servo motor

              http://www.google.co.uk/search?q=cac...ehm-4640&hl=en

              maybe there will be a different chain of thought in the replies now .
              all the best ...mark

              Comment


              • #8
                Where the heck is Dave??? He's always like:
                "Oh I just threw together a triple-rectified field coupler for my CNC butt wiper to provide fine motor control of the X-axis feed. Got a wave generating diode out of a weed-wacker ignition and wired it in series with a variable potentiometer from a GE toaster to compensate for toilet paper thickness..."
                Oh No... can I use a servo motor as a regular motor. Just bid on a DC motor control...Probabably'll need it for something...

                [This message has been edited by hoffman (edited 01-02-2005).]
                Techno-Anarchist

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                • #9
                  dave's having a few problems.



                  all the best..mark

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                  • #10
                    Aboard:
                    Ya got it wrong, it should be "black" electrical tape around that thumb (I am a electrician). It has not slowed me down. I still type 60wpm... then go back and fix 40 of them.. HA..
                    I been working on my shop guys.. I love this high sixties weather and can't stay inside. To heck with the computer. Remember I am a fledge-ling wanna-be machinist.

                    Lemme see.. You know the field "slowes" the motor? right? If you lose the field it'll break and run WOT. We used to use Field trim rheostats in the carpet mills on the drive motors, a rack common DC drive and individual trim on the rheostats. YOU know add resistance to the field circuit and the motor speeds up? You only have about 20% trim in speed using the field.

                    Yes, it can work as a servo or dc motor. With a simple 90vdc motor go to harbor Freight and get you a "router speed Control" for $15. Use a rectifier diode in series with the 115v to the field , half wave and the router speed control for the armature.

                    Cheap enough? Okay.. now do it right, buy a dc drive from Ebay, email me the ones you find and if I get time later on I'll pick one or more out for you. (on ebay you never get the first one you want) You can adjust the current control to make it last more than a week with a real dc drive. The other one has no current feedback or protection. Just like a light dimmer with receptacle.

                    Email me for my phone number if I can help.

                    TODAY? I mounted the TennSmith 36" roller onto a height adjustable table, installed a gearbox and 3/4 hp dc motor, then cut the motor leads, the power leads, bugged a reversing two contactor relay in, two foot switches. NOW, push one foot switch it goes forward, let off, push the other and it goes reverse. Stand there adjusting the takeup roll bolts and you can rock the metal back and forth making a custom conical curve. I am working on a SPECIAL project. "highly secret" Shussshhhh...

                    David

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                    • #11
                      Simple answer is that you can use direct full-wave rectified 120V for the field. The average voltage is what counts there, and it is about 66% of peak line voltage. At 170V peak from 120V, you are about right, even if line is lower.

                      If you are nervous about the slight (10%) overage, you could always use a dropping resistor.

                      For armature, the simplest, although not cheapest is rectifying the output of a variable transformer(variac or equivalent).

                      If field is constant, varying armature will get you between a 3x to 5x ratio of speed, at what I would assume are acceptable torque.

                      It will go much slower, but torque will fall.

                      While it is true that field failure may lead to overspeeding (similar to no load on a series motor), In a practical motor with gear train, it will just stop and draw a bunch of current, becuase the field is required to produce torque.

                      A large number of DC controllers are available for 90V motors.

                      Ebay is fine, BUT be sure you get a technical manual with it, OR get it from manufacturer on the net.

                      Otherwise, you may not be able to optimally connect and set it up. And, with no manual you are up the creek fixing it later, unless you are pretty savvy.
                      CNC machines only go through the motions.

                      Ideas expressed may be mine, or from anyone else in the universe.
                      Not responsible for clerical errors. Or those made by lay people either.
                      Number formats and units may be chosen at random depending on what day it is.
                      I reserve the right to use a number system with any integer base without prior notice.
                      Generalizations are understood to be "often" true, but not true in every case.

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                      • #12
                        Thanks guys. I have a bid on one of these:
                        http://www.grainger.com/Grainger/pro...673009&ccitem=
                        At least I'll have something to check this motor out with. If it works out I may just convert my mill spindle to DC and forget about 3 phase...
                        I'd really like to get a handle on this DC stuff because there are just so many applications.
                        Techno-Anarchist

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                        • #13
                          Using a old parallel port, I can generate PWM waveforms out replacing dc drives. Reading encoders directly into a port is childs play.

                          Problem is I wrote it in WIndows, and windows does not like to follow orders. It goes off on some quest to send information back to bill or who-ever and your machine is left in the on-off state where it was when it left. read that stopped or wide open.

                          Since I have more time than money I may look back into that.

                          My machine here in the house? I found "SEVEN open ports" through my DSL router out to "other people" I guess what I have done is of some interest to them. I closed the door and my DSL is working like it should. After the cow escaped. I joined a Visual basic group on Yahoo.. serves me right. Damn bunch of ragheads that are in there.

                          David

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                          • #14
                            I have used the "dart" drives in industrial installations where the machinery runs 24/7.

                            A pretty hardy drive. Good! Looks like you overrated it. When you get it I'll help you set it up. I think I still have a book here close by. Problem is the duty factor, starting and stopping and dissipating heat. You want to leave the DB alone. That brings in more heat than anything else. (DYnamic braking) Let it coast-stop


                            David

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                            • #15
                              Thanks Dave. Finally some good news! Just read your angle grinder post That's quite a visual...
                              Man, when you be gonna post on my kondia k-76 mill? I've been waiting for you to chime in. I posted it a few days ago. Don't think I'll need the DB it's gonna be a quill feed so it'll have enough mechanical resistance to stop it. I'll probably just hook it up with a small timing belt. Nothing fancy. I just want to get the electrics figured out before I dive into any mechanical stuff.
                              Cleaned up the ways on the mill today. Rust came right off with a little steel wool/WD-40 and elbow grease. You can still see the frosting or scrape marks under the rust so It's gonna be OK.

                              ------------------
                              Hoffman in Warner Robins Ga
                              Techno-Anarchist

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