Announcement

Collapse
No announcement yet.

A.C.to D.C. conversion

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • A.C.to D.C. conversion

    Just finished installing a 1/2hp.1750 rpm.D.C. motor on my 10 inch Atlas lathe.Removed the 1/3hp. motor,the original,bearings were starting to make some noise. The DC.motor came with a control box, with switches for on-off,forward-reverse and start-stop and a speed control. Haven't made a chip yet,what should I expect to be different from the original? The DC.motor and control were from a woodworking plant auction.

  • #2
    I assume the control box is an AC-DC convertor already. If not, you got to find a way to get DC to the motor, as AC will destroy it (unless it's a universal motor, which I doubt). So you either need a huge bank of car batteries or an ac-dc convertor, called a rectifier. A bridge would be best along with a couple of large electrolytic capacitors for filtering. Also an isolation transformer to, uh, isolate the circuit from the AC line. A fuse can't hurt, either. The rectifier diodes, capacitors, and transformer will need to handle 150-200% of the motor's rated current, probably more to allow for extra current draw on a heavily loaded motor. Might be cheaper to just get an AC motor. Course if the control box is all that, then you'll notice no difference at all except for the extra power.

    Comment


    • #3

      You don't need an isolation transformer or
      filtering caps... what you want is a simple
      triac speed control circuit. If it has
      back-emf sensing all the better. This
      is pretty straightforward.

      DC motors work very nicely for variable
      speed drives; it's only been recently
      (last 20 years) that variable speed AC
      drives are practical.


      ------------------
      Bart Smaalders
      http://smaalders.net/barts
      Bart Smaalders
      http://smaalders.net/barts

      Comment


      • #4
        George:

        Does the control box have any kind of label on it? The various commercial units vary in complexity (and features). I have used a DC motor on my 9" S.B. for several years, and really like it. I use a KBC speed control on it, all the features you describe plus constant torque. You must dial in the speed and sort of get the "feel" for rpm's (unluss you have a tach). The reverse feature is really nice for tapping, etc.

        Ken aka Ozarks Hermit
        Shell Knob, Mo
        Ken aka Ozarks Hermit
        Shell Knob, Mo

        Comment


        • #5
          My reply is actually a question. How would one go about building an AC to DC converter? I'm looking for a way that I could do it myself. Affordably, I must add, because money is a bit tight right now.

          Comment


          • #6
            Ok I was just about to post a query along these lines, so here is what I would like to ask...
            I am thinking maybe instead of going to 3 phase VFD that DC might be the answer for my application. I am currently running a 2hp 3 phase motor through a phase convertor and it works fine except I don't have speed control... If I were to consider DC, what would I need to convert AC to DC, control the speed and this needs to have instant reversing, as this operates the table on a large knife grinder...
            Thanks again guys for your expected excellent answers... Now to add to Thruds comments on this BBS, he is right, this is the best damn bulletin board on the internet for us gear heads, right?
            Regards Jim
            Jim

            Comment


            • #7
              The motor and control came as a unit,someone else did all the brain work. I just replaced burnt up toggle switches and replaced the speed adj. knob. Just took a look,the motor is a Reliance DC 1 Perm.Magnet,90 volt,Power matched/RPM. 9" long,5 3/4" dia. 5/8 shaft. The speed control does not completely stop the motor,but seems to have plenty of torque from the slowest to the top speed. The control box is an Emerson Focus 1. About 1/3 of the cover is a heat sink. The bearings on my grinder went out and I needed that,so I haven't tried the lathe yet.

              Comment


              • #8
                Shaque,for your blade grinder,have you considered a garage door opener motor? The newer ones have the instant reverseing and I don't believe they use brushes,so a router speed control might work. The motors might not be continous duty though.

                Comment


                • #9
                  George;
                  Yes I thought of that, but as I remember they are only 1/2 hp, and I need 2hp, as this traversing table is 10 ft long and is made out of cast iron. come to think of it don't garage door openers have plastic gears? Oh yeah the table is quite heavy and is about 10 ft long.
                  Yhanks
                  Jim
                  Jim

                  Comment


                  • #10
                    Converting to dc is no big deal. The more power you want out of it the bigger the semiconductors(stud type) and heatsinks you have to use. Instant reversing is best done using power MOSFET's - they really have the balls the handle the back emf without complaining very much. The power MOSFETS can also handle the speed control. The only filtering you will really need is for the drive control electronics.

                    Comment


                    • #11
                      Browsing through the message threads looking for this exact topic. Did anyone ever answer the question on how to make an AC to DC controller. Anyone have a URL that has the info. Please don't say just get this and that and through them together. My electrical expertise is limited however I am real good at following directions.

                      Jim

                      Comment


                      • #12
                        Teaching you advanced power control electronics via a text based BBS is asking a lot. I would suggest that your best course of action might be to ask yout local high school electronics teacher, tech school, or university engineering department for assistance. You would be surprised how helpful these people are when you explain you situation and ask their help. Often the Tech School or Professor will have top students design one for you as a project. Get involved with your schools.

                        Comment


                        • #13
                          I converted my south bend 9" to dc a few months ago with no real problems so far. I am using a 2 hp dc motor and the control/converter that it used in its first life. If any one is interested I usually have several of these motors in my shop available for almost nothing or trade and I also have the converters/controllers that use a simple potentiometer for controll. Being a newbie at this I do not know if they are Ideal, but the motors and controls are used in a pretty tough application as is, and they are cheap when available.
                          Brian

                          Comment


                          • #14
                            Brian,

                            I would be interested in buying a controller from you. My email is [email protected] if you want to pursue this offline.

                            Jim

                            Comment


                            • #15
                              I've been using my lathe quite a lot lately and am in love with the variable speed of the DC motor. Just finished cutting the welds holding sprockets on 6 different shafts,for a neighbor. Also turned and tapped 6 nuts for some threaded castors that I had. All done without shifting any belts ! I did use the back gear for tapping.

                              Comment

                              Working...
                              X