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  • Small DC motor and control questions.

    Been piddling/minor cleaning in the shop today and bumped into this motor. It was on an auto air suspension compressor and I had previously carved off the compressor housing and other non-essential bits. The commutator was worn some so I set it up in the lathe, turned it smooth, polished it and cleaned out the grooves. It’s a PM type with a ball bearing on the drive end and an oilite bushing on the other end.

    I set it up for some tests today and here’s what I found: 2.3A @ 13.5VDC, 3350 rpm w/no load. The output shaft was too short to apply a load by hand and still measure rpm but I’m guessing it drops to about 2000 rpm under its previous design load and pulls 4 to 5 amps.

    My intended use for it is an auxiliary drill/mill spindle attachment to mount on the carriage of the ORAC CNC lathe like Jim did on his for small hole drilling and light milling. I’m thinking it doesn’t have enough “oomph” to do much good but may fool around with it a bit longer and see what it can do. Ya’ll think it’s a waste of time? So far I’ve had no luck finding a (cheap) small 90VDC motor to go with my preferred KB speed controls.



    I have this modified KB controller with a PECO auxiliary board on it that has terminals marked 120VAC in, slow/fast and fwd/rev. The KB is marked 36V input so that must be fast speed and I’m guessing slow must be 18 to 20V?? Does anyone have any experience with this control? I’d like to use it but haven’t been able to find a manual for it to see how to hook it up to select slow/fast or forward/reverse. The HP resistor is marked 1/8 – 1/5 so it should be close to the above motor rating? I think the motor would work OK at 18V under intermittent use.

    Milton

    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

  • #2
    Milton, Given that you have that spindle you have posted, the Er one with parallel shak then have a look at this post.

    http://madmodder.net/index.php/topic....html#msg73831

    Very interesting article.
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



    Comment


    • #3
      Look at the total energy INPUT...... about 60W.

      So that is no more than about 1/12 HP electrical input, and obviously no more than that in shaft output.

      If that will do your job, you have enough "oomph". Otherwise not.

      There are tables of metal removal in volume per unit time, for various power inputs and drilling vs milling vs grinding vs lathe turning, etc. You can use that as a rough guide to whether you have any chance of getting the performance you want from that motor. Drilling is pretty efficient, actually.
      Last edited by J Tiers; 09-30-2012, 07:26 PM.
      1601

      Keep eye on ball.
      Hashim Khan

      Comment


      • #4
        Milton;

        Not sure if this will help but one of the handyest power supplies I ever came up with is with a Variac (Variable AC transformer). Those are often seen to vary the speed of feeder bowls. Before I retired I worked with feeder bowls.

        I found a enough room inside a variac transformer to wire in a rectifyer and a capacitor. What I ended up with is a variable DC powersupply. It is unregulated however. I went on to install an analog volt meter on the side of the variac so I would know what the power setting was. I use this power supply to run proximity sensors or anything DC powered. The variac has a built in 10A fuse holder so I assume the transformer can handle that kind of current.

        I reiceved my Johnson DC motors Saturday. Two motors are 24VDC and one is
        12VDC. I plan to use my variable DC power supply to run the motors and make the motors variable speed. I'll know in a couple of day how they are going to work.

        I have also worked with those KB motor controls and those 90VDC motors. I have box full of 90VDC motors in my basement. One thing I learned the hard way is to not use my variable volt DC powersupply on those 90VDC motors. Not sure what happened but I smoked the capacitor. Most of the time I use a Minarik RD16U to vary the speed of 1/10 hp 90VDC motors. I use the KB motor control for 1/4hp DC motors. I think those DC motor controls vary the frequency
        instead of varying the voltage for changing speeds.

        I thought about using a DC motor to run my high speed spindle but the motors I have on hand have a max speed of around 1800 RPM.

        Hey John: I emailed the "Madmodder" about the high speed spindle bearings he uses and never heard back.
        So much to learn, so little time

        Comment


        • #5
          If that motor draws 2amps + at idle, it's easily capable of drawing 10 amps under load. I would suspect that to be about the normal current draw in its intended application. This is not the type of motor that you would leave running while you intermittently drill, as you might on a normal drill press. It's going to get pretty warm after a few minutes of running, even with no load. If the idle current was lower, say 1/2 amp or so, it would be better suited, but I'd say run it for 2 or 3 minutes, then give it a minute to give the heat from the armature to dissipate into the case. If the case doesn't seem to get too hot, then maybe you have a suitable motor there. Note that it doesn't have any method of cooling, and would be rated for intermittent duty, probably something like 20% ( four minutes of cooling off for every minute of running).

          If it's doing 3350 rpm no-load, you might consider that 2500 rpm loaded would be about the right area of operation. I wonder if that's fast enough for small hole drilling-

          You certainly don't need to be encumbering it with belts and pulleys to raise the rpm for your application. I think it's worth trying to boost the rpm by using a higher voltage- it all boils down to how hot the armature gets under use. I think that motor is physically large enough to be useful, but it could sure use some airflow through it.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

          Comment


          • #6
            The small auto suspension compressors are not rated very high, you need something like this ebay 320990096788, or check out Maxon motors for High RPM, but you need to seek one with higher wattage range, also they are usually in the 12-24vdc range.
            Max.

            Comment


            • #7
              Electrical things have no "fixed" rating.... The motor folks rate them on heating. if they don't overheat, they are not overloaded.

              The most power you can get out legitimately without overheating will be the continuous rating. There will be a short term rating. Actually there will be a whole "curve" of them, different conditions and times that all reach but do not exceed the maximum temperature.

              Still and all, you can get only so much power in, and therefore only less than that out, since some of the power is wasted in heating up the windings etc. You have to determine if the maximum probable power output is enough, and hopefully is more than enough, to do what you want.

              In the heavily loaded conditions, the motor is typically less efficient. The "copper" losses go up as the square of the current. So if the motor could draw 2A continuous and just barely go to maximum temp, it might be able to draw 4A and put out more total power. But it would also WASTE 4x more power as heat, and it could likely only draw that for about 1/4 or less of the time it took to reach max temp at 2A.

              Now, for small drills, it probably is good. but you will HAVE to run it fast, or use belts , because if you slow it for larger drills, it will lose power.
              1601

              Keep eye on ball.
              Hashim Khan

              Comment


              • #8
                One of these days I'm going to get one of those brushless model motors to play with. I have played with super magnets in regular motors, and I'll say one thing- if you keep within the heat-dissipating capabilities of the armature, the difference between the no-load rpm and full load rpm is not very much. In other words you might have a no-load rpm of say 5000 rpm, and the full power rpm might be 4500. If you stress the motor by allowing it to draw as much current as it wants as you load it, you can get relatively large amounts of power out of it- for short periods of time. For a drill press this could be nearly ideal. The time-to-drill might be relatively short compared to the time between switch-on and switch-off. In the meantime, you can use the high torque capability to maintain the rpm and get the hole drilled relatively quickly.

                What you can't do is rely on any of the motor bearings to take the thrust load of drilling, so assuming you would want to go direct-drive, you would support the drill chuck arbor on its own bearings.

                Those little brushless model motors have lots of power in very small packages, but would often need a speed reduction to drive the chuck arbor. Fortunately, it's usually pretty easy to set this up, and you'd normally be able to hang the small motor off the side somewhere anyway. I read the specs on one a few weeks back, and it said 100,000 rpm max (not a typo). You could reduce that by 10 times and still have 10,000 rpm on the output shaft. Of course you would need a special controller.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                Comment


                • #9
                  Originally posted by darryl View Post
                  I read the specs on one a few weeks back, and it said 100,000 rpm max (not a typo). .
                  100,000rpm, I would be interested in a link to that!
                  Max.

                  Comment


                  • #10
                    I replied awhile ago, but it seems it got lost. Here it is again-
                    www.koford.com/48HS.pdf
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                    Comment


                    • #11
                      Thanks for ya'll's learned responses; knowledge is a wonderful thing!

                      Can't believe I didn't think to drill some cooling holes in the ends while I had the motor apart. That'd increase its power handling capacity a bunch especially with a muffin fan added like I did on the treadmill motor.

                      It should have more than enough power for the one job I get a few times a year that I'd use it on for sure. It's a precision little cut in aluminum on the side of a turned part with a 5/32" endmill. I do it in the mill now but is a pain to set up. It'd be so much easier under CNC before the part is parted off in the lathe. If I go to all the trouble of building it I'd like to make it as flexible as possible with high and low speed options. I'm sure there will be many other uses that'd come up for it to make it a worthwhile project. "Build it and they will come."



                      If I can get the KB/PECO control to work with this motor I may spend some more time messing with it. Unfortunately I have a mental problem that fits my budget perfectly. I LOVE to re-purpose stuff I have lying around and tend to be penny-wise & pound foolish. If I could find a cheap motor that was a 1/3 to 1/4 scale clone of your typical 5000 rpm treadmill motor I'd be good to go but it ain't happening so far.

                      Here's another pic of the PECO board with the terminals marked. Any of you CSI Electrical® cast members care to make an educated guess as to how to make this thing fire up in the slow speed mode? The 120VAC and the A-/A+ terminals I can handle; it's the others I'm not sure about. Apparently my Google-Fu sucks because I can find where to buy the things but no neat little .pdf's to show how to hook it up.

                      Milton

                      "Accuracy is the sum total of your compensating mistakes."

                      "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

                      Comment


                      • #12
                        I would think if you need around 10krpm in that size, one of the many DC Maxon on ebay would do the trick?
                        Max.

                        Comment


                        • #13
                          Ain't it funny how things work out sometimes? Jim (Mr. outback nice guy) made me a deal I couldn't refuse on a Pittman 24V motor and it arrived today. It's a well-built (Made in Pittsburgh!) beefy little motor with dual ball bearings, replaceable brushes and a 1/4" output shaft. Thanks so much Jim; I hope I can do a good deed for you very soon in return!

                          I ran the motor first with the Tamura 24V/2.4A linear regulated power supply I got for peanuts on ebay a while back and the Pittman motor ran 3450 rpm, no load @ about .18 amps. I could squeeze the shaft with a rag almost as hard as I could and it went up to 2 amps and still was holding 2800 or so. That would've worked fine for my needs as-is with a 2 to 2.5/1 belt ratio.

                          BUT...I dragged out the $30 (ebay) KB control with the aux. PECO board on top. The PECO board is supposed to drop 120V down to 36V for the modified 36V KBIC-120 and allow 2 speeds + forward & reverse.

                          I haven't found any hookup info for the PECO yet so I decided to just remove it and run the KB straight from an external 36VAC source. I don't have an appropriate 36V xfmr (yet) so I preset the variac to 36V and connected it directly to the KB as normal using an external 5K pot to control the speed.

                          The KB adjustment pots were all out of whack but after fooling around a bit I had smooth, precise control all the way from a crawl up to 5400 rpm @ 34V! The motor runs smooth & quiet at that speed and showed no sign of stress or overheating. I can bear down on the shaft with a rag and the KB instantly compensates. Even at very low speed the KB does its magic and instantly compensates when a load is applied. I love it!

                          The other fortunate thing that happened was while I was digging around for the power supply, I found the long-lost little box with 2 nice chunks of 2024T-3 aluminum a friend in N. Carolina sent me. Perfect for the ER-16 spindle project!

                          When the 2 5200-2RS ACB's arrive and the little Atlas compound slide gets here, I'll have to dream up another excuse not to get started on the CNC aux spindle project for the ORAC.




                          PS: I'm writing this with no fried extremities or muscle spasms so I have now successfully mocked-up & tested (for me) a complex electrical project without hurting myself or my equipment.
                          Milton

                          "Accuracy is the sum total of your compensating mistakes."

                          "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

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