RPM Speed Controller Suggestions Needed

Discussion in 'DIY' started by ghazzer, Mar 10, 2018.

  1. ghazzer

    ghazzer Sansui addict Subscriber

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    {I wrote this about 2:00 and guess I forgot to "post" it. Still applies.}

    Retrovert: "I suggest you not rely upon the advice random people, . . ."

    Your suggestion is self fulfilling. As you say, I am asking for suggestions from random people (like yourself), not solutions. I also have a background in EE, but it is so far back that many of today's options were not available then.

    I am currently in the "hunter/gatherer" mode - trying to search for useful information and then research that info before I make any decision. Each "suggestion" deserves consideration. A lot of the actual decision depends on the final application and how it will be used. I feel certain that there are more than one pertinent factor(s) that I failed to mention, and my brain is probably not something that most folks would try to "read".

    Your post contains some relevant information, that I have read and it will help with my additional research. There is more than one way to implement a motor controller, and I suspect that some will work better than others for my planned project. ==> More research.

    I am not opposed to bread boarding a circuit for this. I can even etch a PCB if necessary. Kinda depends on the complexity and availability of parts.

    Thanks -
     

     

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  2. ghazzer

    ghazzer Sansui addict Subscriber

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    STOP THE BICKERING!!!!!!! Both of you!

    Nobody needs this crap!

    Thanks for your suggestions, but if you cannot act like reasonable adults at least start your own thread!

    Everyone is entitled to their own opinion, but once you have stated it civilly, go somewhere else.
     
  3. neevo

    neevo Super Member

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    That was roughly the plan. Copper pipe around the motor to transfer heat. Water pump from a small reservoir feeding in to a heat exchange (I was looking at computer cores) with a small fan to assist with heat transfer on the core.

    I bought a KB Electronics PWM for my setup (KBMM). Probably overkill for what you want but they are pretty high quality in my uneducated opinion.

    Be careful what you’re doing, I got told off when I was doing my build as playing with mains voltage is dangerous.

    https://www.kbelectronics.com/Variable_Speed_DC_Drives.html
     
    Last edited: Mar 13, 2018
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  4. dB happy

    dB happy Active Member

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    Problem solved, show ignored content? Nope!

    If you use copper tube around the motor, use a copper/brass heater core. If you use aluminum tubing, use an aluminum/plastic heater core.

    A mismatch in metals forms a battery, and results in corrosion.
     
  5. Retrovert

    Retrovert AK Subscriber Subscriber

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    A substantial difference exists between someone posting schematics of dangerous circuits found with a ten second search in order to be "helpful" and explaining why the solution is incorrect. You should be able to trivially verify the truth or falsity of the analysis, whereas analyzing the circuit might be beyond your abilities and knowledge.

    I explained the issues and why the proposed phase control used for incandescent light dimmers would not work on AC motors, and why cycle control was how AC motors are controlled.

    Cycle control has been around since the SCR and TRIAC were first available in the late 1950s and early 1960s. The price substantially dropped in the mid to late 1960s and cycle control became the standard for AC motor control.

    I fully explained the issues since the suggestions were incorrect and dangerous, and specifically urged you to do your own research as you, or anyone later facing a similar issue and reading the dangerous nonsense, should now be aware of the safety issues:
    Posting No. 18:
    The takeway from all of this verbiage is to never trust a horologist or audio hobbyist to tell you about your power controller. Don't believe what catalog blurbs tell you. Don't believe website listings. Don't believe what I or anyone else writes, research it for yourself. The issues should, given the above, be a bit more understandable.

    Posting No. 20:
    What I wrote should give the OP sufficient information to research which type of commercial motor controller is appropriate.

    Posting No. 20:
    One can correctly solve the problem and not worry about motor overheating, buzzing, or burnout, and learn something about how motor control works as well as why asking random people to regurgitate endlessly re-circulating misinformation about power control is a bad idea. Or one can incorrectly solve the problem using a bunch of misinformation which puts the motor at risk of failure and replacement, and creates more dogma and reinforces absolute nonsense.

    Posting No. 32:
    I wrote up an explanation about the basic issues involved and included enough material to allow anyone to properly evaluate the suitability for a commercial unit. I suggested the OP find a commercial unit, with UL or CE approval, not a bare-bones Chinese unit which omitted key safety features to save on costs or, worse yet, was deceptively marketed.
     
  6. neevo

    neevo Super Member

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    Hadn't even thought about that. Good call. Do you think that copper pipe would allow enough heat transfer if it was wound around the motor?
     

     

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  7. dB happy

    dB happy Active Member

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    I really don't know, never really thought about liquid cooling a motor like that. Honestly, I'd go for a bigger motor, or changing the drive ratio before I tried that. I always go for overkill when I put a different motor on something.

    The motors on my mills barely get warm, and they can remove serious metal. The mill is a 1.5hp dc treadmill motor, and the big mill is a 2hp 3 phase motor.
     
  8. neevo

    neevo Super Member

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    Good point re drive ratio. Is it better to run a DC motor faster to get the hp vs using high current and torque?
     
  9. dB happy

    dB happy Active Member

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    Yes, all motors run hot trying to run them too slow. If they have an internal fan, it isn't spinning fast enough. The iron of the armature has too much time to saturate. Current flows too long for each winding on a brush type motor. There's a bunch of reasons for it.
     
  10. neevo

    neevo Super Member

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    I assume a smaller pulley too would increase effective torque and reduce the load on the motor further too.
     
  11. dB happy

    dB happy Active Member

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    Yes, but too small of a pulley, and you don't get enough surface area. It will slip, and over tensioning the belt will destroy the bearings in the motor.
     

     

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  12. avionic

    avionic " Black Knights " Subscriber

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    Galvanic corrosion.A real issue on high performance aircraft.
     
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  13. neevo

    neevo Super Member

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    Its already a 2.5" pulley, so I think a higher ratio is out of the equation.

    Water jacket is worth having a go at if its not too expensive.
     
  14. danbisawsum

    danbisawsum Active Member

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    What a mess of a thread... we have people talking about watercooling homebrew mills and two folks having a cordial standoff. The guy that seemed to be most helpful, Retrovert, ended up on someone else's ignore list... yeesh. Poor ghazzer had to pull out the caps lock, bold, and underlines... we shouldn't be putting him through that. Everyone just calm down.

    I have a masters in mechanical engineering and design custom machinery for a living and I haven't had even a coupling fail yet in any design of my 10yr career (aw look at that, he's a sassy young buck). Torque, speeds, feeds, VFD/ASD are every day terms for myself. I've spec'd motors and VFD's for converting lines that run 24/7/365 at 1500 ft/min web speed and a single day of downtime costs the company $200k and I've designed slow moving apparati that turn in the single rev per hour range. Here's my take...

    Retrovert hasn't said anything I'd disagree with really. But he could have went further and I will now. If you want safe speed control and roughly constant torque there is only one sensical solution... A properly sized VFD powering a properly sized (speed and torque) motor that is inverter duty rated for the intended rpm range of the application. No other solution is as robust. There are plenty of good motor manufacturers. I don't like recommending specifics even though I have no affiliation to any producers of commercial drive equipment. If forced to pick favorites, I'd say an Allen Bradley Powerflex unit powering a Baldor motor (yeah it's pricey but they are solid and everyone knows how to use them and they're available - like Windows OS, in many ways).

    http://www.baldor.com/brands/baldor...iable-speed-ac/ac-inverter-vector-duty-motors
    https://ab.rockwellautomation.com/Drives/Compact

    If I were in ghazzer's shoes, I probably wouldn't go with what I just recommended above because of cost. Pulleys are the cheapest way to get the best out of your current motor but you probably need a decent speed range for your different turning applications (if diameter of parts change significantly, for instance) but that can get to be a pain in the butt... you might have to change pulleys in the middle of turning a part, that'd be whack. So you definitely want a motor with speed control.

    Here's the cheapest VFDs I would recommend:

    https://www.automationdirect.com/ad...t=0&Product__F__Accessory_Type_ms="AC+Drives"

    Same source has some cheap inverter rated AC motors:

    https://www.automationdirect.com/ad...umber=-1&searchqty=10&start=0&start=0&rows=10

    Do some reading on what the turndown ratio (the thing that makes a motor inverter rated) implies... it basically says how much abuse a motor can withstand due to heat due to current due to messin with it's nominal power. Also, do some thinking about the type of integrated cooling the motor might have or need. I lean towards fans, usually motors I spec are going in hot and cramped environments and I trust the heat transfer abilities of the fan over fins and natural convection.

    I've totally ignored the DC alternative. Without going into any details, all I will say is that I cannot fathom one advantage you'd gain in this application by going that route... other than you might stumble upon a DC motor more easily than an inverter rated AC motor. DC motors can be easy to control speed-wise, but good luck getting full torque. The only way to do that via DC entails a lot more expense (look at a servo controller cost... yeah the motor might be cheap but controls won't be). I stumble upon TV tubes and transformers all the time that could produce audio but not easily or safely or to code and if it did all those well then not efficiently. You have to know when to hold them and when to fold them and if you don't... read until you do. It's like when someone comes here looking for advice on how to fuse or ground their old two prong 5 tube radio. A whole cast of folks that have done something (right, wrong, or indifferent) come in saying what they did... usually not why, usually with little context to what model or other specifics, and that is what's wrong with the "all opinions were created equal" attitude. Demonstration should be kept aside from understanding. Just because someone else has been lucky in what you've gathered to be an analogous circumstance to yours does not mean you will be too.

    Save the sewing machine motor for a time when 6,000 rpm is closer to right for the application. Or cobble something together and find some backups for when things fail. If you go the cobble route, I trust you'll fuse or breaker or put the adequate safety measures in so you don't burn anything down. Either do it dirty and own it or do it right and forget about it.
     
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  15. ghazzer

    ghazzer Sansui addict Subscriber

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    Thanks Dan. I value your judgement, and I am still reading.
     
  16. neevo

    neevo Super Member

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    I’d also concur that the best option when I was doing my DIY option was a quality motor and VFD. If you have the space for the motor and the cash (it’s not the cheapest option) it seems to deliver the best most reliable performance.
     
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  17. ghazzer

    ghazzer Sansui addict Subscriber

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    Right now I am looking for a "good" solution that will get me through this current project. After that I will evaluate how much I will be using the lathe in the future and what I expect to do with it. So far, my total "turning" time with the lathe has been about 10 minutes. That is roughly 0.0000528% of my "waking hours" since I was 18, so not very much.
     
  18. dB happy

    dB happy Active Member

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    If you go the vfd 3 phase motor route, you don't have to use an inverter duty motor. Most 220v 3 phase motors do just fine on a vfd. The 400v motors, not so much. You should use an inverter duty motor, they're designed to take the high switching frequency, and usually have better cooling for low speed. However, if I found a good deal on a suitable 3 phase motor, I'd go for it. I'm sure I'll be told how wrong I am for this.

    I know the sewing machine motor will work, but you'll probably want more torque. 6000 rpm is kinda high for this application. I wouldn't spend a bunch of time and $$ on it.
     
  19. ghazzer

    ghazzer Sansui addict Subscriber

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    Thanks. I will stick with the SMM or the original K&D motor if I can revive it. This is a small lathe and I am not trying to turn parts for an aircraft carrier, so I suspect that the torque will be adequate. Right now I'm just trying not to lose too much of it at slower speeds.

    There is still much to be learned - - -
     

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