Re: [CAD_CAM_EDM_DRO] AC Speed Controller for Lathe: Meat or Accident?
Posted by
Jon Elson
on 2003-09-17 10:47:12 UTC
Abby Katt wrote:
voltage. Yes, if you turn the voltage down until the motor is insufficently
excited, there will be NO torque! It will hum, and not start.
Because of the starting switch, single-phase AC motors do not take
to speed control well.
of them on eBay at any time) or a DC motor. DC will be hard to come
by, and you will easily burn up several hundred $ getting a DC speed
controller
to work reliably.
nicely. Hey, you also get braking with a VFD! Stops the spindle in
a couple of seconds, instead of waiting 20 seconds for it to coast down.
(And, I can't even lift PART of the tailstock on it without extreme
exertion!)
Jon
>Swarfer-breatheren,No, this does not work. AC motors speed depends on FREQUENCY, not
>
>I seemed to have (accidentally) bought myself a massive big old lathe
>at an auction. When I picked it up however, I found that the motor
>was some horrid 3-phase electical fire with a rats nest in it, so I
>dropped this and decided to just buy a new one of ebay. However: as
>I'm now missing the belt-drive and motor assembly I'll have to make
>this up.
>
>I thought this would be the best place to ask this: I'm thinking
>about building my own AC motor speed controller (with some
>thyristors) and just leaving the motor belted on one setting or the
>other. I was wondering what advice people would have on this? I'd
>have asked this on another forum, but as you all are so terribly
>nice, and experienced with this type of thing I thought I'd ask here
>(and hey! I'll probably convert the lathe to CNC in the future
>anyway. :) )
>
>So what's the deal? Is this good science, or bad science? Will the
>lower voltage mean the motor will turn really slow, but also have no
>torque what-so-ever?
>
voltage. Yes, if you turn the voltage down until the motor is insufficently
excited, there will be NO torque! It will hum, and not start.
Because of the starting switch, single-phase AC motors do not take
to speed control well.
> Should I use some other kind of circuit? Or isYour choice is a 3-phase AC motor and a surplus VFD (there are 20-30
>this is all just a terrible idea that's going to wreak havoc on the
>electrical grid for blocks around as I throw rude-pulses at a 2KW
>motor? Should I use a DC motor instead? (I want to do this on the
>cheap, really)
>
>
of them on eBay at any time) or a DC motor. DC will be hard to come
by, and you will easily burn up several hundred $ getting a DC speed
controller
to work reliably.
>BTW> This is a BIG old lathe! 5foot long and weighs.. well.. theA VFD runs the 5 Hp motor on my 3500 Lb Sheldon 15" lathe VERY
>tailstock weighs about a third of my weight. :P
>
>
nicely. Hey, you also get braking with a VFD! Stops the spindle in
a couple of seconds, instead of waiting 20 seconds for it to coast down.
(And, I can't even lift PART of the tailstock on it without extreme
exertion!)
Jon
Discussion Thread
Abby Katt
2003-09-17 03:32:50 UTC
AC Speed Controller for Lathe: Meat or Accident?
Marv Frankel
2003-09-17 05:56:05 UTC
Re: [CAD_CAM_EDM_DRO] AC Speed Controller for Lathe: Meat or Accident?
turbulatordude
2003-09-17 06:25:05 UTC
Re: AC Speed Controller for Lathe: Meat or Accident?
Harvey White
2003-09-17 09:04:21 UTC
Re: [CAD_CAM_EDM_DRO] AC Speed Controller for Lathe: Meat or Accident?
Jon Elson
2003-09-17 10:47:12 UTC
Re: [CAD_CAM_EDM_DRO] AC Speed Controller for Lathe: Meat or Accident?