Lathe went down.

[Bluechip]

Doesn't have to be sinusoidal Andy ... you can get the r.m.s. of anything repetitive if you want to .
http://en.wikipedia.org/wiki/Root_mean_square
You don't have to stick with the ' root two ' bit .
All that stuff meant some thing to me once. I was OK with electrical stuff once, but it all changed after Faraday poked his nose in then I lost the plot somewhat ... 
 
Dave BC
 

[DICKEYBIRD]

...with an encoder attached to run the tach on the front of the machine.

Hmmm, I wonder what the encoder out put is?  Some of the KB's (incl. my KBCC, yay!) accept a 7VDC or 50VDC per 1000 rpm tach input and will regulate the speed to <1% of set speed.  If I have trouble with speed wobblies when threading, I'll hook up one of my old PM brushed ball-bearing model airplane motors to the Baldor & use it as a tach generator.

[andyf]

..... All that stuff meant some thing to me once. I was OK with electrical stuff once, but it all changed after Faraday poked his nose in then I lost the plot somewhat ... 
 
Dave BC

Me too, Dave. Had to learn all that sort of stuff for the Amateur Radio exams, but that's about 30 years ago. I got distinctions, but that's nothing to boast about; the questions were tick the box multiple choice, and included things like this:

Q1.
[schematic of something]
What does this diagram show?
(a) a common base amplifier (b) a common collector amplifier (c) a low pass filter (d) a power supply

Q2
In the diagram of a common collector amplifier shown in Q1, what is the function of R1?
(a)        (b)          (c)            (d)

Andy

[John Rudd]

When sourcing replacement diodes or scr's for that matter, remember the KB or the Minarik decies are isolated tab....  Dont think of fitting anything else without using isolation bushes and micas if you need to else you will continue to blow fuses

[ibuildstuff4u]

 John I wondered about the isolation on the tab because there isn't any type of isolation on this drive and I'm pretty sure I'm the first to take it apart.  There is just a thin film of thermal compound between the tab on the diodes and scr's to the heat sink.  There are NO bushings, or micas between them or any evidence that their was ever one there as the micas usually leave a mark larger than the tab on the heat sink when you remove them.

Sounds like I should add some isolation?

Dale P.



Milton,  I thought it was funny that the lathe had an encoder for a built in Tach and also a optical pickup to provide the computer with the spindle speed.  Seems like there would be an easy way to provide the computer and RPM gauge with the same signal.  It's also strange as both gauges aren't the same and are off by about 20 to 30 RPM, but that could be due to the pulley ratio on the encoder verses the optical pickup being mounted right on the spindle.

It sure would be neat to have the speed controller hooked up to the encoder so the speed is more constant to what you set it to.  I still have to spend time on my machine to get the RPM to match what the computer is asking it to be.

Dale P.

[John Rudd]

I wondered about the isolation on the tab because there isn't any type of isolation just a thin film of thermal compound between the tab on the diodes and scr's to the heat sink.  There are NO bushings, or micas between them
Dale P.

Dale,

Perhaps I wasnt as concise as I thought...
The OEM devices have an isolated tab....Nothing else required....

If you obtain devise from another manufacturer, they may need micas and bushes..

[ibuildstuff4u]

Ok I get it.  Makes sense now.  Thanks for the tip, I will check out the info sheet on the diodes and see if the tab is isolated or not.  Guess I could just test them with a meter too, or just insulate them to be on the safe side.

Thanks for the tip, Dale P.

[trevoratxtal]

ibuildstuff4u I dropped out of this post As John and others were giving good advice particularly to supply's your side of the pond.
It is very gratifying to see so many Electrical/Electronic knowledgeable folk.
I salute you all. 
Trev
PS do not forget a capacitor across the brushes on DC motors. It also cuts down RFI.

[ibuildstuff4u]

Your guys rock!  I didn't know a lot of you guys are interested in electronics too!  I loved playing around with the stuff as a kid and am interested in getting back into electronics as well as doing more metal working in the future.  I think I'm going to add a lab area to my shop for electronics and pick up some equipment such as a nice variable power supply and an oscilloscope. 

I'm 37 years old and have been going to night school for the past few years to be a machinist, but recently changed my degree to an Automated Systems Technician and I can't wait to take some of the core classes and learn more about machine controls, and electronics in general.  Right now I'm working my way through a math class that I take Saturday mornings and it has been tough!  It's all self paced with NO formal instruction so you have to teach your self and work on homework 3 to 4 days a week. 

Trevoatxtal,   When I add the caps, do they have to be right by the motor, or can I place them closer to the speed control?  Also do they get mounted one from neutral to ground and then a second one mounted from the hot to ground?  Or do the go right across the hot and neutral leads?  Years ago I ran RC cars and we added caps to the motor to prevent interference to the radio and the caps were soldered right to the motor case.  One cap went from the + lead to the motor case and the second cap went to the - lead to the motor case.

Thanks again for all the help!  My new parts come on Wednesday so hopefully that's all I need to get it working again.

[John Rudd]

If the motor is earthed( grounded) then connect a cap from each motor terminal to the casing....

I hope the caps you are using are not polarised......A suitable value would be around 100nF (0.1 mfd_

[trevoratxtal]

I concur with John Rudd but add must be high voltage working 1000v min, you could get away with .01µf  with the frequency's the controller runs at but .1µf is better but 10 times bigger physically so harder to place.
Good luck
Trev  

[ibuildstuff4u]

The parts came today and the lathe is back up and running again!  It's always a great feeling when you can fix something instead of having to buy a new one.  It put a nice big smile on my face when I pushed the button to start the spindle and the lights didn't go out. 

Thanks again for all the help!

Dale P.

[andyf]

  We like stories with happy endings!

Andy

[ibuildstuff4u]

I just bumped in to this on E-bay.  For around $100.00 I can get the whole box that contains the motor controller.  It would provide me with a spare motor drive as well as a, RPM gauge, and two solid state relays.

Very tempting, but funds are tight right now.  I will have to sleep on it.

Dale P.

http://www.ebay.com/itm/261197635324?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649