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Delta Midi speed controller?

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Hi
I've had a Delta midi lathe model 46-460 variable speed since 2010 and it has been a fine machine. But yesterday, the moron in me switched it on then looked away, without realizing the spindle was locked. Belt-slipping noises and the smell of burning phenolic. After it cooled the reset button flipped like it should and the lathe runs, but only at top speed, the variable speed controller is fried. So now I have a three-speed lathe, unless I can replace the controller unit.

On the Delta parts site a new controller is $268 plus freight, about half the cost of a whole new machine and more than I have to invest. But on a number of industrial sites, a Teco-Westinghouse after-market controller rated for 1hp 120v single phase, is "only" $150.

Looks like it would work. But before I jump, does anybody have any experience with this situation? Is the Teco controller likely to work properly?
 
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No I didn't know that, are you sure? Was just trying to figure that out. Two wires (black and white) go to motor, plus green ground. There is a fat capacitor on the circuit board which I thought was the motor starter. Was hoping it would be a three-phase so the Teco controller would work, guess not.
 

Bill Boehme

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It is a DC motor. And, the speed controller is just a simple variable voltage device hardly any different than a light dimmer or the speed controller on a router or hand drill. Too bad about the outrageous price ... there's probably not more than $20 worth of parts in the controller. You might try talking to Delta tech support to see if they have any troubleshooting suggestions such as the possibility of a fuse in the controller. You might also search for a generic DC motor speed controller. Since you ozone from a frying electrical component, you could look inside the controller for any obvious sign of the problem. There's the possibility that the controller can be repaired.
 
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It is not a straight DC motor but controlled by pulse width modulation I believe. Is it a type I or Type II? One of our guild members with electronics knowledge repaired one that had burned out. On another forum a fellow bought the replacement controller board recently for type II and repaired it. Part was delivered in a couple of days. He had to wait on phone for a hour or more for support.
 

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It is not a straight DC motor but controlled by pulse width modulation I believe. Is it a type I or Type II? One of our guild members with electronics knowledge repaired one that had burned out. On another forum a fellow bought the replacement controller board recently for type II and repaired it. Part was delivered in a couple of days. He had to wait on phone for a hour or more for support.

Pulse width modulation is used to synthesize variable frequency to control the speed of three phase AC motors. For controlling the speed of a DC motor, the controller is basically controlling the voltage to the motor since the speed of a DC motor is proportional to the applied voltage (the exact speed vs. voltage relationship depends on whether the motor is series wound or shunt wound). The variable voltage is created using a thyristor (or one of it's derivatives) which turns off the AC voltage during part of its cycle and then filters it to create the DC voltage. This might be the pulsed voltage that you are thinking of ... and it's essentially the way that incandescent light dimmers work. The figure below shows an AC waveform in red and the waveform after it has been rectified by a thyristor shown in green. The effective voltage of the rectified waveform below would be about a fourth of the AC voltage.

AC_Rect_In_90_edit.png


Low cost variable speed mini and midi lathes all use DC motors with variable voltage controllers. It's not the frequency of the rectified pulses that control the speed ... the frequency of the rectified pulses is constant (either 60 Hz or 120 Hz if a full wave controller is used) and only the cycle ON-time changes.
 
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I wonder if a treadmill speed controller would work for you. I found a treadmill on the side of the road and salvaged the electronics. I replaced the treadmill controls with a potentiometer to control the speed. It also has a DC motor, so I suspect this might work for you.

FWIW, there are tons of used treadmills on craigslist on any given day for next-to-nothing.
 

Bill Boehme

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I wonder if a treadmill speed controller would work for you. I found a treadmill on the side of the road and salvaged the electronics. I replaced the treadmill controls with a potentiometer to control the speed. It also has a DC motor, so I suspect this might work for you.

FWIW, there are tons of used treadmills on craigslist on any given day for next-to-nothing.

I think that this motor claims to be 1 HP and may require a beefier controller than the one in a treadmill.
 
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I think that this motor claims to be 1 HP and may require a beefier controller than the one in a treadmill.
The motor that I salvaged is labeled 1.5HP continuous @95VDC. (It also says 2.65HP which I presume is a marketing number.) 21.4A. That would be more than the 1HP in this lathe.
 

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I think that it would also be necessary to determine the Delta motor: winding configuration, peak current, and maximum voltage. The treadmill controller might require tachometer feedback from the motor which would complicate things.
 
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Thanks for the replies, and the electronics tutorial!

Looks like more parts in there than a light dimmer, I'm guessing (and you guys are confirming) that most of the circuit board is acting as the inverter to clip the incoming AC. There's a couple smears of soot near what looks like an aluminum heat sink on one edge of the circuit board, guessing that is the part that fried, would that heat sink be associated with the thyristor? BTW running the lathe at full speed last night, the motor got unusually hot after about a half hour and I quit. I'm mystified about how it runs at all, if indeed it's the thyristor that fried. No visible fuses anywhere.

The lathe is marked Type 1, not clear what that means. The manual says nothing about what kind of a motor it is. Delta tech support kept me on hold for a big part of yesterday, with a maddening tape every minute or so telling me how important my call was to them, just wait for the next available tech. Yeah right.

Anyway I'm back to my original question, would a Teco type controller, which works by converting regular 1-phase AC into 3 phase, be able to feed that DC motor? Or shall I be saving my pocket change for a new/used machine?
 
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To be clear, I was pointing one possible option, given that the OP was looking at an alternative to the control circuit, and wanted a lower cost option. I agree that it would be unwise to take a suggestion from an internet forum without vetting it. I clearly did not do any of the due diligence that I expect John would want to perform before implementing such a suggestion.

The treadmill motor speed controller works without tachometer feedback, FWIW.
 
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<snip>
BTW running the lathe at full speed last night, the motor got unusually hot after about a half hour and I quit. I'm mystified about how it runs at all, if indeed it's the thyristor that fried. No visible fuses anywhere.
When you say it got hot, this concerns me. I melted the plastic casing around the brushes on my metal lathe following a problem with the speed controller. I don't know for certain that the speed controller was the cause (it had not been controlling the speed 'normally' just prior to this), but I pushed it to the point that I now have a lathe with a failing controller AND a broken motor. This is the reason that I was looking at treadmill motor/controllers for a replacement in the first place.

I would avoid running the lathe until you get this sorted out, to avoid further damage to the motor.
 

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Anyway I'm back to my original question, would a Teco type controller, which works by converting regular 1-phase AC into 3 phase, be able to feed that DC motor? Or shall I be saving my pocket change for a new/used machine?

Definitely not! That would be just like converting money into smoke ... literally.

Back to your question about the thyristor, yes it would be the device on the heat sink. It sounds like the thyristor is what failed. I'm surprised that the controller doesn't have some sort of fault protection for situations like you encountered, but then we're talking about consumer electronics and not something for NASA.

My one experience with a thyristor failure was the same as your experience ... it became a dead short so that the motor only ran at full speed.

Barry, I was just speculating that a treadmill would have some type of closed loop speed control such as a tach or encoder for safety reasons. Foolish me.
 
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Thanks Bill very helpful. I'll dig a bit and see if the thyristor ca't be replaced, that is if I can find any specs or numbers on it.

But if I am understanding this correctly, with the thyristor a dead short, there is no inverter-like action so the DC motor is getting straight AC modified by whatever on the circuit board remains in the loop. It shouldn't run at all. But it does.
 
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Surplus Center sells a dc motor controller for $87 and shipping that I have used with misc dc motors in the past. Likely will not fit in the delta box, but will drive up to a 1 hp motor with 120 volt ac feed.

Have used that brand with success in the past.
 
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This machine has become almost a throw away machine, unless you are exceptionally talented in designing electronic work arounds, or can troubleshoot circuit boards. If you nurse it along with one kind of fix, you will also run into an issue with another electronic part sooner or latter. Just saying, about everything in that control box has failed for someone. At one point, there was blame put on people turning bowls and "overworking" the electronics. It's a great machine, until it fails. Then you have to decide what kind of money to spend. If you have a type 1, that was the original machine. Those machines had a ton of issues with switches. I'd vote for buying a new lathe and move on from this money pit. By the way, I have a type 2. Still hold my breath every time I use it. Don't believe me? Just Google 46-460 failures.
 
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At our guild, four years ago we replaced the entire controller box on a Type I with what I believe is a Type II Controller (has the new style main switch). That was under the 5 year warranty. Don't know if there is any difference in the motor, but we do experience some hesitation with it and a simple touch on the handwheel gets it going. Would be nice if someone could find a three phase AC motor that would fit and then a VFD would likely be simple to find. Rest of the lathe is excellent. Controller is the weak point of all these variable speed midis.
 
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If the motor has brushes (the plastic things at one end of the motor and has a slot in it) it is a DC. Doubt it is a brushless DC.

As such any DC controller should work.

Just got a Penn State catalog today. They have a 1/2HP motor and controller kit (TCLVSKIT) conversion that they say will fit a Delta or Jet for $119.95.

Stu
 
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Pulse width modulation is used to synthesize variable frequency to control the speed of three phase AC motors. For controlling the speed of a DC motor, the controller is basically controlling the voltage to the motor since the speed of a DC motor is proportional to the applied voltage (the exact speed vs. voltage relationship depends on whether the motor is series wound or shunt wound). The variable voltage is created using a thyristor (or one of it's derivatives) which turns off the AC voltage during part of its cycle and then filters it to create the DC voltage. This might be the pulsed voltage that you are thinking of ... and it's essentially the way that incandescent light dimmers work. The figure below shows an AC waveform in red and the waveform after it has been rectified by a thyristor shown in green. The effective voltage of the rectified waveform below would be about a fourth of the AC voltage.

AC_Rect_In_90_edit.png


Low cost variable speed mini and midi lathes all use DC motors with variable voltage controllers. It's not the frequency of the rectified pulses that control the speed ... the frequency of the rectified pulses is constant (either 60 Hz or 120 Hz if a full wave controller is used) and only the cycle ON-time changes.
Thanks Bill. We tried reading digital voltages with a DVM and it was impossible with my old simple Radio Shack model.
 

Bill Boehme

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Thanks Bill very helpful. I'll dig a bit and see if the thyristor ca't be replaced, that is if I can find any specs or numbers on it....

Finding the part number is the challenge if it isn't stamped on the part. This is a good time to have a bud whose hobby is electronics or just do it yourself if you feel adventurous. If it's the stud-mounted type then removing and replacing it is pretty straightforward if you can do electronic soldering (this is where the electronics buddy comes in handy). If you DIY, you need to put a dab of thermal paste/compound between the thyristor and the heat sink.

... But if I am understanding this correctly, with the thyristor a dead short, there is no inverter-like action so the DC motor is getting straight AC modified by whatever on the circuit board remains in the loop. It shouldn't run at all. But it does.

That's probably correct, but there might also be a failure mode in which the thyristor behaves as a regular diode rectifier, but I sort of doubt it.

There might be a bridge rectifier upstream of the thyristor that is converting the AC to pulsed DC.

Also, some types of DC motors are perfectly happy with AC power. Handheld power tools such as drills, routers, and sanders all have series wound universal motors which are one kind of DC motor.

The reason for the motor overheating could be because the failed thyristor is causing the motor voltage to be too high.

Bill, I was just clarifying, and not implying you were foolish. Please accept my apology if it sounded that way.

I didn't mean to imply that you were implying. :) I was just tongue in cheek saying that I was foolish for thinking that the manufacturer would design the treadmill to be fail-safe (meaning fails to a safe condition rather than a dangerous condition such as the treadmill suddenly taking off at warp speed).

This machine has become almost a throw away machine, unless you are exceptionally talented in designing electronic work arounds, or can troubleshoot circuit boards. If you nurse it along with one kind of fix, you will also run into an issue with another electronic part sooner or latter. Just saying, about everything in that control box has failed for someone. At one point, there was blame put on people turning bowls and "overworking" the electronics. It's a great machine, until it fails. Then you have to decide what kind of money to spend. If you have a type 1, that was the original machine. Those machines had a ton of issues with switches. I'd vote for buying a new lathe and move on from this money pit. By the way, I have a type 2. Still hold my breath every time I use it. Don't believe me? Just Google 46-460 failures.

Switch problems seem to be almost universal on imported power tools, not just this particular lathe. When it comes to Googling for gripes, we all know that the Internet is the place to go for rational well considered product reviews. :D

Delta went through a tough transition when they were spun off by Stanley tools and the big problem at the time was they were suddenly without a repair parts network. Quite a few other members in my club have the Delta midi lathe and I haven't heard of any problems. I have used that model on numerous occasions in classes and have always been impressed. I think that John concluded it was operator error that was the root cause of the current problem so beating up on Delta seems a bit out of context.When it comes to the hyperinflated price of repair parts, unfortunately that's standard practice for everything. :( I checked the Grainger catalog to see what the prices were for DC motor controllers and they were even higher than the Delta price. :eek:
 
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