Ok, here's what I think is happening:

The machine has two different routers of equal power, but different brands. One is a Milwawkee 5625-20 of 3-1/2 HP, and the other one is a Dewalt Dewalt 7518 of very similar characteristics.
The main difference between the two is that the Milwawkee has an internal resolver of the magnetic type, which it uses to regulate its RPMs. The Dewalt has no such feature, and I believe that it's regulating its RPSs by measuring its back EMF.
The Milwawkee's RPMs are unnaffected when I activate the PWM control on the 90VDC motor, whereas the Dewalt suddenly plunges its RPMs when this happens.

​

Personally, I think the Milwawkee is of far better quality and more robust than the Dewalt, but that's besides the point.

The point is that it seems that my circuit is sending noise (I'm pulsing the 90VDC motor at about 3.7 kHz) back through the line, and that noise is reaching the Dewalt. And it's possible that the Dewalt is thinking that it's spinning faster than it actually is, and that's why the RPM's go down when it tries to compensate.

What I'm going to do now is install one of these EMI filters (I have two with me) at my circuit's AC input see if it improves, or perhaps eliminates, the problem.

​

 

Question, what type of power supply is the 90VDC coming from? Linear or a switcher? Switchers don't play well with big motors or stepper motors. Small DC motors aren't much of a problem with switchers but they have a problem keeping up with the others. The large output cap on a linear works to keep the power up to snuff.

 

Question, what type of power supply is the 90VDC coming from? Linear or a switcher? Switchers don't play well with big motors or stepper motors. Small DC motors aren't much of a problem with switchers but they have a problem keeping up with the others. The large output cap on a linear works to keep the power up to snuff.

The power supply is a simple 1:1 isolation transformer delivering 120VAC. It's output is then rectified using a diode bridge rectifier. The voltage I'm feeding into the circuit is not regulated, so it's not a smooth 120 VDC output, but rather a half sinewave that peaks at about 168V. But it's actually 120VDC RMS.

​

This half sinewave is then switched by my PWM circuit to control the motor. And other than the noise being produced, it's working great.

 

Got to thinking about something else, that may be part of the problem. Your giving a PWM output to a router that has built in PWM(speed control). Won't that cause problems? The router is expecting a mains voltage AC input, that then goes into a PWM type circuit to control the motor. If the voltage of your PWM circuit isn't in sync with the routers internal PWM control won't that cause problems? Maybe try bypassing the routers internal circuit, run the input voltage your giving it directly to the motor. Hope I'm being coherent in my explanation of this.

 

Ok, here's what I think is happening:

The machine has two different routers of equal power, but different brands. One is a Milwawkee 5625-20 of 3-1/2 HP, and the other one is a Dewalt Dewalt 7518 of very similar characteristics.
The main difference between the two is that the Milwawkee has an internal resolver of the magnetic type, which it uses to regulate its RPMs. The Dewalt has no such feature, and I believe that it's regulating its RPSs by measuring its back EMF.
The Milwawkee's RPMs are unnaffected when I activate the PWM control on the 90VDC motor, whereas the Dewalt suddenly plunges its RPMs when this happens.

View attachment 123713 View attachment 123714​

Personally, I think the Milwawkee is of far better quality and more robust than the Dewalt, but that's besides the point.

The point is that it seems that my circuit is sending noise (I'm pulsing the 90VDC motor at about 3.7 kHz) back through the line, and that noise is reaching the Dewalt. And it's possible that the Dewalt is thinking that it's spinning faster than it actually is, and that's why the RPM's go down when it tries to compensate.

What I'm going to do now is install one of these EMI filters (I have two with me) at my circuit's AC input see if it improves, or perhaps eliminates, the problem.
Sounds good. We have a saying one if by wire two if by radiation.

View attachment 123715​

 

We have a saying one if by wire two if by radiation.

that does sound funny ... but I don't get it ... mind elaborating?

 

that does sound funny ... but I don't get it ... mind elaborating? View attachment 123779

Yea, an American war thing:
One if by Land Two if by Sea
The origin of the phrase
“One, if by land, and two, if by sea” phrase was coined by the American poet, Henry W. Longfellow in his poem, Paul Revere’s Ride. It was a reference to the secret signal orchestrated by Revere during his historic ride from Boston to Concord on the verge of American Revolutionary War. The signal was meant to alert patriots about the route the British troops chose to advance to Concord.

http://www.paul-revere-heritage.com/one-if-by-land-two-if-by-sea.html

 

I tend to agree with Shortbus. You probably should not try to externally control a motor that has an internal speed controller. They will interact.
The sort of speed control you are trying to use should be just for a plain universal motor without an internal controller.
If the motor already has a speed controller, why not try to just use that?
Also, if you are PWMing the power, why do you not have a capacitor on the supply to run it on a smoother DC?

 

I tend to agree with Shortbus. You probably should not try to externally control a motor that has an internal speed controller. They will interact.
The sort of speed control you are trying to use should be just for a plain universal motor without an internal controller.
If the motor already has a speed controller, why not try to just use that?
Also, if you are PWMing the power, why do you not have a capacitor on the supply to run it on a smoother DC?

Hi,
I think his motor is just a simple dc motor. It's way back at the beginning. The speed controlled motors are what he is moving around with it.

 

You probably should not try to externally control a motor that has an internal speed controller. They will interact.

No. That is not what I'm trying to do.

Just to clarify:

• There are two motors, one's a router with its own independent internal speed control, and the other one is a 90VDC motor whose control I'm developing.
• Both motors are connected to the same power supply
• It seems that the speed control circuit for the 90VDC motor (the one being discussed throughout this thread) is causing such noise that it's traveling back through the power line and affecting the router's speed controller, which apparently runs using a back-EMF measuring technique.

why do you not have a capacitor on the supply to run it on a smoother DC?

Doing that would be too cumbersome and expensive. We're talking about a 90VDC motor with an output of 75W (1/10 HP). The point of this project is designing a good circuit for a DC motor that can work with the direct, unregulated output of a full wave diode rectifier.

 

Hi,
I think his motor is just a simple dc motor. It's way back at the beginning. The speed controlled motors are what he is moving around with it.

Thank you, Ron. It seems that @dendad is late to the thread. But I appreciate all help and informed opinions I can get. That's why I've put him up to speed in my last post.

I'm going to make yet again another PCB that includes the EMI filter I described, but I'm also going to integrate a current-limiting circuit as I mentioned in previous posts. See if I can make two steps forward in a single shot. And I intend to keep my promise of posting all my results in the finished projects section when I'm done... God willing.

 

Oh then forget what I was saying I was under the idea that your PWM was for the router speed not a motor to mve the routers from place to place.

Another probably dumb idea, why not a separate 1:1 isolation transformer from your original 120V transformer to give line voltage to the routers? Wouldn't that isolate them from any noise and pulses in the rest of the circuit?

 

Wouldn't that isolate them from any noise and pulses in the rest of the circuit?

It probably would, except that that's the power supply for the whole machine, and it's a requirement it should be connected that way.

 

I have never seen any PWM or VFD drives fed from a Unfiltered AC?
Is there any reason you did not use a large Cap on the DC?
If so it would probably help in filtering somewhat.
I tend to prefer to prevent the source instead of patching the effect.
Max.

 

Is there any reason you did not use a large Cap on the DC?

Yeah, the reason is trying to keep a low component count, and to save a buck... but it seems that what you're suggesting will become unavoidable.
I'm going to test my circuit with the EMI filter that I showed in my previous posts, and if it doesn't cut it then I'll add the yuge cap that you're suggesting. See if that works.

 

Of course this will increase the mean DC level so you may find it affects a given PWM level setting used previously.
Max.

 

Of course this will increase the mean DC level so you may find it affects a given PWM level setting used previously.
Max.

True... thanks for pointing that out. I'll try the emi filter first, and if that doesn't work I'll add the caps.

 

Or use a DC motor driver module for just the movement of the head, like a Bodine or K-B.

http://www.bodine-electric.com/
http://www.kbelectronics.com/

 

Or use a DC motor driver module for just the movement of the head, like a Bodine or K-B.

http://www.bodine-electric.com/
http://www.kbelectronics.com/

Those look rather nice and professional... but it's far more fun to make them than to buy them...
Still... I itch to open up one of those and peek inside... thanks for the links.

 

Both KB and Bodine make SCR bridge type and the better PWM type also.
But not intended for motion/position control, just velocity.
Max.