Hello Guest it is October 21, 2019, 07:09:57 PM

Author Topic: Speed controller won't hold steady speed - where is the problem?  (Read 9506 times)

0 Members and 2 Guests are viewing this topic.

Offline simpson36

*
  •  1,374 1,374
    • View Profile
Re: Speed controller won't hold steady speed - where is the problem?
« Reply #10 on: January 12, 2009, 02:38:08 PM »
Ray,

I lost more than time. I also lost two $200 Minarik MM drives that immediately fried as soon as the C6 was connected and everything powered on. This is how I learned what an 'isolated' signal was. The CNC4PC document noted by sparkness is, and continues to be completely inadequate at explaining the issue. I informed both CNC4PC and the Minarik sales rep of my rather dramatic results the first time thru and neither mentioned the 'isolation' requirement. I got a new controller from CNC4PC and the Minarik sales rep sold me the identical drive again. Not surprisingly, I had the exact result the second time around. When I finally spoke to a support engineer at Minarik, his FIRST question was 'are you using an isolated control voltage'. I now have Minarik drives with control voltage isolation built into the drives.

Homann, on the other hand has big red warnings all over the place about mains potential voltages present in many drive's control circuits, and how NOT to hook things up. Had I gone with Homann to begin with, I probably would not have fried the drives . . which took out other components as well.  It remains the most expensive part of my learning curve thus far.

I did buy a Digispeed DC06 a couple months ago to replace the C6. I finally tried last weekend to hook it up. It worked for only a few minutes and then got locked on full speed. I may have done something wrong to kill it, but at this point I don't know. It is going back for repair. It did seem to have a steady output voltage while it was working, but while I was trying to configure MACH for it, the DC06 stopped responding so I never got to see if the motor would run steady. The output did seem steady while the thing was working briefly.

Peter responded immediately when I emailed him that the DC06 was kaput. I'll get it fixed and give the Digispeed another go before looking at the much more expensive PMDX product. I'm not going to mess with the C6 any further.
« Last Edit: January 12, 2009, 02:53:47 PM by simpson36 »
Re: Speed controller won't hold steady speed - where is the problem?
« Reply #11 on: January 12, 2009, 02:48:02 PM »
Hi Ray,
I've only used PMDX on 1 machine so far, (my 2nd). The 122/106 is a GREAT combination.
I have 3 more machines planned, all will use the afore mentioned, 2 with the SS.
RC
Re: Speed controller won't hold steady speed - where is the problem?
« Reply #12 on: January 12, 2009, 05:39:06 PM »
Ray,

I lost more than time. I also lost two $200 Minarik MM drives that immediately fried as soon as the C6 was connected and everything powered on. This is how I learned what an 'isolated' signal was. The CNC4PC document noted by sparkness is, and continues to be completely inadequate at explaining the issue. I informed both CNC4PC and the Minarik sales rep of my rather dramatic results the first time thru and neither mentioned the 'isolation' requirement. I got a new controller from CNC4PC and the Minarik sales rep sold me the identical drive again. Not surprisingly, I had the exact result the second time around. When I finally spoke to a support engineer at Minarik, his FIRST question was 'are you using an isolated control voltage'. I now have Minarik drives with control voltage isolation built into the drives.

Homann, on the other hand has big red warnings all over the place about mains potential voltages present in many drive's control circuits, and how NOT to hook things up. Had I gone with Homann to begin with, I probably would not have fried the drives . . which took out other components as well.  It remains the most expensive part of my learning curve thus far.

I did buy a Digispeed DC06 a couple months ago to replace the C6. I finally tried last weekend to hook it up. It worked for only a few minutes and then got locked on full speed. I may have done something wrong to kill it, but at this point I don't know. It is going back for repair. It did seem to have a steady output voltage while it was working, but while I was trying to configure MACH for it, the DC06 stopped responding so I never got to see if the motor would run steady. The output did seem steady while the thing was working briefly.

Peter responded immediately when I emailed him that the DC06 was kaput. I'll get it fixed and give the Digispeed another go before looking at the much more expensive PMDX product. I'm not going to mess with the C6 any further.


OUCH!!
Regards,
Ray L.
Re: Speed controller won't hold steady speed - where is the problem?
« Reply #13 on: January 12, 2009, 06:34:06 PM »
After a lengthy struggle with a C-11 with no resolution, I went with a PMDX-106 which worked flawlessly from the get-go.
Great support too.....so they say. Didn't NEED any.
RC

Hi RC,

The Step/Dir to analog converters based on the LM2907 chip should not be better/worse than a PWM solution. As I produce both types, I have done a comparison of both. THE Step/Dir and PWM both produce very linear outputs with respect to their inputs. The Step/Dir has a slightly better response due to the faster update rate.

That said you need to understand how the LM2907 works to apply it correctly. Just implementing the datasheet application note does not really cut it.

The LM2907 converts the energy in the step pluses to a voltage using a charge pump. Basically, the more step pulses or the bigger(longer) the step pulses, the higher the voltage output. Therefore to get an accurate output voltage you need a number of things;

1. Regulated power supply. The power supply for the LM2907 needs to be consistent with the minimum of noise. VFDs are usually OK at suppling an adequate 10V supply. Many controllers such as the KBIC120 style are marginal. They use a 15V zener shunt power supply designed to supply a couple of mA to a 5K or 10K  potentiometer. If it can't provide enough current, then the voltage supply will start to sag.

To make things worse, the controllers also have a max speed trimpot. This is just a resistor in series with the power supply. The voltage across this resistor is dependant on the current being drawn by the LM2907. The problem is that the current it draws changes depending on what voltage the LM2907 is producing. The result of this is that the power supply to the LM2907 sags, resulting in linearity problems with the output voltage.

The DC-06 overcomes this problem by providing an optional DC/DC converter that produces  a consistant and regulated powersupply for the LM2907.


2. Constant and accurate step frequency. - Mach3 provides this.



3. Consistent and known step pulse width. - This is where most let them selves down. If you don't know what pulse width you are dealing with then you can't size the charge pump components correctly.  The result of this is that if the step pulse is too narrow, not enough energy is being provided to the charge pump in the LM2907. If the pulse is too wide, then the chargepump ends up being saturated.

Having to adjust the step pulse width in Mach to get the charge pump in the LM2907 to work correctly, is poor design. The adjustment is there to cater for different types on interfaces to drives, opto isolated, bufferred etc.

The DC-06 contains a monostable that produces a constant width pulse to the charge pump in the LM2907. This occurs irrespective of the step pulse width input. That way, the energy per step pulse is known and the charge pump components can be sized correctly.


It basically comes done to understanding what you are designing and the environment that it will be working in. The datasheet applications are meant to be a starting point, not a finished design.

While I'm explaining the features of the DC-06. It also has a jumper to select the polarity of the input signals as some people use active hi signals and others use active lo.

I hope the above helps a bit.

Cheers,

Peter.
----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com
Re: Speed controller won't hold steady speed - where is the problem?
« Reply #14 on: January 13, 2009, 04:05:33 PM »
Hello Peter,
   I appreciate your reply and am envious of your knowledge. If your reply was in defence of Mr. Duncan's C-11 board, I'm sure he will appreciate it as well. There were serious issues beyond what you are describing. Anyway...after 3 boards, multiple chip changes and general I/O problems. I debated about going with yours or Steve's....flipped a coin basically. Steve won and his worked right out of the box, same setup, exactly as his docs. described.
If by chance it craps out...you are next.
Thanks Pete,
RC
Re: Speed controller won't hold steady speed - where is the problem?
« Reply #15 on: January 13, 2009, 04:13:34 PM »
Hello Peter,
   I appreciate your reply and am envious of your knowledge. If your reply was in defence of Mr. Duncan's C-11 board, I'm sure he will appreciate it as well. There were serious issues beyond what you are describing. Anyway...after 3 boards, multiple chip changes and general I/O problems. I debated about going with yours or Steve's....flipped a coin basically. Steve won and his worked right out of the box, same setup, exactly as his docs. described.
If by chance it craps out...you are next.
Thanks Pete,
RC

Hi RC,

It wasn't really in defence of any maker. People make up their own mind as to what they believe is a good buy. Some buy on price alone, while others want quality, and others service. I try to deliver it all :)

 It was in defence of the LM2907. It  does a good job at converting frequency to voltage. It just needs to be correrctly applied.

Steve's stuff at PMDX is excellent quality and he also know his stuff.

Cheers,


Peter.
----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com