Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: simpson36 on January 12, 2009, 03:13:41 AM
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I have two CNC4PC C6 speed controllers. Neither will hold a steady speed. Observing with an analog volt meter confirms the output voltage is fluctuating. I replaced the hook ups with shielded wire, but it didn't help.
Drive is a Minarik MM series which holds dead steady speed using a pot.
I am just curious if anyone is using this controller with success before I spend a lot of time trying to get it to work right if this is just a characteristic of the CNC4PC controller or Mach.
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Hi,
What are you using to power the C6?. Check and see if the power supply to the C6 is fluxuating as well.
If so, there is your problem.
Cheers,
Peter.
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I'm not using a C6, but a C11, and I have the same problem. Often, first thing in the morning, the speed control is completely whacked, and commanding a very slow speed will result in a very high speed, or a wildly fluctuating speed. After being powered for 10-15 minutes, it finally settles down and starts behaving. It seems completely unpredictable, as some days it works fine, other days it doesn't. I had one day that I couldn't get it to behave at all. I gave up, and went back into the house for the day. Came out the next morning, and it was working fine. In every case where I've looked, the supply voltage from the VFD was fine, and the pulsetrain from the SmoothStepper was fine, but the output from the C11 was just whacked.
Regards,
Ray L.
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one possibility is the VFD. The VFD produces a lot of electrical noise, you may need to have a reactor and an EMI filter. all VFD mfg's recommend them. Also check the power supply for the speed controller it should be regulated.
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one more thing, the power to the speed controller must NOT share common ground to keep all things isolated
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Peter: The C6 requires 12v. I am using an old PC power supply for both the 5v for the breakout and the 12 for relays and the C6. The 12V and 5v both read dead steady with the same analog volt meter that clearly showed the fluctuations in the C6 output.
Ray: I have not had any success so far with either of the C6 that I have. I have the same situation as you in that the problem is not consistent, but in my case it is not nearly as severe as you describe, but still not steady enough to be usefull.
I am using the C6 only for the relays and I control the spindle manually using a pot. It would be nice to be able to program increasing spindle speeds as multiple cuts reduce the diameter of a workpiece.
As a newbee, I don't have the experience to now if this is a solvable problem. What I don't like to do is chase my tail for a long while only to find out that the issue I am trying to fix is not fixable, so I was wondering if anyone is using the C6 with success.
Sparkness: I am not using a VFD. It is a PWM drive. The mystery is that the C6 output wavers even if there is no power to the PWM drive, so the problem cannot be RF from the drive . . AND the PWM drive works perfectly using a pot. Additionally, the C6 exibits the same behavior when it is connected to the breakout board with a very short piece of shielded cable and the output is measured doirectly off the output terminals of the C6, so I am perplexed as to where it might be getting interference from.
As a guess, I would put the wavering at about one second peak to peak, but I have not measured it.
TheC6 speed controller uses two voltages. The 5v comes off the breakout (supplied to the breakout by a PC power supply) and the 12v for the follow voltage comes from the same PC power supply directly to the C6. I've checked both and they seem steady on an analog volt meter. In both cases, the power ground is from the same source as the positive voltage. I don't understand what you mean by not sharing a common ground.
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You might want to try the DigiSpeed from Homann Designs. That's what I plan to do someday when I rebuild my electronics enclosure.
http://homanndesigns.com/store/index.php?main_page=product_info&products_id=39&zenid=7eacd8d7ccf63c46c89881b4949c2234
Peter Homann is a regular here, so if you do have any problems, you'll have no trouble getting it resolved.
Regards,
Ray L.
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here is the documentation from cnc4pc explaining how to keep the grounds isolated
http://cnc4pc.com/Tech_Docs/C6R5_WG.pdf (http://cnc4pc.com/Tech_Docs/C6R5_WG.pdf)
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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
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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
RC,
I'm in the same boat. I've had three C11s now, all different revs, and every one has had serious problems I've had to work around by modifying the circuitry. I'm currently running on one that I had to re-bias the optos to get them to work above a 40kHz step rate with SmoothStepper (At 96K steps/inch, 40kHz doesn't buy you much....). The speed control has been an on-going problem I just haven't had time to deal with. Were I to design my own (and I've seriously considered it....) I'd do the speed control in exactly the way Peter Homann did on his DigiSpeed, using a microcontroller, and eliminating the analog circuitry altogether. I've lost more than a few whole days of work to all the problems.
A friend of mine has a PMDX board, and his has also been flawless.
Regards,
Ray L.
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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.
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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
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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!!
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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.
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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
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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.