PowerFlex DC Drive RPM output vs. analog input value.

yam785

Lifetime Supporting Member
Join Date
Jul 2004
Location
pa.
Posts
153
I have a line where I am giving the Powerflex DC Drive a reference of 9.86V which I verified with Drive Executive looking at the parameters. The motor RPM is 1750. So I am thinking this would give me roughly 175 RPM output, per volt input to the analog input 0-10V.

With the analog input of 9.86V, I am only getting 1602 rpm output. By my calculations, I should be getting an rpm output of 1725.5 rpm. Below is the drive information. A zipped Drive Executive Parameter File is too big to attach or I would have it also. Any help would be very appreciated.

Drive Info:
Allen-Bradley 50Hp PowerFlex DC Drive
Catalog # 20P41AD086RA0NNN
Series A
Frame A
Armature Amps 86
Field Amps 14

14 Drive Info.jpg
 
yam785

Check your Max Fwd Spd and Max rev Spd should be Parm 520 and 521 depending on what firmware you are using in the drive. It will not go beyond what is set here no matter what it is commanded to do.

make sure that is not set to 1602
 
Check your Max Fwd Spd and Max rev Spd should be Parm 520 and 521 depending on what firmware you are using in the drive. It will not go beyond what is set here no matter what it is commanded to do.

Checked these. They are both 1750 rpm. Feedback is DC Tach, 50V per 1000 revs. Drive is running at 1602 rpm, feedback is showing 1602 rpm. Armature current is about 10A, field current is a little over 3A. The Drive has only been installed for about a year. The only things that I know were done, is the reference pot was changed, and the motor was changed. I'm not sure exactly when this problem arose, as they run different speeds for different products.

I will get with tech support today. Hopefully they will have some suggestions. Thanks for the ideas.
 
First, check that the motor field amps is exactly as stated on the motor nameplate. It could well be that the field amps are a bit high which would limit the top speed at top armature voltage.

Second, if the field amps is correct, check to see if the armature volts reaches the motor nameplate value at full speed. It could be that this is a little low.

Finally, if for some reason the armature voltage simply cannot be brought up to full value (low AC power supply, for example), and you can do without a couple of percent of available motor torque, simply set the field amp regulator a small amount low. This shifts the available armature shaft speed upward for each armature volt while simultaneously reducing available motor torque a little.

I would suggest providing motor nameplate data to us and also measured values of full speed field amps and armature voltage.
 
Dick,

Thank you for the input. It does not seem like the Drive is having a problem driving the motor, as the Drive is telling it run 1602 rpm, and the feedback is showing that it is. It seems like my speed reference, which max's out at 9.86V, doesn't align with the speed I would expect out. I'm thinking at this reference, the Drive should be telling the motor to run about 1725 rpm.

I am thinking about doing a Parameter 259(Analog In1 Tune), which from the way I'm understanding it, would set my highest reference of 9.86V equivalent to 1750 rpm.

Motor Data:
Volts - 500
Armature Amps - 86
Field Amps - 3.95
Max Speed - 1750

Drive Info while running 1602 rpm :
Armature Amps - 11.868
Field Amps - 3.655
Output Voltage - 207.125

Let me know your thoughts about the Parameter 259(Analog In1 Tune)

Thanks again all.
Bob
 
Something is quite wrong here. A DC motor with a 500VDC armature would not be expected to operate near its base speed with only 208V on it. Even with the field current reduced from 3.95 to 3.66amps, I wouldn't expect that much speed.

Is this DC drive fed from a 480VAC source?
 
Dick,

This is a spinning beam, with only 362 fine threads going into it, with little tension. Very little load once up and running. I compared this to another line running the using the same model drive, and the output voltages seems pretty close, as they are running fairly close speed wise, and beam size is close to the same.

Yes it is 480V AC feed to drive. I'm not sure, but I think the output voltage is normal, for the load.

I'm thinking if it was something to do with what the drive was doing, I wouldn't be reading 1602 rpm on the HIM, and having it show "AT SPEED". I am by no means a drive expert, so I appreciate you taking time out, to give input.
 
yam785, you are correct that if the drive is displaying a speed command of 1602rpm then you can't very well expect it to run the motor faster than that. So, you need to redefine 9.85VDC on the speed reference input as 1750rpm or whatever max speed you want. Not being fully familiar with the AB drive you have, if they offer an input "tune" function, that may well be what you need. Other schemes would have an offset and gain adjustment for the speed reference analog input. In this case, you would want to reduce the gain from 100% down so, at 9.85Vdc you would reach your desired max speed.

But, I am baffled by the data you have sent. I know of no way that a motor nameplated 500VDC armature voltage and 1750rpm base speed will run 1602rpm with only 208vdc on it, even with no load. Something still doesn't make sense with the data.
 
Dick. I agree with the tuning of the reference, and I'm also in agreement with you on the low voltage output. This may be possibly because the DC Tach is driven by a press roll which rides up against the beam. So the actual rpm may be much higher than the actual motor rpm. This is done so we maintain constant Yards per Minute surface speed. The drive actually slows the motor down, as the beam circumference gets bigger, and drives the tach faster, so we maintain constant surface speed.

I'm going to go see if I can possibly tach the motor itself, while it's running.

Could this possibly explain the low voltage output?
 
I made a design like that two years ago, and i use a controllogix to control powerflex dc drive thru devicenet and a 1756-hsc to receive pulses from an encoder, in my case I have another encoder coupled to the dc motor and connected to the powerflex and other encoder coupled to a roller and connected to the 1756-hsc module so linear speed can be controlled.
 
So, now we find that the tach is not on the motor shaft? (grimace) Such a small detail!!!!!!!!!!

OK, this kind of arrangement requires a completely different setup. What is the mechanical ratio between the motor shaft and the shaft with the tach?
 
It is all starting to make sense now. When I uploaded the parameters from the drive, the beam was close to full. So even though the drive was showing 1602 rpm, motor rpm was probably down to about 850 rpm, which would explain only around 200V output out of the drive. I just tached the motor on a empty beam, and the motor speed was 1325 rpm, and the drive was showing 1525 rpm, and I had around 400V output from the drive.

Now back to the original issue. Max speed reference from the pot, doesn't give me enough top speed. My thinking is if I do a Parameter 259 (Anal In1 Tune) with my pot set to max, my issue will be resolved, or at least close enough, where I can get it perfect with Parameter 73 (Anlg1 Tune Scale).

Would all agree, this should resolve my issue?
Thanks for all the support.
 
Dick, the ratio changes on the fly, as the circumference of the beam gets bigger. The bigger the beam circumference gets, the more the drive slows down, to maintain constand YPM of the threads running through the machine, which is required to maintain a constant tension on the threads thoughout the whole beam.
 

Similar Topics

Dear We are working in AB Studio 5000 and the drive is a PowerFlex 755T. For this project I need to control a conveyor to a certain set point...
Replies
2
Views
115
I have a client who's Powerflex 755 VFD has one of its inverter cards failed. the card is with the model number SK-R1-IG1-C770D740. Does anyone...
Replies
0
Views
250
Is it possible to set IP address of Powerflex drive, without powering up the entire 3 phase circuit? Is there some way to just power up the keypad...
Replies
3
Views
678
Hello, I have a machine with 4 powerflex 4m drives that are networked using a 22-XCOMM-DC-BASE with a 22-comm-e card attached. Backstory....There...
Replies
0
Views
428
Hey all, I wanted to discuss an issue with achieving a constant flow rate of around 10 GPM on a glycol circulation pumps in a 1200-1300 PSI...
Replies
4
Views
903
Back
Top Bottom