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  #1  
Old Fri 13 March 2009, 20:25
kwang90020
Just call me: krod
 
California
United States of America
Cannot get good jog speeds - first thought PS voltage too low, then current error

I'm about to complete the mm thanks to this excellent website but having problem configuring mach3.
I set mach3 with configuration according to Gear Speed Steps Freq Calculator but I can't get the max velocity. I'm only getting about 500 in/min.
I have PK296A1A-SG7.2, 30tooth pinion, gecko 203.

X axis
Steps per inch: 3055.8
Acceleration in/sec/sec: 25
max velocity 500in / min.

Even w/o load (just motor), I can barely achieve 1000 in/min.
I changed the kernel frequency to 65khz.
I also adjusted Gecko but getting the proper speed.

What am I doing wrong?
Thanks alot.
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  #2  
Old Sat 14 March 2009, 00:18
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by kwang90020 View Post
. . . .I have PK296A1A-SG7.2 . . . .
How did you wire the motor? (halfcoil or series)
What is the voltage of your power supply?
Did you check the Gecko resistors with an Ohm-meter?
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  #3  
Old Sat 14 March 2009, 11:13
kwang90020
Just call me: krod
 
California
United States of America
Gerald,

Thank you for the reply.
The motor is wired half coil.
Power supply is 40V and the resistor is 12k Ohm.
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  #4  
Old Sat 14 March 2009, 12:10
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The PK296A1A motor, when wired half-coil, has an inductance rating of 7.7mH. So, 32 X SQRT(7.7) = 88V. The Gecko stepper drivers can handle 80V. I would use a power supply that is about 70V to give just a little margin for those days when the power company gives you more voltage than you would normally expect.

The PK296A2A-SG7.2 motor, when wired half-coil, has an inductance rating of 1.5mH. So, 32 X SQRT(1.5) = 39V. A 35V (to 40V) power supply works well with that motor and half-coil wiring.

Also, the A1A motor is limited to 1.5A, which is why you're using the 12K resistor. TheA2A motor can handle 3A.
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  #5  
Old Sat 14 March 2009, 12:55
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Krod, you might be able to re-configure the output windings on your power supply transformer to double your voltage and get the full potential from your motors.
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  #6  
Old Sat 14 March 2009, 18:58
kwang90020
Just call me: krod
 
California
United States of America
I'm currently using 40V by parallel connection, so if I connect them in serial it will be 80V. Do you think that is too much voltage?

My resistor is fine then, right?

Thanks.
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  #7  
Old Sat 14 March 2009, 19:41
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The resistor is the correct value for a PK296A1A motor wired unipolar (half-coil). The Gecko stepper drivers are rated at 80VDC (and can handle up to 100VDC before damage is done to the Geckos). Also, the PK296A1A motor, when wired half-coil can handle more voltage than the Geckos, so, you should be fine at 80V.

Make sure you check the power supply capacitors to verify that they are rated at about 100VDC working voltage. Capacitors need to be rated higher than the actual power supply voltage by about 25% or so.
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  #8  
Old Sat 14 March 2009, 22:37
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Thanks for remembering about the capacitor limits Mike. If Krod has two caps in parallel now, would he be okay to re-wire them serial?
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  #9  
Old Sat 14 March 2009, 23:10
kwang90020
Just call me: krod
 
California
United States of America
Thanks, Mike and Gerald.
I have to change the capacitor. I have one cap and it is only rated 50V.
I'll make the changes and give you the update.
Thanks again for your help.
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  #10  
Old Sun 15 March 2009, 01:31
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Krod, bear in mind that the voltage increase may not be the total solution to your low speed problem. You may also have a problem that your PC cannot pump out pulses quickly and smoothly enough. Increasing the kernel speed could actually make it worse - calculate the minimum kernel speed needed and set the kernel speed as low as possible.

Also see this thread:
Runs out of steam? Machine freezes during cutting - controlling PC's performance
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  #11  
Old Tue 17 March 2009, 14:21
kwang90020
Just call me: krod
 
California
United States of America
Gerald and Richard,
Oops, I made a mistake. My motor is PK296A2A not PK296A1A.
I changed the resistorsto 33k and mm is running fine.
Those resistors make big difference!
I thank you guys again for the great support.
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  #12  
Old Tue 17 March 2009, 14:28
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Hahaha Krod!

I have also made a resistor mistake before, and it sure makes a BIG difference.
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