[JBV]

I have:
2,2 Nm bipolar steppers (~310 oz/in).
A Xylotex 4 axis board (8 microsteps). Adjusted current to 2,5A
A 12V, 8A computer psu.
P2 300, 128 Mb ram
Turbocnc 4.01

At the moment i have only one stepper connected to the board (parallel). And when i run the stepper with no load at over 5500 hz it stalls and just vibrates until the software start to deaccelerate. At 4500 hz it don't stall without braking the stepper shaft a little with the fingers.
(edit: The stepper stalled at the same steprate when mounted to the mill)

I have 2 mm pitch leadscrews, so 4500 hz gives about 340mm/minute.

What should i expect with this setup? What could be wrong here?

/Jay

[Mariss Freimanis]

High motor inductance (low phase current) + low power supply voltage (12VDC) = low speed. Doubling your supply voltage (24VDC) will double your speed.

Mariss

[ger21]

Use 24V. Also, quite a few people that recently switched to Mach3 have reported much smoother running and faster speeds, just by switching control software. You'd need a faster PC, though.

Definately increase the voltage, though.

[JBV]

I'll try with a better psu and faster computer!

Thnx for the replies!

[davidmb]

Hi Jay,
Not sure what voltage the Xyltex drivers run up to but 12V would seem a little low, most modern stepper drivers utlise a current limited switching method almost like a switchmode psu, so the drive to the motor windings is like a sawtooth waveform cutting off at the pre-set current, the higher the drive voltage the shorter the rise time and more torque at higher speeds, so go back and check the Xylotex documentation, this will give you the upper voltage that you should not go above, my driver for example will go upto 45V but I use 27V ( the most I can get out of my adjusted 24V switchmode (ex mainframe psu)).

Regards

DavidB.

[JBV]

Max 35V but they seem to recomend 24V for safety. I only used the old computer psu to get started

[davidmb]

Something like a simple linear psu ( 20V toroidal psu rated at the sum of the max current all your drives will take ) so if your motor current is set to say 2.5A per winding, 2 windings per motor so 1 motor could draw 5A with both windings energised / 3 motors gives peak current at 15A so you would need a transformer rated at 300VA or more, a bridge rectifier rated at say 20A for a bit of headroom and a largish capacitor 5000 to 20000 uF rated at 35V. Often cheaper than an good computer psu, of course you may still need a separate 5V supply for the controller.

Oops, sorry Jay, 20V transformer would give you 28V DC, to get 24V DC you would need a 17V transformer.

[pminmo]

JBV,
How many wires on your motor? If it's a six or 8 wire motor there are other possibilities also.

[JBV]

8 wires, it is the 220Ncm model here

[ger21]

so if your motor current is set to say 2.5A per winding, 2 windings per motor so 1 motor could draw 5A with both windings energised / 3 motors gives peak current at 15A

With a chopper drive like the Xylotex, or Geckos, both coils are never fully energized together. Gecko recommends 2/3 of 1 phase, or 1.6a per motor. I've read that the Xylotex will rarely ever need more than 4.5a for 3 motors rated at 2.5a.

[davidmb]

Hi Ger21,
With my driver I can have the condition where both coils are energised but I'm only working in 1/2 step mode and I'm not familiar with the Xylotex or Gecko drives, I guess they automatically reduce current at the point where both coils would be on to provide smoother torque.

[pminmo]

jbv,
Your not going to get a lot of performance on a 7.5V coil with a 12V ps. To get full performance and speed from that motor you need to run it bipolar parallel and the xylotex doesn't have enough current capability. With the Xylotex, I would give just using two coils a try (half coil in a 6 wire motor) at 2.5A. But you still need a higher voltage PS.