stepper drive amperes

[crosslakeguy]

this I am sure has been hashed to death, but, the drivers I am looking at,
one is adjustable to 2.5 or 3.5 amps one is 2.5 or 3.0 amps
the motor is rated at 3.2 amps, Am i correct in assuming not to run over rated amp. the drive does have a current limit at rest. will not be running over 1000pps i dont think, but as low as 100pps. Am i correct to assume the extra .3a will overheat the motor. I already bought the 2.5-3.5amp drive how much torque am I going to lose running at 2.5 amps? ( In the past i intentionaly set below rated amperage to keep motors cool, so wondering of others thoughts on this?) I have also heard of over amping to gain high end speed? I understand the best fix for that is to increase voltage though. I would just like to hear others thoughts who have more knowledge and experience than I do.

[doorknob]

With the torque proportional to current, you would be looking at approximately a 20% reduction in torque if you run the motor at 2.5 amps.

[H500]

A higher current setting will not increase your upper speed unless your system is so heavily loaded. At higher speeds, the current does not have enough time to reach the set level.

Unless your system need a lot of low speed torque, the power is just wasted heating the motor. 2.5 amps might actually make no difference to your performance.

[James Newton]

For greater speed, increase voltage but only with a current regulating supply which will prevent the motor from getting more than it's rated current. Even then, a hot motor will loose power, so you are right to run it a bit under the maximum setting.
From
techref.massmind.org/techref/io/steppers.htm

Think of it like this: If you have a /really/ long garden hose, and you want a trickle of water out the far end, you can supply a trickle at the valve and just wait... eventually, the water will trickle out the other end. But if you want that trickle NOW, you turn the water value on full, then wait for the water to start coming out the end before you turn it down. Of course, if you fail to turn it down, you are going to swamp the motor at the other end of the hose! That is why the motor driver must regulate the current by turning down the drive voltage once the coil reaches it's maximum current flow.

Higher supply voltage allows faster changes to the current and field strenght in the motor coils and so faster rotation. But there is also a balance; at higher PSU voltages the motor will get hotter (because of increased wattage) and it will jerk faster from step to step, so you get more resonance and more problems with stalling. A higher voltage can actually stop the motor getting through resonance bands.