stepper motor amperage

[Large519]

Have recently wired in new stepper drivers, but am not sure if I have the correct amperage for the motors as the machine is losing steps, obv this could be a multitude of factors, but firstly thought I'd try the motor power, the spec on the original stepper motors is 3.1 A, I currently have them set @ 2.8A, can the amp be increased and by how much without damaging the motor? Or should I set them as the original digiplan stepper drivers which were set @ 2 amp for x and y and 3 amp for z.

[angel-tech]

are they getting hot when just sat there under power ?

[Large519]

The stepper driver or motor? Not that I have noticed either getting hot, the x axis motor does sound like it is arcing at times though when moving

[angel-tech]

motor

[Large519]

No, the motors aren't getting hot when sitting under power. The max amp output of my drivers is 4.5, will increasing the amp damage the motor in anyway. I had managed to slow a programe run down to 400mm/m and an acel of 7 in mach3, to avoid losing steps but for me it is too slow and I know it is capable of more then that, especially as the original denford setup used to be capable of 1000mm/m

[angel-tech]

you're probably ok with the current if the motors are cool, what voltage are you running the drivers on.

[Large519]

These drivers - http://www.cnc4you.co.uk/index.php?rout ... duct_id=31

From this PSU - http://www.cnc4you.co.uk/index.php?rout ... duct_id=49

The PSU is 36v.

[angel-tech]

what step mode are you running.

[Large519]

2.8A
Half current
10 Micro step

[angel-tech]

try running them on half step, the original setup is half step and if you've kept the original gearing that's certainly accurate enough. You maybe trying to get too much out of those motors with 30 odd volts and 10 microsteps. That's assuming you've kept the original gearing on the motors.

[Large519]

Yeah I have the original gearing.

What would half step be - 5 microsteps?

The mach3, step per setup has given me from 999 to 1001 steps per on the x,y,z axis, I know the original drivers were setup for 400 steps per.

But would I be right to assume though that not enough Amperage, means that the motor is gonna be under powered and lower torque. I'll increase the X and Y drivers to 3.2A and the Z to 3.7A as the Z motor is rated @3.5A. An extra 0.1A and 0.2A I think is not gonna overload the motors.

Also I believe that the Y slider is not receiving any oil, this too may be a contributing factor, so this needs checking too.

[angel-tech]

even though the motors were setup on 400 steps (1/2 step) the steps per in mach would be 200. The ballscrew pitch is 5mm, and the pulley reduction for the stepper triac is 2.5:1.
Are you using the original motors ?

The y slider oiler is a common fault, I've replaced a few. Arc euro do the part.

[Large519]

Yeah, the original motors

Which part would you be referring to? I have a schematic of the oiling system.

[angel-tech]

It's a restrictor, and is sited inside the base of the pillar. The best way to check if the restrictor has failed is to take the table off and operate the oiler by pulling the plunger. If the oilways remain dry then it's clogged up, and it needs changing. The restrictor is marked with the correct value on it, and you need to get the correct one.

[Large519]

Well, sussed the oil. Reluctantly Stripped the x and y axis down, (quite simple once you get into it) holes blocked in the cross slide bracket, quick blow out with air and sorted, glad I did strip it dow now though, a big build up old dirty grease and oil doesnt make for smooth acting slideways. Found one of the ballscrew bearings was loose on the x axis, not good for backlash. Does anyone know of a replacement part for the ballscrew bearings? One is looking a bit worse for wear, may need replacing in future.

[angel-tech]

the bearings should have their type marked on one side, 7000 series angular contact.

[Steve]

If the motor is 3.1 A 8 lead then it can be wired in parallel which would allow 4.2A or in series limited to 2.1 A

In the origional drive was set to 2A the motor would have been wired in series.

If you are using an external drive the motor could be wired in parallel and the drive set to 4.2A.

Generally series wired motors have higher torque but this tails off at a lower speed than parallel wired motors

[Large519]

AH, thankyou steve that explains better why the originals were set at 2Amp. Am I to assume that too much amp into the motor would eventually burn it out?

MMM, dont think I'll be re-wiring any motors soon. Think I'll take my setup back to original settings and work from there.

the bearings should have their type marked on one side, 7000 series angular contact.

My mistake on decsription not the bearing but the ballnut that the ballscrew runs through.

[Steve]

The winding resistance in series is higher than in parallel so the magnetic field takes longer to generate. This effects the speed of motor rotation.

Running at a higher current will generate heat. Running slightly higher current would be OK but as the motor warms up the resistance can increase slightly which can reduce performance.

A higher motor bus voltage would also improve performance as long as you dont exceed the rating of the stepper drive the motor will be fine. Increasing the voltage improves performance as the magnetic field in the motor is generated more quickly.

[angel-tech]

the bearings should have their type marked on one side, 7000 series angular contact.

My mistake on decsription not the bearing but the ballnut that the ballscrew runs through.

For that ballscrew I would doubt you can just buy another nut, the quality of them would mean the nut would have been assembled for that specific screw.

Cheap Chinese ballscrews will have the nuts separate, but a quality screw will have the nut or nuts made for it.