Why do i need to crank up Amps?

[methuso]

HI
NOOB warning

Just finished converting a Proxxon MF70 (really small mill) only took 3 years.
I have a Hobby CNC 4 AUPC REV 2 all axes set to Async and 1/8 step.
i run at 12V now (12Ah battery) which should be ok for testing right ?

Now my Japan Servo Co., Ltd. KP56QM2-001 is speced to 1.4A/ph and that works (on Z) when setting the vRef for this (1.4*0.18) but my Astrosyn Minebea 23LM-C352-08 is marked 1.3 amps on the motor but i need to crank it up to about 2.2 amps (vRef 0.398) to run.
OK it might work on a little lower but i winged it.

*why is this?
*is it safe
*should i multiply the A/ph and number of phases to see the correct Amp to use ?
*should i still be able to stop them easily by holding their shafts by my fingers?


/Ulf

[steve323]

As you have already found out, different stepper motors produce different amounts of torque. They have different size wires with different numbers of turns with different magnet strengths. The combinations are endless as to why one motor at a similar current rating has a different torque.

It is usually safe to overdrive the current of a stepper motor. The limit is the operating temperature. More current means more heat. If you operate at a higher current for a long enough time, you will start to melt wires and/or dry out the bearings. Adding cooling fins or blowing air past the motors might let them run at higher currents for a longer time before overheating.

If this is just for the Z-axis, then you might be safe to turn on the idle current reduction so the average current is close to the 1.4A limit even if it bumps up to 2.2A while moving.

There are also plenty of really strong stepper motors that will work with the HobbyCNC board if you want to updrade. You might also want to try at least 24V for your power supply.

Steve

[methuso]

thanks.
I shall raise my voltage and overcurrent the drives a bit then
the 2.2A i pointed out was what i turned the pot to (0.398volt)
/Ulf

[steve323]

Just keep an eye on the temperature. I think steppers are safe up to at around 90C or so, although I am not 100% certain. This is hot enough to cause blisters if you hold on to it too long. If they get too hot, then you might want to back off on the current.

Steve