Do steppers draw a lot of current stopping and starting? And more.

[boydage]

I have decided to upgrade my wiring throughout a cnc router that is years in the making. Kind of one of those spaggetti functioning machines haha. Needs a good tidyup.

Stepper motors arrive with very small power wires. I measured mine they are 18awg I think. Quite small. Running with my 60v power supply I will have approx 5 metres from the motor to the driver. Nema 23 closed loop steppers, I am thinking that whilst 4C HMC04 1.0 mm2 would be ample, would it be better to spend a little more and go to 1.5mm2? Do steppers draw a lot of current when starting and stopping rapidly lots of times?

Also - curious as too what the largest voltage you can go on a Nema 23 and Nema 24? I have heard 80v but am too scared to do that?

Would love to hear a GURU speak.

Boydage

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[joeavaerage]

Hi,
I have Vexta 5-phase steppers and the genuine Vexta driver has 230VAC input but applies about 150VDC to the steppers!!
They go like hell, I run them at 2400 rpm at traverse speeds but have taken them as high as 3000rpm.

Most of the steppers we are familiar are called hybrid steppers. They were a extension of an earlier design called 'variable reluctance motors'
They are broadly similar but had very much fewer steps in a revolution, sometimes as few as 72 steps/rev or 5 degrees per step. These things
were big, several horsepower and were driven at hundreds of volts.

The effective voltage limit of a modern stepper is determined by the voltage 'withstand' of the highspeed electronics within the drive rather than the
stepper itself.

As you know steppers are constant current devices, even when they are not moving they still absorb rated current. Note that many drivers
can detect when the stepper is stationary and reduces the current to reduce the heating but the principle is still that steppers absorb current
even when idle.

Like any electric motor a stepper produces a back EMF, especially when decelerating. The back EMF will attempt to drive a current in the
drive/winding circuit, but the drive will attempt to keep it constant, after all that's what the drive is supposed to do.

So the answer to your question....'does the stepper current change when decelerating'....yes it does, but not by much. The current will be the vector
sum of the normal driver supplied current and the current induced by the back EMF.

Craig

[machinedude]

best to stick within what the motor is rated at voltage wise. they run a lot better running at the edge of the rating. i have smaller ones and larger ones that are rated for 80 V and have a 70 V power supply on them. never had any issues.

[dazp1976]

Mine:
4A, 4nm Nema23, 60V, 18awg, 3 meters, GX20 connectors.
No issues whatsoever.
In fact the short wires pre-wired rom the motors themselves are 20awg.

My 5.6A, 7nm Nema 34 has short pre-wired 18awg.