PDA

View Full Version : Steppers, Series, Parallel



Ricardoco
12-01-2013, 10:56 AM
At the moment I'm deep in doing the Electrics for my new machine. I have read that you can have the stepper motor coils in a series or parallel arrangement.

My questions are, which is preferable and why, and how much difference does it really make, and thridly would it be a feature to put in some relays to switch between the two wiring types..


Rick

Jonathan
12-01-2013, 12:38 PM
My post here (http://www.mycncuk.com/forums/general-discussion/3861-my-cnc-sessions-now-like-laundry-day.html#post25191) explains why, but the simple answer is that in most cases parallel is the best arrangement. You get slightly greater torque at low speeds from bipolar-series, but since the difference is small you're better off using parallel it gets better torque at high speed due to the lower inductance.

There might be something to gain by switching between the two, but I doubt it's worth the trouble here especially since switching whilst the driver it turned on could damage it.

Ricardoco
12-01-2013, 01:29 PM
I assume the numbers will be reresented in a graph somewhere. As for the switching my panel is a one time sequenced progression so you can only progress to the next switch once you have made a choice on the previous one and if you make a mistake you must start again, so i would put that choice above the stepper power switch.. But it seems imaterial if there is so little difference..

Rick

Ricardoco
12-01-2013, 01:44 PM
Also how do you tell the maximum voltage to drive the motors at and is this different with the two arrangements?

Rick

JAZZCNC
12-01-2013, 02:00 PM
thridly would it be a feature to put in some relays to switch between the two wiring types..

Not that easy has the voltage requirements would change has well. Serial requires much higher voltage(roughly double parallel) also the chance of blowing the drive is great.
The switching would have to happen with the power to drives off has it's 99% sure the drives will pop.!!

Not required anyway so keep it simple.!!

Ricardoco
12-01-2013, 02:19 PM
My drives can be take upto 80-vac or 100vdc but it appears the concensus is parallel so Parallel it is then...

Rick

gavztheouch
12-01-2013, 03:27 PM
Parallel works best for me, you get faster rapids and cooler running motors.

I have blown up quite a few drivers running in series due to the back emf/motor inductance.

Robin Hewitt
12-01-2013, 04:09 PM
Parallel works best for me, you get faster rapids and cooler running motors.

That's a surprise because I tried wiring in parallel once. Once being the operative word. I got little appreciable speed advantage and lots more heat.

Also, why is everyone worrying about Volts, our drivers already have lots of Volts? Parallel wiring requires twice the Amps.

Jonathan
12-01-2013, 04:12 PM
That's a surprise because I tried wiring in parallel once. Once being the operative word. I got little appreciable speed advantage and lots more heat.

But aren't your motors on mains voltage, or something silly high, in which case it's hardly surprising that they would overheat in parallel?


Also, why is everyone worrying about Volts, our drivers already have lots of Volts? Parallel wiring requires twice the Amps.

See the post I linked to earlier - it's because the inductance is 4 times greater when in series, so you need a higher voltage to 'overcome' that.

JAZZCNC
12-01-2013, 04:24 PM
Also, why is everyone worrying about Volts, our drivers already have lots of Volts? Parallel wiring requires twice the Amps.

They have what ever volts they are provided with.!! Give a 50V drive 24v and wire the motor in series and see how fast it goes or were it runs out of torque.!!

Volts make all the difference to a stepper and I'm surprised at that comment Robin.?

Robin Hewitt
12-01-2013, 05:31 PM
But aren't your motors on mains voltage, or something silly high, in which case it's hardly surprising that they would overheat in parallel?

I wasn't born with them, I used lower Voltages for years then woke up one morning and found 220 Volts suddenly seemed like a good idea :hysterical:

And, Cor blimey, I wasn't trying to be controversial, just observing that you need twice as much power supply if you want to go in series.

But while we are on the subject of Volts and inductance I can't resist one more quick pop as I seem to have struck a nerve :distracted:


If you full step the motor all the inductance has to be overcome when you step, the coil goes from full power in one direction to full power in the other.

If you half step the coil gets an off period between the two extremes and the inductance becomes less of a problem.

If go beyond half step you introduce fractional current steps reduce the current switching inductance problem even more.

Stepper heaven is to have the current in two sine waves 90 degrees out of phase, doesn't step at all, turns smoothly.

BUT... he says putting on his asbestos knickers... I have never seen a stepper turn faster than when I full step it and the inductance is hardest to overcome.

Ricardoco
12-01-2013, 06:29 PM
Ok so looking at the motors and Drivers below:-
79417942

how is the final Required Motor Voltage calculated
What would the suggested setup be..
What sort of rpm could be expected.
I will be using an AC supply with the drivers.

Rick

m_c
12-01-2013, 07:07 PM
32 * Sqrt inductance is the most accurate approximation. Failing that, somewhere within 4-20 times rated stepper voltage.

Ricardoco
12-01-2013, 07:25 PM
32 * Sqrt inductance is the most accurate approximation. Failing that, somewhere within 4-20 times rated stepper voltage.So 55-56v max? so what is the optimal then?

Rick

JAZZCNC
12-01-2013, 07:28 PM
how is the final Required Motor Voltage calculated
What would the suggested setup be..
What sort of rpm could be expected.
I will be using an AC supply with the drivers.

Rick

I'd run them at 70V and use a DC Toroidal supply not AC. The motors "Safe" running is 55V but we know from experience they will handle 70V without any trouble so thats where I'd be running them.
Reason I'd run DC is because the capacitors handle back EMF better and deliver smoother power. Don't know these drives or the Supply your using so hard to say how they will handle any Back Emf but it's something you need to consider esp if the Gantrys heavy and you plan to run the machine fast.?