Help wiring M60STH88-3008DF Steppers Motors to 752 Drivers

[Robin Hewitt]

So what's the max current I should be using given my 43v supply and why am I using 43v when the data sheet says 5.46v?

As Jonathan says, you need it to overcome the inductance of the motor windings.

Inductance tells you how unwilling a circuit is to change the flow of current. It's all about building up and collapsing magnetic fields.

You apply 43 Volts and the current in the coil changes a jolly sight faster than if you applied 5.46 Volts. This is really useful if you want to reverse the current in a stepper coil umpteen times a second.

When it switches the current off, the coil doesn't want to stop flowing current. If you don't give that current somewhere to go the volts will simply rise until a transistor blows or ithe arcs to ground. Seriously bad idea. The fix is to allow the current to flow back to the start of the coil, round and round until the coil resistance turns it in to heat. Thus the coil inductance is a double whammy, it gets you when you turn the power on and when you turn the current off.

Luckily the driver sorts it all out for you. Some are cleverer than others though. Ignore everything on the motor label except the current.

Of course what you really need is the graph which shows motor torque over a speed range for a given current and voltage. Unfortunately the sellers of stepper motors have realised that the only thing their customers seem to care about is the holding torque so that is what they sell you. Who cares if the torque nose dives at 5rpm? It's a 3Nm motor, has to be good, dunnit!

[Karl]

Thank you folks; most useful. Now I can't immediately remember the really good reason why I chose to wire the motors as bipolar series (there was one) but there seems to be a suggestion that bipolar parallel would be better(?). So off to find and read a thread on bipolar-series v -parallel wiring. Thanks again.

[Gary]

Going parallel means the inductance is lower, so the driver can push the current through the phase quicker and run the motor faster.
This also means you dont need as much voltage either.
If you dont need the motor to spin fast, then go series.

[Karl]

OK, so in terms of wiring a motor bipolar-series versus -parallel, what does 'fast' mean?

My problem is that on occasion my motors lose steps when motoring round a corner (X to Y travel transition) - motors drive a compound table.

Setup:
Motors: SY60STH88-3008BF
Driver: PM542 @ 1,600 pulses per rev, 2.37A(Peak) [1.69A(RMS)]
Supply: 43V
MACH3 motor config': 627 steps per mm, 500mm per min

So:
If the motor data sheet gives bipolar-series 2.1A and bipolar-parallel 4.2A are those currents peak or RMS?
Given above settings, should I wire the motors Bipolar-series or -parallel (and why?) to, presumably, get the maximum torque within my desired 0-500mm/min operating range?

Thanks in advance.

[Robin Hewitt]

there seems to be a suggestion that bipolar parallel would be better(?).

If you look at the graphs, wiring in paralel doesn't actually give you a big torque speed advantage. OTOH, experience shows you will get a lot more heat that needs to go somewhere.

Consider where you will dump that extra heat.

As I understand it, any flaws in the soft iron motor lamination act as little, shorted out, single turn, transformer coils. When you switch the motor windings you generate "eddy currents" around those flaws which heat the lamination. Halving the coil inductance boosts the eddy current heating.

Some reckon that the gain ain't worth the pain.