Ideal Voltage for Inductance.

[xrayxray]

Ive purchased this motor with BOB,Drives and power supply as per there KIT

http://www.wantmotor.com/ProductsView.asp?id=162&pid=80

the price for 4 pcs Nema 34 with 880oz-in stepper motors+ 4 pcs matching drivers DQ860MA + 1 pc 350W,48VDC power supply + 1 pc breakout board+ cable=462USD.

Model # 85BYGH450D-007

The specs on the motor show 15mH inductance,power supply is 48 volts.
I'm learning lots every day and obviously don't know enough so can someone explain if this is an inadequate voltage for this inductance.

I have learnt today that - 32 x square root of mH = ideal voltage.

I will be reducing the drive ratio 3 to 1.

[ger21]

I'm learning lots every day and obviously don't know enough so can someone explain if this is an inadequate voltage for this inductance.

Most people here would say yes, but that wouldn't be an accurate answer.
To answer that question accurately, you need to determine how fast you want the machine to move, and how fast you want to accelerate to that speed, then do a bunch of math to determine what voltage you need to achieve those goals. Without an accurate torque curve chart, using the same drives you'll be using, you may need to make a few assumptions to get an answer.

I have learnt today that - 32 x square root of mH = ideal voltage.

Actually, 32 x square root of mH = absolute maximum voltage you should use.

The ideal voltage would be the lowest voltage that will allow the machine to reach your performance goals. That voltage would use less energy, and your motors would run cooler.

If you need the maximum rpm and power that those motors can deliver, then you'll need to supply them with 120V. At 48V, you'll only be able to use about 40% of the motors top speed.

But, if your design only requires those motors to spin at 300-400rpm (just a guess here), then 48V might be perfectly adequate.

[doorknob]

The spec sheet is not 100% clear on the inductance rating - if that is the rating for a single winding, then since it is an 8-wire motor you can wire it up in the bipolar parallel configuration. Paralleling the windings will reduce the inductance.

[xrayxray]

So much to learn...
I always work on a presumption of a good compromise and balance,as with most things what you loose on the roundabout you gain on the swing.

I would like to use what other people find best based on above....big ask I know but am trying to achieve a good result in plasma and a good result in router mode if there is such a thing possible...I don't think speed is my ultimate objective....this won't be used in time management fabrication.

I accept this as a compromise not as a perfect result for both.

I do not need to re-invent the wheel so I prefer to use what others use and follow the valuable advise and experience of other members.

Thanks to those for your input.

Regards.

[ger21]

The spec sheet is not 100% clear on the inductance rating - if that is the rating for a single winding, then since it is an 8-wire motor you can wire it up in the bipolar parallel configuration. Paralleling the windings will reduce the inductance.

It looks like those are unipolar ratings, as 4.4Nm is 623oz-in, not 880.
With an 8 wire motor, the inductance for bipolar parallel is the same as for unipolar. So, it looks like the 15mH is the bipolar parallel inductance.

[doorknob]

Wouldn't it be nice if Chinese motor manufacturers could give complete specs instead of leaving things as an exercise for the reader (or worse, leaving things up to the reader's imagination)...

[xrayxray]

My intended use in plasma would require 300 ipm for traverse and 150 ipm for cut...using specs off another machine.

So I now need to find the torque curves...what else is required to find out if these motors are suitable?

[xrayxray]

here is a pulse torque curve on the website, last one on the page for these motors
Hybrid Stepping Motor 85BYGH:Hybrid Stepping Motor 85BYGH wholesaler

Could someone help with an explanation?

Regards.

[xrayxray]

ok...done the googling etc and here is what Ive come up with.

According to manufactures web site...Pulse Torque curve @ 1200 PPS= 180 RPM @ half step.
Torque = 180Kg/Cm or 250 oz/in...note I'm presuming it Kg/Cm on the specification - torque curve is hard to read.
20 tooth module 2 spur gear @ 40 mm pitch DIA = 4.9 inches linear travel.

So at 180 RPM traverse = 882 Ipm at 250oz/in.
with 3 to 1 reduction pulleys = 294 Ipm with 750 oz/in.
Torque curve - 2.0 amps @ 30 volts.

I think that my parameters are met if my calculations and assumptions are correct.

Any Advise or comments greatly appreciated.

Regards.

[ger21]

To find the force you'll have at your 294 ipm, divide the torque by the pinion radius

750/.787in = 952 ounces, or 59 lbs of force.

[xrayxray]

Thanks Gerry,
You answered something I was looking for.
2 drives on the x axis so should be about 120lbs or 50 kilograms of force.
My presumption then is that the y gantry should weigh less than 50 kilograms for these motors to be of use, is that correct?

Do my other calculations look ok?

Regards.

[ger21]

That depends on how fast you want to accelerate.

I can't read the chart, but your numbers seem correct.

Since those drives are capable of handling 80V, switching to a 72V power supply should greatly increase your torque.