Need Help!- Power supply and stepper pairing question.

[Dorado23JD]

Can someone please clarify for me, the proper way to figure out what size power supply I will need. I am purchasing the following steppers and plan on wiring them in parallel:

3 Keling NEMA 34 Steppers Model KL34H280-45-8A When wired in a Bipolar parallel connection the specs show these as being 6.3A per phase with a 2.2mH phase inductance.

1 Keling NEMA 34 Stepper Model KL34H295-43-8A When wired in a Bipolar parallel connection the specs show these as being 6.1A per phase with a 3.3mH phase inductance.

I understand when wiring a 4 phase motor in a bipolar connection, you essentially end up with 2 phases. My question is when using the standard 2/3 current rule I keep reading about, how does the current rating work? What I mean is do I add up the current rating of all 8 phases or is it the average current rating per motor? Which one of these is correct?

(6.3+6.3)+(6.3+6.3)+(6.3+6.3)+(6.1+6.1)=50A * .67 =33.5A Needed from power supply

--or--

6.3+6.3+6.3+6.1=25A * .67 = 16.75A Needed from power supply

I think I've got the voltage formula down which I found to be √Inductance *32=Voltage Needed
I'm assuming that since the H295 motor has the highest inductance rating I should use that to figure out the voltage required, therefore:
√3.3 * 32= 58.1 V Required (or whatever standard rating is closest like 60V) Is this correct?

I know these may be dumb questions but for some reason I'm just really stumped by this one. I appreciate any and all help.

[doorknob]

Originally Posted by Dorado23JD I think I've got the voltage formula down which I found to be √Inductance *32=Voltage Needed I'm assuming that since the H295 motor has the highest inductance rating I should use that to figure out the voltage required, therefore: √3.3 * 32= 58.1 V Required (or whatever standard rating is closest like 60V) Is this correct? I know these may be dumb questions but for some reason I'm just really stumped by this one. I appreciate any and all help.

I'm not an expert on this, so this may just be a case of the blind leading the blind, but here's my take. I'm going to do a little bit of thinking out loud here, I apologize in advance for the rambling. Maybe someone who is an expert will chime in and throw some cold water on this. But, nothing ventured, nothing gained, so here goes:

If you are wiring the H295 motor as bipolar parallel, then based on the typical formula for inductors in parallel, the net inductance of wiring two 3.3 mH coils in parallel would be about 1.6 mH.

IIRC, the formula for two inductors in parallel that I used assumes that there is no mutual inductance between the two inductors. I'm not sure that that condition holds true for the two stepper phases that are being wired together.

If indeed there is mutual inductance between the two phases, then the formula would need to be modified to take that into account. Maybe there's a reference somewhere that addresses the mutual inductance issue within steppers, but I haven't run across it yet. I would note that Jones (Jones on Stepping Motor Types) says that 8-wire steppers are wound with bifilar windings - if that is truly the case, then I'd expect that indeed mutual inductance would be a factor, and so my simple inductors-in-parallel calculation is probably wrong, because it does not incorporate the mutual inductance factor.

If I'm reading it correctly, Jones talks about how to determine the operating voltage for bifilar windings in series, but not in parallel - unless you consider the following quote:

It is worth noting that some permanent magnet stepping motors have 4 independent windings, organized as two sets of two. Within each set, if the two windings are wired in series, the result can be used as a high voltage bipolar motor. If they are wired in parallel, the result can be used as a low voltage bipolar motor.

So, one way to interpret that would be to simply take my original approach of treating the two windings as independent inductors in parallel, giving a combined 1.6 mH inductance, which is what I will do here.

Also, I do not know the assumptions behind the commonly-stated suggestion for choosing a voltage that is 32 x the square root of the coil inductance in mH. So, maybe that would be a good one to research as well, to see whether those assumptions hold true in the case of wiring the phases for bipolar parallel.

But if you take that as a given, then the square root of 1.6 is something like 1.26, and so 32 * 1.26 would give a result of about 40 volts for the recommended operating voltage.

[doorknob]

I may want to revise that, though - I'm reading the following page which may offer some additional insight:

UniPolar vs BiPolar wiring schemes for 2-phase Stepper Motors

If I'm reading it correctly, it says to use the name plate inductance, which in this case would be the original 3.3 mH.

So, at this point I'm not certain what to advise. Maybe I'll do some more research.

[doorknob]

One other reference that I'm looking at is:

http://www.cnczone.com/forums/faq_cn...l_bipolar.html


As with the previous reference, it recommends using the name plate rating inductance directly, rather than calculating the inductance in parallel.

So, according to that approach, your original voltage calculation would seem to be OK.

However, I would question whether you should be calculating your power supply voltage for the bigger motor or for the smaller motors - it's probably better to use the 2.2 mH inductance of the smaller motors to calculate the max voltage, and run the larger motor at a lower voltage than the maximum calculated for it (rather than running the smaller motors at a much higher voltage than you would calculate for them).

[Dorado23JD]

Thanks for the reply. I think the last link you gave should explain it well enough for me to understand. Now I won't feel like such as a dumba$$.