Newbie- Motor nameplate voltage vs. what works

[oneartisan]

I have just started collecting parts for my future gantry-type router and have completed the stepper motor collecting phase. All of the motors are Pacific Scientific E series NEMA 34 3 and 4 stack plus one NEMA 42 2 stack. All are 65 VDC, 4 or 5 amps with the sole exception of the NEMA 42. It has a rating of 4.55 volts and 7.9 amps. How can an 18 pound motor have these specs?

I have read that the supply voltage should be between 4x and 20x rated voltage. Maybe that applies to the 4.55v motor but I'm uneasy with the thought of pumping 3000 volts into the 34 frame motors. Being that the motors are all from the same manufacturer, something must be wrong or I shouldn't be playing with electricity.

Thanks!

[dilbert0815]

Originally Posted by oneartisan I have just started collecting parts for my future gantry-type router and have completed the stepper motor collecting phase. All of the motors are Pacific Scientific E series NEMA 34 3 and 4 stack plus one NEMA 42 2 stack. All are 65 VDC, 4 or 5 amps with the sole exception of the NEMA 42. It has a rating of 4.55 volts and 7.9 amps. How can an 18 pound motor have these specs?

I think the spec of the 34 and 42 may be refering to different parameters.
The motors are characterised by current and coil resistance only. The rated voltage is a means of telling the resistance (R=U/I).
For the NEMA 42 the rated voltage makes sense and indicates a resistance of 0,57Ohms.

For the NEMA 34 the numbers seem not to make sense.
Just a quick mental calc tells us for 65V rated voltage you would have a thermal rating of ~260W per coil, 520W total. This would be ridiculously high for NEMA 34.

I belive there are two options.
They may have specified the isolation voltage, not the real "rated" voltage. This would mean they would suggest using no more than 65V driver supply to avoid safety risk for the operator.
The only plausible second alternative would be 6,5VDC rating when there is a missing dezimal point.

If you have type numbers someone may be able to check available spec documents if these assumptions may be correct.

Peter

[ger21]

A lot of PacSci motors are labeled with Max voltage, which is what the 65V is. YOU CAN probably find the actual ratings here.
http://www.xylotex.com/PacSciDS.pdf

The ideal max voltage is 32 time the square root of the rated inductance. This is what Gecko recommends with their drives.

[oneartisan]

Thanks for the link, Jerry. Using inductance to calculate max voltage works pretty well. I have two E34HLHT motors with nameplate V=65 @ 5.2A. Looking at the PDF from the link the inductance is 8.7 mH. Using the sqrt formula the max V is 94. These motors have a nameplate rating of 180w.

The 42 frame motors (UPS brought another today, 99 cents on eBay) work out differently.
E42HCLC series connected (nameplate rating) 4.89V @ 7.4A, phase inductance (from PDF) = 10.6 mH calculates to 104V.

E42HCHT parallel connected (nameplate rating) 4.55V @ 7.9A, phase inductance (from PDF) = 7.8 mH calculates to 89V.

It seems that the 4x to 20x rule of thumb applies to the 42 frame motors but not to any others. So, Peter, it looks like your theory of different parameters may be the case. If not,and the max V is <5V on the 42 frame, then these would be 36w motors?

The phase resistance on the series 42 is 0.47 ohms and on the parallel 42 it's 0.41 ohms. With all this in mind, how do I pick a proper voltage? I have no problem designing the necessary structural rigidity into this machine but I'd like to get the electrical specs nailed on the first try.

Thanks for your help,
Jim

[dilbert0815]

Originally Posted by oneartisan I have two E34HLHT motors with nameplate V=65 @ 5.2A. Looking at the PDF from the link the inductance is 8.7 mH. Using the sqrt formula the max V is 94. These motors have a nameplate rating of 180w.

The spec sheet tell you the coils have 0.7Ohms. 5.2*0.7 = 3,64V rated voltage and the thermal (resistive) load is 5.2A*3,64V = ~19W (x2).
There will be some added thermal effect from the magnetic field of cause, but I would not guess more than the same as the thermal from the resistance.
.
I would guess the 180W are a mechanical power output equivalent and are not a thermal rating.
The 65V for the Nema34 seems indeed only the isolation rating.

And by the way the 4x..20x would then apply also for your Nema34.

regards