Hey folks,
  I have an older Parker Compumotor indexing drive, AX model.
See the clip about the inductance.
I have quite a variety of stepper motors, none of which are near 20 mH. Most, if not all, are 2 - 5 or so. (or is 5 higher than 20 in inductance ... ?)
I've hooked some of them up to this drive anyway and they seem to run OK during testing but get hotter than expected. (current set with DIP switches to accommodate)
Right at too hot to touch after 20 minutes or so, so I figured the temp maxed but unhooked it at that point anyway.

So, Is Parker the only cats that make stp mtrs over 20 mH inductance ?  Whats the deal ? And, what is the actual danger to the drive ... or motor ?
Also, what does it mean by "measured end to end" ?

Thanks,
Russ

Russ,
20 is higher than 5 mH.
I am guessing that the drive is meant to be used with a large motor. When the stepper gets too hot to maintain touch your at around 130 to 140 F and in short time at 140 F you'll get a burn. FWIW, i have found that many of the steppers i tried that got hot started skipping and
acting wierd. ( actualy easy for me to do since use a reistor switch box here beacuse all three machines require different current settings and sometimes i forget and apply high current to a lower current motor). A lot of motors have insulation rated to 180 to 200 F. Yet,if the motor is not getting warm then the motor is not doing much work so to speak.

Not sure what settings are available for setting current but would try the lowest. Does  the manual give current values vrs settings?
Guessing here that the drive is meant for big motors to maintain holding power / torque / indexing and not necessarily speed. So the time constant  ( sort of like an RC circuit ) is meant to be low and if you pulse a lower inductive motor with high current then the back EMF can ruin the drive. Well my quess on it FWIW.

Not sure about the "end to end" but when I measure inductance it is across the complete coil of the motor including cable ie; how it's wired for use else you will get an incorrect reading.

RICH
 

Hi Rich,
  This drive came from an electric cylinder. Nema 23 double stack stepper w/no info on the motor.
I'm pretty sure it's the AXL drive as the AXH has a fan attached according to the manual.
I tried the lowest amp settings that would turn the motor that I'm using which is a Step-Syn 24-300v 6.7A
See the chart. This drive puts out 130v .
With the drive set at 2a, the motor will get too hot to keep my hand on for more than a couple of seconds, I'm sure it will cook if left on .. the motor as well as my hand.

Other than the heat, and the WARNING message, it runs the Step-Syn fine .. up to 3000RPM

Just afraid it will burn up and thought it might be an inductance issue.
Your "end to end" description sounds reasonable, bet you're right on.
Thanks RICH,
Russ

Russ - you say the drive "puts out" 130V. Do you mean your power supply is 130V? If so that's WAAAAAAAAY over for a 2mH inductance motor. Voltage should be around 45Vdc tops.

That said - I think your heading for an ultimate burn-out here - if the drive and motor matters to you I'd heed the manufacturer's warning.

Ian

Hi Ian,
  Here is a bit more info.
I was off a bit with the V.
The motor does say 12-300v on the label, but no v is listed on the motor spec sheet.
Using the Gecko formula at 2mH would be 45.25V.
                                      20           "      143
                                      28.2               170                                  
I found a small 17 size motor to try. 22mH , .220A, set the jumpers accordingly and it got quite hot but seemed to peak at "just above bearable".

So I guess I should only use this drive for quick testing, or only use a Parker motor made specifically for use with it. Or use an off brand at least 20 mH.
Comes down to the voltage and inductance then. Even if the Denki motor can take the heat, it could destroy the drive.
 

Thanks Ian,
Russ

edit:
  attached motor specs .... note the inductance of these cats !

Hi Russ - That's why I said at 2mH your supply voltage *should* be around 45Vdc but what voltage power supply are you ACTUALLY using?

Ian

Ian,
  It's all in a self contained unit.
Very nice, but an antique.
The newer ones are OEM650(750)X and are quite small.
Russ

just noticed that according to the spec sheet that things at 170Vdc - wooooooohhhhhhaaaaaaa - waaaaaaaay too much for a 2mH motor. However much you can turn down the current I reckon you still have the makings of a good toaster 

Ian

ha ha   yep, noticed that earlier also.
Isn't it strange then that the Denki motor is labeled 12-300V  ,  2 mH  , 6.7 (9.5) A  ?
Must be pretty tough little critters.
Maybe with special considerations that I have not found yet ? Some do have finned alu heat sinks attached.
Don't see any temp specs for them either.
Russ

Maybe with special considerations that I have not found yet ? Some do have finned alu heat sinks attached.

I'm thinking you're on the right track there Russ. Here's a snip from gecko's stepper blurb after stating the 32*sqrt(L) rule.

As shown earlier, motor output power is proportional to power supply voltage, doubling the voltage doubles the output power. However, iron losses outpace motor power by increasing non-linearly with increasing power supply voltage. Eventually the point is reached where the iron losses are so great that the motor cannot dissipate the heat generated. In a way this is nature’s way of keeping someone from getting 500HP from a NEMA 23 motor by using a 10kV power supply.

Ian