Machsupport Forum
Tangent Corner => Tangent Corner => Topic started by: Overloaded on May 10, 2012, 02:25:46 PM
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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
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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
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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
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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
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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 !
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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
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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
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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 ;D
Ian
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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
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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
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That is a great illustration Ian, thanks.
OK, so now I'm gonna climb out on my limb.
Is there any device, or way, to introduce something between the drive and the motor to "create" higher inductance to make the drive happy ... and possibly reduce the temp of the motor ?
Or, knock the output voltage down to an exceptable level maybe ?
I really would like to use these together, mainly needing the indexing drive.
Just trying to use what's on hand.
Thanks
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well.... I know there's inductors which can be used to alter a circuits inductance and I know there's potential dividers that drop voltages... but whether thay can be used to do what you need is beyond my pay scale. 'twould be interesting to know though. If you're on the zone I reckon you should ask in "stepper motors and drivers" - maybe Marris will come forth. I reckon he's your man for this. Be sure to keep us informed though - interesting question.
Ian
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Might just do that Ian. Havent been there for quite a while.
The larger Parker motors are petty scarce, found only 1 at auction ... in Singapore.
Cool calc. here - http://www.diyaudioandvideo.com/Calculator/Inductor/
Interesting to enter various gauges of wire and observe the results.
If I persue this further, I'll post back.
Thanks for your time folks,
Russ
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Russ,
I don't know how that drive works ie; remember in a typical ac motor if one lowers the voltage the amps go up ( that's how you burn up motors
since the resistance to the increased current becomes heat and without thermal protection amps go to infinity if the ability is there to do so).
Typicaly for a stepper a low voltage will limit the max rpm possible since the the abillity to energise the motor winding is diminished. If voltage is ok but amps are low the motor won't work right, since you can't energize the inductive field enough to hold the torque or step it. At very low amps it may not even turn. The lower the inductance of the motor the faster the current gets to the windings. If one increases the amps it works correctly but then as the fields alternate the losses due to inductance becomes heat. Putting fins on the motor would allow for conducting some of the heat away ( maybe 10 degrees or so unless you have forced air cooling / convection like a fan blowing over the fins).
But forget all of the above since don't know how that drive is sensing current or voltage and adjusting accordingly given some designed inductance.
So not sure what affect putting additional external inductance will have on the drive and for that matter how the phases will react to the external inductance.
I would call Parker and talk to one of their tech support guys. Sometimes if you just tell them upfront what your concerns are and that your trying to save some money for the "company" ( btw, some are responsive to hobbiest if they are not busy!) .
Always interesting to find out dumb ( hey hey ....me :D not you folks .....) when you get into the expertise of a different discipline. ;)
RICH
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Thanks Rich !
I did not inquire further regarding the external inductors. Magnet wire is not cheap, not bad at auction though. I did find a Nema 23 stepper that should work OK with this drive but it's a little smaller than I' like.
I will keep watch for a matched Parker motor, or get a more modern indexing drive.
There are several servos and indexing drives here but are for other applications.
Thanks again Gents,
Russ