Current drop on motor run

[George]

Finally I have my stepper running at 60 RPM. Lots of torque (I think) at least I cant stop the motor with my fingers anymore.

Running at 12volts with 2.2 OHM resistors the stepper is drawing around 8 1/2 amps static. As soon as the motor runs the current drops to 7 1/2 amps. This is same for either direction. Is this normal ??

George

[ger21]

How are you measuring the current draw, and what type of drives are you using.

[George]

Hi Gerry,

I am using the Delagrange 4 axix x10Amp controller.
Mach 3 software
Applied motion 4023-828D steppers (6 wire) rated at 1.7V 0.4 Ohm 4.7Amps
Two Phases connected in series, centre tap of phase connected to the common of a Fluke digi ammeter, other terminal of ammeter connected to 12 volt 10Amp supply.
Each phase leg then connected to a 2.2 Ohm 50W resitor (thats four resistors in total)

Ok that's how it's all wired. Hope that's clear enough.
Torque seems to be ok, but remember this is a test only and the steppers are laying on the workbench and not under any load.

Hope it's correct, any help would be appreciated.

Cheers

George

[ger21]

I know that with a chopper type drive, you can't measure the current that way. With yours, though, maybe you can. I believe the motor will draw less current the faster it spins, because the current can't flow into the coils fast enough. That's why steppers lose torque as speed increases.

[George]

That makes good sense, thanks Gerry..

So now that the motors are running I now have to decide which ball screws I need to buy.

My bench mill uses a 1 inch diameter 10 turn per inch (imperial) screw at the moment

I am considering using direct drive from the motor to the new screw. I will purchase a ball screw with 5mm per turn. that works out at about 5 turns to the inch.

Do you consider this adequate. I plan to be milling either aluminium or small steel parts for model engines, so nothing too big and heavy.

What maximum speed should I set the motors at ?

George

[DTLLC]

Hi George,

When the motor is not spining the current is steady and at its max flowing through the coils of the motor. This is how you measure the current on this board. When the motor takes steps, the current flow is turned on and off so you are reading this not the actual current. The board you have is a L/R Drive so to measure the current you do it without the motor spinning.

David Delagrange, Owner
Delagrange Technology LLC
4024 Fairfield Avenue
Fort Wayne, IN 46807

Phone: (260) 557-9280
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