How to test voltage on stepper motors

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How to test voltage on stepper motors

Postby Panopticon » Sat Feb 22, 2014 6:30 pm

I recently purchased an Innova 3310 digital multimeter (something I should of had a long time ago!). I'm curious about what's the best method to test the currents going to my stepper motors. This is something I have not done yet since building my printer. I do have a few questions:

-What settings should the multimeter be set to?
- What is the appropriate voltage the stepper motors should be receiving to function properly?
-If my currents are not correct how can I adjust them? (I know I can adjust the voltage using a screwdriver on the trim-pots on the steppers themselves, though how do I get readings off of them?)

Here is a link to the multimeter itself:

http://www.autoaccessoriesgarage.com/im ... 1_1_lg.jpg

Any help would be great! And hopefully other folks would learn a thing or two as well.
Panopticon
 
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Re: How to test voltage on stepper motors

Postby blah_59 » Sat Feb 22, 2014 9:34 pm

You want to use the DCV section (yellow on your picture) to measure the voltage on the stepper drivers. Setting it to 20 should work. On the stepper driver there is a VREF (normally next to the trim pot) where you'll (carefully) place the tip of your red probe (some drivers will let you use the trim pot itself as the VREF) and then you'll place the tip of your black probe on ground (you need to check the wiring diagram for your stepper drivers to see where ground is). You want to do this carefully because you don't want to accidentally redirect voltage to the wrong spot on the driver chip. Then you'll take your reading and multiply it by n to get the current (on some of my stepper drivers (SD82B compattable with A4988/A4983) I multiply by 2.5 and on my others (SD8825) I multiply by 2 so you need to check the specs on the drivers you're using).

To adjust current, turn in small increments clockwise to raise current and counter-clockwise to lower it. Somewhere between 1 amp and 1.2 is usually good but you really want to find a good spot for your machine where it's high enough so the motors don't skip any steps but low enough where the motors/stepper drivers don't overheat.

Here's links to the user guides for the stepper drivers I have:
http://files.panucatt.com/datasheets/sd8825_user_guide.pdf
http://files.panucatt.com/datasheets/sd82_user_guide.pdf
blah_59
 
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Re: How to test voltage on stepper motors

Postby Panopticon » Sun Feb 23, 2014 7:24 pm

Thank you blah! Very helpful indeed.

Currently I have the A4988 Pololu stepper drivers running on my board. You're right the VREF is actually the trim-pot itself and the ground is right beside it. It definitely takes some steady hands to get the readings, sometimes I bumped the wrong part of the stepper causing the machine to restart and having to wait to get the readings again.

I actually tested each stepper and made adjustments - some were a little too low or too high. The initial readings I got off the steppers ranged anywhere between .35 to .50V. I took your advice into account, multiplying the initial readings by 2.5 and made adjustments to get amps anywhere between 1.25-1.75 on each stepper. So far so good the motors are turning fine - just need to start printing and see if there are any improvements.
Panopticon
 
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