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IndustryArena Forum > CNC Electronics > Stepper Motors / Drives > TB6600 Testing and Troubleshooting
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  1. #1

    TB6600 Testing and Troubleshooting

    I recently purchased a TB6600 stepper drive from ebay. I have followed alot of the posts here regarding torque issues, specifically those noted by Lucas. I setup a couple test so that I could observe for myself the characteristics of these drives. I'm not as concerned with the actual torque characteristics right now, as I am with what I observed from a purely education/understanding perspective.

    My drive is setup to full step (1/1) and current limit to 1.8 Amps. The test done in the picture was with the drive idling.

    Pictured you'll see two meters. The setup of these meters is as follows:

    The left meter is in series with the "A" winding of my stepper, measuring current in the winding. The right meter is the voltage measured across the sense resistor for the aforementioned winding.

    As you can see from the picture, the left meter is reading a current of .628 amps through the winding, while the right meter is reading a mere .015 volts across the sense resistor.

    Doing the math, with .628 amps and .015 volts I would expect the sense resistor to be .023 ohms. It is not. The sense resistor was measured at exactly .22 ohms.

    Again, through calculation, with the sense resistor being .22 ohms, and the measured current being .628 amps I would expect to see a .138 Volt drop across the sense resistor, but its not even close.

    Any ideas why im seeing this discrepancy? Where is the remaining current flowing if not through the sense resistor?

    I checked both the current readings, and voltage readings with 3 different meters, and the were all identical in readings.

    What am I missing?

    (As noted earlier these drives idle at 30% current, which leads me to believe my current reading was correct, being that .628 amps is roughly 30% of my full current setting of 1.8 amps)

    http://s27.postimg.org/51nc35u1f/20140529_110019.jpg

  2. #2
    Join Date
    Nov 2011
    Posts
    205

    Re: TB6600 Testing and Troubleshooting

    Check this thread.

    http://www.cnczone.com/forums/steppe...rive-ebay.html

    You are not the only one with this problem.

    On the ones I have, I get the same results with any switch setting.

    Don

  3. #3
    Join Date
    Jan 2005
    Posts
    364

    Re: TB6600 Testing and Troubleshooting

    Quote Originally Posted by Leander86 View Post

    The left meter is in series with the "A" winding of my stepper, measuring current in the winding. The right meter is the voltage measured across the sense resistor for the aforementioned winding.

    As you can see from the picture, the left meter is reading a current of .628 amps through the winding, while the right meter is reading a mere .015 volts across the sense resistor.

    Doing the math, with .628 amps and .015 volts I would expect the sense resistor to be .023 ohms. It is not. The sense resistor was measured at exactly .22 ohms.

    Again, through calculation, with the sense resistor being .22 ohms, and the measured current being .628 amps I would expect to see a .138 Volt drop across the sense resistor, but its not even close.

    Any ideas why im seeing this discrepancy? Where is the remaining current flowing if not through the sense resistor?

    I checked both the current readings, and voltage readings with 3 different meters, and the were all identical in readings.

    What am I missing?
    A normal DVM isn't suited for these kind of measurements, they are spec'd for DC and low frequency (50-60Hz AC only).
    You could use them to measure the current on the supply input and compare the power consumption betwwen drives with the same motor, settings and supply.

    You really need a scope to check what's going on.
    Open source CNC electronics and accessories:
    http://users.skynet.be/ldt/CNC%20electronics/THB6064AH.html

  4. #4
    Join Date
    Jan 2005
    Posts
    1695

    Re: TB6600 Testing and Troubleshooting

    The current measure is OK, but keep in mind that the voltage waveform across the resistor is not continuous DC. It is pulse width modulated. Depending on the decay mode, the voltage across the sensing resistor can reverse polarity during the off cycle. The "missing" current flows through the bridge transistors.

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