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  1. #1
    Hello,

    first post here.

    I am somewhat confused by the guidance on line about voltages and currents, and please bear with me a little as I'm new to this.

    1) the guidance seems to be to run steppers at a higher voltage (say 36v or 42v) as they will drive better at higher speed than trying to run the same driver at say 12 or 24V, given that this is correct, given

    XL = 2*Pi*Freq*L

    that would bode true, as Z = R + XL (ignoring Xc as it would be relatively small).

    2) with regards to the TB6600 drives, the datasheet state that they can run drives up to 5A and ~45V, but the limiting power of the chips is 40W, so if you were running at drive at 42V, then is the limiting current of the drive 40W / 42V = ~0.95A?


    3) if I was intending to use 3.1Nm stepper motors rated at 4.2A, 3.2mH, 0.65\Omega & 2.73V (in parrallel 4 wire arrangement), using TB6600's, the maximum driving voltage of these drives at 4.2A would be 40W / 4.2A = ~9.5V? Have I got something wrong here?


    4) the limiting voltage guidance on these stepper motors is:

    32 * \sqrt{L} = 32 * \sqrt{3.2mH} = 57V

    or 25 * Motor Rated Voltage (2.73V) = 68.25V

    5) The long and the short is can someone confirm that the TB6600's will never drive these steppers fully at a higher voltage that ~10V to achieve maximum torque?

    I must admit at this point that as I got the common TB6600 smoke signal with one of these motors running at 42V I was more cautious with a second and placed a current meter on the stepper drive power supply feed to ensure that I'd got the current setting correct, but the stepper drive was only drawing about ~0.9A before it went into fault (thermal cutout) mode, (the motor was not moving at the time), which seems to tally with about 40W.

    Would it be correct to presume that these drives should be drawing 4.2A even at 42V when measured on the drive supply side? Or have I misunderstood something? This being the case 4.2 * 42 would require a drive with a rating of better than ~176W! (quite a long way from a TB6600 rating + can't seem to see anything with that sort of rating).


    Any guidance would be greatly appreciated.

    (application is to direct drive a plasma table (timing belt drive) , however I'd like the flexibility to be able to pull the motors off and reuse them on maybe converting my mill and lathe in the future (direct drive application), and also be able to reuse my driver arrangement as space is at a premium in my garage and I can't accommodate 4 sets of drives for a plasma, 2 x mills and lathe)

    Thanks

    Brett

  2. #2
    To cut a long story short, you want to be using these; http://www.leadshine.com/productdeta...EM&model=EM806
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  3. #3
    The old style TB6560 drivers said they were good up to 32V but in fact you couldn't run them at any more than 24V without the magic smoke escaping. Ditch the all in one board and go with what EddyCurrent linked to. It's a false economy scrimping on the electronics especially if you want to reuse them on a mill. I started off like you with the TB drive but now have Leadshine dtives after having the error of my ways pointed out on here.
    Last edited by njhussey; 24-12-2014 at 05:23 PM.
    Neil...

    Build log...here

  4. #4
    Not getting into the why's etc becasue it's been said so many times just search forum. But in a nut shell for best performance it boils down to 2 setups. NONE include the TB based chips.!!

    Motors less than 2nm then go with 50V drives running 42-44Vdc.
    Motors above 2Nm then go with 70-80v drives running 60-70Vdc.

    Buy digital drives likes been suggested if you have the money has they are worth every penny.
    Personally I'd just buy 80vdc drives and 3Nm motors running 68Vdc as they cover a massive machine range and allow excellent performance on any machine large or small.

  5. #5
    Quote Originally Posted by EddyCurrent View Post
    To cut a long story short, you want to be using these; http://www.leadshine.com/productdeta...EM&model=EM806


  6. #6
    I'm well aware of the issues with some of the TB6600 boards, and I've read a load of stuff on various forums.

    The leadshine drives look nice (92 + VAT + del is a bit pricey), and I've noted the helpful comment above about 80V drives (which is essentially what the leadshine drive listed appears to be with a few added benefits (not a clue why you would need an RS232 interface directly on a drive but hey ho!).

    But what's confusing me is the statement to run the steppers at 68V as they are 3nm steppers? Using the gecko guidance that seems to be a well tauted about rule of thumb (32 x SQRT (L) = Max Voltage), the drives are suppose to have a maximum voltage of 57V or the 25 x Motor Rated Voltage (68V), seems a little close if not slightly beyond the guidance on the gecko rules of thumb.

    How critical is the stepper motor current rating? (given most of the drives have a range but no normally quite 4.2A as a current setting)

    How does the RMS and MAX ampage ratings on the drives relate to the motor current rating (which setting should I use)?

    Am I not just likley to end up with the same conundrum of actual current being lower than the motor rated current, given if the drives are 60W rated, and they are running at 60V..... it just means that they will be running at 1 Amp (still)....?

    I'm not so much questioning the TB6600's [given yes I appreciate that everyone seems to feel that the issue is done to death], but curious why they appear to be only running at less than 1A current draw....

    Thanks

  7. #7
    Quote Originally Posted by CNCStudent View Post
    The leadshine drives look nice (92 + VAT + del is a bit pricey), and I've noted the helpful comment above about 80V drives (which is essentially what the leadshine drive listed appears to be with a few added benefits (not a clue why you would need an RS232 interface directly on a drive but hey ho!).
    They can be got for much less than that but have no doubts they are worth every penny and I've used just about every drive worth bothering with. I don't even class the TB rubbish as drives, I've had Josh sticks that last longer and smoke less than these and they can't be compared in any way shape or form to these drives.

    The RS232 is so you can connect directly to the drives thru software and configure it's parameters for things like resonance.

    Quote Originally Posted by CNCStudent View Post
    But what's confusing me is the statement to run the steppers at 68V as they are 3nm steppers? Using the gecko guidance that seems to be a well tauted about rule of thumb (32 x SQRT (L) = Max Voltage), the drives are suppose to have a maximum voltage of 57V or the 25 x Motor Rated Voltage (68V), seems a little close if not slightly beyond the guidance on the gecko rules of thumb.

    How critical is the stepper motor current rating? (given most of the drives have a range but no normally quite 4.2A as a current setting)

    How does the RMS and MAX ampage ratings on the drives relate to the motor current rating (which setting should I use)?
    The Gecko thing is exactly that a guide and in practice you can run the motors quite safely with much higher voltage. It does lead to some iron losses etc which will eventually shorten there life span but it's nothing to worry about and at less than 30 a motor then the performance advantage is more than worth the price of a motor say every 5-6yrs, if that.!

    Motor current rating is quite critical for best performance so just set the drives to motor PEAK rating or close to it. For best performance you want the motors wired parallel.
    Last edited by JAZZCNC; 25-12-2014 at 12:09 AM.

  8. #8
    Quote Originally Posted by CNCStudent View Post
    I'm not so much questioning the TB6600's [given yes I appreciate that everyone seems to feel that the issue is done to death], but curious why they appear to be only running at less than 1A current draw...
    The input current doesn't have to be the same as the output current, but the power does, so given that, what can you say about the output current when the supply voltage is higher than the motor rated voltage?
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  9. #9
    Jazcnc thanks very much for the very informative post I've learnt a lot

    Next daft question does anyone know what the actual difference is between the leadshine em806 drives and it's predecessor the am882 and also the dm870?

    The first two appear to be the same (hence is there a diff paying extra for the new one when the old one is still being sold new) and the dm870 appears to not offer sensorless stall detection although that is only above 300 rpm which for a direct drive application is a bit fast in my plasma application. Is it worth it is there anything else different?

    Thanks again for your time and hope you have a happy christmas

    Jonathan is current not consistent. Input must equal total output? But measuring the input would be smoother than measuring just one of the channels

  10. #10
    I asked about the AM882/EM806 difference a week or so ago. The answer is that the AM882 is an older version, now obsoleted by the EM806 which is in some unknown way "better" - but I'm not sure quite why or how! Zapp only have one of the AM882s left and as it's the same price as the newer model, it might be there for a while (unless someone needs a replacement, maybe). Don't know about the DM870.
    As far as current is concerned, are there some measurement problems given that the output is generally PWM and this might not correctly read on a digital meter? Just thinking out loud. Ditto power measurements - need to take phase difference between voltage and current into account with a highly inductive load.

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