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  1. #11
    Quote Originally Posted by CNCStudent View Post
    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?
    I've used all three series. The EM806 appears to give slightly smoother motors at lower speeds and gives slightly more torque at higher speeds so can tune motors that little bit more aggresive. The case is slightly larger and gives better cooling but Basicly the EM series are the same as AM series but with tweaked software. Put it this way the difference is that if I couldn't get the EM and only had the AM I'd take them. If I had the choice and was 5-10 difference I'd take the EM every time.

    The DM series on the other hand don't have stall detect and the software isn't has advanced and it shows in the motor smoothness at slower speeds. I also noticed that the motors get hotter compared to AM/EM so don't think they manage the amps/resonance the same. Compared to the EM/AM I wasn't so impressed. Still very good drives but not quite as good.! On a lesser note the DM are also limted to 7A motors so no use for larger 34's.
    Last edited by JAZZCNC; 26-12-2014 at 12:18 AM.

  2. #12
    Thanks for the quick response Neale, I did read the original question some time ago on the em/am drives but didn't see the one from last week (still doesn't answer the question really except it's just better or an improvement [product development])

    Jazzcnc thanks very much perfect answer (just 882 or 806 decision now and as it's direct drive may end up 806 with your write up)

    I guess I'm asking as there are a fair few 882's on ebay but not the 806's and the 882's can be got for about 60 inc p&p but can't find the 806's less than 90 per drive hence 120 on 4 drives is a fair premium for the new model that appears the same as the old one.

    No disrespect to zapp, but they are not listed as a distributor hence probably have a modest second tier profit margin after buying from a distributor (although there costs are not actually that high considering you get them in a few days not 4-6 weeks). I'll probably buy them from them after the christmas break but thought I'd sound out on here before taking the plunge and learn something.

    With regards to the current yes I'd expect some variance given the meter (fluke 88) was set on dc amps and although the the drive signal is pwm if it's a 50% duty cycle over the two stepper coils (a & b) then I would expect the primary current to the drive to be fairly close to the demand. I'd also expect the switching frequency to be quite high so almost akin to peak given the rms value will

    I tried to put the scope (fluke scopemeter 97) across the current sense resistors of the tb6600 drives but did not get a good reading in the time I had available (this is a hobby at home)

    Not trying to be a smart a{#%^ just hoping to learn something and dispell some of the conflicting info out there as every tom dick and Harry seems to have a cnc of some sort these days as I know little thought I'd learn something too thanks for your time

  3. Consider the motor winding is a series inductance and resistance. Now what can you say about the torque which is proportional to winding current w.r.t. different step voltages applied to the winding. What do you suppose the current sense resistors are there for?

  4. We are not listed as a distributor for political reasons, you will also see that MCP are not also listed as a distributor and they used to be their main European distributor.
    Nuff said about that.
    The AM882 was the original driver that had the advanced current control and the sensor-less stall detect.
    The EM range replaced the AM882 about 2 years ago and has had further development that the AM882 did not, because the EM range is Leadshines main focus for stepper drivers.
    If all you want is torque and speed from the motor, then there is little difference between the AM and EM range, but power is not the only factor.
    Smoothness, noise, reduced resonance can also be important.
    .
    Th
    Quote Originally Posted by CNCStudent View Post
    Thanks for the quick response Neale, I did read the original question some time ago on the em/am drives but didn't see the one from last week (still doesn't answer the question really except it's just better or an improvement [product development])

    Jazzcnc thanks very much perfect answer (just 882 or 806 decision now and as it's direct drive may end up 806 with your write up)

    I guess I'm asking as there are a fair few 882's on ebay but not the 806's and the 882's can be got for about 60 inc p&p but can't find the 806's less than 90 per drive hence 120 on 4 drives is a fair premium for the new model that appears the same as the old one.

    No disrespect to zapp, but they are not listed as a distributor hence probably have a modest second tier profit margin after buying from a distributor (although there costs are not actually that high considering you get them in a few days not 4-6 weeks). I'll probably buy them from them after the christmas break but thought I'd sound out on here before taking the plunge and learn something.

    With regards to the current yes I'd expect some variance given the meter (fluke 88) was set on dc amps and although the the drive signal is pwm if it's a 50% duty cycle over the two stepper coils (a & b) then I would expect the primary current to the drive to be fairly close to the demand. I'd also expect the switching frequency to be quite high so almost akin to peak given the rms value will

    I tried to put the scope (fluke scopemeter 97) across the current sense resistors of the tb6600 drives but did not get a good reading in the time I had available (this is a hobby at home)

    Not trying to be a smart a{#%^ just hoping to learn something and dispell some of the conflicting info out there as every tom dick and Harry seems to have a cnc of some sort these days as I know little thought I'd learn something too thanks for your time

  5. #15
    Gary thanks for taking the time to respond. When are zapp back, monday next week, 2nd or 5th (I can work out delivery options then and know when to place an order. Let's me know when I need to make a decision too still researching at present). Thanks to all for the steer

  6. Back on the 2nd

  7. #17
    Quote Originally Posted by CNCStudent View Post
    Jonathan is current not consistent. Input must equal total output? But measuring the input would be smoother than measuring just one of the channels
    The formula you need to recall is power=voltage*current. I said in the previous post that the output power fro the motor driver must be roughly equal to the input power. In reality there are losses in the driver, but if we assume they're small then we can equate the input and output power to get .
    Now do you see why the input current, , is lower than the output?

    Here's an example of the same concept with a different stepper driver - in this case a 2m542 driver with a 3Nm motor from CNC4you connected to a lab PSU:



    Current is on the left, voltage on the right.
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    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  8. #18
    Thanks for taking the time to wire up a stepper & drive to a lab power supply Jonathan. I thought that the Power In = Power Out (V*I[in] = V*I[out]) only applied to transformers and voltage doubler circuits, given the stepper is acting as a chopper circuit, and no voltage change is taking place [albeit the stepper coil is an inductor].

    separate AM882 question ->

    seems you can get 3 variants of the AM882 drive, the AM882 (which has a datasheet from Leadshine), an AM882H, which seems to be above to take AC + DC and at a slightly higher voltage, and a AM882-DK (which is apparently a dedicated drive for an engraving machine).

    The AM882H seems to have a fan as well, anyone got any experience of these (as I can't find an English language PDF) are they the same as the AM882, but with a heatsink mounted fan, and has a listed supply voltage of 18-70 VAC & 24-100VDC, with the supply terminals listed as "AC"

    seems the AM882H can be had for ~48

    Any comments / experience would be very much appreciated.

    Thanks again for your time,

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