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CNCStudent
24-12-2014, 09:24 AM
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 (http://cnc4you.co.uk/resources/Stepper%20Motor%20Nema%2023%2060BYGH301B%203.1Nm.p df) 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

EddyCurrent
24-12-2014, 02:11 PM
To cut a long story short, you want to be using these; http://www.leadshine.com/productdetail.aspx?type=products&category=stepper-products&producttype=stepper-drives&series=EM&model=EM806

njhussey
24-12-2014, 04:23 PM
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.

JAZZCNC
24-12-2014, 05:02 PM
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.

kingcreaky
24-12-2014, 05:16 PM
To cut a long story short, you want to be using these; http://www.leadshine.com/productdetail.aspx?type=products&category=stepper-products&producttype=stepper-drives&series=EM&model=EM806

:hysterical:

CNCStudent
24-12-2014, 07:18 PM
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

JAZZCNC
24-12-2014, 11:08 PM
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.

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.

Jonathan
25-12-2014, 04:32 PM
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?

CNCStudent
25-12-2014, 09:46 PM
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

Neale
25-12-2014, 10:09 PM
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.

JAZZCNC
25-12-2014, 11:18 PM
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.

CNCStudent
25-12-2014, 11:24 PM
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

irving2008
26-12-2014, 12:58 AM
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?

Gary
26-12-2014, 08:46 AM
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.
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

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

CNCStudent
26-12-2014, 12:46 PM
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

Gary
26-12-2014, 12:58 PM
Back on the 2nd

Jonathan
26-12-2014, 08:19 PM
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 V_{out}*I_{out}=V_{in}*I_{in}.
Now do you see why the input current, I_{in}, 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 (http://www.cnc4you.co.uk/Stepper-Motor/Nema23-3.1Nm/Nema23-Stepper-Motor-3.1Nm-60BYGH301B) connected to a lab PSU:

http://www.mycncuk.com/attachment.php?attachmentid=14207&stc=1

Current is on the left, voltage on the right.

CNCStudent
29-12-2014, 09:16 AM
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.