G540 - 4 motor connection problem

[m_c]

Not quite, Jazz - the problem is reading the Gecko manual. Their kit of current-set resistors includes the 3.48K resistor specifically for this drive. Why they use this daft value is anyone's guess, though. But then, Gecko are also responsible for the widely-quoted max voltage based on motor inductance formula which at best leads people astray - or perhaps it suits their drivers better? I also run Nema23 at 65V via a Chinese digital drive and I'm very happy with it. And a linear/toroidal PSU... And I have complete freedom to choose my own micro-step ratios and motor current at the flick of a DIP switch. Americans buy Gecko because they know that "American (products) are great". The rest of the world is forced to buy on price/performance/reliability alone. Oh, pity the rest of the world.

I'm sure they only supply that resistor to minimise people asking how they set 3.5A if they've not got a resistor.

The max voltage based on inductance is a valid figure. You can run higher voltage, however unless you're running the stepper motors at speed, it has no benefit and will do no harm.
Any problem will arise when the motor is spinning fast enough that back emf increases the required voltage to drive the set motor current through the motor windings, to the point where you get diminishing returns for the voltage applied.
The key thing to remember is just because you have a 65V supply, is the motor will rarely see that applied. While stationery the motor should only see the rated stepper motor coil voltage, as there is no back emf to require a higher voltage to get the rated current flowing through the motor windings. It's only as the motor starts turning and back emf increases, that the required voltage increases.
Combine that with the laws of physics, where by power = volts time current, and with a stepper using a couple amps running flat out at maximum voltage, will be getting over one hundred watts of power applied. How long do you think your Nema23 could handle that before overheating and demagnetising?

As I said, that Gecko guide is pretty good. I can remember Marris's posts over on CNC zone where he explained a lot about stepper motors, drives, and the theory behind the figures. He didn't build a very successful business by plucking figures out of no where. Which is essentially what you've done by saying your 65V supply hasn't given you any problems, despite you not understanding the theory behind why it probably really isn't a good idea.

[JAZZCNC]

I'm sure they only supply that resistor to minimise people asking how they set 3.5A if they've not got a resistor.

The max voltage based on inductance is a valid figure. You can run higher voltage, however unless you're running the stepper motors at speed, it has no benefit and will do no harm.
Any problem will arise when the motor is spinning fast enough that back emf increases the required voltage to drive the set motor current through the motor windings, to the point where you get diminishing returns for the voltage applied.
The key thing to remember is just because you have a 65V supply, is the motor will rarely see that applied. While stationery the motor should only see the rated stepper motor coil voltage, as there is no back emf to require a higher voltage to get the rated current flowing through the motor windings. It's only as the motor starts turning and back emf increases, that the required voltage increases.
Combine that with the laws of physics, where by power = volts time current, and with a stepper using a couple amps running flat out at maximum voltage, will be getting over one hundred watts of power applied. How long do you think your Nema23 could handle that before overheating and demagnetising?

As I said, that Gecko guide is pretty good. I can remember Marris's posts over on CNC zone where he explained a lot about stepper motors, drives, and the theory behind the figures. He didn't build a very successful business by plucking figures out of no where. Which is essentially what you've done by saying your 65V supply hasn't given you any problems, despite you not understanding the theory behind why it probably really isn't a good idea.

Moray what you say is correct upto to point.? Can't argue with Laws of Pyhisics and like You I've got Massive respect for Marris.

However what your saying about 65V Killing steppers isn't really valid because takes many years to have this affect and the fact they are cheap as chips make it none starter. I've been running my machine for nearly 8yrs with same motors running 70+Vdc and built many many machines using same setup without any issues. In fact never had single stepper fail or go weak.

Now where it gets fuzzy is when to use the higher voltage.? For milling machine or lathe then it's wasted and like you say not benificial. However for Router then the extra voltage makes all the difference. . . Horses for courses.!!

[m_c]

I'm well aware of the benefits, but how often do the motors run fast enough and long enough to have the full voltage applied?
The only time you'd see problems is during prolonged time at high speed, which even on a router, I'd doubt you'd sustain for long enough. But it's worth bearing in mind, that you could easily destroy a stepper motor very quickly by pushing too far.

Regardless, the point I was making, is before people go stating random figures and dismissing known good advice, understand the reasoning behind those figures and the advice. Just because something works for you, doesn't mean it'll work for others.

[JAZZCNC]

Regardless, the point I was making, is before people go stating random figures and dismissing known good advice, understand the reasoning behind those figures and the advice. Just because something works for you, doesn't mean it'll work for others.

I get your point and I do agree on lot of it.! However your just has guilty the others for dismissing Known Good advise by not listening to or trying to put down experienced people like ME.! . . . Do you think I'd go to the trouble of buying more expenisive transformers and Drives which can handle higher voltages if I didn't KNOW there was benifit in doing so.? . . . . No I wouldn't.
Can I give you the calculations and science behind why then NO I can't.!! . . . . All can tell you is I just build the bloody things and thru lots trial error plus lot of patience found that 70Vdc works better for router than 54Vdc which calcs show for same motor..!! . . . . I don't need pyhisics or calculations to tell me this it's obvious from machines performance and to me that's all that matters.

I liken it to what Manufacturers recommend for Octane rating for engines best performance.!!. . . . . But you don't see many performance cars using fuel from your local esso garage do ya.!!

[Neale]

I'm sure they only supply that resistor to minimise people asking how they set 3.5A if they've not got a resistor.

Probably true! Just slightly puzzled why it's not a round 3.5K, but there we are.

...by plucking figures out of no where. Which is essentially what you've done by saying your 65V supply hasn't given you any problems, despite you not understanding the theory behind why it probably really isn't a good idea.

My problem with those kinds of rule-of-thumb formulae is that they take on a kind of mystical significance, where really they are just a "do this and you won't be far wrong" guideline. In fact, my problem with this one is that I don't see any theoretical basis for it (and I don't think that Ohm's Law and the di/dt stuff has changed that much since I studied it 40-odd years ago). However, I do see a reason why higher voltages can give better performance when used with appropriate drives and settings. I won't use a higher voltage still because that means much more expensive drives and power supplies, and why risk the insulation breakdown in the motor? I won't use a lower voltage because I do not believe that I am unreasonably stressing the motor at 65V as the driver is controlling the motor current for me and any excess power is being dissipated in a fan-cooled heatsink - but I'm going to get faster di/dt hence higher peak initial torque this way, so better performance. Can I quantify this? No, but it costs me very little to do it. I'm still tweaking my new machine but I have every intention of sticking an oscilloscope across various bits of the power supply to see what's happening. I'm interested both in the main PSU ripple given that it's a conventional linear PSU, and what's happening across the motor windings under load, just to see what voltages do appear there in practice.

Good engineering is a compromise. Understanding the trade-offs from both a theoretical and practical perspective is useful if you are going to go outside the "just do it my way and it'll be OK" approach. A lot of forum members here do lack an electronics background and look for advice and help, which they often find. Unfortunately, blindly following a published rule of thumb is a bit like buying a kit of electronic bits - it will probably work but won't be optimum in all but a few cases.

In the OP's case, it sounds as if the PSU is at the source of the problem as all the other bits seem to work. Whether it's a paranoid PSU overload circuit which doesn't like the pulse load of four chopper stepper drivers, or is underspecified, or is faulty, is a bit moot but replacing it, even on a temporary basis, with something that is known good is one way to find out. I would probably try reducing motor current in all four motors as well, if appropriate current-set resistors are to hand, to see if that helps. That might also point to whether it's the PSU.

[John S]

I'm well aware of the benefits, but how often do the motors run fast enough and long enough to have the full voltage applied?
The only time you'd see problems is during prolonged time at high speed, which even on a router, I'd doubt you'd sustain for long enough. But it's worth bearing in mind, that you could easily destroy a stepper motor very quickly by pushing too far.

It's not about maximum speed but percentages of the same.
If your 40v system is running at 1/2 speed on acceleration it probably used 20 volts.
If an 80 volt system is running at half speed it gets 40v and so even in the short distance it can reach the designed acceleration faster.

What we also have to take into account this that the home hobby CNC market has bee around for quite a while now.
Anyone remember the fledgling CAD_CAM_DRO group on Yahoo. I quick look at a stored database tells me it started in December 2003 [ edit 1999 ]

In that time a lot has changed but the same information gets repeated, that's the way of the internet.
Marris was very popular on there and he stated a lot of things that have now moved on.
I remember him being very vocal about Leadshine pinching his designs, this for a basically one man band accusing a large corporation with over 300 just employed in R&D alone ?

Leadshine now have closed loop digital drives and have had they for years whereas Gecko never produced a digital drive, they are all analogue.

The Gecko's might go down well in America as it's a large market and there are a lot of loyal rednecks but by the time you get a Gecko drive over here with the £ to $ shuffle, the 19% import duty and the 20 % VAT you are paying thru the nose for outdated technology.

The outdated 542 drive from Leadshine is a far better drive and for more reliable but as i say even that is now outdated.

Another thing that has slowly impinged on the scene are the switched mode supplies.
It was stated in the early days that they were not as good as a decently designed and made torroid but because they have become more affordable and popular early advise is being ignored.

Fact is a switched mode power supply cannot handle back EMF from motors and the faster they run the more you need that facility.

But they are now being bundled with a set of drives and motors that may well match someones purse but it doesn't mean to say they are a good match machine wise.

Switched mode is fine for logic power supplies that supply 5v / 12v / 24v end of story.

Whilst drives and motors have improved no end with advanced R&D and materials the basics behind them hasn't

Always over spec everything if a drive is running at 50 % it will never get hot, it will never be placed in an overload position and so it will last.
Buy well designed drives that have large heat finned cases for just the previous reasons.

Steer clear of micro based units that for some reason the designed has deemed it will look better if it's the size of a postage stamp.

There are physical limitation in running four 7A rated tracks side by side to a motor, 10 thou spacing whilst looking neat does not meet that criteria.

Above all seer clear of the integral motor and drive units.
It's a fact of life that stepper motors want to run hot and drive want to run cool, so why would some twonk want to bolt them together. Or cram 4 drives onto the smallest possible heat sink that will hold them without one falling off the edge ??

[JAZZCNC]

so why would some twonk want to bolt them together.

TWONK.!! . . . That's word of the day for Me.!! . . . . My days been full of TWONKS . .

[magicniner]

TWONK.!! . . . That's word of the day for Me.!!

My day has been full of Knobsocks :D

[JAZZCNC]

My day has been full of Knobsocks :D

Ah that was Friday.!

[dachopper]

Provided you're remaining below the maximum voltage of the gecko drives, and allowing a reasonable safety margin, it should make no difference.

I can't remember, but are there any LEDs on the G540 to let you know any statuses?

I'd suggest temporarily disabling the chargepump input on the G540, and see if fault still occurs. It could be a noise issue that with the higher power, the G540 isn't seeing a good charge pump signal, so it is disabling all the drives. However if that was the case, I would expect problems with the step/dir signals aswell, however that probably wouldn't be noticeable if you're not actually working the machine to notice a position loss.

The Charge Pump was disabled when the issue began, I enabled it and the issue remained