G540 - 4 motor connection problem

[paulus.v]

4x3.5A =14A and you have a 12.5A PSU. Am I missing something?

For a switching power supply you need to be at least 18A.

(edit: I may be wrong here but Leadshine, among others, recommend adding 1/3 more to the rated motor current when using a switching PSU; 4*3.5*4/3=18.66A).

For a linear one you will be fine with 10A.

(edit: a bipolar parallel steppper requires a maximum of 2/3 of the rated amps/phase; 4*3.5*2/3=9.33A).

I would go with a toroidal PSU as Clive said.

[m_c]

4x3.5A =14A and you have a 12.5A PSU. Am I missing something?

In short, yes.

And before I give a Jazz style response about people commenting on things they don't understand, go and read the gecko drive stepper motor basics guide, as they explain quite well all about power supply requirements for stepper drives.

[paulus.v]

In short, yes.

And before I give a Jazz style response about people commenting on things they don't understand, go and read the gecko drive stepper motor basics guide, as they explain quite well all about power supply requirements for stepper drives.

Sorry for that, I edited my post to better explain my point of view.

[JAZZCNC]

Jazz style response not sure I like sound of that. . .Lol

Anyway I think the answer is obvious but all of you have failed to RTFM.!!! . . . . . With 3.5A motor current set resistor isn't required.

However I'd still throw that switched mode supply away and build one.!. . . . As well not RTFM you didn't RTFF . . . Because you'd seen said many times NEVER BUY KIT.!! . .

EDIT: Just seen this.!!!!!!!

Is there anything I can do to try make it work at 48 / 50 volts

You don't want 50v or even 48V because the Geckos are only rated 50Vdc so doesn't leave big enoigh safety margin. You will KILL the drives quickly if run at this voltage.
44Vdc is about high as would run these drives from safety point of view. The 4-5v differnence will hardly be noticable in performance terms but the Smell of magic smoke will be.!!

If you want higher performance then sell the drives and use 80Vdc Digital drives with 70Vdc and then you'll see difference.! . . .Big one.!!

Gecko's are living on there reputation from years ago but sadly today they are behind in the Digital race.

[Neale]

Anyway I think the answer is obvious but all of you have failed to RTFM.!!! . . . . .

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.

[JAZZCNC]

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.

Yes has do lots of other Manufactures who use this type of current limiting but just because resistor is provided doesn't mean you have to use the bloody thing does it.? . . . Only use if required and this motor doesn't require resistor.

Edit: By the way I don't think this is the problem anyway. Personally I'm guessing the PSU is faulty.

[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.!!

[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.

[dachopper]

Jazz style response not sure I like sound of that. . .Lol

Anyway I think the answer is obvious but all of you have failed to RTFM.!!! . . . . . With 3.5A motor current set resistor isn't required.

However I'd still throw that switched mode supply away and build one.!. . . . As well not RTFM you didn't RTFF . . . Because you'd seen said many times NEVER BUY KIT.!! . .

EDIT: Just seen this.!!!!!!!



You don't want 50v or even 48V because the Geckos are only rated 50Vdc so doesn't leave big enoigh safety margin. You will KILL the drives quickly if run at this voltage.
44Vdc is about high as would run these drives from safety point of view. The 4-5v differnence will hardly be noticable in performance terms but the Smell of magic smoke will be.!!

If you want higher performance then sell the drives and use 80Vdc Digital drives with 70Vdc and then you'll see difference.! . . .Big one.!!

Gecko's are living on there reputation from years ago but sadly today they are behind in the Digital race.

I have read the manual, the drive IS DESIGNED to be operated at 50Volts, and already has a 10 volt buffer - it works up to 60 Volts.

I have measures the input voltage and current on the switch mode power and it is rock stable at 48/50/46/42 volts, whatever I set with the resistor

The total system current draw is only around 2.6 to 3.3 Amps - when I hooked it up to my 30 Volt power supply