Matching driver and PSu

[anedic]

I am new here, and sorry for less knowledge about CNC electronics.
I recently bought 4 Nema23 step motors 0.9deg, 2.8A/phase, inductance 5.6mH/phase, nominal voltage 3.2V/phase, resistance 1.13 Ohm/phase, holding torque 18kgcm, detent torque 680gcm.
Using formula that max voltage for motor is 32*sqrt (L), L is inductance in mH, I found that maximal voltage for stepper is around 76 V. Safe area would be about 70V.
I chose driver Leadshire driver DM856, with voltage range to 80V.
I chose PSU DC 70V 14.3A. (2/3*4*2.8=7,6 A).
Could I use this driver and PSU for those motors?
Besides, in many specifications I found that the stepper driver JK1545 and PSU of 36V is enough.
Should I use JK1545 with 36V (or 48V) PSU, or DM856 and 70V PSU? What is better to me?
I am afraid that I am burn down my steppers with 70V PSU.

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[ger21]

The 70V power supply will give you double the speed of the 36V supply.

The 70V won't hurt the steppers at all.

[anedic]

Ok.
And what about torque at 70V and 36 V?

[john-100]

the torque depends on the current set by the stepper driver

the time taken for the current reach the set value depends on the motor coils inductance and the power supply voltage

the higher the inductance the longer the time taken to build up to the set current
but the higher the voltage the shorter the time taken

so your looking for a low inductance and a high supply voltage to step the motor a high speed

(the faster you want to step, the shorter the time between steps you have for the current to build up !
eventually your going to reach an upper limit due to motor heating and a limit in the insulation)



Geckodrive.com
give an example for the G540 to estimate the required supply voltage as

32 times the square root of the motors inductance in mH

for a 2mH motor
32 x root 2 = 45V

ideally for your 5.6mH motor

32 x 2.366 = 75.7V so you need drivers that can work from an 80v supply

DM856 and 70V PSU is the closest of the options your looking at

note-
depending on which manufactures data sheet you look at
stepper motors run at 70 to 80 degrees C
too hot to touch for very long !!

if the motor is bolted to a metal machine it will act as a heat sink to help to cool the motor
also very many stepper driver will reduce the motor current when idle
which helps to reduce the motors temperature


John

[anedic]

John,
Thanks, I am match clear to this subject.
You are right about insulation resistance and temperature rise. However, dielectric strength is 500 V DC in 1 minute or 100Ohm, but max temperature rise is 80deg, which can easily be reached on that voltage. And yes, the motor is on aluminium plate 6mm thin.
In the other hand, I think about resonance and motor vibrations on 70V are much higher and there is possibility that due to vibrations work on that machine will be very hard.
So, I am thinking of using 48V to 60V PSU, as safe area. I think on those voltages there are less vibrations and motor is cooler. Motor will be slower and have a less torque, but it will be enough.
I have 4 oh those motors. In your opinion what is the best power source in this case (48 or 60 V) and which amperage?
Alex

[john-100]

the DM856 driver has built in anti resonance and if you set the micro stepping to around 8 to 10 micro steps should be OK

depending on the chopping frequency of the current control circuit & the speed you are stepping the motor you will hear audible tones from the motor
(that have nothing to do with resonance)

john

[anedic]

Ok. Thanks John.
One more question. Regards that Leadshine DM856 has optoisolated inputs, which MACH3 breakout board is best solution to me?
I know that BOB`s with 74HC245 are not good solution because they have also optoisolated inputs.
Regards,
Alex

[john-100]

which breakout boards have you looked at ?

this is the first result searching ebay
https://www.ebay.co.uk/itm/5-Axis-MA...-/121924104910



this looks like a cut down version of the TX14175 breakout board

it only has 6 opto isolators for the 5 inputs and the PMW to analogue 10V converter

the one possible catch is the power supply for the PWM to analogue circuit also powers the LED's in opto-isolators for the 5 inputs !!
and will make the limit switches live if the analogue 0 to 10V control output is connected to live terminals on a speed control board

so it can not be connected to a speed control board the has the speed control potentiometer connected to the mains like the F250 board in my mini lathe

John

see posts 17 & 22 for details of the ebay BOB & TX14175 circuits /schematics

http://www.cnczone.com/forums/gecko-...ml#post2151930

[anedic]

What about PDMX-126 or Mk3/4 controller? What is, in you opinion better one?

[john-100]

The Mk3/4 controller is a motion controller that runs under the control its own dedicated software so its not a breakout board

the PDMX-126 is a breakout board that has its own on board power supply and charge pump circuit to detect a 10kH signal sent by a working PC to prevent erratic motion at switch on

the PDMX-126 can either be connected to two PC printer ports or a smooth stepper motion controller
you will also need mach 3 (or 4 ) or other control software

John

[A_Camera]

So, I am thinking of using 48V to 60V PSU, as safe area. I think on those voltages there are less vibrations and motor is cooler. Motor will be slower and have a less torque, but it will be enough.
I have 4 oh those motors. In your opinion what is the best power source in this case (48 or 60 V) and which amperage?
Alex

Chose an analogue PSU if you can. It is also pretty simple to build one, but if you intend to buy one it is still better than a switching supply. It is a bit more expensive but you'd not regret the use of it.

Regarding the current, the math is simple. 4 x motor current + ~10 - 20% is a good rule. That way you don't need to worry about torque. So, in your case 4 * 2.8 = 11.2A so don't go for anything weaker than 12-14A.

For voltage, as high as possible, depending on the driver and the PSU. Don't worry about heat, that's not a big issue. Also, heat depends not only on the voltage and the current, but also on the driver. Some drivers cause more motor heat than others, but heat is really not a big issue.