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Issue 249 Arduino Controller Indexer

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john fletcher 122/05/2022 11:12:33
794 forum posts

Several years ago as I'm sure other readers did, I followed the article on page 64 of issue 249 of MEW and made myself a controller. Recently a friend has asked me to buy the component parts for him as he hasn't a computer and he would also like to make a controller. I can find NEMA 23 steppers motors OK, but when I scroll down and read its specifications I see they have an input voltage of between 24/48. Following the article on page 66 I bought a 12 volt 5 amp power supply and it all works very well and has done for 5 years. I'm confused will 24/48 volt stepper be OK. Will a reader explain to me. John

John Haine22/05/2022 12:04:54
4673 forum posts
273 photos

I assume that the motors you mention don't have an integrated driver? Could you provide a link to the details?

Stepper mjotors as such don't really have a "working voltage". Modern stepper drivers actually supply a regulated constant current to the stepper using a switched-mode technique where they apply the supply voltage direct to the stepper windings for a short period then switch it off and let the current flow through a diode, with an on/off ratio set to get the required current. The currents in the windings are then modulated to get the required stepping/microstepping. If you could look at the voltage on the actual winding it would vary between the supply voltage when "on" and zero when "off" though with a very spiky waveform. The average might be only a few volts, but the supply could be much greater. The higher the supply voltage the better the motor works, provided the current doesn't get too big and cause it to overheat.

The 24/48V (assuming the motors don't have an integrated driver) is therefore fairly meaningless for a normal stepper motor, but it would be a normal sort of supply voltage range for a modern stepper driver. If your stepper works on 12V that's probably fine for a dividing head which shouldn't need much torque or high speed. I run my Ward divider from 20V, or the same mechanics+stepper from 24V for rotary/linear feed on my big mill; and about 40V using it on the CNC mill.

I hope this helps.

Speedy Builder522/05/2022 13:01:06
2613 forum posts
212 photos

Probably doesn't help, but I run my NEMA 23 off of a 36volt 5 amp PSU.

power feed schematic.jpg

SillyOldDuffer22/05/2022 14:39:33
Moderator
8690 forum posts
1967 photos

Wot John said. The motors are current driven, so the volts aren't critical. However, higher voltages allow the motor to step faster and with more torque because the rise time of the pulses is reduced, packing more energy into the time available. Lower voltages clip what should be a perfect square wave and stop the motor receiving maximum power from each pulse.

As John says, a divider isn't demanding in terms of speed or torque and 12V should be fine for that. (It's what I used on my project, though with hindsight, a 24, 36 or 48V supply would have let me turn the divider a shade faster. Boy racer motive though - nippier performance is nice rather than essential.)

Getting the power supply right only becomes fussy when the motor must run fast with a significant load and it's important not to miss steps. Then it's worth making sure the power supply has the volts and amp timings necessary for peak performance.

The ideal stepper power supply is a simple one. A bridge rectifier with a transformer and capacitor big enough to pulse current at full whack, without any extra complications. In fact, stabilised power supplies aren't good for stepper applications because the motor's spiky pulse load forces the stabiliser into wasteful electronic gymnastics to keep the volts steady, when the motor wants high volts at kick-off and then is only interested in amps

Despite that, I always use stabilised switch mode power supplies on stepper projects because they're cheaper and easier to buy than plain ones.

Dave

duncan webster22/05/2022 21:07:46
3984 forum posts
65 photos

Is it that the quoted voltage is what you need to pass the current? The dual voltage might reflect unipolar or bipolar configuration

John Haine22/05/2022 22:00:49
4673 forum posts
273 photos

All decent modern motors will be bipolar since bipolar drives are now ubiquitous.

John Haine23/05/2022 07:10:59
4673 forum posts
273 photos
Posted by duncan webster on 22/05/2022 21:07:46:

Is it that the quoted voltage is what you need to pass the current? The dual voltage might reflect unipolar or bipolar configuration

Well as an example the motor data sheet I have on my desk (admittedly a NEMA14 type) gives a winding resistance of 6.8 ohms/phase and max current 0.8 A. At 12 V the winding current would be 1.8A, double that at 24.

Provided that this is just a stepper motor the OP is talking about and doesn't have an integrated driver, the quoted voltages are just spurious information.

Joseph Noci 123/05/2022 08:32:25
1081 forum posts
1309 photos
Posted by duncan webster on 22/05/2022 21:07:46:

Is it that the quoted voltage is what you need to pass the current?

This question is important...The steppers all (except the OP) are referring to are 'run off the mill' , ie, low voltage 'high' current. A motor plate rating of say 3V / 1,5A means apply 3volts to get 1.5amps flowing. John indicates a voltage of 24 or 48 volts ( why the two? - probably because the motors can be wired series or parallel - 4 or 8 wire motor-)

However, the issue is the 24/48volts - if that IS the namplate voltage for winding rated current, then the stepper controller will need to have a much higher input voltage to ensure di/dt constraints are met. One normally applies anywhere from 12v to 60v to the stepper driver to drive 'normal' 3v or 5v type steppers. The same relationship applies if the stepper is a 24v or whatever motor. A 24v winding will also demand lower current ( field strength is related to number of turns in the winding and teh current thru said winding), but the resistance is greater and also inductance, so a higher voltage is needed to get the current flowing fast...

Running such a motor from a 24v stepper driver will lead to tears...

As usual, lots of speculation with insufficient data input -

post the namplate specs of the motor or a link to its spec sheet...volts, amps, inductance...

Howi23/05/2022 09:18:43
avatar
359 forum posts
19 photos

the basic NEMA stepper motors do not normally come with integrated drivers, 12v should work fine so long as the load is not too great. When I made my Ward controller, I used an old laptop power supply at 19.5v and 3.5 amps and is more than sufficient to drive the NEMA 23 stepper. The more demanding your application on the stepper the higher you need to go on the stepper voltage, 24v is typical if windings in parallel but NOT critical.

john fletcher 123/05/2022 09:55:34
794 forum posts

Many thanks chaps for all the guidance. Don't go away, as I think my friend rotary table has a ratio of 60 and the data Sketch) is for 90 so I could be back. John

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