setting current for no name stepper motor

Hello. i can't find the answer to my question via google search, even though i would think this would be a common DIY problem for trash builders. So i thought i ask at the source of diy 3d printers.

I am trying to fit a 1$ used stepper motor with no info to ender 3 oryginal arduino based controller.
But i have no idea what current can this stepper motor handle, let alone what it would ideally be. I didn't buy this motor for use as a motor though, I got it as a bearing holder with a shaft for idler gear for my mini ramps printer and this was just a spare one i had laying around, but i have to fix extruder on something else using creality controller board. And i don't have any other spares at the moment.

Motor technically works, spins right direction and doesn't get warm (controller is still adjusted for creality motor it came with), is of similar dimensions as oryginal creality motor , only dc resistance of the coils is different 1,1Ohm vs 2,6 on creality motor.
The only problem i having is that it doesn't have the strength to push trough the nozzle if it prints longer than few minutes (skipping). With small nozzles heat creap is basically blocking the printer when printing small details, but works ok-ish with bigger nozzles and fast printing big areas, when heat creep doesn't have time to expand the filement.
i can't use oryginal creality motor from broken plastic extruder because of permanently bonded gear and shaft itself being too short. New extruder have 1/3 smaller wheels so it technically should have more mechanical adventage over old one, but still lack some power.


So i was wondering how you exactly test unknown stepper motor for current handling, how to adjust for the most power without breaking the controller board? because i either don't know how to google for it, what key words to use, or it simply does not exist on internet
or should i not worry and just jolo with the driver adjustmen "by ear"

printer it goes to uses 24V power suply and i can bypas the creality stepper with a stepstick boardif i need to , i probably have some spares. i also have few arduino boards

if this topic is of a trash value i wouldn't mind it being deleted, if you can point me to a right direction i would be very thankfull

... gently rise the current, until the motor gets warm ... then reduce by some percents ... its OK, if it's only "luke-warm", but not too hot to touch

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Take a look on stepperonline or another stepper motor catalog and look for motors with the same size (including length) as your motor. Pick the one with the closest resistance and use the rated current of that one as a guide to the maximum current you should use. If the resistance does not match exactly, the rated current varies approximately with the inverse square root of the resistance. Taking your Crealty motor as an example, the rated current of your motor will be about sqrt(2.6/1.1) times the rated current of the Crealty motor, if they are both the same size.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

From the authopsy i can say it has 4 coils, in 2 paralell pairs , i could technically rewire it in series. then i would match most of 1,5A motors in those datasheets online. But i can't find anything of this dimentions with resistance that low.
Does that means it is wired for ~3A?
I have spare coil assembly from the motors i used as bearing blocks, and this motor was apart few times also so there is no fear in breaking it or anything, If anything i can always get another for 1 euro or dolar from local ebay, they still have a lot of them.

As for dimensional comparacy to creality 42-40 motor, this no name one is more 42-38 and has a bit less wire inside overall,

Pcb is routed for 6 wires, middle being center tap of a coil, and is not used curently, So just moving 2 ends of oposite coils to it would make for series wounded motor with split coil pins..

Still it would be nice to just benchmark the motor for current outtside the printer with some kind oft echnique or device and just get the end resoult. Oh well more experiments to run because there science to be done .

I think i made it work, but not without few surprizes.

1 Don't assume just because your controller board came out of oryginal ender 3 it is the 8 bit version.

Aparently it is the 4.2.2 variant with 32bit controller and 4988 drivers and by factory all motors run on 50% rated power. or it came out from different printer before it ended up in that ender i took apart

2 Don't asume increasing current is a cure for all problems

My stepper motor low resistance really didn't want to play with 4988 drivers and motor was skipping while still being stone cold and driver was already getting pretty toasty so i rewired motor from parallel to series.
i did find very very similar motor on one of the catalogue sites 42x39 2A 1.1ohm, but yeah stepper driver can only do 2A with adequate coling and staying under 1A is kind of what it do best at.

3 learn ohm law already for the love of god

Yes i made a slight miscalculation without even thinking. 1 ohm resoulting from 2 parallel coils of 2 ohm each and in series it is 4 not 2 :]


Anyway it does kind of work now
Oryginal extruder stepper was working at a current of 0,6A (0,723V vref), replacement is running at 0,8A (0,96V vref) and driver is keeping in acceptable temperature range, motor is getting warm ~40 degree but at least it pusthes trough polistyren filement trough 0.2mm nozzle without skipping, which was never the case for oryginal motor in oryginal extruder plus new extruder has better "resolution" 141 vs 92 (micro)steps per mm
But also i had to make some more room between motor gear and extruder arm because it was rubbing. cheap chinese quality products

What is funny though, all remaining motors are labeled as 42-34 but each of them is different, so maybe even the controller wasn't oryginally from this printer

anyway thanks for help, i still need to tune slicer for printer that overextrudes rather than underextrudes but that is easy compared to fighting with unknown

Edited 1 time(s). Last edit at 10/22/2023 11:36AM by kokodin.