[KOC62]

Ok thanks, and about you said me that there is a voltage to start movement and other higher when running fast, then, the 2.3V of the label what of both is?
Because perhaps is better to use another voltage to calculate resistance instead the labeled voltage of motors...

Thanks!
David

The basic idea is to provide a constant current source for the motor coils when you want the motor to turn on. Your motor current rating per phase should not be exceeded.
Your controller is just a switch which places the power supply voltage across the motor coils. Hence, you have no control of the coil current. To control the coil current you either fix the power supply voltage until the desired current rating is reached, or you use a fixed resistor to limit the current until the designed phase current is reached.
But if different motors have different current ratings you would then need different power supply voltage settings to keep the coil current controlled, or different resistors for a given power supply voltage. Your calculations should work to get the right resistance. You could also use an ammeter and an adjustable power resistor until you reach the desired current.

The next issue you will find is that as the RPM goes up the fast switching of the coils causes too little time for the current to reach the full value and your torque decreases and possibly stall your motor. Raising the power supply voltage will help higher RPM but also causes too much current at lower RPM. That is why I don't recommend your controllers. You should get a controller that can, say use 36VDC, and still keep the coil current constant for all RPM (until 36VDC becomes too low for the much higher RPM).

[john-100]

if the data for the motor only specifies the coil voltage and current you can work out what the coil resistance is
(or measure it with a 4-wire kelvin resistance meter used to measure low values of resistance so
the resistance of the test leads does not add to the coils resistance causing large errors)

with a 3.6v @ 1.2a coil the resistance must be 3.6/1.2 = 3 ohms
so far so good until the driver switches the current to through the other half of the coil
when the inductance rears its head and limits the initial current through the coil -
the higher the inductance the longer it takes to reach the current limited just by the resistance


one solution for simple stepper drivers like the K179 is to use a supply voltage several times the motors rated voltage and drop the excess with a resistor

with a high enough supply voltage the current limiting action of the resistor will dominate

if you used a 36V supply (the maximum for the K179)
for the coil voltage to remain as 3.6V the volt drop across the resistor will need to be 36-3.6 = 32.4V !
the power dissipated by the resistor will be 32.4 x 1.2 = 38.88 W !!!!!

this is why modern designs use switch mode current control that use the voltdrop across a
fractional ohm resistor to measure the current and switch the current on and off at high frequency and varying the on to off time to control the current


John

[davurpi]

Wow! ok, then i have to add something to provide constant current source. I just seen here that this person added a controller to do it. Perhaps i have to do the same circuit and will be good for my motors (adapting to my voltage)?
http://www.thebackshed.com/cnc/images/RouterVer1.gif
Or here.
It use K142C, Optoisolators, and resistances.

At other hand there are people that use Arduino stepper motors controllers like it:Click here
David

[KOC62]

Yes, the link circuit does use a constant current source, one for each driver board, along with input opto-isolators. You adjust the current as per motor phase current requirement.

[davurpi]

Yes, the link circuit does use a constant current source, one for each driver board, along with input opto-isolators. You adjust the current as per motor phase current requirement.

In here:
TheBackShed.com - DIY CNC
I seen that use the K142 to get constant current, but i don't found this circuit to buy. Any alternative?

Thank you!
David

[john-100]

a version of the constant current supply kit , if I remember correctly was published in the Austrailian Silicon Chip magazine (about 2002)

a web search found this kit -
Oatley Electronics

this is one version of the circuit -
Attachment 331824

John

PS

you need to subscribe to read it all but this will give you some more information

Silicon Chip Online - Constant High-Current Source

[KOC62]

You buy them here; Oatley Electronics
You need one for each motor.

I would prefer this alternative controller which includes the constant current source; RULMS3:LiniStepper Driver kit NEW V3! massmind
James Newton on the CNCForum runs the website/store. You can discuss with him what is a better deal than the one you were looking to buy.
You can also buy the blank board and buy the parts elsewhere if it is cheaper for you.