Thread: Selecting the right driver
01-09-2009 #11Visit Us: www.zappautomation.com
Electronic devices should never be run at the absolute maximum voltage quoted. Depending on the circuit this might either be the protective trip voltage or the voltage at which damage can occur due to internal breakdown of the device (which then results in high peak currents frying the device unless there is an external curent limit). In this instance its the protective trip. If you were to feed the driver with 50v there is the possibility that back-EMF from the motor when pushing energy back into the power supply (on the overrun/braking cycle) would cause the power supply voltage to rise and trip which would be inconvenient at best and catastrophic to the workpiece at worst! If your power supply is really good, with a regulation of better than 2% then you might get away with running it at 48v or so. But I'd stay below 45v on these drivers.
From the motor torque curves on Gary's site you can see that at 500steps/sec (150rpm) the torque is already down at 2Nm. Below 150rpm the torque will tend towards the holding torque but the relationship isn't linear. You will notice from these torque curves that the curve for 60v/4.3A is flatter/more linear than that for 40v/4.3A but the difference isnt really apparent below 2500steps/sec (750rpm). In other words if you are never going above 750rpm on the motor then 40v will perform as well as 60v. If you have only got 40v drivers then this information can be used to factor any gearing to keep the motor in the sweet spot.
The stepper driver is a constant current device. whatever the motor winding resistance the driver will never allow more than the rated current through the winding. For a driver set at 4.2A this is the maximum it will allow. The voltage rating of a stepper motor is irrelevant, it is merely the steady state voltage across the windings at the rated current due to the winding resistance. With a chopper or PWM current controller it has no meaning as the driver will switch the drive voltage on and off at high frequency to maintain the average current at the set value. Since it is being switched the winding inductance has a part to play as this controls the rate at which the current can change in the winding. This is where the higher voltage comes into play as a higher voltage can 'force' a higher current in a shorter time therefore maintaining the torque at higher speeds.
I'm guessing the meaning of your last question... refering to the data sheet for the motor again, when wired bipolar parallel the first phase has A and /C connected together and /A and C connected together. When that phase is energised, 4.2A of current flows from the driver along the connecting wire to the A + /C junction where it splits - 2.1A into each winding - and recombines at the /A + C junction, where 4.2A of current flows back to the driver. Therefore every one of the 4 wires connecting the driver to the motor carries 4.2A and needs to be rated for that.
Hope this helps...
Hi Irving, thanks for taking the time to go into details I appreciate it.
Now I don’t have one of the motors on the data sheet to hand, but I’m confident that this will be the same…
On the motors I have got here in front of me ( two different manufacturers ) the wire's coming from the motors is only 16/0.02, this motor is 4.2a in bipolar parallel setup.
I’ve looked at a few different websites selling the 16/0.02 equipment wire and they all seem to say that 16/0.02 wire is rated at 3a, if that is true then the wire on these motors is under rated for what the motor could potentially be doing ?.Me
Ahhh yes 2 windings ! Sorry !
Ok but if the cables connecting to the driver are carrying 4.2a, is that devided by 4 wires if the motor is in a bipolar parallel operation ?
Basicly Irving i just want to know what the correct rating of the wire should be that i use to connect the drivers to each motor/XLR. Can i not just use the same rated wire as whats on the motors or is it better to step down as you go?.Me
Thanks mate !.Me
I've just purchased the stepper noted in #8 [ Nema23 3Nm motor (PDF), the document said: Bipolar Parallel 2.73v, 4.2a, 3Nm], connected to my existing driver and hey ho smoke all around.
Iím very interested to know, did you decide on a driver as I clearly need to upgrade what I had ?
i have nema 23 3nm motors, on pm542 drivers from zapp driving them with 40v power supply , they work really well together , 4.2 amps parallel , tried to run those motors at 2.5 amps 24v, before i upgraded .
waste of time and money, to slow and motors stalling. now have plenty speed and torque .......... maybe have to upgrade machine now. at £35 you cant go wrong
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