I am using a 24V, 5amp bipolar stepper motor for a project however I would like to control its speed using a motor shield. The motor shields I have found online only supports 12V, can I power my servo motor externally and still use this board?I don't fully understand how a motor shield works, from what I've read it seems like it only varies the current sent to the motor so I am wondering if I can power the servo externally but connect it to the motor shield for current input, is that a thing?
Or should I find a motor shield which supports higher voltage?
Are you certain of those figures? That would be a high power motor, and for 5 ampere coil current, you would need an industrial stepping motor driver like this one.
Post a link to the data sheet or the motor product page.
Have a look at this discussion. There are some more discussions about the faulty design of the Chinese driver you are aiming at. If your budget allows, go for something more professional which can really and reliably deliver your required 5A.
Having said this, if you are really going for a 5A stepper motor (and are able to run it at that current - see remarks below), then have a stronger driver which at least can be operated 10-20% higher (chip-wise).
It seems that your project requires high torque (indication: your chosen NEMA34 motor). Have a look into the datasheet of the stepper - then look at the diagram with the torque/speed relationship.
Torque is proportional to the winding current and the number of turns of wire. To increase torque by 20%, increase the current by about 20%. To decrease the torque by 50%, reduce the current by 50%. But - when coils turn, inductance comes into the play. Inductance reduces a stepper motor’s high speed torque performance. Inductance is the reason all motors eventually lose torque at higher speeds. Each stepper motor winding has a certain value of inductance and resistance which determine the resulting current in the windings (=>torque).
At low speed the inductance is no big issue and a 24V power supply might be able to drive the 5A you are looking for and thus resulting in your required torque. But at higher speeds the inductance rises and thus the current and torque decline as long as you stay with the 24V. That's why high torque steppers are driven with much higher voltage if you need high torque at high speed.
So: if you need high torque at high speed - you have to go for much higher voltage than 24V (48V, 60V or higher - if your driver can be operated at that voltage). If not, 24V might work at low speed.
Make sure that your driver can be controlled on TTL (=5V, Arduino) level. Most of them comply, but you never know
If your operational environment requires that the stepper motor is working for longer periods of time close to the 5A, have a look at the temperature (both the motor and the driver) and consider to add an adequate fan.
No, not really. Get an industrial drive, not a repackaged single-chip driver. You need a driver with
MOSFETs with on-resistance of < 0.05 ohms ideally. The TB6600 will get hotter that the motor, it
has 0.5 ohm on-resistance (compared to motor's 1.0 ohm) and much less metal to spread the heat.
Gecko drive perhaps?
Or DRV8711 BoosterPack?
By the way that is not a 24V motor, its a 5A, 1ohm motor - the voltage is not a parameter to
a low-impedance bipolar motor. Your link suggests a power supply voltage of 24 to 60V, for instance
(higher = more performance).
in general I agree. But we don't know how the operation looks like.
It much depends on the speed of the axis that shall be motorized and how the ratio is between run and stop.
In specific cases the 24V/5A power supply with a suitable driver (not the crap Chinese one) might be sufficient.
But as another driver has to be bought anyway - and I fully support your comments on the MOSFET approach - the bigger power supply doesn't add that much to the cost and will guarantee a painless operation at higher speeds.
I've spent a couple of days to understand how to boost stepper motor shields.
Some higher powered driver chips do exist but the absolute limit seems to be around two 2.5A full bridge drivers - 4A peak - to power one single stepper.
Considering the microstepping control and overcurrent protection of those chips which is regulated over Isense resistors in the ground return path of the low side of each bridge, it is no simple task to boost the maximum current of the system by just driving another heavier external bridge.
It can be done though, theoretically, by taking into account an adapted current limit detection circuit on the external bridge and a suitable driving mechanism using the bridge outputs of the controller chip.
Also, in order to respect the regulation loop for the internal PWM and DAC comparators that organize the microstepping, you MUST take into account the extra delays added to the loop by the external power bridge. Could be tricky.
In any case, you will have to lower the maximum switching frequency of the controller.
If that's not enough to take care off, you will be in big trouble still if the controller driver starts to use these mixed modes in the PWM/DAC controller where it drives only the high side or the low side of the bridge. You are not able to easily detect and implement these modes externally because on most controllers these pins are not available.
Now, with all this in mind, you will definitely blow a couple of dozens of chips and bridges before you will be in the neighbourhood of a good stable and reproducable solution. In any case you most probably will need to disable mixed driving modes.
It might be wiser to leave this effort to the new chip designers working for very rich companies and buy a 75$ industrial controller that can handle 6A steppers with many extra's on top of that.
The company that builds a single chip controller in SMT that can handle 6 or 8 amps with extra features will be in a good shape. But do they want to do that? It will surely decimate a part of the existing multi billion dollar turnover industrial control market...
dimidevos:
The company that builds a single chip controller in SMT that can handle 6 or 8 amps with extra features will be in a good shape.
Can't be done as a single chip. That's why it isn't. Discete power MOSFETs have metal on both sides of the
chip to carry the current (which flows vertically), and the substrate is the drain. So on a single chip you can
only have high power MOSFETs which share a common drain, not a full H-bridge. The typical DMOS devices
in an integrated H-bridge must use lateral current flow, and the best I've seen are around 200milliohm on-resistance, two orders of magnitude greater than discrete MOSFETs can achieve.
You sometimes see packages with multiple chips, such as the VNH3SP30, which is one way round the
issue.
ST Micro has the POWERSTEP01TR combined chip package for that reason. And CHEAP with that! They have separate MOSFET H-Bridge chips of 15mOhms in there, separated from the great L6480 controler core.
That thing handles 10 amps without extra heatsinking but needs an SPI interface (no sweat with the Arduino SPI library I guess).
I'm playing around now with a L6480 and two H-bridges from Fairchild. Wondering if the L6480 provides enough dynamical drive current to parallel those bridges. That would up the current handling from 8A to 16A or 24A...
Guess I will have to build it first and see if everything survives...
The controller handles up to 85V motor voltage so with he right H-Bridges it would handle the kW region...
Now for safety and European compliance to the LVD (Low Voltage Directive) I would never use it higher than 60V.
More than enough for any decent CNC work at a fraction of industrial controller cost.
