eBay TB6560 Stepper Motor Driver Boards

[Tenson]

I've got one of these boards running my CNC3040.

I'm curious because it is running on 24V and gets nothing like hot, but it sounds like most here find they get rather warm. I think I could even run mine without the fan!

It also doesn't go very fast - I can get a reliable 1200mm/min from it. I did run it at 1900mm/min but found it occasionally skipped steps.

Is this normal? Have I got something set-up wrong?

The stepper motor shows about 2 Ohms across each of the connections to the board. I don't know if this means it is in parallel or series as the connections at the motor end are covered by heat-shrink.

The big resistors near the output (I assume current sense) are 0.4 Ohms.

Measuring across one of these I get 200mV on idle and 280mV at full speed. That is about 0.7A, so does this means the motor is drawing 1.4A because it is each phase? You can see the measurements below.

This is at idle. The time base is 50us/Div


This is at full speed, but please note the time base is now 10ms/Div

[Jonathan]

On the 'idle' graph I make it 12% duty cycle. So since current is 0.5A peak, that makes it:
0.5*0.12=60mA average
0.5*0.12^0.5=173mA RMS.

Can't really find anything useful from the other graph - it just shows how at that speed the current is limited by the inductance of the motor. I guess we could calculate the motor inductance ... T=2.07ms, change in current is 700mA, so dI/dt=700/2.07=1.449A/s (linear approximation).. applied voltage is 24V minus a bit for losses so call it 23V, so the inductance L=24/1.449=15.9mH (roughly, oversimplifying a bit there). That's either a pathetic motor or I've done something wrong! Unless it's wired in bipolar series, that would be reasonable since the same motor in bipolar parallel would be about 3mH which is not bad.

Either way these numbers seem a bit fishy.. please could you link to the motors you are using (datasheet?) and confirm that the resistor you're measuring across is definately 0.4ohms, not two 0.4 ohm resistors in parallel or something like that.

The simple answer is just increase the current and so long as the motors don't get too hot, i.e. above 80°C on the case, it's fine.