Thread: PWM motor controller

Originally Posted by RustyArc

In my case, "a bit higher" would be more like 30V, but that would be with a current-limiting driver, which that one doesn't appear to be.

Yep, with current limiting the motor won't actually 'see' a constant 30V, but it allows a much faster initial rise time, improving torque.
Even without current limiting, you can apply over 5V, but usually not much higher without heat problems.

Originally Posted by Bob Willson

I'm sorry, I don't understand. Is that a compliment or an insult?

It was just stirring - I guess a compliment... that's why I put in the smilie....

Anyway, Rusty made an important point: this driver does NOT have a current limiting facility, so you will have to measure the current with the motor running as you increace the voltage.
The 5V bit has nothing to do with the motor, it is the controller power supply and must NOT be over 5V. I used an old phone charger to provide that voltage. The motor power supply is separate and connected at the other end of the little board, right next to the motor connections. I suggest you try with 12V first WITH A METER connected and see what the current draw is. If it is less that 2A, (if higher, immediately disconnect and try a lower voltage) increase it until it is just below. That will be the most power (torque and speed) you can get out of your stepper motor with that controller. You may find it's enough. If not, then things get a little more complicated, as I don't know of any manual controllers with larger current and current control. The bigger ones all expect to be connected to a pulse and direction control system.

Well the motor I have is labeled XY57STH56-2804B
I know it is a 3 amp motor, Nema 23 and has a double ended shaft.
I believe the last number of 2804B breaks down as follows.
28 = distance from rear of motor to front of shaft in inches (2.8")
04 = number of wires (4)
B = double ended shaft.

Aha, I just found a site that has a description of these motors

So
Voltage = 2.5
Current per phase = 2.8
Resistance per phase 0.9 Ohms
Inductance 2.5 milli Henrys
Holding torque 12.6Kg-cm

Originally Posted by Bob Willson

Well the motor I have is labeled XY57STH56-2804B
I know it is a 3 amp motor, Nema 23 and has a double ended shaft.
I believe the last number of 2804B breaks down as follows.
28 = distance from rear of motor to front of shaft in inches (2.8")
04 = number of wires (4)
B = double ended shaft.

Aha, I just found a site that has a description of these motors

So
Voltage = 2.5
Current per phase = 2.8
Resistance per phase 0.9 Ohms
Inductance 2.5 milli Henrys
Holding torque 12.6Kg-cm

That helps. So, since this is a motor intended for 2.5V, it won't work on the 2A driver, even if you apply a 2.5V motor supply. Not without current limiting, at least, since 2.5V into 0.9 ohms is 2.8A. A 1.8V motor supply would work, but with drastically reduced torque.

Sounds like a nice gutsy little motor, (for a stepper). For a curtain opener/closer, I think that a DC motor would be more suitable, with a pair of microswitches for position/limit feedback.

For other purposes, you might find a suitable driver for 3A/2.5V on eBay, since Nema 23 motors are reasonably common, but not as easy to find as a 5V 2A one.
(A higher voltage driver, current-limited at 2.8A, would do it too.) Good luck in your hunt. A couple of years ago I could have made it for you, but my eyes are beyond that lately.

Thanks for that hermit.
Incidentally, a 2.5 volt stepper motor can take up to about 80 volts. I think the general rule is the stated voltage * 40 or thereabouts. My CNC table uses 70 volts unregulated for the steppers.

Originally Posted by Bob Willson

Thanks for that hermit.
Incidentally, a 2.5 volt stepper motor can take up to about 80 volts. I think the general rule is the stated voltage * 40 or thereabouts. My CNC table uses 70 volts unregulated for the steppers.

Yep, the actual voltage is irrelevant if the current is controlled. Without current limiting, however, your 2.8A motor would draw 77.8A on a 70V supply. Bang!

As another famous Queenslander is oft quoted as saying ... please explain.

Originally Posted by Bob Willson

As another famous Queenslander is oft quoted as saying ... please explain.

I'll try - the voltage means very little, except that with no current limiting, the current will rise to match the voltage following the I=V/R rule, where I is current in amps, V is voltage in volts and R is the effective resistance in ohms.

When there is current limiting, regardless of the applied voltage, the voltage that the coil sees is I x R, where I is the current limit. ie. With 70V applied into an 0.9 ohm coil, with 2.8A current limiting the motor sees 2.8 x 0.9 = 2.52 (volts), it's rated voltage.

I don't think I've explained it real well, but I hope you followed.
(Thinking about dinner. Off to eat it now.)

Zoom zoom zoom

My Head

Originally Posted by Bob Willson

Zoom zoom zoom

My Head

Yeah, it's a bit like that.

Put a bit more simply, (now that I've eaten and thought about it some more), in effect the current limiter acts just like a voltage regulator, but adjusts the voltage to allow a pre-defined maximum current to flow by monitoring current, whereas a voltage regulator monitors the output voltage itself.

Hi Bob, Hermit

The easy way to visualise it is to think of a water hose, with voltage as water pressure and current as analogous to flow rate.

So a constant voltage supply is similar to constant pressure, irrespective of flow

And a constant current is constant flow irrespective of pressure.

Stepper motor supplies often use constant current, the higher supply voltage allows for faster switching times and more torque at higher step rates than a lower voltage supply.

Regards
Ray

Originally Posted by RayG

Hi Bob, Hermit

The easy way to visualise it is to think of a water hose, with voltage as water pressure and current as analogous to flow rate.

So a constant voltage supply is similar to constant pressure, irrespective of flow

And a constant current is constant flow irrespective of pressure.

Stepper motor supplies often use constant current, the higher supply voltage allows for faster switching times and more torque at higher step rates than a lower voltage supply.

Regards
Ray

That's the way they taught us too - to equate water pressure with voltage.

One small point, though, current-limiting is a little different to constant-current. Irrelevant here.