At 20V I calculate it could go at most 25 RPM while hitting 3A for each of 4 phases at 200 steps / rev.

 

I looked up the motor specs. and they show it as 3V, 1.8 Ohms, 3.5mH, so it should certainly step at lower than 20 Volts!

What about the driver specifications?
I am thinking that if the stepper is to be powered by batteries, either three 6 volt gell-cell types or two 12 volt batteries would be close. Or a six plus a 12 string. A 20 volt motor should even step if the supply is only 12 volts. The torque will be less, of course.

 

I looked up the motor specs. and they show it as 3V, 1.8 Ohms, 3.5mH, so it should certainly step at lower than 20 Volts!

The reason for higher voltage supplies for a stepper motor, which, BTW should operate at the plate rated CURRENT ar ALL times. Is in order to be able to maintain the rated current as the Inductive reactance increases with RPM.
IOW, the important value is the Motor Rated Current

 

For functional verification, not for maximum possible performance, a lower voltage can work.
How often do you drive your car with the engine delivering it's rated horsepower. Only racers do that. And even then, not 100% of the time, usually.

 

The only bearing on using a higher that rated voltage is in order to maintain the correct (rated) current .
Overcoming the effect of increasing inductive reactance at higher RPM,s
This is exactly what the specific stepper controller IC's achieve.

 

None of my applications required the stepper to run fast, or anything near fast. So those high performance schemes were not requited at all. So a bit lower current and lower voltage will not be an issue for a lot of us.

 

None of my applications required the stepper to run fast, or anything near fast. So those high performance schemes were not requited at all. So a bit lower current and lower voltage will not be an issue for a lot of us.

Interesting to hear just what type of controller you use? If a variation from the norm!

 

Interesting to hear just what type of controller you use? If a variation from the norm!

For the one machine I used the standard "Superior Electric" standard controller,but with a lower voltage power supply, 15 volts, I think, and reduced value series resistors. The application of those systems was adjusting the swash-plate that set the flow delivery in hydraulic pump control systems. So the rated torque was often required but the speed was not great. That meant that the motor inductance that tends to limit high speed torque was never an issue.
I wonder that it was not published about how great an efficiency improvement was available for those who did not need high speed full torque operation.
Consider that with 24 volt supplies but only 4 volts needed across the motor, that meant 20 volts dropped across the resistors at all times. And every bit of that power wasted as heat.

 

As I mentioned before the important issue is to maintain the motor rated CURRENT throughout the RPM range, the higher than rated voltage is used in order to maintain this current throughout the full RPM range. Regardless of what RPM you require.
This is how just about all the specialized IC's aimed at Stepper control function by offering this feature.
My references are The "The Design Engineers Guide to DC Stepper Motor Control" by Superior Electric.
The other is by Oriental Motor, these are two of the best known and among the oldest stepper manuf, there are.
e.g. If one consults the performance curves of the typical stepper motor, fed with the exact rated voltage, the torque drops very rapidly with any increase in RPM , due to this increase in inductive reactance.

 

Is it actually an increase in reactance with RPM? That would be due to back EMF, right?

Even is the reactance stays the same, the current takes a specific time to ramp up depending on the voltage. If that time becomes greater to the period for a phase then it will never achieve the rated current.

My calculation of max RPM was based only on the static inductance. With the back EMF it is probably much worse.

 

Is it actually an increase in reactance with RPM?

As Inductive reactance increases with RPM, causing a decrease in current then increasing the voltage as this occurs, maintains the rated current.
Before the advent of the specialized IC's, it was often typically done with a suitable series resistor.

 

What I am wondering about is the mechanism for the increased inductance you are talking about. Is it the same as back EMF? I can see that decreasing the driving voltage and hence make the effective inductance higher. Is that what you mean?

I was also pointing out that increased RPM would give less time for the current ramping up and thus limit the RPM even without an increase in inductance. Do you agree with that?

 

What I am wondering about is the mechanism for the increased inductance you are talking about. Is it the same as back EMF? I can see that decreasing the driving voltage and hence make the effective inductance higher. Is that what you mean?
I was also pointing out that increased RPM would give less time for the current ramping up and thus limit the RPM even without an increase in inductance. Do you agree with that?

Not increased inductance, that does not change, Inductive Reactance is the term and relies on the frequency of switching. .
On constant current drives, The "chopping" method of the applied voltage actually improves the rate of current rise (dl/dt), by increasing the driving voltage, the windings can reach a higher current level — even when the pulse rate is high, meaning more torque is produced at higher speed.

 

Max bet me to the same explanation!! EXactly correct!!

 

Thank you! So you are talking about the same thing I was, the need for faster rise time at higher RPM.

Wouldn’t back EMF also enter into it? I would think it basically lowers the effective driving voltage with higher RPM.

 

Thank you! So you are talking about the same thing I was, the need for faster rise time at higher RPM.

Wouldn’t back EMF also enter into it? I would think it basically lowers the effective driving voltage with higher RPM.

It would have some effect and the higher voltage would enter into combating this by retaining the rated current.

 

What we have no clues about is how and if the TS has even connected the stepper motor to the driver and tried anything.
AND, what is a "TB600" driver?? If the TS has one, did it come with a data sheet that we could see a copy of. OR is it an item that comes with totally not one speck of information.?
And if I try to research it I get 1754 hits of folks wanting to sell them to me, amazon claiming to have them in stock, and Ebay wnting to sell me some TB6 chainsaw parts.

 

Here are the principle specs.
Bi-polar Stepper required.

 

Here are the principle specs.
Bi-polar Stepper required.
View attachment 328519

That tells me nothing about the connections, and even less about how the TS has connected the motor, or what input they have supplied to the motor. Some driver packages include a pulse generator, some even are programmable. and some driver packages need both "step" and "Direction" inputs. And some suppliers will only be able to provide price and shipping weight information.

 

For the full info :-
https://www.dfrobot.com/product-1547.html

It is quite simple & straight forward to me !?