[jfong]

The purpose and function of a Chopper drive is to drive a low voltage motor from a high voltage power supply by maintaining constant current drive using a switching action.

This part is correct. It really contradicts what you wrote earlier.

The chopper drive will maintain a peak constant current. The average current is less and works out to be about 2/3 of the peak for a parallel winding connected motor.

It doesn't matter what the power supply voltage is (beside being less than what the driver can handle), the driver has to maintain a peak constant current value. The power supply still has to be able to deliver that. A 2.7 amp power supply isn't enough for three 3amp stepper motors. The average current would be about 6 amps and you will need a power supply that will deliver that.

Because of the chopper effect, you can't read the current with a standard DVM meter. You will get a much lower value. You will need a oscilloscope with proper current probes to see the peak value.

[millhead]

Jim,
A chopper type stepper motor drive work just as a switching power supply. The current taken from the input power source depends on the voltage.
Here are the specifications printed on my Laptop Power supply:
Output: 15 Volts, 5 Amps
Input 120 Volts, 1.2Amps or 240 Volts, 0.6 Amps

A chopper drive works the same way.

Actually, since the chopper frequency is of the order of 20 to 40 Khz, if you measure the current using an Oscilloscope with a current probe, or series resistor and differential probe, you will see very little ripple, because the capacitors in the PSU and the stepper drive will absorb all the ripple. For this reason, you CAN measure the current with a regular DC ampere meter. Jim, I know you are into electronics, so measure the current with a scope, and see how much current is taken from a 30 or 40V PSU when the motors are running.

I will try to do the same this week end, and post the results.


Of course, a PSU with higher current rating will work perfectly OK, but it will be delivering a fraction of it's capacity.
I was merely trying to help people to spend a little less money on their CNC Power supplies.

[jfong]

When the motors are spinning, the average current is always going to be much less. The coil inductance limits how fast you can spin the motor and current draw. The most current a stepper motors uses is when it is at zero rpm. That is the current requirement for max holding torque. It also depends on what step position in the cycle the motor position is at. At one point in the cycle both windings are fully energized. That is the position when you need to take your current readings for maximum draw. Power supply needs to be able to handle that for the number of motors connected. Else maximum holding torque will not be achieved.

[A_Camera]

Response to A_Camera: If you really take 3A per winding from a 40V Power Supply, the total power taken is 40 X 3 X 2 windings = 240 Watts.
Your motor and Driver will be red hot.

The purpose and function of a Chopper drive is to drive a low voltage motor from a high voltage power supply by maintaining constant current drive using a switching action.

Again, you are confusing inductive load with resistive.

Also, with that logic you could just as well run a CNC using a 5V supply, and that is obviously not working that well. But, whatever rocks your boat is fine for me. Others will learn the hard way and as other type of questions, like "why does my motors stall", or "why can't I run this fast" and similar and will get the answer I have given.

BTW, my motors get pretty hot, which is normal for motors. Not "red hot" but about 50 degree Celsius. Also my PSU rectifier gets heated up pretty fast, but that is kept at around 35-40 degrees with a fan.

[millhead]

Jim,
Agree with you 100% on the speed.
I will take the measurements at a very low speed, since when stationary, my drives will go to lower holding current.

Also agree that when spinning, even at a slow rate, the current measured will be about 2/3 of the peak.

[A_Camera]

Jim,
A chopper type stepper motor drive work just as a switching power supply. The current taken from the input power source depends on the voltage.
Here are the specifications printed on my Laptop Power supply:
Output: 15 Volts, 5 Amps
Input 120 Volts, 1.2Amps or 240 Volts, 0.6 Amps

A chopper drive works the same way.

Actually, since the chopper frequency is of the order of 20 to 40 Khz, if you measure the current using an Oscilloscope with a current probe, or series resistor and differential probe, you will see very little ripple, because the capacitors in the PSU and the stepper drive will absorb all the ripple. For this reason, you CAN measure the current with a regular DC ampere meter.

No, you can't. Again, we are talking about inductive load. Also, the load is not constant, like when you switch on a lamp, but is high when a step pulse is given and low in between. So, the reading you get is false because it shows an average at best, assuming your simple DC amp meter can cope with the frequency of stepping, which is by far the case for simple and cheap amp meters.

Of course, a PSU with higher current rating will work perfectly OK, but it will be delivering a fraction of it's capacity.
I was merely trying to help people to spend a little less money on their CNC Power supplies.

I have an amp meter permanently wired to the PSU on the 43V side, now when the machine is in idle, the motors are disabled, the current reading is 0.1A, when the motors are enabled the reading jumps to 2A, and when the driver lowers to holding current it reads 1.6A, after a second it drops to 1.2A. This is fine, but like I said, it is not the real current when the motors are running, only when the motors are not running. Here is a short video I just made if you want to watch it, you can see what is happening.

https://youtu.be/m1zxi-BjIhc

Note that current will increase even more once cutting starts.

[A_Camera]

I will take the measurements at a very low speed,

Again, not the right approach since the stepping pulses will not be longer if you run slow, they supposed to be constant and just a few micro seconds each. At least on my driver, that is the case.

[jfong]

Jim,
Agree with you 100% on the speed.
I will take the measurements at a very low speed, since when stationary, my drives will go to lower holding current.

Also agree that when spinning, even at a slow rate, the current measured will be about 2/3 of the peak.

I have a rotary 4th axis with the drivers current reduction turned off. I want maximum holding torque available when the axis isn't moving. One of the few times where it is desired.

[millhead]

The current draw is exactly as I predicted.
Stepper motors do not take any more current under load. Your axle motor will take more current as you start cutting, but not the steppers.

I noticed from the video that you were running all three axes. The max current I noticed was 2.2 Amps. At 42 volts, that is 92 Watts.
So, assuming you have 3 identical motors, each motor takes approx. 30 watts. I do not know what your motor specs are, but if you
multiply the stated current and voltage of your motors, I expect the number to be approx 20% less than 15, around 12 watts.

The numbers are exactly as i said in the first post.
By the way, this is not to have an argument with you or anyone else. I am simply providing some facts based on my knowledge as a BSEE with 25 plus years industry experience as an R&D engineer.
By the way, your home made mill looks better than many commercial machines I have seen. Congratulations.

Do you have a build log on the machine? I would love to see it.
Regards.
Have a great weekend.
Daya.

[Dan911]

No, you can't. Again, we are talking about inductive load. Also, the load is not constant, like when you switch on a lamp, but is high when a step pulse is given and low in between. So, the reading you get is false because it shows an average at best, assuming your simple DC amp meter can cope with the frequency of stepping, which is by far the case for simple and cheap amp meters.



I have an amp meter permanently wired to the PSU on the 43V side, now when the machine is in idle, the motors are disabled, the current reading is 0.1A, when the motors are enabled the reading jumps to 2A, and when the driver lowers to holding current it reads 1.6A, after a second it drops to 1.2A. This is fine, but like I said, it is not the real current when the motors are running, only when the motors are not running. Here is a short video I just made if you want to watch it, you can see what is happening.

https://youtu.be/m1zxi-BjIhc

Note that current will increase even more once cutting starts.

Hey AC nice vid, I noticed you have the MODBUSEZ plugin enabled. I hope its working well for you.

Dan

[109jb]

The theoretical max current of a microstepping drive is 141% of the current setting. For example a 3 amp per phase current setting would mean the drive would draw a max of 4.23 amps.

At full step setting it is exactly what the current is set for. This is because at full step one coil is on and the other is off. When in-between full steps each coil is partially energized and it follows a sine-cosine type curve. At exactly 1/2 step each coil gets 70.7% of the full current setting, but there are 2 coils energized, so 70.7% x 2 = 141.4%

If the drive has the motor positioned at 1/2 step position and the drive is not set to reduce current at idle, then the idle current will also be 141% of the current setting.

[A_Camera]

The theoretical max current of a microstepping drive is 141% of the current setting. For example a 3 amp per phase current setting would mean the drive would draw a max of 4.23 amps.

At full step setting it is exactly what the current is set for. This is because at full step one coil is on and the other is off. When in-between full steps each coil is partially energized and it follows a sine-cosine type curve. At exactly 1/2 step each coil gets 70.7% of the full current setting, but there are 2 coils energized, so 70.7% x 2 = 141.4%

If the drive has the motor positioned at 1/2 step position and the drive is not set to reduce current at idle, then the idle current will also be 141% of the current setting.

This is very true. I am though not sure if the motors I have are 3A peak or RMS, so currently I have the drivers set to 3.32A peak current, which is of course 2.36A RMS. It is also true that the current is per coil, so we must find an intermediate step position where the motor should be put to hold at full current. Currently my drivers are set for half current holding, but that's only for a second, if within that time no step pulses are sensed then the current drops even more.

[A_Camera]

The current draw is exactly as I predicted.
Stepper motors do not take any more current under load. Your axle motor will take more current as you start cutting, but not the steppers.

They should take more current under load, just like any other motors, but of course, current is limited by the driver.

I noticed from the video that you were running all three axes. The max current I noticed was 2.2 Amps. At 42 volts, that is 92 Watts.
So, assuming you have 3 identical motors, each motor takes approx. 30 watts. I do not know what your motor specs are, but if you
multiply the stated current and voltage of your motors, I expect the number to be approx 20% less than 15, around 12 watts.

The numbers are exactly as i said in the first post.
By the way, this is not to have an argument with you or anyone else. I am simply providing some facts based on my knowledge as a BSEE with 25 plus years industry experience as an R&D engineer.

This is what we all missed:

https://youtu.be/WVLjoR4yyW0

The voltage is actually AC because the polarity is constantly changing, not just between 0 and + but also from 0 to -, just like ordinary AC. The voltage on the steppers is NOT that low, actually it is the same as the PSU voltage. I hooked up two DMMs set to AC and measured the voltage. It is going up to 43VAC on each coil. Next time I will measure the AC current.

By the way, your home made mill looks better than many commercial machines I have seen. Congratulations.

Do you have a build log on the machine? I would love to see it.
Regards.
Have a great weekend.
Daya.

Thank you. No, I don't have a build log, but running a blog with a lot of information about my CNC and other technical stuff.

The latest post about the current specifications is this one:

https://adapting-camera.blogspot.se/...nt-status.html

[millhead]

Stepper motors are very different from regular series motors. A regular motor is a rotating device. Give them power, and they rotate. Increase the load, and they slow down just a little, and take more current. Of course, you can add a controller to make the speed variable etc.

A stepper on the other hand is a position and hold device. They have to be driven by a controller, and when we give it a step pulse, it moves to the next position. We make them rotate by giving a continuous stream of pulses. If you increase the load to a stepper, it will continue to hold, until the force exceeds the holding torque (At the rated current) and then start to slip.

In order to understand how a chopper drive works, let us define some parameters to simplify things:
Our motor has 1 Ohm, 3 Ampere windings with a 3mH inductance.
We have set the drive to full step mode. (We will discuss microstepping later)
We are driving this motor with a 40 Volt power supply.
The drive has a chopping frequency of 20kHz. (50 microsecond period)
Let us also assume that we have disabled the hold current reduction of the drive.

The time constant 'T' of an L-R circuit is L/R, which in our case is .003/1 = .003 seconds, or 3 milliseconds.
Now, if we try to drive this 3 volt motor with a 3 volt power supply, it will take about 5 time constants or 15 milliseconds to reach the full current of 3 Amps. This will seriousely limit the speed of the motor.

That is the reason we use a higher voltage PSU with a chopper driver.

So, at the very start, the drive applies 40 volts across the winding. Because of the higher voltage, the current will rise to 3 Amps in approx 0.23 milliseconds, (much faster than the 15 milliseconds with jut a 3V drive.)

As soon as the current reaches 3 Amps, the chopper cuts off the 40 volts, and switches a diode across the coil. The diode allows the current to decay slowly. (Some driver chips have more complex ways of current decay.)
Next, as soon as the next chopper cycle comes by, the 40V is switched on, and the current starts to increase. As soon as it reaches 3A, it is cut off, and this switching on and off continues until the next step pulse comes in.
During this steady state, the 40 volts is on for a very small part of the 50 microsecond chopper cycle, and off for most of the time. Because of this, two things happen. The AVERAGE current taken from the power supply is far less than 3A, since the duty cycle is small. The motor current never exceeds 3A, because the chopper cuts off pover at 3A.

Sometime later, when the next step pulse is applied, the same process repeats, except the H-Bridge applies reverse polarity to the coil. This operation is transparent to the power supply, which is outside the drver circuitry.

Also, since the switching on and off of the power happens at 20 kHz, all the short current steps are absorbed by the large capacitors in the drive, and the current drawn from the PSU is more or less a steady DC current which can be measured with a regular ampere meter to a good degree of accuracy.

With real world stepper drives, the H-bridge driver devices have on resistance in the range of 0.3 to 0.6 ohms, which will add to the power dissipation of the drive. This is what causes drives to heat up.
The overall effect of this is 20 to 30% more current drawn from the power supply.

[A_Camera]

They should take more current under load, just like any other motors, but of course, current is limited by the driver.



This is what we all missed:

https://youtu.be/WVLjoR4yyW0

The voltage is actually AC because the polarity is constantly changing, not just between 0 and + but also from 0 to -, just like ordinary AC. The voltage on the steppers is NOT that low, actually it is the same as the PSU voltage. I hooked up two DMMs set to AC and measured the voltage. It is going up to 43VAC on each coil. Next time I will measure the AC current.



Thank you. No, I don't have a build log, but running a blog with a lot of information about my CNC and other technical stuff.

The latest post about the current specifications is this one:

https://adapting-camera.blogspot.se/...nt-status.html

I made a third video regarding the measurements. This video shows why an ordinary DMM can NOT be used to measure the current, not even if set to measure AC current. Voltage seems to work better but current measurements are not so reliable.

https://www.youtube.com/watch?v=iC5mDShOSts

[millhead]

1. Your chopper frequency can be anywhere in the range of 20 to 100 Khz.
2. Chopper frequency and step rate can interact to create complex waveforms, and harmonics
3. A simple frequency meter cannot measure such complex waveforms, you need to capture them using a frequency analyzer.
4. What is the objective?
5. You have a high Amperage Power supply, which will serve you well, and I have a low amperage PSU which serves me well, so let us move on, and make some metal chips.


By the way, I looked at you website, and your mill looks nice. You said that you started your photography hobby with a Zenith E.
I also had a Zenith E in the early 70s, then graduated to a Cannon SLR, but did not go further.

Best Regards.

[A_Camera]

1. Your chopper frequency can be anywhere in the range of 20 to 100 Khz.
2. Chopper frequency and step rate can interact to create complex waveforms, and harmonics
3. A simple frequency meter cannot measure such complex waveforms, you need to capture them using a frequency analyzer.

The idea was not to analyse the frequency but to see why the current measurements are invalid. For that, this is enough. I don't whant to hook up my scope to analyse in more details because I don't want to risk frying it. I already fried the driver because I forgot to twist the switch from A to Hz when I hooked up the instrument for the frequency measurement, which shorted the stepper coil and when I started the G-code that killed the driver. No big deal, probably just a fuse. I have not had time to remove and check the faulty driver, just replaced it for now.

4. What is the objective?

The objective was to make measurements and show why an ordinary DMM can not be used to measure the current and in some cases, the voltage. I have never made any measurements on the stepper side, and since we discussed the subject, I wanted to see how it is on my side. Have you made the measurements you mentioned in post #244? What were the results?

5. You have a high Amperage Power supply, which will serve you well, and I have a low amperage PSU which serves me well, so let us move on, and make some metal chips.

Well, I am not making many metal chips since I mostly work on plastics and PCB, but sure, back to "business" this weekend.

By the way, I looked at you website, and your mill looks nice. You said that you started your photography hobby with a Zenith E.
I also had a Zenith E in the early 70s, then graduated to a Cannon SLR, but did not go further.

I went through many cameras since 1970 but except the G10, I never had a Canon still image camera. My camcorder is a Canon... Anyway, photography is still the main hobby I have and even my DIY CNC is tightly connected to it and in fact, photography led me to making my CNC the first place. Without photography as hobby, I would have most probably never entered this area and never developed this hobby.

Cheers

[millhead]

Finally got some scope traces.
40 V linear PSU feeding stepper driver thru one Ohm 3 Watt resistor, scope channel one on power supply end of resistor and channel 2 on driver side.
Driver set to 3 Amps and 8 microsteps.
Scope set to AC coupling, 200 mV, 5 milliseconds per div, Channel 2 invert and add.
In the photos below, top trace channel one, bottom trace channel two, middle trace is ch1 plus inverted ch2

As you can see, most of the fast ripple is absorbed by the driver capacitors, and all you see at the PSU interface is 120Hz ripple from the PSU.
So, a regurar DC ampere meter should give a reasonably accurate average reading.
In my testing, the idle test recorded about 260 milli amperes from the 40V PSU, and running at 8000 microsteps a second recoeded about 0.9Amps from the PSU.
Attachment 356470

[bobdxcool]

The drive has arrived yesterday, I ordered a TB1H from First-Supply to have it fast (they deliver from the UK).
The one I received is a HY-DIV268N-5A wich looks exactly the same.

I couldn't wait to have a look at the inside and removed the cover.
The board is floating inside, it has no screws holding it in place. The chip is fixed to the heatsink and the board is held in place horizontally by the cover screws wich go through the holes but these have some play. See picture.
The chip pins experience all the mechanical stress when the plugs are installed or removed.

Next I removed the chip to have a look a the bottom side of the PCB. There's no thermal paste or pad..... and the mounting holes have some burrs, the chip will not make good contact with the heatsink.
Deburred the holes and remounted with thermal paste for testing.

I use a 33V supply, 4Amp Sanyo Denki bipolar motor and did set the drive at 2.5A and 1/8 microstepping.
The drive works but the stepping rate seems wrong, checked the swicth settings again .... Short story: the microstepping table is wrong, looks like 2 colums need to be swapped.

To be continued...

Lucas, I want to drive a NEMA34 (5.5 amp motor, 3.6mH, 46kgcm) stepper motor using the TB6600 driver (4A TB6600 Stepper Motor Driver Controller 9~42V TTL 16 Micro-Step CNC 1 Axis | eBay).

So to increase the current limit, I can solder 0.47 ohms in parallel with the current sense resistors (R620)?
Also, as it has been stated in this forum that these drivers are designed to provide only 30% torque. But as per one of the posts, connecting a jumper between Vreg (pin 24) and pin 3 on the TB6600 would provide 100% torque always, right ?

Just as an alternative I was also considering ordering another stepper driver from leadshine (Leadshine DM542 Digital Stepper Driver 20-50 VDC with 1.0-4.2A - US$). Do you have any idea about this driver ? If so, would this be a good one without needing any modifications to drive at 100% torque ?

[petsat]

TB6600 analysis and suggested modifications.

High All,

After many hours of reading, testing and experimenting I gathered all data that apply to MY Tb6600 board, made all modifications to comply to datasheet suggestions and several modifications suggested by other members here!

My verdict:
It is a fine board to kill many hours in learning how not to design a board!
Did this work before the mods? Sort of.
Does this work after the mods? YES
Did I make it reliable? No! I would not claim that! I would not use it for serious work!

It was fun though and educational!

I would say: buy it if you have time, knowledge and patience!

Petsat