About Stepper Motors

[_q12x_]

Actually there is another forum discussion until reaching this cct here. It was an entire evolution of it.
This cct is working ok but in certain parameters. It is limited to power and heat over the Tr's.
Is working fine in the 5V range for 2 of my stepper motors that I tested with it. But if Im bringing up the voltage, to 10V, I get 140dgrC on one Tr and about 60dgrC on a few others. At 5V, everything stays at a constant 50dgrC which I call it normal and safe.
One of the test motor is a Nema17 17HS4401. The other one is a scrapped stepper. Both work fine at 5V and even at 10V, no one was heating. Over 5V, especially at 10V, only the driver's Tr's were cooked to (almost)death. I stopped the power after smelling hot metal in the air.
I am also receiving a couple of L298N IC's. They are coming in the mail, not arrived yet. But I dont expect much difference from them, compared to what I have here. It would be nice to be better ! I hope so.
- My question:
- How to make this cct more powerful? To drive more power through the coils of the stepper motor? (and not blow up it's Tr's!)
I already have 2 answers to this question in my mind, but I dont want to influence your answer. I expect to be pleasantly surprised. Haha.

Thank you !

 

[_q12x_]

Mister @marconi , good morning to England. A few words about my cct here?

 

[Julie.]

You have a fundamental problem with using BJTs like that, in that the switch off time is longer than the switch on time.

As the lower BJT only needs the voltage to go from 0 to 0.7v or so, whilst the upper one needs the voltage to swing down much further.

So when you drive one transistor on, the other which is on via the inverter will remain on for some time before switching off, resulting in both transistors on in series across the supply for a brief time.

I assume it is the lower one which gets too hot BTW.

You either need a delay between switching one off and the other on, or use FETs/MOSFETS which as long as you drive the gates correctly will avoid this.

EDIT:

You could of course just replace the whole driver circuit with a dual H bridge chip, which control this internally, something like the DRV8841, this is good for diving circ 2.5A in the coils up to 24V or so, which will allow a 5V circuit to drive a higher voltage on the motor, or the one you suggest.

 

[marconi]

Mister @marconi , good morning to England. A few words about my cct here?

I will have a ponder and respond as soon as I can. What is it you want to drive which requires more mechanical power?

 

[_q12x_]

What is it you want to drive which requires more mechanical power?

A stepper motor NEMA 17

 

[_q12x_]

Here is the conclusion of this cct:

 

[marconi]

I have studied what you presented and here is a quick response.

1. The 2 phase bipolar stepper motor is being driven by the circuit in 'wave mode'. This means that only one of the two coils is energised at a time. The angular steps of rotation are 90 degrees.

2. The use of the CD4017 provides a state sequence 1000, 0100, 0010, 0001. This 4 bit code controls the two H bridges to energise the stepper motor as I have shown in the attached electrical art.

3. You could produce more torque by a factor of sqrt(2) ie 1.414 if you had a switching sequence which energised two coils at a time - see the link below and the section on 'Full Step two phase on' mode. Steps are still 90 degrees.

4. If you used the mode mentioned in (3) you could stick with the present coil currents and yet produce more torque. Would this be helpful? Of course the transistors need heat sinks etcetera.

5. I would use a H bridge ic designed for the purpose rather than make my own as you have done. If I had to make my own I would use paired npn and pnp power transistors but preferably complementary power mosfets - in both cases to avoid the inverters.

6. The use of a 4017 decade counter limits your ability to generate switching waveforms to control the H bridges. I would use binary counters with decoding to switch transistors by combinational logic or an eeprom.

Have a read through this:

Stepper Motor Basics - https://www.orientalmotor.com/stepper-motors/technology/stepper-motor-basics.html#:~:text=In%20the%20wave%20drive%20method,only%20one%20phase%20is%20energized.

 

[_q12x_]

Thank you @marconi

 

[_q12x_]

Here is the version that I tested already and is NOT working with the current logic cct and the IRFZ44N mosfets. I believe it should have worked with what I have here already. No?

 

[marconi]

There are two versions of this enhancement mode mosfet. The IRFZ44N which requires a gate to source voltage of at least 3V to start to turn on and 10V to be fully conducting. Your drive circuit does not achieve this for the upper two transistors.

There is also a version suited to being driven by 5V logic - the IRLZ44N - which turns on at about 3V and is fully conducting with 5V between gate and source.

But there is another problem with this circuit which is that the source of the upper transistors is not directly connected to 0V. So these source pins will be at a higher potential than 0V because there is the coil between their source pin and ground. And the coil is switched by the upper mosfet to a positive rail which can have a voltage higher than 5V. Your 4017 has a maximum output of about 4 to 5V and thus is unable to elevate the upper mosfet gate potential sufficiently high to turn the IRFZ44Ns on fully. The potential on these gates may not even exceed the minimum gate source voltage of 3V required to begin to turn them on.

I will say more tomorrow. A bit rushed but I hope you get the idea. Fortunately there are solutions.

 

[_q12x_]

You explained this one very well ! I completely understand it ! Well done.
I only have the IRFZ44N and not the IRLZ44N. So a 10V for the full gate opening we will require.
I believe it is used a Bootstrap Driver, made from a capacitor and a diode. I recently learned about it on my other forum. So that will pull up the gate voltage and activate the 1st Tr. Very good that you tell me this stuff ! Im not that good with mosfets. I know something, but not much enough.

 

[_q12x_]

Here are some observed data I collected, using my other cct with BJT NPN in it.
All this data is not related to the problem in question with the mosfets right now.
But is some useful information for a better context.
This is from the other forum:
Well, at 5V, the 4wire steppers are consuming a constant 300mA. Well the entire cct. I read it directly from the PSU screen. They barely rotate but they do it and is good enough to tell if they work.
At 6V the amperage rises to 480mA. (The speed is a bit better but not very)
At 10V the amperage rises to 630mA but the speed (and most possibly the torque) is greatly improved and visible.
I didnt test them at 15V or 20V yet. But the google says that a Nema17 like the one I have, can be run at 12-24V.

And I know this specific search I did is not the best to do but it does get me some close result.
The problem I face is simple. I want to run them at 15V or 20V ! This means at higher amperage as well. Im not sure if 20V with 1.7A will be fine for my new motor or not. But the NPN's are definitely burning if keep them too long to work. The temperature rises too much for my comfort. Over 100dgrC. And the aluminium radiator on each transistor will not really do much difference. Maybe 2or3 dgrC lower. Really, its too high. So we need to attack it with something else. With other weapons of war. Soon the L298 IC will arrive. Probably less than 1 month - I hope. Then after that my P-ch Mosfets.
Until all of them arrive, I will try to make the same circuit here but with the mosfets that I have, only N-ch, IRFZ44N.
Here is my Nema 17 stepper model number: 17HS4401 data:

All this being said, we will concentrate on the mosfet problem. I only put this here as a reminder for me, and possibly helpful for you.

 

[marconi]

You explained this one very well ! I completely understand it ! Well done.
I only have the IRFZ44N and not the IRLZ44N. So a 10V for the full gate opening we will require.
I believe it is used a Bootstrap Driver, made from a capacitor and a diode. I recently learned about it on my other forum. So that will pull up the gate voltage and activate the 1st Tr. Very good that you tell me this stuff ! Im not that good with mosfets. I know something, but not much enough.

Just like me !

 

[_q12x_]

Ok. I did this and here are my conclusions:
Nema17 17HS4401 measured coil resistance = 2.4R per coil
I know the Resistance, I know the Voltage, I want the Amperage to know
So I =V/R = 5V/2.4R = 2.08A
and P=VI=5V*2.08A=10.4W


In datasheet, 17HS4401 has a maximum of 1.7A.
This means that V=IR=1.7A*2.4R=4.08V
and P=VI=5V*1.7A=6.9W
So nominally is 4.08V @ 1.7A with 6.9W

 

[marconi]

The maximum power produced by Ohmic heating in the mosfet is Pm = Isquared x Ro where Ro is the resistance source to drain when the mosfet if fully conducting. The datasheet has a figure for Ro. It will be a figure in milli-Ohms.

We then consider the duty cycle ie for what percentage of the time the mosfet is on compared to off. If the ratio was 1 to 3, ie off three times longer than on, then the the average power will be Pav = 1/(1 + 3) x Pm.

 

[_q12x_]

Nonono, all this Heavy math I did here is for (1 coil or motor) that I have brand new.
This is a very important math to be done! Is essential. I am not doing it every day. So thats my excuse not knowing it - not using it. I had to discover it myself from a movie I watched last night on youtube. And I didnt discover it, but I remember it, and I said aaaah, that thing... haha. And I quickly adapt it to my thing here.

 

[marconi]

Yes I understand your maths was for one coil. Mine was to give you a 'leg up' for the mosfet power to size the heat sink/radiator.

 

[_q12x_]

Yes I understand your math was for one coil.

But I am driving 1 coil at a time, right? I dont need to *2 for both coils. Right?

 

[marconi]

But I am driving 1 coil at a time, right? I dont need to *2 for both coils. Right?

Yes you are right.

 

[marconi]

https://www.farnell.com/datasheets/2303998.pdf

I had in mind last night the use of these opto-isolaters to control the mosfets.