About Stepper Motors

[_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.