1. Yes, we are looking at the current waveforms through a winding.
2. 50A scale, but the current probe was probably set on (100x)
3. The two waveforms you see are not referenced to the same zero axis.
I moved them so they wouldn't lie on top of each.

My VDD is 5V. And my PFD is at 3.1V.
Slow decay is weak, but the motor runs best there.

According to Allegro, my 10mH is big.

My end user is using Applied Motion Motors:
http://www.applied-motion.com/produc...s/sizeht23.php
Type: HT23-397. Series Connection.

I had a quick look at your motor. Looks like it has more torque than mine.
My end user has asked us to look into changing the motor. It was recomended I use Hurst & Airpax.


In your note, you said...

1.05V > PFD > 6V
i use 2V...

Did you mean?

1.05V < PFD < 3V
i use 2V...

 

yes... my mistake
1.05V < PFD < 3V - mean mixed decay for a3977
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Some time ago, I have changed project of driver's PCB.
I have added transoptors on inputs.

Now it is cooler radiator
I carry all tests at Itripmax=3A step=1/8 Vbb=32V

Disturbances remain still...
Engine executes erroneous step sometimes...

Now next test executes... new pcb... new a3977

 

new PCB is better

I have made tests of Rt=10k/Ct=10nF <-- Noise* can be heard...
Rt=10k/Ct=4,7nF <-- Noise* still can be heard

---
* noise of stepper... and driver

 

What type of motor are you using?
Do you know the mH of the winding?

 

I'm curious to know what size motors people here are using on their A3977. I'm using a NEMA 23. 10mH, 1.4 Amps.

I hooked my motor up to a "complete" stepper motor drive, I'm still curious to know how to get the power/torque, and lower that annoying whine while sitting still! 4 motors at once is very annoying.

Is the motor noise something that bothers most?

Anyway, I found out that this stepper drive only powers one of the windings to the stepper when there is no STEP. A low DC voltage.
This keeps the motor quiet and cool.

This stepper drive also has ramp up speed.
So, if I try and feed it a 2khz STEP, it brings the motor up to speed quickly and smoothly. While the A3977 trys to hammer the stepper hard at the 2Khz signal. I do find the A3977 throws the stepper around pretty hard.

This is not to say that the A3977 can't do this, it can, but it takes some work. For example, if you have the I/O, you could vary the REF input to the A3977 while sitting still. When still, or no STEP, you could turn the REF right down.

Try this, power up your board, and enable the motor. Start turning down the REF value and you will hear the noise from the motor slightly dissappearing.

Also, control the frequency of the STEP signal, from a start.
RAMP the STEP signal up.


Remember, I'm not a pro!!
I'm just learning this as I go.....and sharing what I learn.
If you have anything to add....please let me know!

 

I use stepper motor 2.8A, 3.6mH - this need 10/20k & > 1.5nF


I connected small motors too:
sanyo denki 103g771-0611 1,82A
sanyo denki 103-771-1242 1.35A
this work with 10k/1n (51k/1n <- pminmo settings for Rt/Ct)

I come for conclusion...
For engines with big inductance we need to make big Tblank

big Tblank => big Ct => audible chopper -->> "annoying whine"
my 3,6mH motor need big Ct to work properly ;(

i have PIC in my driver for make current reduction (Vref reduction)

now I'm working on driver with a3986...
http://www.electro-tech-online.com/e...ver-a3986.html

 

Hello all,
I'm back!

I've been having issues with the allegro A3977 dying for no reason.
Never dies during use, I just found the system down.
I've been going through chips and wasn't sure what was happening.
I think I've just figured out what's going on.

My board has 4 A3977's driving 4 steppers. (10mH each).
When I have the board powered up (24V) and the A3977 is not enabled, I find that moving the steppers around by hand is killng the Allegros.
Moving the steppers around on the carriage also trips the 24V power supply that drives my Allegro board. While I had a meter monitoring VBB-24V I saw the meter jump to 56V and 61V....

So in short, moving the steppers around brings inductive noise back into my board.
When the motors are enabled, this doesn't happen. mind you when the motors are enabled their not easy to move.


Got any tips for me?
Can you point me in the direction of some lite reading material on the subject in question.

Thanks,
Matilda

 

Driving the shaft of a stepper motor will generate a lot of back-emf. I think the standard approach is to disconnect the motor from the driver completely. I don't have any references available, but I'm pretty sure back driving steppers is one of those "don't do that" things...

A modification might be to throw in a transistor/resistor/zener diode combo to clamp the supply rail to a maximum value to prevent the 3977's from dying from overvoltage. I think they're sometimes refered to as braking resistors. Obviously this will appear as drag when moving the stuff around - so it's probably better to just disconnect the windings.

 

this work for my ster3977

 

hjames & markcomp77,

The steppers are driving a gantry system thats about 4' by 4'.
When the user wants to bring the steppers home, they believe grabbing the steppers and pulling them home is fast and safe.
I'v mentioned disconnecting the steppers from the system for this action, but they don't seem to listen!

markcomp77, in regards to the schematic you have there.
Is the T1 line the VBB?
Also, I was looking at the other schematic you posted earlier. It shows two diodes and a TIP41...is that performing the same job?

And finally, what's the purpose of the 8 BYV diodes?
I thought they would have handle the back-emf?

Thanks again,
M

 

The diodes do *handle* the back-emf - they prevent the A3977 from dying immediately and instead shunt the generated power to the main powersupply - where it then goes and nukes everything.

Well, from the design perspective - when the A3977 goes into standby, use a relay to disconnect the motor. Or make it home automatically. Or never put into standby and make it difficult to manually move the head. Or make them pay for replacement parts. (Followed by increasingly hostile options...)

 

Interesting...
You say "instead shunt the generated power to the main powersupply"
Do you mean to ground, or to push it to VBB?

Allegro says VBB must NOT exceed 35V.

The relay idea would be good if I only had a couple of boards to fix.
But there are quite a few to upgrade.

I think I'll do some testing with the TIP41 method.
It looks easy......and cheap!

M

 

yes - T1 (transistor tip122..121..) - its collector is connected to Vbb

yes...
important change - R24.. value 100-200R

I use a3977 with 8 ext. diodes to drive 3A stepper

 

Mark,
I don't mean to have you doing my work for me! But in your case, what have you got for R21 & D1? Are these components as a group known as a shunt regulator?? I'm trying to find some documention. My VBB is 24V and I need to calculate the best valued components.

Currently my plan will be to make a daughter board and solder it just above the 8 BYV diodes. The arrows in my photo show the points as GND & +24V. Plus it's nice and close to the motor.

I'm finding info on Back-Emf....but nothing to promising.

Any more pointers you got for me??

Thanks!

Attached Images

DSCF0009.JPG (136.8 KB, 36 views)

 

R21... 4k7 (not important value)
D1 - zener
Vd1 smallest or equal ... 35 - 2*0.7
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what is "RN214-2,5/02" ?